Don't sweat the BMS continuous current rating too much. As a rule, the equivalent resistance of LiFEPO4 batteries is largely inversely proportionate to their capacities. The batteries will mostly current share, with the smaller battery only producing it's percentage of overall capacity in current. In this configuration, if you used a DC clamp meter on the output terminals of each battery, The smaller battery would show about 18% of the total draw of the inverter, while the larger battery would supply about 82% of the current. If the big battery has a 250 amp current limit, the small battery only needs to be about 55 amps, to allow full loading of the bigger battery management system. (BMS)
I would have expected it to behave this way. Because both batteries will be at almost identical voltage the current flow will be greater from the greater capacity battery. It's not common you see this configuration but nothing wrong with it.
And I use lead acid car batteries so doing that test for myself would risk damaging them if my home made chinese low voltage cut-off / 200A relay combo lets me down.
Im running 28 12.8v Li Time batteries in parallel, 4 batteries / 7 individual shunts. Hooked to 5 renogy inverters. 2- 3000 watt 2- 1000 watt 1- 2000 watt They are running dedicated rooms in our off grid cabin. Hope to have a single 18k EG4 the first of next year , to run our electric stove , clothes dryer and water heater. I enjoy your informative videos
"DIFFERENT Capacity in Parallel - What Happens?!" Provided they have the same voltage, *nothing happens* . As you draw power, the one with less capacity will start to drop voltage, but of course, it cannot; so most of the load starts drawing from the battery with more capacity. Thus, their SOC (state of charge) draws down uniformly.
well when i connect them i see lots of power leak from higher one to smaller one as smaller ones voltahe is in general less even if charged full there is small change... you can use a voltmeter and ampermeter to check the voltage difference ..
@@ahmetmutlu348thats just nonsense… Capacity has nothing to do with voltage. AGM batteries, 40Ah, 90Ah, 120Ah ALL have ~12,9V when new and fully charged
@@PM-wt3yeIm not sure.. but when i left them unmonitored things goes wrong in general and i suspected that they are discharging each other and checked voltage flow and i allmost allways see lots of power flow from one to another... if you have time you can make may be an arduino that creates statistics for how that goes.😊 but there is allmost allways atleast 0.5 volts flow from one to another may not be a problem of you charge them regularly anyway... may be thats what they call self discharge pr whatewer but what ive seen is they do discharge a lot.😊
@@matb748I dont have detailed stats but you can do the test yourself.. connect 2 batteries in paralel and use a voltmeter or led on one of the cables serially... youll see led will light up indicating discharge from one to another.
@@stinkycheese804 The first GOOD answer I found. I guess your googling works better. I was complimenting the video creator, not inviting snarky comments.
those are the basics of electrical engineering, I don't remember if I learned it in elementary school or just in high school, if you're still in kindergarten, don't worry, that will come later
@@makantahi3731 I'm not an electrical engineer, so I look for answers. If you learned about lithium battery balancing and charging and what can affect their capacities in the long-term in elementary school, wow.
Damn, I've always wondered about that. Great experiment, valuable info. Good to know if you happen to be in an emergency situation and have access to multiple batteries.
You have to imagine it like this. The large battery is a wide container for energy, the small battery is a narrow container for energy. Now you connect both in parallel, this equalizes the height of energy (Volt), but the width of the batteries remains the same. When unloading, both are unloaded in height (Volt), but the Ampere balance each other out. To the point where both are empty. Due to the internal resistance, the cells can discharge at different rates. But things even out again.
Great informative video & advice, thanks. It would have been good to also monitor the current share between the two batteries and graph the battery voltage till drop off & shutdown.
Well I just learned something new. Which is why I am subscribed to your channel. Great information to know. I am glad that when you do this type of videos, they are directed to the novice audiences getting into solar power and batteries and you do not assume that we already know. Great, great explanation and great job.
As you will see in my videos, my channel, for years I have Lead acid AND LiFePO4 running in one bank. 13 LiFePO4 Batteries connected to one main buss bar. 2 @ 400ah, 5 @ 200ah and 6 are 100ah. Been running fine for over 26 months. The method is your cable sizing. You use resistive cable gauging to keep them working together. 6 awg from each 100ah, 4 awg from each 200ah, and 2 awg from each 400ah. The outcome is defaulted charge and draw due to wire/ load resistance(heat). As you demand too much from the 100ah, the 6 awg starts to "road block" basically resist pull over 70 amps and defaults to the 200ah, the 200 ah 4 awg starts to get resistance in its cable when you exceed 125 amps and defaults to the 400ah using 2 awg. It all auto balances itself to the main buss bar so I get 70% ability of all the BMS's at the same time as it is in use. to make matters even more insane, for almost 2 years I have 28 GC2 Rolls Surrettes 235ah Lead Acid Batteries connected via 2/0 cable to those LiFePO4 Buss Bar. The inverters and all loads pull direct from the Lead Acid which gets its voltage support ( not its main amp draw ) from the Lithium. My total result is thousands of Amp hours. The Lead Acid is like new even though 3-1/2 years old since they have voltage support and never see over 45% DOD. They even now have 1/3 the water loss due to the LiFePO4 all night supporting voltage stability refill. I learned this in the Telecom industry when they used Ni-mh for lead acid support the same way in the 1990's.
No, if you connected all the batteries using a 6" x 1/2" COPPER BUS BAR, they would all deplete at exactly the same % each, irrespective of "rated current loading", because if the LOAD is more than the smallest battery, IT IS NOT SUPPLYING ALL OF THAT LOAD, just a small percentage of the over-rated load. THINK, all a battery is, is a container with a specified rated current at a certain voltage. One can use see-through plastic water containers, (instead of batteries) such as using ALL at a 1M height - but of different diameters, or shapes, (or squares shapes too, as that's what an IBC is, a square pipe 1M high) such that ALL will be filled to maximum height (1M) before you open the combined drain pipes, to drain at whatever rate your "output loading" is, thus if you draw far more "capaciy" than your smallest container's capacity, don't worry at all, because that IS NOT the only container there. It will NOT drain it's capacity any faster than any other, so when your smallest battery gets to HALF of it's capacity - all others will also be at 50%. ALL will be self-balanced (at that same 50% level), thus there will also be no "intercharging (flow) effects" either, between any two. There is no need as all will have the same height of upper water levels, (which is comparible to a batteries toal capacity left) - meaning that no ONE battery will be supplying anything to any other, with them ALL at the same % capacity left. THE PROBLEM IS THIS, many people assume, that because they are using 12v batteries, they can combine NEW fully charged batteries, with depleted ones, to get the shock (quite literally) of their lives, when a MASSIVE instantainious flow occurs, between the fully charged batteries and the depleted ones, that ARE NOW BEING RECHARGED by the new batteries, far beyond the "rated capacities of the new batteries, causing THEM to explode. The recharging one's won't explode as they still aren't fully recharged, and never will be if the new batteries explode.
@@QUIX4U Almost on my 28th month running over 900 amps start peak flow, 400 continuous and my designed cable resistance effect is @peak pulling 75% from the lead acid and 25% from the Lithium then when the high start load ends they balance in a matter of minutes. No wire heat happens or failures of BMS has happen as I was constantly told would happen. My lead acid water use is less than half it should be, their DOD is never seeing 50%, and the lithium/lead has performed just identical as the USN submariner electrical handbook said 2 chemistries should and would ( SLA and NiCad 1982 Section 4-8b )
@@QUIX4U Thankyou for your very informative reply. The water analogy applies to the solar panel on the roof. The inverter senses the mains pressure and uplifts slightly to either supplement or overcome the mains. However in the battery connections, you will not have a zero resistance bus bar and thus slightly different voltages at each battery connection on charging and discharging. Is that not a problem over the long term?
One thing to keep in mind is the voltage difference between the two batteries under use. For example, if the voltage output of the smaller battery falls below the voltage output of the large battery, the large battery will end up charging the smaller battery instead of putting all it's current output towards the load. The usual way to prevent this is through the use of so-called "steering diodes." This prevents one battery from discharging some or all of it's current output into another battery. Unfortunately it also lowers the overall output voltage by 0.7 volts for each diode that ends up being between the final output from the batteries and the load.
"the large battery will end up charging the smaller battery instead of putting all it's current output towards the load." While unlikely, this is also harmless; since the *charge* is still available to the load.
Yeah but there will be a drop in efficiency due to losses caused by the larger battery charging the small one. Though the efficiency will be a lot lower than the one caused by the diodes.
@@holyscrap4445 "but there will be a drop in efficiency due to losses caused by the larger battery charging the small one." It is unlikely the larger one tries to charge the smaller one. As I explained already, what will happen is the rate of discharge of the smaller battery will decline faster than the rate of discharge of the larger battery simply because of the higher internal resistance of the smaller battery. Thus, both batteries will deplete their proportion of charge at about the same rate; the larger battery will be at 2/3 charge and the smaller battery will also be at 2/3 charge and their voltages will still be the same. Thus, each battery provides current into the load proportional to their internal resistance and neither battery will attempt to charge the other. Only in the case that you have a fully charged battery connected to a depleted battery will one charge the other, and it won't matter which is *larger* what matters is which has the higher voltage. But connected to a load, each battery will drive the load and not each other. Steering diodes will certainly help when *charging* the batteries also in the case that their voltages are not the same (different chemistry or ages).
@@thomasmaughan4798 Its actually true and is the reason you should always use matched batteries when they are not rechargeable for obvious reasons. The secret is separate BMS for each battery. Don't try to use one BMS for both batteries.
Also. From last question. If need i can use separate invertors on a on, off as needed for different items. If needed the pull on batteries will be hi at times so i want to keep toped of, or at least helping them from a high drain.
What you said about the issues with different batteries in series explains why consumer electronics that use disposable alkalines tell you not to mix old and new, different brands etc. I think as kids many of us have experienced what happens when you violate those rules and the chemistries decide to leave the batteries.
Great video! This works out because the internal resistance of the cell is lower for the battery with the larger ampacity. In other words more of the load is drawn from the larger cell battery. That is why the experiment worked, and different sized batteries in parallel discharged in the same time frame. It can even help balance out the surge scenario, as more of the load comes from the battery with the lower internal resistance. However, it is still great advice and wise to avoid major imbalances in the lead acid batteries and not to mix types. It is also important to note the age and condition impact the internal resistance, and the health of the cells can effect how well they play together.
The bigger capacity battery will charge the lower capacity as well as provide external power. Then, when the capacity becomes the same, they both will charge external load until depleted.
This is helpful as I was contemplating buying a second lead acid deep cycle 12 volt battery to put in parallel with the one that came with my RV. I wasn't sure how closely I needed to match the original battery. Apparently it's not that critical
That's exactly what I did for my touring caravan to maximise the benefit when charging from either the car or the PV panels, not had any issues and over doubled the time I can run without a mains hookup
To both you and @Paul-FrancisB What neither of you have done (or intend to do) has a daul battery isolator in the charging circuit (from the alternator), as they will just become as if a single battery bank, that could well go "below" the required vehicle starting voltage, with a result of being unable to recharge anything, if away from a mains recharging facility. It's far better in an RV to have a battery isolator in the form of a dual battery circuit, where if needed, you can switch across between one battery or the other, or if a vehicle's battery gets drained (you accidentally leave the lights on or similar) you can JUMP the vehicle's battery with the RV's on-board house battey, just enough to restart the vehicle to recharge the main 1st until it's nearly recharged, and then the dual battery isolator automatically switches the 2nd battery (the house battery) into the charging circuit, to then recharge both batteries. Having both interconnected as if a single batter, may sound easy, but overdraining the house battery, will also drain the vehicle's battery, and visa versa, often well below the capability to restart the vehicle. Having a dual battery isolater connected, you will also more than likely have some way of having a low battery alarm, on at least the vehicle's battery, if not on both batteries. TO WARN if either one is getting too low Then you should quickly restart the vehicle, to recharge both to a suitable level - to ensure that you aren't marooned with two flat batteries and a dead motor
@@QUIX4U hi you have mis read my reply, I don't have an RV it is a Car and Caravan. 2 batteries in the caravan in parallel, as it is 12V. The car, oddly has 2 manufacturer fitted batteries also, Mercedes 280 (the 2nd smaller one is for the ABS and self levelling suspension). The auxiliary power (blue wire in the UK) is only energised for charging and the fridge if the alternator is charging. The caravan (camper trailer, I believe the American phrase is) cannot drain the car batteries. The solar can top up the leisure batteries if it is sunny, a rare event in the UK, or the mains hookup if available. I hope this helps you understand my reply. My understanding of the OP is he was going to double up the leisure (deep cycle) battery in the RV, and not mess with the engine starting battery or the split charge system if he has one. So he would have 3 batteries in total.
