Divided opinion about balancing, balancers, BMS. How to and why to balance LiFePO4.
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- Опубликовано: 1 окт 2024
- I had a lot of thoughts and questions about balancing. Balancing at the top or at the bottom, with or without BMS. A balancer? What for? What's the benefit? Is top balancing better? Do you need a BMS when bottom balancing?
All these questions are dividing the nation! I'm trying to highlight some of the benefits of different methods of balancing. I also discuss if a balancer is useful and if it benefits or rather harms the cells.
Keen to read all your thoughts...
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Joe how is your Oscilloscope coming a long mate. Morning from Victoria mate. My new batteries are on it's way.
Good to see you here Joe, Looks like Andy picked up some good tips from you. lol
Hope it works!!!! 😁
You bottom balance when your cells are often at low state of charge (think EVs). You top balance when they are often at high state of charge (think solar). In either case, your battery is only as good as your weakest cell. The thing an active balancer does when there is an imbalance between cells is prevent the BMS to trip while it's compensating for this weak cell, and through this compensation you can get overall more capacity out of the pack - the downside being the stress placed on the weak cell in doing this. However, all of this is rather moot since the difference between cells in general is a couple Ah, not 180Ah as per your example, so an active balancer won't put real stress on the cell, and in addition, knowing you have a weak cell, lower the Ah of the total pack to the Ah rating of the lowest cell - no more need for an active balancer, accept some 'capacity loss', and just charge to the Ah of the weakest cell with some safety charge/discharge margin (like 80/20, or 90/10). Need more power? Add a battery.
OK, so bottom balance... but how do I add a second battery then? They won't have the same overall voltage and will start balancing...
@@OffGridGarageAustralia the way I add my battery power is to have another system . I will let the main battery to be charged untill full while using the subsidiary battery .
@@OffGridGarageAustralia I would (and I do) top balance. I have two (soon 4) sets of 16 280Ah cell batteries. You just top balance the new one, make sure that both are within reasonable voltage of one another, and put in parallel. Let them 'talk' to each other, it doesn't matter, it will settle. You will always have some cell drift at the top and bottom and if you have a balancer (like yours, or active one I have in my BMS, a JK/HELTEC one) this will help. Just accept you will have some capacity loss (even 250Ah or less) per battery (your lowest cell in essence) and stay between 80%-20% or 90%-10% of that capacity. Whatever cell drift between these margins should be small and shouldn't matter.
Since the total Ah for the system is determined by that one weak cell, if it's a significant difference, then wouldn't replacing that one cell with a new one would raise the system capability to the next lowest? It may be a bit of a waste having a new cell among all the old ones, but would it be better than having the limiting bad cell in the mix or replacing them all?
@@wingerrrrrrrrr
I think this is one of the best videos explaining the purpose and different kinds of balancing. Very well done! Thanks for your work.
Awesome, thank you!
@@OffGridGarageAustraliaYa! 👈👁️🐽👁️👍
VERY SIMPLE: Top balancing: your cells remain in an area of SOC where the internal resistance is lower. Lower internal resistance = better performances and less heat generated as well as less aging. Just check the internal resistance curve vs SOC on LiFePO4.. That is your answer. When bottom balancing, your average cell voltage ( also called NOMINAL voltage) is a bit lower than on top balancing. You get more Wh per Ah when top balancing because the total pack voltage is higher. Also ask yourself.. do the cells prefer remaining long period at 100% SOC during balancing or if they prefer remaining long period at 05 soc during balancing? At low voltage (bottom balancing) , cells get their copper anode disssolved.. At high voltage, ( top balancing) you get lithium plating..
Thank you for your comment.
Internal resistance is the lowest between 25%-75%. Sometime it increases already at 50% SOC, depending on the method been used to measure that.
I top balance. In either case, your battery only has the usable capacity of the smallest cell. There are 3 differences between cells, even if the cells have consecutive serial numbers, having had come off the assembly line, one right after the next. The three differences are, Capacity, internal resistance, and self-discharge rate. Top balancing addresses all 3, if you ONLY balance, during absorption/float charge. When the battery is discharged, the balancing should be OFF. Once discharged, and you begin to charge, leave the balancer OFF. Disabling the balancer during discharge and bulk recharge addresses differences in internal resistance by not falsely sensing different states of charge, due to differences in voltage drop caused by load/charge current. Waiting until it's charged enough for the current to roll off, reduces those differences. Capacity is also addressed, exactly as you described. Once you have used that hundred amp hours, you put back the hundred amp hours, and once the current rolls off, you will find that the cells are almost nearly equal in voltage again. The ONLY reason for voltage balancing, is to compensate for self-discharge rate, and should be done when the battery is in a "standby" condition, with little to no current across its terminals. Self-discharge is a time based thing, having surprisingly little to do with charge/discharge cycles, or for the most part, even depth of discharge. Self-discharge happens, whether the battery is used or not. This becomes even more critical, as the battery ages, whether by cycles, or calendar life. Differences in self-discharge rates become greater, as the battery ages. I personally, like to maintain my batteries at ~3.5 volts per cell, and, voltage balancing ON, when not in use. Using voltage balancing ONLY during float/absorption charging helps a battery to be as reliable as a single cell.
Failing to post an episode yesterday has already been marked down in your permanent record.
Oh, Sh*t!!! 😑
LOL... Thanks for the plug Andy, great to see the Bus Bars going into use again.
I can't really comment much on the balancing issue this time, you covered just about all of it. The important thing for people to remember, is that there's no "one size fits all" solution. Each person and each setup will have different priorities and needs, so people really need to weigh up the pro's and con's, and make their own decision. That's where videos like yours are so good, because they nearly always show all the variants and explain them enough for people to make that decision. Nice work.
Thank you very much Paul!
As for the second part in your demonstration there are active balancers that you can add a relay to that's what I've done to mine and then I'm using my victron equipment to switch the relay on only when I'm at a high enough voltage so they are active balancing but they're only doing it when I say so and I'm only doing it on a higher voltage that prevents them from charging the lowest battery when the pack is low and then you charge it and then it has to immediately take all that power back out of the lower capacity cell
Thanks for this info.
I did the same with a JK-BMS (it has an external power supply pin that can be used to turn it on during charging, when DC voltage > 16*3.45V)
I would have loved to see your wireless BMS that you say don't exist. People don't believe me either when I tell them I have nuclear fusion power at my place until I point to my roof.
Top balance and just forget bottom balance from will prose says not nesscary and your top bal. Was very clear i put it on solar never higher then13.6 nor lower then 12.1 0r 12.2 dod
Top or Bottom balance, your pack will still become unbalanced over time. It's not just capacity of each cell in play. Internal resistance variation is a problem, and this is a major contributor to unbalancing at high load, or high charge current. My suggestion if they are good/new cells, top balance, if they are crap mixed capacity cells made from old laptop batteries then bottom balance. Now pay attention this is key, DO NOT cycle between 2.5, and 3.6, set it up to cycle between something like 2.7, and 3.5. Also I think I might eventually recommend the heltec active balancer, I've been playing with it, and will do a video soon.
Thank you. I cycle between 3.1V and 3.45V which gives me 90% capacity. I'm still not sure about the balancer, if this is good or bad. I've got some here and have tested also. Seems to work but this constant amps back and forth... don't know...
@@OffGridGarageAustralia Right on. With the 3.1 cutoff that's fine until you have a heavy load. Then it might cut off sooner than your 90% calculation because of voltage sag. A brief heavy load such as a power saw may sag the voltage under 3.1 then your BMS cut out, but you still really have over 90% capacity. Something to consider.
@@BradCagle Oh, no no, 3.1V is not the cut off but that's usually what I have seen to be the lowest when I discharge the battery under normal usage. The inverter cut-off is set to 3V under load and to 2.8V under light load. The inverter adjusts automatically dependent on the load at this time
@@OffGridGarageAustralia Got ya! Check out the vid I just did on the Heltec ruclips.net/video/yM3v1-K1q4w/видео.html
Hi Andy.. I am recommending you to discuss about low frequency and high frequency inverters including low and high voltages connections.
I've never heard that keeping a cell at 3.6V degrades the cell. Are you sure?
What you are missing is cells with different capacity and impedance will have different charge and discharge efficiency for a given current level. The higher the %C rate of charge or discharge current for a given battery, the worse the efficiencies. So putting in 100 AH's does not mean all cells are filled by 100 AH's. The difference in yield will accumulate over time and will diverge their relative state of charge AH capacity.