That's totally unnecessary, they will balance each other once connected in parallel. You just don't want a big enough voltage difference that any of the batteries could charge or discharge too quickly when connected.
@bobbygetsbanned6049 I agree. And that is what I do when building packs with raw cells. Putting a 3.5v cell with a 3.7 volt cell is not going to cause a lot of amperage between them. But a 4.1V cell and 3.9v cell could cause some inappropriate current. So for people that know that they’re good. For people that don’t I just tell them to manually balance to 0.1 volts. It’s the safest way to give instructions on that in my mind.
I built a 120 AH LFP first then later a 280 AH. I’ve had EG4 100 AH server rack batteries paralleled at times also . As long as the individual bms protects its battery,the pool of energy is fine. In solar power systems in homes with a large battery bank the amp draw never challenges the battery. My combined 400AH battery is currently running a 5KW inverter that seldom runs over 75% capacity. Even if the smaller battery carried the whole load, it would still be discharging at less than 1C. Certainly there are ways to maximize the efficiency to avoid conversion loss,but solar panels have become so cheap that my focus is safety and lifespan of the system by never push any component to its limit.
That was good information and I'm frankly not surprised by the results. I agree with your conclusions, but I suspect that a good number of people will not agree.
I have a "6 pack" of 2.4 volt Lithium Titanate batteries that store 12.6 volts for 40 Ah, tied to a Lithium Iron/ 100Ah. (with BMS). They are supplying power to 5 exterior 12 volt/ 2 watt lights, and 2 -2 watt bulbs (for half of the night interior lighting). I wake up in the morning to a charge reading of 12.8 to 13 volts EVERY MORNING!
Should you not mention that booth batteries be at the same voltage before you hook them up to stop a surge of power from the highest voltage to the lower voltage battery.
Extremely important to say again. Make sure the current voltage of each battery is within 1/10th of a volt or you might overload one of your batteries.
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@@vadnegru even low drop shottky diodes should help in some cases, like low power long term load.
To expand a little on your point about BMS capacity ratings. If you were pulling a high load, say 150 amps in your demonstration, and the 460 AH battery BMS went into low voltage shutdown first, that entire 150 amp load would be shifted to the the 100 AH battery, exceeding its current specification limit. Because BMS limit shutdowns cannot be predicted and will never be exactly simultaneous, the rule I follow with parallel batteries is this: never charge or discharge at a rate that exceeds a single (or the smallest in dissimilar capacity configurations) battery's limits. There are also eddie current (balancing currents flowing between the batteries) considerations that occur when charging is terminated, so I fuse every battery at its terminals according to each battery's rating. I use MRBF fuses. I've never had one of those terminal fuses blow, but there are failure scenarios where they could.
This is what I'm curious about. I'm trying to connect two 170 amp hour renogy lithium batteries and one different brand 280 amp hour lithium battery to a 3000 w inverter. Should I use fuses in between each battery and different cable sizes?
In "no" particular order, neither battery - will totally deplete itself before the other one starts to take the load, because THEY ARE NOT individually switched, via contactors or relays, thus BOTH share the load, reducing only in voltage as they deplete, when the voltage is about 11.5V BOTH batteries will have depleted to about 20% remaining (completely irrespective of capacities), as NEITHER simply provides all the loa current, until the battery's capacity is depleted - leaving the other with a "higher volage and remaining Ahrs. They are "after all" connected together. Same goes for two as for a hundred or more, of the SAME VOLTAGE but different types and ratings.. as ALL different capacity batteries would simply be "extra storage" at the same voltage (below I compare these with see-through water tanks with the same upper water levels) which would all deplete at exactly the "same levels" when interconnected as parrallels, because when each shares the total load - no battery will be individually depleting itself, before any other. THINK and respct the equation. BOTH batteries are comparible with TWO (or more) tall & "same height" see-through plastic water containers that could be connected together irrespective of capacity, thus a 1L container 1M high could be parralled to an IBC which is 1,000 L and 1M tall interconnected at or above the upper level of each (or 1,000,000 such tanks of various capacity, all 1M high) such that their lowest output vent, is at the same lower level as the other's lowest output vent. FILLING BOTH (or all) water containers to the SAME upper level, and then "opening" the one combined output supply pipe at their lower vents, ONLY reduces the total "level" as the load draws content (either water or electricity) from whichever "parralled" connection you have. The batteries will drain in EXACTLY the same way as the two interconnected water containers, it's just that the see-through tanks let you SEE what the dimishing current levels would be like, inside the enclosed (non-viewable) batteries.. NEITHER (OR NONE) of any interconnected battery, EVER depletes more rapidly than any other. Thus the BATTERIES would go below 1% capacity - at EXACTLY the same time. Neither (or none if more than two) would be "left" with any higher capacity level than their interconnected total "loading" capability levels, as BOTH (all) drain equally as the levels reduce. Anyone thinking otherwise, has ZERO idea what a "parralleled battery circuit" does, when any loads are connected to the one output point..
The smaller battery will deliver power in paralell to the larger one, and will draw power from the largest one in pralell with the load, so it balances out.
Just as noted in the next comment, you didn't mention that the capacities are additive when wired in parallel. Exceeding the discharge rate of the smaller battery isn't an issue when wired this way.
Manufacturers will not usually instruct against this if the technology is the same for the two batteries - same maximum charge voltage, same discharge curve, same end voltage on discharge. If they do it is probably the legal department overruling the engineering department! It will work very well, has been done for decades.
Thank you for the video. If you are interested in doing comparisons on pure sine inverters to modulated, there are important factors with different electronic devices. For example, my 120V house furnace (300W) won't run off of a modulated inverter but will run off of a pure sine wave inverter. But if my modulated inverter feeds a Vevor voltage converter, (120V to 120V) that satisfies my furnace electronics. That would be very important to know if the power goes out for any length of time in the winter!
Electric motors, like the one in your furnace, do not like simulated sine. The simulated sine causes spiky current (high, low, high low) which causes noise and excessive heat in the motor windings. Pure sine inverters should run motors just as well as the mains power does. The simulated sine wave creates similar spiky current within electronics, which some switching power supplies, such as PC power supplies are ok with, while others do not like it. Again, excessive heat can build up in certain components of the power supply. The simulated sine works very well for resistive loads, such as heaters, incandesent light bulbs, halogen bulbs, devices powered by transformers, such as the older (pre 2010) stereo systems.
@@javaman2883 Unless of course, the installer knows this and also installs HUGE power factor correction capacitors, that soak up th =e spikes and empty when the lows hit, meaning theyautomatically balance the modulations into a sine wave pattern. It's simple 101 with any electrician who has built any high power factor correction switchboards. My "job" for over ten years was exactly that - building heavy Industrial Switch Boards,some with up to 2,000 kWh ratings. MOST had banks of capacitors, that could be brought online, by an assortment of contacters, all controlled by a large POWER FACTOR CORRECTION meter, as the loads altered. That meant that the incoming mains cables DID NOT have to contend with high inpout currents when spiked motor startups were in operation, to start huge motors DOL or via Star-Dalta switching circuits. As these were ALL corrected by the banks of PF Correction capacitors, so the mains wasn't fluctuating around, but appearing as if a balanced sine wave current load, meaning smaller input mains cables. The huge circulating currents, inside the motor circuits and the switchboards PF capacitors, was handled by HUGE thickover rated copper bus bars, that easily handled whatever the balancing currents needed. Every other commenter here, is obviously "oblivious" of what happens to loads, which have to be balanced, as they are NOT done by the supply cables, but by the bus-bars interconnecting PF capacitors that DUMP huge currents into the circuits when needed to offset huge current draws. When motors are at running speeds and with fairly constant loads, the input current drawn from the mains is FAR smaller than the startup currents, which often exceed ten times their running currents.
Nice to see that the real world actually matches what we were taught at school. :) I'm working on the assumption that a bank of lead-acid batteries will achieve the same - although I don't think that they deliver as much as 90% of their rated capacity.
On my Harley I added a capacitor in parallel with the battery, without the cap the starter always seems to run down the battery when starting, with capacitor starter turns over like it should. Capacitor in parallel is good for heavy startup loads like when the starter motor kicks in or when an inverter kicks in to run a refrigerator, when a motor starts initially it is similar to a dead short.
True, but it needs to be a super cap to hold enough juice to be useful. The downside is that super caps can be pretty dangerous, simply because of the rate at which they can discharge, that is a short circuit will make a very big bang and at higher voltages a shock will be lethal.
@@nickwinn7812 On my Harley I used a 10,000 UF 25v electrolytic capacitor and it makes a difference because motorcycle batteries are so small. For a Truck they make 16v Audio Capacitors that are .5 farad and above, they ususally have a voltage display that would be a voltage drain while engine is off, I would remove that part then use just the plain capacitors and attach parallel to battery with short leads.
do not mix the two cases because they are not the same, the capacitor on the ac motor serves to compensate for the reactive current and not as an additional energy reserve
@@makantahi3731 What 2 cases do you think we are mixing here? Nobody is talking about motor capacitors. An HD starter motor is a DC brushed motor and has no capacitor in any case.
Works just fine in parallel. Just basic physics. They will always be the the same voltage, and during discharge they will just share the current according to their internal resistances (server power supplies share loads in a similar way, look up droop mode). The BMS is of no consequence here, since the smaller battery should never see the larger current - and if the 250A BMS shuts down for whatever reason, the 100A BMS has a very good reason to do the same. You might just want to keep the smaller batteries at the far end of the wire connection, since the little resistance in the wires will cause the front battery to see a larger voltage drop, and if the small battery is in front, some high inrush current might trigger the smaller BMS. In series, connecting two batteries with different voltages but EQUAL capacity is possible, but it is very rarely done.
Make sure to read the existing battery/s voltage/s and ensure that the NEW batteries (to be added) are at exactly (or within 0.5% of) that reading - when connecting them in, or you could become "the cable" that makes the shorting circuit, resulting in a nasty jolt between fingers, or worse, across your shoulders (and critical internal organs).
16 дней назад
Gotta be careful tho if the wear is different, as they will try to equalize and the strongest battery will constantly try to pull up the weakest one. What i usually do as a test is charge both batteries together, let them equalize, then disconnect from the charging source and check with the ammeter if there is significant load transfer between them over time. It's a problem really only if it's there's no external charge for a long time. Like i had a weather station pulling only 10W and needing to last as long as possible between charges, so i decided to put as many lead-acid battery i could in parallel, the last one i added was supposed to give me roughly 40Ah more, but ended up giving me only 5Ah at best on the long run and wearing out other batteries faster in constant equalizing, so i pulled it out. Great video tho.
If we assume that we get full capacity (or 90% of it) the BMS in the larger battery with its 250A limit is actually the limiting factor for large current draws - not the smaller battery with its 100A limit (7:26 time stamp). The reason is that the large battery is 4.6X larger in capacity than the smaller battery and will provide a current that is 4.6X larger. So the smaller battery and its 100A limit would correspond to a 460A limit on the larger battery but it is only rated for 250A.
@@occamraiser Did you watch the video? He days that the smaller battery has a max BMS output of 100A and it has a capacity of 100Ah. This is NOT what my comment is about. The question is - which battry is the limiting factor for large currents.
Great video. I have 2 banks of 4 LiFePO4 batteries each bank is a different "brand". All 100 A/Hr. When I say different brand I mean the name on the battery is different. The BMS is Bluetooth enabled and both brands use the same app and the manual is the same except for a couple of pages added. So I think the OEM is the same. When I connected the banks in parallel the BMS reported much different current readings. I got concern so I disconnected one bank, but from the video it sounds like I shouldn't worry. Comments, suggestions.