Round trip charge/discharge efficiency at 25 degs C for 0.1C rate current for LFP cells are about 99%, 0.5C is about 95%, 1C is about 91%. These numbers get a little better for warm ambient temps and much worse at colder temps. Cell leakage is about 2% of capacity /mo at 25C, 1%/mo. or less at cold temps, 5%/mo at 40C.
Bottom balancing (or top balancing) will not do anything to avoid this. The closer cells are matched the less the divergence.
Roind trip charging efficiency consist of 2 parts: coulombic efficiency (how much you get from each Coulomb you out in) and voltage efficiency (how high is discharge voltage compared to charge voltage)
Charging / discharging at high rate ONLY worsens voltage efficiency (I^2*r losses), but NOT coulombic one. Coulombic efficiency (and variations of it beetwen cells) is one thing, responsible for cells staying within balance. You don't put / take same amount of energy into series connected cells, but same amount of charge
I have tried various strategies. One thing I know that helps is having a 2s configuration. I have an active balancer and I monitor the high cells and low cells over a period of time. I then split the 2s groups and swap the high and low cells to minimise the difference between the pairs of cells. This works.
I have now set my balancer to only start balancing when the voltage difference is 0.03 volts so the balancing only operates at the top and bottom of the charge and discharge cycles. My BMS balancing is turned off because it fights against the active balancer.
That is great, thank you so much for sharing, Colin.
Yeh I've considered that too. Rate every cell (which could take a long time), and then mix the low and high ones to create an average.
@@PowerPaulAu all I did was watch the balancer and note which cells were lowest and which ones were highest and lowest and swapped one cell from each pair, and I repeated this a month later with very good results after only the second swap.
You remind me of my 6 grade math teacher, except he was clean shaved.
Irrefutable fact: It doesn't matter if you top balance and shut off discharge on weakest, or bottom balance and shut off charge on weakest, or capacitor balance and get significantly more usable capacity out of your pack by doing both, your weakest cell *ALWAYS* gets the most wear and tear on it.
I think I would agree.
If you bottom balance, all your cells get the same amount of cycles, but your weakest cell always experiences the highest charge voltage.
If you top balance, you're putting extra discharge cycles on the weakest cell, and it experiences the lowest charge voltage.
If you active balance, you're putting micro cycles on everything, and significantly more micro charge cycles on the weakest cell(s).
Active capacitor balancing will always get you the highest yield, but lowest longevity.
Unless somebody makes a highly sophisticated BMS that monitors capacity and modulates current draw on a per-cell basis, then there will always be a weakest link. Such a BMS could distribute the wear evenly.
The best way to maximize longevity is to keep the DoD as low, and the SoC as close to 50%, as possible.
E.x. Low voltage shutoff 3.0v, high voltage shutoff 3.3v, bottom balance at setup, no balancing during operation.
This ensures same # of cycles for all cells, but leaves enough SoC buffer that cell life is greatly increased, and any normal deviation minimally impacts cell degradation. All that is likely required is a pack balance every hundred cycles or so. Obvious drawback is greatly reduced total capacity.
So at the end of the day, unless you have a magic do-it-all BMS, a set it and forget it system will always have a weakest link that degrades exponentially.
@@MicroplaysMC I recently contacted loads of Chines LFP companies and the 5 that replied all said the same... keep the DOD between 20 - 80% for best compromise on cycle life and 2 of them further said 50 - 80% DOD for max cycles. CATL claim >8000 cycles at 50/80 you just need a larger battery due to only using 30% of what is available.
please give me the borring video....the one with the Whiteboard !
if i look than i look.!!!
i have to bring a lead acid bank and a lifepo4 bank to work in harmony.
I am aware that i have to split them from time to time To reach the 15,5 v for .(i do not know the term aufkochen der speicher batterien \ säureumwälzung)...
frostige Grüße aus dem Bayerwald.
.
You mean equalization voltage for lead acid batteries.
Another edge of your seat saga of As the Electron Flows…
Yeah, it looks like it... there is always more to discover and thing about.
Thanks for your massive and multiple beer donations 🍺🍺🍺🍺🍺🍺🍺🍺🍺
What do you need to do is do a test bottom balance load test with active BMS. Then top balance load test with active BMS and I bet you’ll find a top balance gives you more power.
I've always liked the idea of bottom balancing. The BMS should be there as a redundant safety device if your charger malfunctions. Don't depend on it alone to protect from an over voltage. No one wants to start a fire.
Especially not a Daly...ruclips.net/video/JbnFyU79Nf0/видео.html
It seems to make more sense to bottom balance but it's harder to rectify again over time.
Schneider NSX DC mccb has over/ under voltage disconnect as precautionery measures
@@jasondevine6014 Thanks for linking that video. Interesting failure. Mosfets can fail closed too. Look into an "emergency/combined disconnect" by Albright International. SD series switch. I got a used one. This acts like an emergency stop pushbutton and a high current DC contactor all in one. I'll post a video of mine when I get it hooked up.
@@OffGridGarageAustralia True what is good for setup purposes might not be good for longevity. And how much of the batteries life does it really sacrifice? Say you had to replace your pack 1 year earlier would that really matter? Maybe the convenience is worth it?
Now i am confusedererer...
But i learned something. Lower voltages are on lower positions. I never noticed this before.
This bottom balancing seems to be a good approach, but i would not use it without BMS, as you mentioned, for safety reasons. And i would also not bet, that it stays forever like that.
You put the same amount of Ah in every cell, but internally the chemistry may do something slightly different in every cell? Also the cell degradation may vary slightly, so i think it will shift over time...
But this are just my thoughts, no experience yet...
And yesterday my first panels were delivered, so i had a chance to try this elejoy tester :-)
Feel free to not upload a video every day ;-)
I would keep the BMS but would turn balancing off while still monitoring the single voltages.
I do top balancing
Bottom balancing is in my mind flawed for solar, since you rely on the pack always have the same voltage distribution when the weakest cell hits a predetermined point (say 3.6v). The sum of all voltages is your charge voltage. In theory this is great, but the cells will drift over time and cause a different voltage distribution. Then, In the case where the weakest cell peaks earlier, the bms will disconnect the charge. All good to save the pack, BUT, that might fry your inverter or charger when the rail voltage suddenly jumps up. Depending on the inverter/controller hardware it might survive a “battery disconnect” even if you have a high solar voltage. In my case the inverter throws an error and shut down, but I’ve have fried a cheap controller by disconnecting the battery (with the solar still connected).
That's exactly what I was referring to in the last two videos. I think it's crazy to bottom balance when you use a BMS as single voltages in your pack may drift over time. The overall voltage of the pack may seem fine but when voltages shift, it may trigger the BMS for a single cell overvoltage. Not good.
Bottom balance without balancer assumes cell properties do not change but thats just wrong. Over multiple cycles capacity as well as internal resistance changes. The worst call will change more then others and when the cells get old this will get a fire hazard.
That's why bottom balancing the pack does not make sense in my eyes...
This is a great topic and there is definitely a solution needed for this. But even more important is what happens if your charge controller does fail, your bms opens, does that fry your inverter from high voltage too? I think we are looking at this the wrong way. We should be cutting off the solar input to the mppt on high voltage cell detection....not just disconnecting batteries. We need a smart bms rated to shunt solar charge current(10-50A per cell)with some relay outputs for charging, bulk inverter, and critical loads.
Yep, I 100% agree. What BMS could do that though.
Also, would both charge controller fail at the same time? If the BMS disconnects, the SCC supply power to the inverter (tested multiple times). At least with Victron gear that seems to work fine.
@@OffGridGarageAustralia If the charge controller failed, then it would also trip the high voltage of the battery as long as it put out over the 200mA. See my point? It doesn't protect against a failing charge controller, it only would stop the batteries from getting overcharged....which might be worse than destroying an inverter...but both can be avoided with a smarter BMS. It still seems odd that all the BMSes use an integrated relay. They should just be the smart part and have a separate relay for over/under voltage. And you wouldn't want to put a relay on the DC side of an inverter either since when it activates again it would get hit by high currents from the capacitors. Better to switch the AC side of the inverter too.
I would like to see if you make a video about, bottom balance 4x 280ah cells, charge them series at 3.6v, and do a capacity test. That will prove what is the correct way. top or bottom. :)
Questions about this:
- so you want me to stop charging once the first cell hits 3.6V?
- how to maintain the balancing over time?
- how can I have two of such batteries in parallel?
@@OffGridGarageAustralia stop charging at 3.45 volts, and do a capacity test of each individual cell to check is charging without a bms is a good idea. i think it isn't a good idea and that the capacity of each cell is not the same. and with a bms it should be the same.
don't use bottom balans in your system. just make a 2p with proper bms.