If the batteries are the same chemical kind and you can open the batteries and have access to all the voltage levels between the cells, then you can cancel the weaker BMS and connect instead the voltage levels in between the cells of both batteries in parallel as well, leaving only the stronger BMS to manage both batteries. In doing this, you are in effect building a physical larger battery, made of the cells of the two batteries, where all cells of the same power level are electrically connected in parallel. And the case boundaries of the batteries do not have an electrical meaning if you do that. The gain is that now you have just a single strong BMS and so you do not need to worry about over current anymore.
Wonder how many amps are going between the batteries when they equalize? If they are not both fully charged, could it damage the battery with the lower voltage?
Yes, he should have explained that. If one battery was a higher voltage than the other when first connected there would be a large amount of current from the higher to the lower voltage battery. Make sure to match the battery voltage before connecting them together. To be safest, attach them together with a resistor or lamp and allow them to equalize before attaching a wire directly between them. This would also be the case when discharged and one of the BMS' disconnects the battery. Re-balance the voltage before reconnecting.
@@nickwinn7812 This is only if there's a MS between the batteries. If they are directly connected to each other there is no protection... besides the wire
Interesting video. Could you please expand on the reasons for not mixing battery chemistries? I'm guessing it becomes an issue at high current draw rather that lower but I really have no idea. Thank you.
@@ecospider5 It's only that you get results you never expected, so lets hope the next one doesn't kill you (as not knowing what will happen when doing dngerous things - will ALWAYS end badly).
@QUIX4U I really enjoy setting something up in a crazy way. Then seeing what happens. The trick is understanding how crazy the setup is so you know what safety procedures to use. Like plugging in a 40 year old amplifier that hasn’t turned on in decades. Don’t do that with 120v. Get a thermal camera and watch the electronics as you increase the voltage starting at 30v. A damaged component will probably heat up too early. Doing it at a low voltage stopped that component from damaging others. Something that surprised me the other day was a fire extinguisher. I had an expired on so discharged it in the yard. If that was in a 12x12 room I would not be able to see for 5 minutes. I do crazy things when it’s safe that way I have more knowledge of what I can do safely in an emergency
Thanks for posting the video. Cool test and good points about the different discharge ratings. 1 question and one concern: If they were providing a total 300A load, wouldn't they split the load according to... Some other factor? (Internal resistance maybe?) The concern I have in this scenario is charging and reduced performance long term. The CV,CC charging stages of each battery are likely reached at different times. In that case it might be best to customize or limit the charging profile, likely resulting in lower total capacity.
It’s probably not a good idea to use this combination for high discharge applications like the 300 amps you described. This would be for slow discharge application. For high amperage uses, both batteries should have the same size BMS so the load can be equally bifurcated between them.
Charging isn't a special concern. You are thinking correctly when wondering about how they split the load, the same logic applies to charging. As for how they split, internal resistance is an issue, but usually a bigger issue, especially with LiFePO4, is the cable and connection resistance. You can test this using a clamp meter to monitor the current in the different wires between the batteries and battery to load/charger. With very different batteries such as in this video, internal resistance will definitely help split the current. That said, you would never want to do this with any load (or charger) close to the maximum supported by the total of the batteries. The current is not going to divide that precisely and it will change depending on the state of charge as the internal resistance curves of the batteries will vary. Beyond a quick surge the imbalance is likely to trip a BMS if operating without enough margin. If using two matched batteries, I'd probably be comfortable with designing for 75% of the total current (i.e. batteries support 2x 100amp, I'd probably be okay planning a 150amp max load). Note how that means even a gross imbalance of 2:1 is within the specification for a single battery. Using a setup like that should be fine. The more batteries or the more different the batteries the more safety margin is required.
Kirchoff had a bit to say about this. The community here would garner a more intuitive understanding and develop a deeper understanding if they studied Kirchoff's and Thevenin's laws. The penny will drop once these are understood and will have these folks designing systems on beer coasters and napkins in no time.....and get it right without assumptions or vague personal models of what's happening. If you connected these batteries in parallel via a busbar with separate tails in parallel, you could measure how much each battery was contributing and see how the larger capacity battery is actually charging the smaller one during periods of the discharge. That was a nice Heath Robinson style demo.
@@walsakaluk1584 Once I stepped out of the classroom into the lab I realized that while Kirchoff, Thevenin, Norton and others provide a brilliant theoretical framework, the real world requires a lot of assumptions and rules of thumb. The first problem encountered is an almost complete lack of specifications necessary to perform the requisite calculations. The second is that we must design for the center and avoid edge cases because of individual component and environmental variance, so the additional analysis is seldom useful. Oh well, the theory does provide some direction in thinking even if the equations are never evaluated.
Great info!! One question though! If you paralleled 2 batteries that were the same size one with Bluetooth and one without. Would the capacity from the Bluetooth battery now represent the entire bank?
@hooligan9968 highly doubtful, since capacity readings (for LFP anyway) are typically done with a shunt that monitors Amps in/out. And that internal shunt is only going to measure the current on that one battery. You COULD add an external BT enabled shunt to the main negative and thereby see the total in/out current.
To match those 2 batteries together for up to 80% of their BMS output capacity use 6 awg from the 100ah, 1 gauge from the 400ah and connect both sets to a single buss bar. When you draw 280 amps on a 3000 watt inverter what will happen is the 6 awg will start to choke back ( resistance starts on it ) draw and more will be pulled from the 400ah battery since it's cable is thicker and not resisting draw. I should show my system better in my videos. See my other comment on here, I explain more.
cable size should never be reduced in order to gain certain voltage drop across them. overheating cables is one of the most common causes for accidental fires. if you need to dissipate energy through resistance - use resistors specifically designed to do that - not just standard insulated wire!
@@laus9953 If you only size your battery system to 100% of your draw, never use cable loading resistance. But if your sizing to have a actual battery bank then your doing it right to size for loading resistance. It's not unsafe unless your only using as example: 300 amps to feed 300 amps of draw. That is not my system that has been running safe for years. It's about 20% maximum draw of 840 amps on all my inverters and DC loads if in peak draw against over 4800 AH / 5300 Amp output capability. I have had LiFePO4 directly connected to Lead Acid for 2 years, cabled as I said. And not once under full loads have we seen more than 2 degrees of temp increase in the restrictive cables to the Lithium section.
Usually, the batteries do not have exactly the same potential at each of the 2 poles. When they have no load, but they are in parallel, regardless of the capacity of each battery, there will current from one (+) to the other (+), and from one ( _ ) to the other ( _ ), until they equalize. Only the potential difference matters, the power drain may be from the small battery to the bigger battery.
I actually did this couple years ago in a 24V system. My LFP batteries back then were horribly imbalanced so I needed the Pb backup for when the BMS would crap itself again. No problems at all.
From what I understand is when you connect them in parallel the bms in both combine so you could say run something that uses 350a continuous so maybe ck that out next and try to run say 250a thru them and I don't think the smaller one will shut off. I been told they would share the load and the smaller one could handle it so let me see you try that next. At least try to run something larger than 100a and see if it shuts down the bms in the smaller battery. We do this with Ebikes and I haven't heard of any that shut down
No, the BMS systems don't "combine". The ratio of the capacities determines, to a first order approximation, the ratio of the currents supplied, so the smaller battery supplies 18% of the total current and the larger one supplies 82% (i.e. 4.6x as much). Since the large battery's BMS limits its maximum current to 250A while the smaller battery's BMS limits its output to 100A, the larger battery's BMS turns out to be the limiting factor (only 2.5x that of the smaller battery). The result is that with a total current draw of 300A, the larger battery would supply 246A and the smaller one would supply 54A. Any more and the larger battery's BMS would trip, immediately followed by the smaller battery's BMS as it tries to supply the full 300A+. So the maximum current you could expect to draw from the system is around 300A.
Enjoyed the advice. I bought 260ah 2x and now I have found 280ah 2x for less. Same brand of batteries. Now my question is what would this do to my Victron shunt reading? 🤔 I am running in parallel, 12v.
One other possible concern is if one battery has an internal heater and the other one doesn't. I have two 100ah batteries in parallel in one bank inside my RV trailer and a 300ah battery with an internal heater outside in a storage box. The two battery banks are connected by an A / B / Both switch. During storage I keep shore power on the trailer, but, set the A / B / Both switch to the 300ah internal heater battery only. That way if I lose power the 300ah battery doesn't try and use the two 100ah batteries to run it's internal heater. I haven't actually tested if it would. During useI run all the A / B / Both switch set to Both. During a recent trip on a particularly cold night I did seem to have an accelerated capacity drop so it might have been the case. So any future cold nights I switched to just using the 300ah battery and then only recombined them after I had shore power and could top off both banks.
This is interesting. I was trying to figure this out, and your video gave me an idea for my problem. I have a UPS with two 12V batteries in series to create 24 volts. Obviously, I can't mix and match batteries in this case, but what I can do in the future is purchase 24V batteries instead. If I wanted to increase capacity, I can just buy another 24V battery and connected it in parallel. Is this correct, or am I missing something?
Did you measure them individually first?? Perfectly true, you can connect a 30ah to a 300ah without issue in parallel and get 330. I do it all the time
People often have a nearly DEAD car battery, with possibly a voltage as low as 5volts. Then along comes BOB the builder, with his work truck, and a pair of 300amp jumper cables, and instantly boosts your battery's voltage back up high enough, (from his battery sitting pretty at about 14.4Volts) for you to restart your vehicle, to thus "run" on it's own while recharging your nearly dead battery itself. What any Bob the Builder NEVER DOES - is check your nearly dead battery's voltage first, he just uses VERY HEAVY DUTY CABLES (that can handle the jumper-currents, as the two batteries "self-balance"). He also ensures that he keeps his own motor running to recharge both batteries, until the jumper cables are removed (with their heavily insulated handles). That way - he can deplete his own battery fairly heavily, to restart your motor (while the two batteries self-level), and do it without risking any electrical shock to himself, with the heavly insulated handles. It's the same situation with following distances, only a fool breaks the 2 second rule. Only a fool touches both battery terminals with wet hands at the same time, or, tries to become the missing starter motor cable - ???? Hello, stupid is as stupid does, but a fool never learns.
Hi! we have two batteries (12V 400A and 12V 100A) parallel connected and the load is 12V 100A. So when the batteries would not feed the load? Less than 1 hour or it would be about less then total current amount / load current?(100 + 400 / 100 = 5 hours) - Thanks
Many thanks for this demo. Just one question, is it ok to connect in parallel 2 batteries one having cylindrical cells and one having prismatic ? all the best from the UK
It’s confusing when you swap between using amp hours and watt hours 2:35 . Simplify it and stick to one term, the one on the batteries, amp hours. Instead of 7000 something watt hours we can immediately see 460 + 100 = 560 amp hours as that’s what’s written on the batts.
He does that because the kill-a-watt meter reports in wh not ah. Even if the meter reported in ah it would be based on 120Vac not 12Vdc. This would be even more confusing as he would need to convert the AC side to wh and then convert from wh to ah for the 12Vdc side.
Watt-hours are actually more convenient as energy is measured in kWh (“units”). Simply do an Ohm’s Law calculation to convert, e.g. 100 Ah at 51.2V use P=V*I ( 51.2 * 100) = 5120 Wh (or 5.12 kWh). Do the reverse to ge Ah.
This might work short term but if you parallel two lead acid batteries of different age or capacity for any length of time they will "fight" each other until they both fail. Personal experience.
I used to design battery management systems and chargers for telecommunications installations. Lead acid batteries of the same technology are frequently connected in parallel. So long as the state of charge to Voltage relationship is the same for the two (or more) batteries they will share and not be damaged. The charger should ensure that both reach the end voltage when charging and are disconnected before being over discharged. These voltages are the same for new or old batteries of the same technology. This is true for Lithium batteries as well. I don't think they can "fight" each other - what would that mean in terms of voltage and current? And they certainly do not fail - they can last decades. On the other hand, similar age, technology and capacity is critically important for series connection.
@@HughCStevenson1My guess (from the very little information, admittedly) is that one/some had significantly more equivalent series resistance, so that the effective voltages are mismatched every time the load changes or charging state flips. (This would happen a lot more often for, say, buffering solar energy than for battery backup for grid power.) I wish ESR were easier to measure to avoid such things.
Simple question: How big a parallel bank of LIFEPO can you build? Yeah, the manual says 4 batts, but can you go 5,6,7,8, etc etc. As you said you can add as your budget increaes.. Thanks
This should be a procedure you don't plan for. It should be what you do in a pinch to get through a low voltage scenario when you're away for the weekend. This "plan B" is good to know when you're away from home. But when you get back home, get matching batteries before your next trip.
No, it is fine for ever. There is no need to have identical capacities. So long as the technology of the batteries is the same. Lead acid wet to lead acid wet, Ni Cd to Ni Cd, LiFePO4 to LiFePO4, don't mix them up...
One thing I've heard and please tell if I'm wrong is an issue with charging using highly electronically controlled or digital type chargers or charging systems that measure capacity. It was stated that this type of charging would essentially turn off the charge rate when the smaller battery gets to full capacity. In this system with a 100ah battery and a 450ah battery would only come to a "full charge" of only 200ah and would then not give the 450ah battery the additional 350ah of charge. I have not tested this myself so I honestly have no idea. The argument does make sense but again please tell me if I'm wrong. Thanks!
This is essentially how solar eystems work all down the voltage on wether your home consumes from the grid or the battery. These will essentially bqlance as the laod will draw from rhw device with the highest volrage.
Nothing happens. Works fine. They balance each other as long as you aren’t pulling huge currents from them like trying to run an AC on batteries (good luck with that). Small camper stuff does fine balancing the load and sharing the capacity. Been running a 100 Ah with a 200ah. Biggest draw is the 12v fridge and vent fan.
In series, the smaller capacity battery will be depleted while the larger will still be going strong. This would cause damage to the smaller one. You would only get the capacity of the smaller. In parallel the bigger battery tries to charge the smaller. In both cases damage will be a long term event while you think everything is doing fine.
Although it is not recommended It is possible to use say 4 12v LiFePo4 batteries in series without any problem. I have run 12 100Ah batteries as 4s3p now for over a year and have had no problems. I have however connected a battery equalizer (HA02) over the batteries to equalize the voltages over the the 3 strings. They are also connected so that it is really 4 x 300Ah as 4s. I use the cheapest LiFePo4 batteries I could find and they where absolutely NOT recommended to be used as I do. The danger as I see it is if 1 set of batteries disconnect and there is a load connected then the disconnected set can have probably up to near 45v over it and the BMS in that set may not be able to handle such a voltage. My solar regulators turn off the charging when my battery setup is full (58.4v) and the inverter turns off at 45.6v. The equalizer makes sure that every s has a similar voltage so that a blow up due to wandering inequality is avoided. At another setup I am using similar "cheap" batteries as 2s2p in both 100Ah and 135Ah ( 2 setup's) and then parallel to 4p 150Ah 24v. I leave some cable in between the different setups to allow some natural over resistance balancing. It all works pretty good - probably not quite to it's limits but that should only be better for the batteries anyway I believe. On my old Golf Cart I use 5s and 2 HA02 equalizers on probably even worse batteries. The overall voltage is never really outside 65-67v so they are not pushed much. I believe that the trick in using sub standard batteries is to use the equalizers and then not push them too hard and then of cause external charge and discharge control. The internal BMS is then only there to balance the single cell's and for absolute security.
If you connect a 200AH and a 50AH battery in parallel (both 12Volts), they’ll share the same voltage, but the 50AH battery will wear out faster. The smaller battery will charge and discharge quicker, which could stress it and shorten its life. There’s also a risk of uneven current flow if one battery is charged more than the other, which can lead to overheating or damage. For the best performance and safety, it’s better to use batteries with the same capacity when connecting them in parallel. Thats it!
Tnx. I wonder if you did pull more than 100 Ah ... why wouldn't the higher amp hour battery try to equalize and the current that is needed would use the cables to pass. I could see maybe too small of cable .. might be an issue... It might be an interesting test. If the BMS shuts it off then you can restart it anyway.
you assume, just talked, did not test, i have doubts: 200 Amps, the bigger battery (both in parallel)i think it will handle the 2oo amps almost alone,because the smaller one has way higher resistance; BUT.... it depends A LOT on the cables, and the time that the test takes.
What about charging? Many regulated chargers? The smaller battery gets overcharged while the larger gets undercharged when connected in parallel. Not to mention, other comments are correct, as they discharge the voltage of the larger continues higher as the smaller depletes faster. When charging this variation I've seen overcharge the smaller causing high heat. Actually have one getting burned outside right now on purpose. I'm reconditioning the battery. Reverse charge at a higher than normal rate to knock the sulfur off, then I'll charge it correctly
I've actually been doing additional testing for a follow-up video and while I'd agree that you probably shouldn't do this for SLA and GEL type (non-Li) chemistries, I still don't see an issue for LFP. The LFP batteries have an internal BMS that keeps them individually from being over-charged or over-discharged. And while their will certainly be some differences in internal resistance at the same voltage (SOC), the differences are not likely to be so significant as to cause any issues that you'd need to be overly concerned about. So they will, more or less, charge and discharge at rates that are proportional to their relative capacities and the larger battery will often provide a small amount of current to the smaller one as they are continually seeking to remain in balance. But this extra charge/discharge activity is not materially different than what is happening naturally in a solar-charging battery/inverter system anyway. So, I stand by my claims from this video - at least with respect to LFP battery chemistry.
@@ReeWrayOutdoors I can understand what you're saying, and while they have internal regulation, would you want to stress or rely on this regulation with lithium? Although lithium is pretty good about letting you know if it doesn't work. Just hope it's in a fireproof container. I'm an Automotive mechanic. I've seen all too often where some cells are bad, we tell the customers the entire thing needs to be replaced because the difference in wear from old to new can cause issues. The customers go to some independent that replaces only the bad cells and the whole thing fails because the charging is unbalanced. I've also seen where cells were bad, the customer stated they didn't want them replaced, they are individually regulated and the capacity will be reduced but they can't afford the repairs. Then it comes back on a tow truck burnt from the battery going up in flames. Lithium is less forgiving than lead acid. There's a reason LiPo batteries need a specific charger as well. They just can't be charged any way, must be a specific way
So they dischage at the same time? And go dead at the same time? Is that why the large battery wont start charging the smaller battery. And thanks for he great videos
Question for you, I have 4 12V 75ah batteries that were originally configured as a 48V series connected pack for an electric riding mower. They were replaced because one battery was weak. I currently am using the 3 good batteries in a 12V parallel pack with an inverter to run essential loads during power outages. Could I add the 4th "weak" battery to my setup for increased capacity?
The BMS only "see" the current of it's own battery, and in a parallell circuit the current is divided by the two batteries. In theory, with identical battery chemistry, two batteries in parallell should provide the part of the current drawn exactly proportional to it's capacity. Meaning, a 250 A battery and a 100 A battery in parallell should in theory be able to provide 350 A, reality isn't that perfect, but well over 300 A should be possible without reaching the current limit of either BMS. In a serial circuit both batteries sees the same current, the full circuit current.
I have a van main battery under the hood. I have a small winch in the back for motorcycle loading. Currently I use a separate battery for the winch. Could I run a wire from the main battery to the winch battery for charging purposes? Would the amp draw of the winch fry the wires connecting the batteries? Basically looking for a work-around for running a big fat expensive wire from the engine bay to the back of the van.
You'd fry the wire running the winch if the rear battery couldn't handle the load. Same if it drew too much charging current. In old RV's there was a "battery isolator" which allowed charging of 2 batteries, then disconnected the engine starting battery when you turned the engine off. Get one of those and your system should work OK. According to your wire run lengths and routing, you might be able to use cheap car jumper cables split in two. Just remember that the insulation isn't very heat or chemical (oil) resistant and the wire gauge may be a size smaller than stated. I don't know why the wire is so much cheaper this way but I've been doing exactly that to get power to the back of my workvans for over 30 years and never a problem of any kind.
Awesome video! Let me throw a question out there, okay, I have 2 similar battery's a 12v Timeusb 230ah battery with no low temp protection and a 12v Timeusb 200ah battery with low temp protection. Will the low temp protection work on the whole system when set up in a parallel application?
@stevenseigneurie5073 I don't think so because even if the low temp protection kicks in, the unprotected battery is still able to provide power to a load since there's still a completed circuit.
Good video. I had a question about two batteries with 50 Amp BMS..if I connect them in parallel will that still only discharge at a max of 50 Amps or will I be able to discharge at 100 amps?
They will 'current share'...so each battery in this scenario will effectively contribute 50% of the current to the load...so would expect to be able to power a 100A load between these 2 50A batteries.
I want to add that as it might not be obvious. You need to be sure when you add batteries in parallel that those realy have equal battery chemistry not just lead-acid vs nickel based vs lithium based. Like if you have Li-ion batteries (Li-NMC, LiFePO 4, LiCoO2, Li-NCA), Li-ion is common nominator for these. And i have seen batteris that don't have anyother label for their battery chemistry (usually due to integrated circuitry which is different story) even if they had same nominal voltage, curves might be different (and will be if chemistry is different) -> then there would happen weird chagings between batteries. and some even have small voltage raises before curve sharply decreases at the end of capacity.
that would be a problem in series connection - why should it be one in parallel? let balancing currents flow - balance will be kept, no?! as long there are sufficient fuses between batteries, in case one does draw or supply too much..
Don't sweat the BMS continuous current rating too much. As a rule, the equivalent resistance of LiFEPO4 batteries is largely inversely proportionate to their capacities. The batteries will mostly current share, with the smaller battery only producing it's percentage of overall capacity in current. In this configuration, if you used a DC clamp meter on the output terminals of each battery, The smaller battery would show about 18% of the total draw of the inverter, while the larger battery would supply about 82% of the current. If the big battery has a 250 amp current limit, the small battery only needs to be about 55 amps, to allow full loading of the bigger battery management system. (BMS)
This is accurate. I run a system with different capacity batteries in parallel connected through bus bars and it behaves exactly as you described.
I would have expected it to behave this way. Because both batteries will be at almost identical voltage the current flow will be greater from the greater capacity battery. It's not common you see this configuration but nothing wrong with it.
It should be true that lower capacity as higher resistance, but different manufacturers may have different resistance for the same capacity
I know some of those words 😌
Pretty much exactly what I was going to say, no joke almost Word for Word but in a slightly different order.
While I already knew this, I'm really happy with your demonstration that proves it beyond doubt. Thank you!! 👍
And I use lead acid car batteries so doing that test for myself would risk damaging them if my home made chinese low voltage cut-off / 200A relay combo lets me down.
Im running 28 12.8v Li Time batteries in parallel, 4 batteries / 7 individual shunts.
Hooked to 5 renogy inverters.
2- 3000 watt
2- 1000 watt
1- 2000 watt
They are running dedicated rooms in our off grid cabin.
Hope to have a single 18k EG4 the first of next year , to run our electric stove , clothes dryer and water heater.
I enjoy your informative videos
"DIFFERENT Capacity in Parallel - What Happens?!"
Provided they have the same voltage, *nothing happens* . As you draw power, the one with less capacity will start to drop voltage, but of course, it cannot; so most of the load starts drawing from the battery with more capacity. Thus, their SOC (state of charge) draws down uniformly.
well when i connect them i see lots of power leak from higher one to smaller one as smaller ones voltahe is in general less even if charged full there is small change... you can use a voltmeter and ampermeter to check the voltage difference ..
@@ahmetmutlu348so you saying that full charge voltage is not same for Comparison of a 10 amp and 40 amp battery? 😮
@@ahmetmutlu348thats just nonsense…
Capacity has nothing to do with voltage. AGM batteries, 40Ah, 90Ah, 120Ah ALL have ~12,9V when new and fully charged
@@PM-wt3yeIm not sure.. but when i left them unmonitored things goes wrong in general and i suspected that they are discharging each other and checked voltage flow and i allmost allways see lots of power flow from one to another... if you have time you can make may be an arduino that creates statistics for how that goes.😊 but there is allmost allways atleast 0.5 volts flow from one to another may not be a problem of you charge them regularly anyway... may be thats what they call self discharge pr whatewer but what ive seen is they do discharge a lot.😊
@@matb748I dont have detailed stats but you can do the test yourself.. connect 2 batteries in paralel and use a voltmeter or led on one of the cables serially... youll see led will light up indicating discharge from one to another.