You make it to dramatic. There is not much difference between prismatic cells of the same size and manufacturer. Let it be a delta of 3%.... You make it TOO BIG! Like I said before do not go above 3,40 volt at cell level and not lower than 3,10 volt and you will never have an idea of disbalance. But when you go high or low, YOU WILL... You like to go there, you like to SEE this problem and MAKE it your problem, BUT it is NOT a problem (if you don't go so high or low) What you see is natural... but you don't like to see that.... Think about that. With BIG prismatic cells, balance is not a thing if you know what is good for your cells and what is bad. Good is cycling, Bad is everything else like; testing, balancing, low and full SOC. Good luck with this "This is NOT A Problem" problem. But you make great video's!
Good video, well I'm going to do a bottom balance on 12v 200ah lifepo4 blue carbon battery, two of the cell are already 2.5v, im going to connect a 12v fan until stop working. Hopefully all the cells gets 2.5v, then I will connect smart charger lifepo4 to the battery until gets full. I don't have Active balancer. I hope this work.... Any advice?
Does the battery has a BMS? These days, all chargers, MPPTs and BMS are designed for top balancing. Nobody really does bottom balancing any more these days due to the fact that we now have BMS available which work reliable and also balance the cells at the top.
@@OffGridGarageAustralia yes, the battery has bms but when they were installed in series never were balanced and one of the two batteries started showing lower voltage, I opened and I noticed two cells with 2.7v.
And u r soo rite I do love a good fart sound! And yes you now have a new subscriber and fartfull viewer thank you for caring
Hahaha, great. OK, that's how it works these days 😂
Very informative video explaining the pros and cons of top and bottom leveling as well as when to use a bms. Thank you!
Hahaha left a 👍🏼just for the fart noise. Shoutout Nacho Libre
It works!
Andy What active balancer are you using? The red one with the coil and caps
I have tested several now and they all work more or less. You always want to make sure to not leave it connected all the time and just balance the top of your charging cycle.
At the moment, I'm not using an active balancer any more but will use the built-in one in the JK-BMS once it is installed. That seemed to work perfectly fine.
Top balance if you are want to use mostly the top part of your battery (i.e. full charge more often than you full discharge).
Bottom balance if you want to use mostly the bottom part of your battery, (i.e. frequently run your battery all the way out, or a full discharge more often than full charge).
Either one can work. It's easier for automated solution to maintain top balance which is why so many BMS include a top balance function. However if you do not fully charge and hold it there with some current but not too much for the balancer, the simple top balancer cannot do its job.
balancing.. in the case you never reach the absorption, bottom balance will drink each watts of you panels.. top balance in the case you like to have your batteries absorbing and have the most power available.. that make sense?? ..but don’t like your idea of batt with stainless screw, aluminum bar and copper cables.. that look more thermocoupler type of junctions and what about heat/cool dilatation different for each of those ones, your contacts will take some slack with time.. that make sense again??
Great video. The problem with balancing is voltage DOES NOT equal capacity 1:1. Every battery is unique. Balance the pack once, then disable balancing, If it looses its TOP/BOTTOM balance then you have another problem you need to fix first.
What is that other problem?
I need help, we are assembling batteries in bulk, cant afford to have individual bunch of 15 cells Top or bottom charge as we have to assemble around 50 units per day. We are facing issues due to these imbalances although cells we use are all A grade of the same batch.
My question is if we don't do the initial balancing and rely on the balancer to eventually balance it after 3-4 complete charge/discharge cycle. Is my approach correct, if not if there is a system where I can do initial balancing in bulk (let's say 150 cells in one go)
New cells with ~ same capacity and ~ same chemistry/resistance so...
Leave 5% buffer on top and bottom. Use 90% or a little less.
Every 3 to 6 months ( depending on the loads) top balance 3,5 -3,6 V low amps and let the BMS balancers do it's job. Repeat balancing if necessary.
It should work.
But as you said it's a religious thing... so...
very gut
I like the term, very gut. I may use this in some of my videos!
It is a conundrum because as Mr. Hairless legs said, no two batteries are the same. So, I guess it would depend on one's individual circumstance. Still, there is a lot of food for thought here, especially given what Doctorbass posted about dissolving anodes and lithium plating.
your a good teacher please how many hours do i need to charge 32 cells of 200Ah with DC supply of 10A?