Great info. I pretty much thought this was the case but never tested it. Nice to have it confirmed...
I have been researching this question for years and this is the first time I've found a solid answer. Thank you.
Years? I could have found the answer in 5 minutes with a google search, but I already knew.
@@stinkycheese804 The first GOOD answer I found. I guess your googling works better.
I was complimenting the video creator, not inviting snarky comments.
me too
those are the basics of electrical engineering, I don't remember if I learned it in elementary school or just in high school, if you're still in kindergarten, don't worry, that will come later
@@makantahi3731 I'm not an electrical engineer, so I look for answers.
If you learned about lithium battery balancing and charging and what can affect their capacities in the long-term in elementary school, wow.
Damn, I've always wondered about that. Great experiment, valuable info. Good to know if you happen to be in an emergency situation and have access to multiple batteries.
You got scared didn't you ?
Adding a 200 and 100 amp bms battery in parrallel means you can draw over 200 amps since the load is distributed across both batteries.
You have to imagine it like this.
The large battery is a wide container for energy, the small battery is a narrow container for energy. Now you connect both in parallel, this equalizes the height of energy (Volt), but the width of the batteries remains the same.
When unloading, both are unloaded in height (Volt), but the Ampere balance each other out.
To the point where both are empty.
Due to the internal resistance, the cells can discharge at different rates.
But things even out again.
Great informative video & advice, thanks.
It would have been good to also monitor the current share between the two batteries and graph the battery voltage till drop off & shutdown.
Well I just learned something new. Which is why I am subscribed to your channel. Great information to know. I am glad that when you do this type of videos, they are directed to the novice audiences getting into solar power and batteries and you do not assume that we already know. Great, great explanation and great job.
Exactly what I thought , but REALLY well explained for those those that have no Technical background .
That battery is a monster. Nice video thanks
If you've got a leisure battery fitted then it's in parallel with the main battery whenever it's charging. Never a problem.
As you will see in my videos, my channel, for years I have Lead acid AND LiFePO4 running in one bank. 13 LiFePO4 Batteries connected to one main buss bar. 2 @ 400ah, 5 @ 200ah and 6 are 100ah. Been running fine for over 26 months. The method is your cable sizing. You use resistive cable gauging to keep them working together. 6 awg from each 100ah, 4 awg from each 200ah, and 2 awg from each 400ah. The outcome is defaulted charge and draw due to wire/ load resistance(heat). As you demand too much from the 100ah, the 6 awg starts to "road block" basically resist pull over 70 amps and defaults to the 200ah, the 200 ah 4 awg starts to get resistance in its cable when you exceed 125 amps and defaults to the 400ah using 2 awg. It all auto balances itself to the main buss bar so I get 70% ability of all the BMS's at the same time as it is in use. to make matters even more insane, for almost 2 years I have 28 GC2 Rolls Surrettes 235ah Lead Acid Batteries connected via 2/0 cable to those LiFePO4 Buss Bar. The inverters and all loads pull direct from the Lead Acid which gets its voltage support ( not its main amp draw ) from the Lithium.
My total result is thousands of Amp hours. The Lead Acid is like new even though 3-1/2 years old since they have voltage support and never see over 45% DOD. They even now have 1/3 the water loss due to the LiFePO4 all night supporting voltage stability refill.
I learned this in the Telecom industry when they used Ni-mh for lead acid support the same way in the 1990's.
I watched you explain a lot of good info on yer channel.😊
When you connect two batteries in parallel over a long period with no demand, is there a risk of one battery continually trying to charge the other?
No, if you connected all the batteries using a 6" x 1/2" COPPER BUS BAR, they would all deplete at exactly the same % each, irrespective of "rated current loading", because if the LOAD is more than the smallest battery, IT IS NOT SUPPLYING ALL OF THAT LOAD, just a small percentage of the over-rated load.
THINK, all a battery is, is a container with a specified rated current at a certain voltage.
One can use see-through plastic water containers, (instead of batteries) such as using ALL at a 1M height - but of different diameters, or shapes, (or squares shapes too, as that's what an IBC is, a square pipe 1M high) such that ALL will be filled to maximum height (1M) before you open the combined drain pipes, to drain at whatever rate your "output loading" is, thus if you draw far more "capaciy" than your smallest container's capacity, don't worry at all, because that IS NOT the only container there.
It will NOT drain it's capacity any faster than any other, so when your smallest battery gets to HALF of it's capacity - all others will also be at 50%.
ALL will be self-balanced (at that same 50% level), thus there will also be no "intercharging (flow) effects" either, between any two.
There is no need as all will have the same height of upper water levels, (which is comparible to a batteries toal capacity left) - meaning that no ONE battery will be supplying anything to any other, with them ALL at the same % capacity left.
THE PROBLEM IS THIS, many people assume, that because they are using 12v batteries, they can combine NEW fully charged batteries, with depleted ones, to get the shock (quite literally) of their lives, when a MASSIVE instantainious flow occurs, between the fully charged batteries and the depleted ones, that ARE NOW BEING RECHARGED by the new batteries, far beyond the "rated capacities of the new batteries, causing THEM to explode.
The recharging one's won't explode as they still aren't fully recharged, and never will be if the new batteries explode.
@@QUIX4U Almost on my 28th month running over 900 amps start peak flow, 400 continuous and my designed cable resistance effect is @peak pulling 75% from the lead acid and 25% from the Lithium then when the high start load ends they balance in a matter of minutes. No wire heat happens or failures of BMS has happen as I was constantly told would happen. My lead acid water use is less than half it should be, their DOD is never seeing 50%, and the lithium/lead has performed just identical as the USN submariner electrical handbook said 2 chemistries should and would ( SLA and NiCad 1982 Section 4-8b )
@@QUIX4U
Thankyou for your very informative reply. The water analogy applies to the solar panel on the roof. The inverter senses the mains pressure and uplifts slightly to either supplement or overcome the mains. However in the battery connections, you will not have a zero resistance bus bar and thus slightly different voltages at each battery connection on charging and discharging. Is that not a problem over the long term?
One thing to keep in mind is the voltage difference between the two batteries under use. For example, if the voltage output of the smaller battery falls below the voltage output of the large battery, the large battery will end up charging the smaller battery instead of putting all it's current output towards the load. The usual way to prevent this is through the use of so-called "steering diodes." This prevents one battery from discharging some or all of it's current output into another battery. Unfortunately it also lowers the overall output voltage by 0.7 volts for each diode that ends up being between the final output from the batteries and the load.
The use of Schottky diodes drops this to about ~0.2VDC.
"the large battery will end up charging the smaller battery instead of putting all it's current output towards the load."
While unlikely, this is also harmless; since the *charge* is still available to the load.
Yeah but there will be a drop in efficiency due to losses caused by the larger battery charging the small one. Though the efficiency will be a lot lower than the one caused by the diodes.
@@holyscrap4445 "but there will be a drop in efficiency due to losses caused by the larger battery charging the small one."
It is unlikely the larger one tries to charge the smaller one. As I explained already, what will happen is the rate of discharge of the smaller battery will decline faster than the rate of discharge of the larger battery simply because of the higher internal resistance of the smaller battery. Thus, both batteries will deplete their proportion of charge at about the same rate; the larger battery will be at 2/3 charge and the smaller battery will also be at 2/3 charge and their voltages will still be the same. Thus, each battery provides current into the load proportional to their internal resistance and neither battery will attempt to charge the other.
Only in the case that you have a fully charged battery connected to a depleted battery will one charge the other, and it won't matter which is *larger* what matters is which has the higher voltage.
But connected to a load, each battery will drive the load and not each other.
Steering diodes will certainly help when *charging* the batteries also in the case that their voltages are not the same (different chemistry or ages).
@@thomasmaughan4798 Its actually true and is the reason you should always use matched batteries when they are not rechargeable for obvious reasons.
The secret is separate BMS for each battery. Don't try to use one BMS for both batteries.
Also. From last question. If need i can use separate invertors on a on, off as needed for different items. If needed the pull on batteries will be hi at times so i want to keep toped of, or at least helping them from a high drain.
After using jumper boxes this is kinda what I expected. Thanks for clarifying!
Thanks. I always find your videos interesting, informative and practical.
What you said about the issues with different batteries in series explains why consumer electronics that use disposable alkalines tell you not to mix old and new, different brands etc. I think as kids many of us have experienced what happens when you violate those rules and the chemistries decide to leave the batteries.
‘Chemistries decide to leave batteries’ By this do you just mean leaks and corrosion?
Great video! This works out because the internal resistance of the cell is lower for the battery with the larger ampacity. In other words more of the load is drawn from the larger cell battery. That is why the experiment worked, and different sized batteries in parallel discharged in the same time frame. It can even help balance out the surge scenario, as more of the load comes from the battery with the lower internal resistance. However, it is still great advice and wise to avoid major imbalances in the lead acid batteries and not to mix types. It is also important to note the age and condition impact the internal resistance, and the health of the cells can effect how well they play together.
The bigger capacity battery will charge the lower capacity as well as provide external power. Then, when the capacity becomes the same, they both will charge external load until depleted.
This is helpful as I was contemplating buying a second lead acid deep cycle 12 volt battery to put in parallel with the one that came with my RV. I wasn't sure how closely I needed to match the original battery. Apparently it's not that critical
That's exactly what I did for my touring caravan to maximise the benefit when charging from either the car or the PV panels, not had any issues and over doubled the time I can run without a mains hookup
To both you and @Paul-FrancisB
What neither of you have done (or intend to do) has a daul battery isolator in the charging circuit (from the alternator), as they will just become as if a single battery bank, that could well go "below" the required vehicle starting voltage, with a result of being unable to recharge anything, if away from a mains recharging facility.
It's far better in an RV to have a battery isolator in the form of a dual battery circuit, where if needed, you can switch across between one battery or the other, or if a vehicle's battery gets drained (you accidentally leave the lights on or similar) you can JUMP the vehicle's battery with the RV's on-board house battey, just enough to restart the vehicle to recharge the main 1st until it's nearly recharged, and then the dual battery isolator automatically switches the 2nd battery (the house battery) into the charging circuit, to then recharge both batteries.
Having both interconnected as if a single batter, may sound easy, but overdraining the house battery, will also drain the vehicle's battery, and visa versa, often well below the capability to restart the vehicle.
Having a dual battery isolater connected, you will also more than likely have some way of having a low battery alarm, on at least the vehicle's battery, if not on both batteries.
TO WARN if either one is getting too low
Then you should quickly restart the vehicle, to recharge both to a suitable level - to ensure that you aren't marooned with two flat batteries and a dead motor
@@QUIX4U hi you have mis read my reply, I don't have an RV it is a Car and Caravan. 2 batteries in the caravan in parallel, as it is 12V. The car, oddly has 2 manufacturer fitted batteries also, Mercedes 280 (the 2nd smaller one is for the ABS and self levelling suspension). The auxiliary power (blue wire in the UK) is only energised for charging and the fridge if the alternator is charging. The caravan (camper trailer, I believe the American phrase is) cannot drain the car batteries.
The solar can top up the leisure batteries if it is sunny, a rare event in the UK, or the mains hookup if available.
I hope this helps you understand my reply.
My understanding of the OP is he was going to double up the leisure (deep cycle) battery in the RV, and not mess with the engine starting battery or the split charge system if he has one. So he would have 3 batteries in total.
Get the batteries within 1/10th of a volt before connecting them in parallel.
That's totally unnecessary, they will balance each other once connected in parallel. You just don't want a big enough voltage difference that any of the batteries could charge or discharge too quickly when connected.
@bobbygetsbanned6049
I agree. And that is what I do when building packs with raw cells. Putting a 3.5v cell with a 3.7 volt cell is not going to cause a lot of amperage between them. But a 4.1V cell and 3.9v cell could cause some inappropriate current.
So for people that know that they’re good. For people that don’t I just tell them to manually balance to 0.1 volts. It’s the safest way to give instructions on that in my mind.