Thanks, Nathan.
10A charge will add 10Ah/h.
If you have all batteries in series: 200Ah divided by 10A = 20h
If you have all batteries in parallel: 32 x 200Ah divided by 10A = 640h
OK thank you very much
please is there any way for me to use traditional 12 battery charger to balance them up
I have one of my 16 cells that will not charge above 3.4 volts - as in its never seen more than 3.3xxx volts. I end up with a voltage difference of 0.125 v when my battery is charged (I charge to around 55.4 volts). I have raised this with the seller and that have said initially that this was "a dynamic voltage so you shouldn't worry about it". After shutting down the battery and checking it with a multi-meter, I am still seeing the same difference after an hour of being turned off. Seller says "within tolerance" and it wont be a problem. I call BS and think it will become an issue in time; probably reducing the life of my battery. Thoughts?
Can you manually charge just this one battery?
I would charge all cells as usually to 55.4V and then connect only this one cell and charge it as well to 3.46V. So it is inline with the others.
@@OffGridGarageAustralia Thanks for your response. I'll try the single cell charge this evening. Watch this space!
@@OffGridGarageAustralia I ended up charging it to 3.5 volts - a little more than the other cells. It took the charge at 25 amps - took around half an hour to get there. I have installed it back into the battery bank and powered everything up. Immediately and as expected the BMS started doing its thing and taking power from that cell to distribute to the others. As of right now, the cells are all sitting 3.324 (53.18) volts - within .001v of each other - around about 88% SOC. Everything looks okay, but I wont know for sure until tomorrow when the solar pumps back up to top the batteries up. I see this behavior normally and then when I go to charge, it wont go above the 3.4 as described. Fair to say that the cell can charge, but isn't doing so in the Battery. Also a few days ago, I did terminate my balance lead again to that particular cell and even tried moving it to another position to rule out the BMS as the issue. I'll update again when I get another charge of sunlight!
@@nonicknamesremain Thanks for the update. The single charged cell may now cause the opposite as before and could trigger OVP in the BMS. Can you leave the battery on a power supply over night and keep it a55.4V to give the balancer time to do its job? That should bring it in line with the other ones again.
Need to somehow put all the cells in parrallel and buck boost the sh*t out of it to 48V. Then they all charge/discharge together.
Other than that, maybe build a smart bus bar that current limits to a common bus in and out.
If you can't quantify the damage to the cells for constant balancing then thats my vote. I don't think the charge/discharge is as large a problem as you think. Your 3 battery banks charge/discharge to each other all the time.
I sold all the 24v stuff and went 12v, no problem no more 🍺🍺🍺 Happy Amps !
"You are constantly transferring energy in and out of the weakest cell" - well, yes and no, yes you are, but during discharge and charge it's better to think of the balancer as *shunting current* PAST the weak cell, ie, the capacitor balance board is partially powering your load in the discharge low end state and partially charging your other cells in the charge high end state.
be kind to your live audience outside the window. i will bet if you put a like button out there they would press it. what i have found out with connection problems (resistance ,heat ,loss ) it to use copper never seize on all of the connections. i have not had any problems since.
What an entertaining video! Was very informative and fun to watch! Subbed!
Thanks a lot!
Dis you refer to this clip? ruclips.net/video/rQC_9TwyjTk/видео.html
Or this one remembers a little about your “full bucket” analogy. ruclips.net/video/0KSFitqvap0/видео.html this third one is more generally on charge balancing ruclips.net/video/tbaeMWdDlqY/видео.html
My cells are charged and discharged up to 80 amps.
The active balancer compensates with a maximum of 5,5 amps.
This means that the cells are simply charged and discharged with a maximum difference of 5,5 amps. I don't think this stresses the cells. Only with high voltage differences does the active balancer have high equalisation currents. I do not switch off my house completely at night. I have a base load of about 150 watts, which is already over 3 apere at 48v.
Li-ion/Lifepo4 Capacitive Balancer Board
Balance start voltage : 3.0V-4.2V
Balance termination voltage : 2.9V (into undervoltage sleep state)
Maximum Balance current : The whole group accuracy is 0.1V1A ; 0.5V3.5A; 1.0V5.5A
So in my opinion there is no additional charging or discharging with the balacer.
I have one active blancer and one BMS (not balancing) per battery pack.
China cells are all used and relabelled in my opinion.