I built a 120 AH LFP first then later a 280 AH. I’ve had EG4 100 AH server rack batteries paralleled at times also .
As long as the individual bms protects its battery,the pool of energy is fine. In solar power systems in homes with a large battery bank the amp draw never challenges the battery. My combined 400AH battery is currently running a 5KW inverter that seldom runs over 75% capacity. Even if the smaller battery carried the whole load, it would still be discharging at less than 1C.
Certainly there are ways to maximize the efficiency to avoid conversion loss,but solar panels have become so cheap that my focus is safety and lifespan of the system by never push any component to its limit.
As long as you have power coming in periodically its not an issue especially with lithium rig with a BMS
I got scared !
That was good information and I'm frankly not surprised by the results. I agree with your conclusions, but I suspect that a good number of people will not agree.
I have a "6 pack" of 2.4 volt Lithium Titanate batteries that store 12.6 volts for 40 Ah, tied to a Lithium Iron/ 100Ah. (with BMS). They are supplying power to 5 exterior 12 volt/ 2 watt lights, and 2 -2 watt bulbs (for half of the night interior lighting). I wake up in the morning to a charge reading of 12.8 to 13 volts EVERY MORNING!
Should you not mention that booth batteries be at the same voltage before you hook them up to stop a surge of power from the highest voltage to the lower voltage battery.
He did.
Essentially, this is what active balancers doing
Extremely important to say again. Make sure the current voltage of each battery is within 1/10th of a volt or you might overload one of your batteries.
@@vadnegru even low drop shottky diodes should help in some cases, like low power long term load.
Great demonstration. Thank you!
To expand a little on your point about BMS capacity ratings. If you were pulling a high load, say 150 amps in your demonstration, and the 460 AH battery BMS went into low voltage shutdown first, that entire 150 amp load would be shifted to the the 100 AH battery, exceeding its current specification limit. Because BMS limit shutdowns cannot be predicted and will never be exactly simultaneous, the rule I follow with parallel batteries is this: never charge or discharge at a rate that exceeds a single (or the smallest in dissimilar capacity configurations) battery's limits. There are also eddie current (balancing currents flowing between the batteries) considerations that occur when charging is terminated, so I fuse every battery at its terminals according to each battery's rating. I use MRBF fuses. I've never had one of those terminal fuses blow, but there are failure scenarios where they could.
This is what I'm curious about. I'm trying to connect two 170 amp hour renogy lithium batteries and one different brand 280 amp hour lithium battery to a 3000 w inverter. Should I use fuses in between each battery and different cable sizes?
In "no" particular order, neither battery - will totally deplete itself before the other one starts to take the load, because THEY ARE NOT individually switched, via contactors or relays, thus BOTH share the load, reducing only in voltage as they deplete, when the voltage is about 11.5V BOTH batteries will have depleted to about 20% remaining (completely irrespective of capacities), as NEITHER simply provides all the loa current, until the battery's capacity is depleted - leaving the other with a "higher volage and remaining Ahrs.
They are "after all" connected together.
Same goes for two as for a hundred or more, of the SAME VOLTAGE but different types and ratings.. as ALL different capacity batteries would simply be "extra storage" at the same voltage (below I compare these with see-through water tanks with the same upper water levels) which would all deplete at exactly the "same levels" when interconnected as parrallels, because when each shares the total load - no battery will be individually depleting itself, before any other.
THINK and respct the equation.
BOTH batteries are comparible with TWO (or more) tall & "same height" see-through plastic water containers that could be connected together irrespective of capacity, thus a 1L container 1M high could be parralled to an IBC which is 1,000 L and 1M tall interconnected at or above the upper level of each (or 1,000,000 such tanks of various capacity, all 1M high) such that their lowest output vent, is at the same lower level as the other's lowest output vent.
FILLING BOTH (or all) water containers to the SAME upper level, and then "opening" the one combined output supply pipe at their lower vents, ONLY reduces the total "level" as the load draws content (either water or electricity) from whichever "parralled" connection you have.
The batteries will drain in EXACTLY the same way as the two interconnected water containers, it's just that the see-through tanks let you SEE what the dimishing current levels would be like, inside the enclosed (non-viewable) batteries..
NEITHER (OR NONE) of any interconnected battery, EVER depletes more rapidly than any other.
Thus the BATTERIES would go below 1% capacity - at EXACTLY the same time.
Neither (or none if more than two) would be "left" with any higher capacity level than their interconnected total "loading" capability levels, as BOTH (all) drain equally as the levels reduce.
Anyone thinking otherwise, has ZERO idea what a "parralleled battery circuit" does, when any loads are connected to the one output point..
It would be a good idea to check that the voltages are similar before connecting them - you could get a big current!
Check out my Part 2 on this video. I actually test that very scenario. At least with LFP, not really an issue.
Hell, I learned that in high school electronics back in the 70's!!
I learned something here, thanks.
The smaller battery will deliver power in paralell to the larger one, and will draw power from the largest one in pralell with the load, so it balances out.
Just as noted in the next comment, you didn't mention that the capacities are additive when wired in parallel. Exceeding the discharge rate of the smaller battery isn't an issue when wired this way.
You can do it personally don't always mean that it is advisable to do it against manufacturer instruction。🤷♂🤷♂
Manufacturers will not usually instruct against this if the technology is the same for the two batteries - same maximum charge voltage, same discharge curve, same end voltage on discharge. If they do it is probably the legal department overruling the engineering department! It will work very well, has been done for decades.
Thank you for doing this video. With all of that being said how long were you able to run the heater in real time?
Thank you for the video. If you are interested in doing comparisons on pure sine inverters to modulated, there are important factors with different electronic devices. For example, my 120V house furnace (300W) won't run off of a modulated inverter but will run off of a pure sine wave inverter. But if my modulated inverter feeds a Vevor voltage converter, (120V to 120V) that satisfies my furnace electronics. That would be very important to know if the power goes out for any length of time in the winter!
Electric motors, like the one in your furnace, do not like simulated sine. The simulated sine causes spiky current (high, low, high low) which causes noise and excessive heat in the motor windings. Pure sine inverters should run motors just as well as the mains power does.
The simulated sine wave creates similar spiky current within electronics, which some switching power supplies, such as PC power supplies are ok with, while others do not like it. Again, excessive heat can build up in certain components of the power supply.
The simulated sine works very well for resistive loads, such as heaters, incandesent light bulbs, halogen bulbs, devices powered by transformers, such as the older (pre 2010) stereo systems.
@@javaman2883 Unless of course, the installer knows this and also installs HUGE power factor correction capacitors, that soak up th =e spikes and empty when the lows hit, meaning theyautomatically balance the modulations into a sine wave pattern.
It's simple 101 with any electrician who has built any high power factor correction switchboards.
My "job" for over ten years was exactly that - building heavy Industrial Switch Boards,some with up to 2,000 kWh ratings.
MOST had banks of capacitors, that could be brought online, by an assortment of contacters, all controlled by a large POWER FACTOR CORRECTION meter, as the loads altered.
That meant that the incoming mains cables DID NOT have to contend with high inpout currents when spiked motor startups were in operation, to start huge motors DOL or via Star-Dalta switching circuits.
As these were ALL corrected by the banks of PF Correction capacitors, so the mains wasn't fluctuating around, but appearing as if a balanced sine wave current load, meaning smaller input mains cables.
The huge circulating currents, inside the motor circuits and the switchboards PF capacitors, was handled by HUGE thickover rated copper bus bars, that easily handled whatever the balancing currents needed.
Every other commenter here, is obviously "oblivious" of what happens to loads, which have to be balanced, as they are NOT done by the supply cables, but by the bus-bars interconnecting PF capacitors that DUMP huge currents into the circuits when needed to offset huge current draws.
When motors are at running speeds and with fairly constant loads, the input current drawn from the mains is FAR smaller than the startup currents, which often exceed ten times their running currents.
Nice to see that the real world actually matches what we were taught at school. :)
I'm working on the assumption that a bank of lead-acid batteries will achieve the same - although I don't think that they deliver as much as 90% of their rated capacity.
On my Harley I added a capacitor in parallel with the battery, without the cap the starter always seems to run down the battery when starting, with capacitor starter turns over like it should. Capacitor in parallel is good for heavy startup loads like when the starter motor kicks in or when an inverter kicks in to run a refrigerator, when a motor starts initially it is similar to a dead short.
True, but it needs to be a super cap to hold enough juice to be useful. The downside is that super caps can be pretty dangerous, simply because of the rate at which they can discharge, that is a short circuit will make a very big bang and at higher voltages a shock will be lethal.
@@nickwinn7812 On my Harley I used a 10,000 UF 25v electrolytic capacitor and it makes a difference because motorcycle batteries are so small. For a Truck they make 16v Audio Capacitors that are .5 farad and above, they ususally have a voltage display that would be a voltage drain while engine is off, I would remove that part then use just the plain capacitors and attach parallel to battery with short leads.
@@miken7629 Do as you please, just know that large capacitors hold nasty surprises for the unwary.
do not mix the two cases because they are not the same, the capacitor on the ac motor serves to compensate for the reactive current and not as an additional energy reserve
@@makantahi3731 What 2 cases do you think we are mixing here? Nobody is talking about motor capacitors. An HD starter motor is a DC brushed motor and has no capacitor in any case.
Works just fine in parallel. Just basic physics. They will always be the the same voltage, and during discharge they will just share the current according to their internal resistances (server power supplies share loads in a similar way, look up droop mode). The BMS is of no consequence here, since the smaller battery should never see the larger current - and if the 250A BMS shuts down for whatever reason, the 100A BMS has a very good reason to do the same. You might just want to keep the smaller batteries at the far end of the wire connection, since the little resistance in the wires will cause the front battery to see a larger voltage drop, and if the small battery is in front, some high inrush current might trigger the smaller BMS.
In series, connecting two batteries with different voltages but EQUAL capacity is possible, but it is very rarely done.
So I can add a couple larger battle born batteries to my current 400ah setup, excellent 😊
Make sure to read the existing battery/s voltage/s and ensure that the NEW batteries (to be added) are at exactly (or within 0.5% of) that reading - when connecting them in, or you could become "the cable" that makes the shorting circuit, resulting in a nasty jolt between fingers, or worse, across your shoulders (and critical internal organs).
Gotta be careful tho if the wear is different, as they will try to equalize and the strongest battery will constantly try to pull up the weakest one. What i usually do as a test is charge both batteries together, let them equalize, then disconnect from the charging source and check with the ammeter if there is significant load transfer between them over time. It's a problem really only if it's there's no external charge for a long time. Like i had a weather station pulling only 10W and needing to last as long as possible between charges, so i decided to put as many lead-acid battery i could in parallel, the last one i added was supposed to give me roughly 40Ah more, but ended up giving me only 5Ah at best on the long run and wearing out other batteries faster in constant equalizing, so i pulled it out. Great video tho.
If we assume that we get full capacity (or 90% of it) the BMS in the larger battery with its 250A limit is actually the limiting factor for large current draws - not the smaller battery with its 100A limit (7:26 time stamp). The reason is that the large battery is 4.6X larger in capacity than the smaller battery and will provide a current that is 4.6X larger. So the smaller battery and its 100A limit would correspond to a 460A limit on the larger battery but it is only rated for 250A.
really? You think that the 100Ah rating of a battery is indicative of a 100A current limit? Those two things are absolutely NOT the same.
@@occamraiser Did you watch the video? He days that the smaller battery has a max BMS output of 100A and it has a capacity of 100Ah. This is NOT what my comment is about. The question is - which battry is the limiting factor for large currents.
Thank you, I've just subscribed because you " have a clue about this "
Great video.
I have 2 banks of 4 LiFePO4 batteries each bank is a different "brand". All 100 A/Hr. When I say different brand I mean the name on the battery is different. The BMS is Bluetooth enabled and both brands use the same app and the manual is the same except for a couple of pages added. So I think the OEM is the same.
When I connected the banks in parallel the BMS reported much different current readings. I got concern so I disconnected one bank, but from the video it sounds like I shouldn't worry. Comments, suggestions.
Theoretically, if the small one has a 100A and the big one 200A and the voltages are the same, 200A load should be fine.
Thank you
If the batteries are the same chemical kind and you can open the batteries and have access to all the voltage levels between the cells, then you can cancel the weaker BMS and connect instead the voltage levels in between the cells of both batteries in parallel as well, leaving only the stronger BMS to manage both batteries. In doing this, you are in effect building a physical larger battery, made of the cells of the two batteries, where all cells of the same power level are electrically connected in parallel. And the case boundaries of the batteries do not have an electrical meaning if you do that. The gain is that now you have just a single strong BMS and so you do not need to worry about over current anymore.
Wonder how many amps are going between the batteries when they equalize?
If they are not both fully charged, could it damage the battery with the lower voltage?
Yes, he should have explained that. If one battery was a higher voltage than the other when first connected there would be a large amount of current from the higher to the lower voltage battery. Make sure to match the battery voltage before connecting them together. To be safest, attach them together with a resistor or lamp and allow them to equalize before attaching a wire directly between them.
This would also be the case when discharged and one of the BMS' disconnects the battery. Re-balance the voltage before reconnecting.
Yes, possibly, but the BMS should prevent a damaging current either entering or leaving both batteries.
@@nickwinn7812 This is only if there's a MS between the batteries. If they are directly connected to each other there is no protection... besides the wire
Interesting video. Could you please expand on the reasons for not mixing battery chemistries? I'm guessing it becomes an issue at high current draw rather that lower but I really have no idea. Thank you.
Just guessing but I think the discharge curve would be different causing overcharging wear on the less energy dense chemistry.
If you know what you are doing you can do anything you want. If you don't, then you can get into trouble no matter what.
I do anything I want. And I definitely don’t know what I’m doing. 😂🤣😁
@@ecospider5 It's only that you get results you never expected, so lets hope the next one doesn't kill you (as not knowing what will happen when doing dngerous things - will ALWAYS end badly).
@QUIX4U
I really enjoy setting something up in a crazy way. Then seeing what happens. The trick is understanding how crazy the setup is so you know what safety procedures to use.
Like plugging in a 40 year old amplifier that hasn’t turned on in decades. Don’t do that with 120v. Get a thermal camera and watch the electronics as you increase the voltage starting at 30v. A damaged component will probably heat up too early. Doing it at a low voltage stopped that component from damaging others.
Something that surprised me the other day was a fire extinguisher. I had an expired on so discharged it in the yard. If that was in a 12x12 room I would not be able to see for 5 minutes.
I do crazy things when it’s safe that way I have more knowledge of what I can do safely in an emergency
As the currents add up the difference of capacity is not to big of an issue.
If you have 100A from one and 250A from the other the total will be 350A.
Metoo you are an Excellent Teacher
@TopperPenquin thank you for kind words. Sincerely.
Thanks for posting the video. Cool test and good points about the different discharge ratings. 1 question and one concern: If they were providing a total 300A load, wouldn't they split the load according to... Some other factor? (Internal resistance maybe?)
The concern I have in this scenario is charging and reduced performance long term. The CV,CC charging stages of each battery are likely reached at different times. In that case it might be best to customize or limit the charging profile, likely resulting in lower total capacity.
It’s probably not a good idea to use this combination for high discharge applications like the 300 amps you described. This would be for slow discharge application. For high amperage uses, both batteries should have the same size BMS so the load can be equally bifurcated between them.
Charging isn't a special concern. You are thinking correctly when wondering about how they split the load, the same logic applies to charging. As for how they split, internal resistance is an issue, but usually a bigger issue, especially with LiFePO4, is the cable and connection resistance. You can test this using a clamp meter to monitor the current in the different wires between the batteries and battery to load/charger. With very different batteries such as in this video, internal resistance will definitely help split the current.
That said, you would never want to do this with any load (or charger) close to the maximum supported by the total of the batteries. The current is not going to divide that precisely and it will change depending on the state of charge as the internal resistance curves of the batteries will vary. Beyond a quick surge the imbalance is likely to trip a BMS if operating without enough margin. If using two matched batteries, I'd probably be comfortable with designing for 75% of the total current (i.e. batteries support 2x 100amp, I'd probably be okay planning a 150amp max load). Note how that means even a gross imbalance of 2:1 is within the specification for a single battery. Using a setup like that should be fine. The more batteries or the more different the batteries the more safety margin is required.
@@Sylvan_dB Very nicely described!
Kirchoff had a bit to say about this.
The community here would garner a more intuitive understanding and develop a deeper understanding if they studied Kirchoff's and Thevenin's laws. The penny will drop once these are understood and will have these folks designing systems on beer coasters and napkins in no time.....and get it right without assumptions or vague personal models of what's happening.
If you connected these batteries in parallel via a busbar with separate tails in parallel, you could measure how much each battery was contributing and see how the larger capacity battery is actually charging the smaller one during periods of the discharge.
That was a nice Heath Robinson style demo.
@@walsakaluk1584 Once I stepped out of the classroom into the lab I realized that while Kirchoff, Thevenin, Norton and others provide a brilliant theoretical framework, the real world requires a lot of assumptions and rules of thumb. The first problem encountered is an almost complete lack of specifications necessary to perform the requisite calculations. The second is that we must design for the center and avoid edge cases because of individual component and environmental variance, so the additional analysis is seldom useful. Oh well, the theory does provide some direction in thinking even if the equations are never evaluated.
Great info!! One question though! If you paralleled 2 batteries that were the same size one with Bluetooth and one without. Would the capacity from the Bluetooth battery now represent the entire bank?
@hooligan9968 highly doubtful, since capacity readings (for LFP anyway) are typically done with a shunt that monitors Amps in/out. And that internal shunt is only going to measure the current on that one battery. You COULD add an external BT enabled shunt to the main negative and thereby see the total in/out current.
To match those 2 batteries together for up to 80% of their BMS output capacity use 6 awg from the 100ah, 1 gauge from the 400ah and connect both sets to a single buss bar. When you draw 280 amps on a 3000 watt inverter what will happen is the 6 awg will start to choke back ( resistance starts on it ) draw and more will be pulled from the 400ah battery since it's cable is thicker and not resisting draw. I should show my system better in my videos.
See my other comment on here, I explain more.
cable size should never be reduced in order to gain certain voltage drop across them. overheating cables is one of the most common causes for accidental fires.
if you need to dissipate energy through resistance - use resistors specifically designed to do that - not just standard insulated wire!
@@laus9953 If you only size your battery system to 100% of your draw, never use cable loading resistance. But if your sizing to have a actual battery bank then your doing it right to size for loading resistance. It's not unsafe unless your only using as example: 300 amps to feed 300 amps of draw. That is not my system that has been running safe for years. It's about 20% maximum draw of 840 amps on all my inverters and DC loads if in peak draw against over 4800 AH / 5300 Amp output capability. I have had LiFePO4 directly connected to Lead Acid for 2 years, cabled as I said. And not once under full loads have we seen more than 2 degrees of temp increase in the restrictive cables to the Lithium section.
Usually, the batteries do not have exactly the same potential at each of the 2 poles.
When they have no load, but they are in parallel, regardless of the capacity of each battery, there will current from one (+) to the other (+), and from one ( _ ) to the other ( _ ), until they equalize.
Only the potential difference matters, the power drain may be from the small battery to the bigger battery.
*So in short, this is a no go area just to be on the safe side!*
You can actually mix chemistry aswell. If using a "12V" LiFePo4 in paralell with a "12V" Pb battery the LiFePo4 battery will do most of work.
I actually did this couple years ago in a 24V system. My LFP batteries back then were horribly imbalanced so I needed the Pb backup for when the BMS would crap itself again. No problems at all.
From what I understand is when you connect them in parallel the bms in both combine so you could say run something that uses 350a continuous so maybe ck that out next and try to run say 250a thru them and I don't think the smaller one will shut off. I been told they would share the load and the smaller one could handle it so let me see you try that next. At least try to run something larger than 100a and see if it shuts down the bms in the smaller battery. We do this with Ebikes and I haven't heard of any that shut down
No, the BMS systems don't "combine". The ratio of the capacities determines, to a first order approximation, the ratio of the currents supplied, so the smaller battery supplies 18% of the total current and the larger one supplies 82% (i.e. 4.6x as much).
Since the large battery's BMS limits its maximum current to 250A while the smaller battery's BMS limits its output to 100A, the larger battery's BMS turns out to be the limiting factor (only 2.5x that of the smaller battery).
The result is that with a total current draw of 300A, the larger battery would supply 246A and the smaller one would supply 54A. Any more and the larger battery's BMS would trip, immediately followed by the smaller battery's BMS as it tries to supply the full 300A+. So the maximum current you could expect to draw from the system is around 300A.
Enjoyed the advice. I bought 260ah 2x and now I have found 280ah 2x for less. Same brand of batteries. Now my question is what would this do to my Victron shunt reading? 🤔 I am running in parallel, 12v.
@scooter6334 shouldn't do anything really. Just need to reset the new Ah capacity total and probably recalibrate to 100% and you should be good.
@@ReeWrayOutdoors Thanks so much for the feedback. Would you set the shunt to the 260ah or the 280ah?
One other possible concern is if one battery has an internal heater and the other one doesn't. I have two 100ah batteries in parallel in one bank inside my RV trailer and a 300ah battery with an internal heater outside in a storage box. The two battery banks are connected by an A / B / Both switch. During storage I keep shore power on the trailer, but, set the A / B / Both switch to the 300ah internal heater battery only. That way if I lose power the 300ah battery doesn't try and use the two 100ah batteries to run it's internal heater. I haven't actually tested if it would. During useI run all the A / B / Both switch set to Both. During a recent trip on a particularly cold night I did seem to have an accelerated capacity drop so it might have been the case. So any future cold nights I switched to just using the 300ah battery and then only recombined them after I had shore power and could top off both banks.
This is interesting. I was trying to figure this out, and your video gave me an idea for my problem. I have a UPS with two 12V batteries in series to create 24 volts. Obviously, I can't mix and match batteries in this case, but what I can do in the future is purchase 24V batteries instead. If I wanted to increase capacity, I can just buy another 24V battery and connected it in parallel. Is this correct, or am I missing something?
Did you measure them individually first?? Perfectly true, you can connect a 30ah to a 300ah without issue in parallel and get 330. I do it all the time
People often have a nearly DEAD car battery, with possibly a voltage as low as 5volts.
Then along comes BOB the builder, with his work truck, and a pair of 300amp jumper cables, and instantly boosts your battery's voltage back up high enough, (from his battery sitting pretty at about 14.4Volts) for you to restart your vehicle, to thus "run" on it's own while recharging your nearly dead battery itself.
What any Bob the Builder NEVER DOES - is check your nearly dead battery's voltage first, he just uses VERY HEAVY DUTY CABLES (that can handle the jumper-currents, as the two batteries "self-balance").
He also ensures that he keeps his own motor running to recharge both batteries, until the jumper cables are removed (with their heavily insulated handles).
That way - he can deplete his own battery fairly heavily, to restart your motor (while the two batteries self-level), and do it without risking any electrical shock to himself, with the heavly insulated handles.
It's the same situation with following distances, only a fool breaks the 2 second rule.
Only a fool touches both battery terminals with wet hands at the same time, or, tries to become the missing starter motor cable - ???? Hello, stupid is as stupid does, but a fool never learns.
Montana Dan the eletronics engineer says your description is close enough to fact that no corrections are required - good job.
Speaking in the third person is kinda weird
@@waldolemmeryea, sounds a bit narc
Seems sus. 🤖
@@waldolemmerlmao
Hi! we have two batteries (12V 400A and 12V 100A) parallel connected and the load is 12V 100A. So when the batteries would not feed the load? Less than 1 hour or it would be about less then total current amount / load current?(100 + 400 / 100 = 5 hours) - Thanks
in case of planning to have 12v, then nothing to be worry about ?
Many thanks for this demo. Just one question, is it ok to connect in parallel 2 batteries one having cylindrical cells and one having prismatic ? all the best from the UK
It’s confusing when you swap between using amp hours and watt hours 2:35 . Simplify it and stick to one term, the one on the batteries, amp hours. Instead of 7000 something watt hours we can immediately see 460 + 100 = 560 amp hours as that’s what’s written on the batts.
He does that because the kill-a-watt meter reports in wh not ah. Even if the meter reported in ah it would be based on 120Vac not 12Vdc.
This would be even more confusing as he would need to convert the AC side to wh and then convert from wh to ah for the 12Vdc side.
Watt-hours are actually more convenient as energy is measured in kWh (“units”). Simply do an Ohm’s Law calculation to convert, e.g. 100 Ah at 51.2V use P=V*I ( 51.2 * 100) = 5120 Wh (or 5.12 kWh). Do the reverse to ge Ah.
This might work short term but if you parallel two lead acid batteries of different age or capacity for any length of time they will "fight" each other until they both fail. Personal experience.
hence, you use batteries with similar age/capacity. ;)
I form lead acid batteries and you are correct.
I used to design battery management systems and chargers for telecommunications installations. Lead acid batteries of the same technology are frequently connected in parallel. So long as the state of charge to Voltage relationship is the same for the two (or more) batteries they will share and not be damaged. The charger should ensure that both reach the end voltage when charging and are disconnected before being over discharged. These voltages are the same for new or old batteries of the same technology. This is true for Lithium batteries as well. I don't think they can "fight" each other - what would that mean in terms of voltage and current? And they certainly do not fail - they can last decades. On the other hand, similar age, technology and capacity is critically important for series connection.
@@HughCStevenson1My guess (from the very little information, admittedly) is that one/some had significantly more equivalent series resistance, so that the effective voltages are mismatched every time the load changes or charging state flips. (This would happen a lot more often for, say, buffering solar energy than for battery backup for grid power.) I wish ESR were easier to measure to avoid such things.
They try to charge eachother if one has different capacity and this process heats the batteries up until they explode
Simple question:
How big a parallel bank of LIFEPO can you build?
Yeah, the manual says 4 batts, but can you go 5,6,7,8, etc etc.
As you said you can add as your budget increaes..
Thanks
I like those 12v rails you got there. NIce presentation mate. Earned yourself a new subscriber here 🙂 Greetings from Brisbane, Australia.
This should be a procedure you don't plan for. It should be what you do in a pinch to get through a low voltage scenario when you're away for the weekend. This "plan B" is good to know when you're away from home. But when you get back home, get matching batteries before your next trip.
No, it is fine for ever. There is no need to have identical capacities. So long as the technology of the batteries is the same. Lead acid wet to lead acid wet, Ni Cd to Ni Cd, LiFePO4 to LiFePO4, don't mix them up...
One thing I've heard and please tell if I'm wrong is an issue with charging using highly electronically controlled or digital type chargers or charging systems that measure capacity. It was stated that this type of charging would essentially turn off the charge rate when the smaller battery gets to full capacity. In this system with a 100ah battery and a 450ah battery would only come to a "full charge" of only 200ah and would then not give the 450ah battery the additional 350ah of charge. I have not tested this myself so I honestly have no idea. The argument does make sense but again please tell me if I'm wrong. Thanks!
Most of the charge current would flow into the larger capacity battery,, so the SOC of both batteries would rise to 100% in sync with each other.
All I heard was the auto start stop battery on newer vehicles can be bypassed with a slightly stronger CCA battery.
Or am I missing something?
This is essentially how solar eystems work all down the voltage on wether your home consumes from the grid or the battery. These will essentially bqlance as the laod will draw from rhw device with the highest volrage.
Thank you!
lol…. Nice and simple. I like simple!
Well done.
Nothing happens. Works fine. They balance each other as long as you aren’t pulling huge currents from them like trying to run an AC on batteries (good luck with that). Small camper stuff does fine balancing the load and sharing the capacity. Been running a 100 Ah with a 200ah. Biggest draw is the 12v fridge and vent fan.
There's so many people who run mini splits off of batteries and solar successfully, why the (good luck with that)?
I run a 5k ac unit off battery just fine
Luck not needed, just some intelligence.
In series, the smaller capacity battery will be depleted while the larger will still be going strong. This would cause damage to the smaller one. You would only get the capacity of the smaller.
In parallel the bigger battery tries to charge the smaller.
In both cases damage will be a long term event while you think everything is doing fine.
@@redfields5070only damage to the larger could occur if the smaller developed a short and there were no fuse between them.
Although it is not recommended It is possible to use say 4 12v LiFePo4 batteries in series without any problem. I have run 12 100Ah batteries as 4s3p now for over a year and have had no problems. I have however connected a battery equalizer (HA02) over the batteries to equalize the voltages over the the 3 strings. They are also connected so that it is really 4 x 300Ah as 4s.
I use the cheapest LiFePo4 batteries I could find and they where absolutely NOT recommended to be used as I do.
The danger as I see it is if 1 set of batteries disconnect and there is a load connected then the disconnected set can have probably up to near 45v over it and the BMS in that set may not be able to handle such a voltage.
My solar regulators turn off the charging when my battery setup is full (58.4v) and the inverter turns off at 45.6v.
The equalizer makes sure that every s has a similar voltage so that a blow up due to wandering inequality is avoided.
At another setup I am using similar "cheap" batteries as 2s2p in both 100Ah and 135Ah ( 2 setup's) and then parallel to 4p 150Ah 24v. I leave some cable in between the different setups to allow some natural over resistance balancing. It all works pretty good - probably not quite to it's limits but that should only be better for the batteries anyway I believe.
On my old Golf Cart I use 5s and 2 HA02 equalizers on probably even worse batteries. The overall voltage is never really outside 65-67v so they are not pushed much.
I believe that the trick in using sub standard batteries is to use the equalizers and then not push them too hard and then of cause external charge and discharge control. The internal BMS is then only there to balance the single cell's and for absolute security.
Discuss the different internal resistances between the Larger Capacity battery and Smaller Capacity battery.
If you connect a 200AH and a 50AH battery in parallel (both 12Volts), they’ll share the same voltage, but the 50AH battery will wear out faster.
The smaller battery will charge and discharge quicker, which could stress it and shorten its life.
There’s also a risk of uneven current flow if one battery is charged more than the other, which can lead to overheating or damage.
For the best performance and safety, it’s better to use batteries with the same capacity when connecting them in parallel.
Thats it!
Thanks
Tnx. I wonder if you did pull more than 100 Ah ... why wouldn't the higher amp hour battery try to equalize and the current that is needed would use the cables to pass. I could see maybe too small of cable .. might be an issue... It might be an interesting test. If the BMS shuts it off then you can restart it anyway.
you assume, just talked, did not test, i have doubts: 200 Amps, the bigger battery (both in parallel)i think it will handle the 2oo amps almost alone,because the smaller one has way higher resistance;
BUT.... it depends A LOT on the cables, and the time that the test takes.
What about charging? Many regulated chargers? The smaller battery gets overcharged while the larger gets undercharged when connected in parallel. Not to mention, other comments are correct, as they discharge the voltage of the larger continues higher as the smaller depletes faster. When charging this variation I've seen overcharge the smaller causing high heat. Actually have one getting burned outside right now on purpose. I'm reconditioning the battery. Reverse charge at a higher than normal rate to knock the sulfur off, then I'll charge it correctly
I've actually been doing additional testing for a follow-up video and while I'd agree that you probably shouldn't do this for SLA and GEL type (non-Li) chemistries, I still don't see an issue for LFP. The LFP batteries have an internal BMS that keeps them individually from being over-charged or over-discharged. And while their will certainly be some differences in internal resistance at the same voltage (SOC), the differences are not likely to be so significant as to cause any issues that you'd need to be overly concerned about. So they will, more or less, charge and discharge at rates that are proportional to their relative capacities and the larger battery will often provide a small amount of current to the smaller one as they are continually seeking to remain in balance. But this extra charge/discharge activity is not materially different than what is happening naturally in a solar-charging battery/inverter system anyway. So, I stand by my claims from this video - at least with respect to LFP battery chemistry.
@@ReeWrayOutdoors I can understand what you're saying, and while they have internal regulation, would you want to stress or rely on this regulation with lithium? Although lithium is pretty good about letting you know if it doesn't work. Just hope it's in a fireproof container. I'm an Automotive mechanic. I've seen all too often where some cells are bad, we tell the customers the entire thing needs to be replaced because the difference in wear from old to new can cause issues. The customers go to some independent that replaces only the bad cells and the whole thing fails because the charging is unbalanced. I've also seen where cells were bad, the customer stated they didn't want them replaced, they are individually regulated and the capacity will be reduced but they can't afford the repairs. Then it comes back on a tow truck burnt from the battery going up in flames. Lithium is less forgiving than lead acid. There's a reason LiPo batteries need a specific charger as well. They just can't be charged any way, must be a specific way
So they dischage at the same time? And go dead at the same time? Is that why the large battery wont start charging the smaller battery. And thanks for he great videos
Question for you, I have 4 12V 75ah batteries that were originally configured as a 48V series connected pack for an electric riding mower. They were replaced because one battery was weak. I currently am using the 3 good batteries in a 12V parallel pack with an inverter to run essential loads during power outages. Could I add the 4th "weak" battery to my setup for increased capacity?
The BMS only "see" the current of it's own battery, and in a parallell circuit the current is divided by the two batteries. In theory, with identical battery chemistry, two batteries in parallell should provide the part of the current drawn exactly proportional to it's capacity. Meaning, a 250 A battery and a 100 A battery in parallell should in theory be able to provide 350 A, reality isn't that perfect, but well over 300 A should be possible without reaching the current limit of either BMS.
In a serial circuit both batteries sees the same current, the full circuit current.
brilliant! thank you.
I have a van main battery under the hood. I have a small winch in the back for motorcycle loading. Currently I use a separate battery for the winch. Could I run a wire from the main battery to the winch battery for charging purposes? Would the amp draw of the winch fry the wires connecting the batteries?
Basically looking for a work-around for running a big fat expensive wire from the engine bay to the back of the van.
You'd fry the wire running the winch if the rear battery couldn't handle the load. Same if it drew too much charging current. In old RV's there was a "battery isolator" which allowed charging of 2 batteries, then disconnected the engine starting battery when you turned the engine off. Get one of those and your system should work OK.
According to your wire run lengths and routing, you might be able to use cheap car jumper cables split in two. Just remember that the insulation isn't very heat or chemical (oil) resistant and the wire gauge may be a size smaller than stated. I don't know why the wire is so much cheaper this way but I've been doing exactly that to get power to the back of my workvans for over 30 years and never a problem of any kind.
Thank you Great Info
If you hook up in parallel 2 of the mini's does the discharge rate double also from 100 amps to 200amps?
@MYCHANNELWITHMYSTUFF yes...total output would be 200A
Awesome video! Let me throw a question out there, okay, I have 2 similar battery's a 12v Timeusb 230ah battery with no low temp protection and a 12v Timeusb 200ah battery with low temp protection. Will the low temp protection work on the whole system when set up in a parallel application?
@stevenseigneurie5073 I don't think so because even if the low temp protection kicks in, the unprotected battery is still able to provide power to a load since there's still a completed circuit.
Good video. I had a question about two batteries with 50 Amp BMS..if I connect them in parallel will that still only discharge at a max of 50 Amps or will I be able to discharge at 100 amps?
They will 'current share'...so each battery in this scenario will effectively contribute 50% of the current to the load...so would expect to be able to power a 100A load between these 2 50A batteries.
@@ReeWrayOutdoors ah ok thank you. I asked because I was considering buying two 50-amp batteries. Sometimes you can pick them up fairly inexpensively.
I want to add that as it might not be obvious. You need to be sure when you add batteries in parallel that those realy have equal battery chemistry not just lead-acid vs nickel based vs lithium based. Like if you have Li-ion batteries (Li-NMC, LiFePO
4, LiCoO2, Li-NCA), Li-ion is common nominator for these. And i have seen batteris that don't have anyother label for their battery chemistry (usually due to integrated circuitry which is different story) even if they had same nominal voltage, curves might be different (and will be if chemistry is different) -> then there would happen weird chagings between batteries. and some even have small voltage raises before curve sharply decreases at the end of capacity.
that would be a problem in series connection - why should it be one in parallel? let balancing currents flow - balance will be kept, no?!
as long there are sufficient fuses between batteries, in case one does draw or supply too much..
Thanks. I learned something.
thanks!