So they need all the care they can get.
Best regards from Austria to Australia
Thanks for sharing, great comment.
Throw away all your aluminium bits bars because they are too long and they look like they could reach the two terminals of a battery. This is dangerous don't you think.
Bottom balance all the cells in parallel once before building the battery, next build the battery pack with a BMS to Top balance from time to time, during the whole life cycle of the battery. The BMS will bring you safety and peace of mind . . . Active balancer is the preferred option, but not available on the market!
In addition to that the c rating of the charge is is slightly higher on the lower capacity cell so you're actually charging it at a faster rate in relation to its actual capacity
Yes, that is true, more wear and tear on the weak one.
FYI, a BMS that has feature of cell impedance readout and external current shunt will likely have greater cell voltage reading accuracy for balancing. This should allow more successful balancing at lower cell voltage giving more balancing time before highest state of charge cell over-voltage trips BMS off.
You made me laugh. Soap Opera ? Really? 🤣
It is like one, right?
The main reason for bottom balancing in EVs is to protect the weakest cell from going into reverse current when the battery is low and you go full throttle.
That is the job of a GOOD BMS.. balanced cells dont protect them... BMS does.
@@Doctorbasss the bottom balancing people did not use a BMS, they just used a low voltage cut off... These people were living for physics at that time🐸
@@mjp0815 So, what happens when one cell drops way below the low voltage knee BEFORE the pack Voltage drops below the cut-off voltage? Are you saying that this does not, or can not, ever happen? Bottom Balancing, then running without a BMS, is not normally done in an off-grid situation.
@@MrSummitville when one cell drops to zero before the pack voltage is at the low voltage cut off really bad things happen as this cell is driven into "reverse polarity" instant destruction. Bottom balancing allows you to use the entire pack safely in high current situations like EVs without BMS, just using voltage monitor without running into this dangerous and expensive issue. Also, the bottom knee of the kurve is nicely visible in bottom balanced packs. Another reason why early DIY EV owners liked to bottom balance their packs.... They could tell that they were empty by simply looking at the pack voltage. The charging process was a low amp thing, lots of time to catch high voltage cells.... History... Today's BMSs top balance the packs now, and monitor each cell for low voltage... Drbass rightly said.
You are going to have two batteries, right? let's call them A and B. You could charge the batteries one after the other, so charge A, until balanced, and then charge battery B, until balanced, go back to battery A etc. when a battery is being charged, us the other one to drive the inverter, unless it is empty. This way you could hit max charge regularly and use a regular BMS. If you do not reach a full state of charge when charging battery A (resp. B), because you consume electricity from it, charge battery A (resp. B) again till full charge. There is a bit of mechanics & computer around that to organize the automatic connecting & disconnecting of batteries to the panels and the inverter. (cheers from Waterloo,BE by the way, we have good beers ;-) ).
Thanks for your comment. That would be ideal to treat the batteries separately but it's a lot of work and I would really preffer having them both connected all the time.
with 1 active balancer you charge and discharge your weak cell with 5 A only, does it count as charge cycles?
Of course with 100Ah against 280Ah the difference is huge, but with more equal cells, the weakest cell wouldn't suffer that much.
If we charge with 50A , shouldn't we need 10 of those 5A balancer in order to shift all the charge as fast as possible, so all voltages remain equal at all times? And we don't need balancing at rest.
I think the balancer will only have to work once there is a voltage difference across the cells, so at the bottom or top of the curve when cells start drifting. It should be very easy to balance such high capacity cells with 5A at this stage. There is no need to have multiple balancers, I actually think they would counter each other and start fighting.
do not use the bus bars he mentions.. in his later videos he has tons of problems with them.. these bus bars are inferior , they make bad connections and heat up ... do not use them they will damage your system.... the bus bars that come with the batteries are much better.
Question, when bottom balancing, when you drain the batteries to 2.5v do them individually or in parralel?
All cells need to be at 2.5V. You can do this by parallel them or on an individual base, it does not matter.
Yes are you a top or a bottom.................... balancer? Yes very funny!
I have a question.
Hypothetically, if I wanted to have a 48v off grid solar system, considering all this battery balancing business why would I buy 24x lesser capacity 450ah 2v cells that cost $7500 with 48 external terminals, over only 8x 550ah 6v cells that cost $4500 with 16 external terminals?
I kind of (but not really) can understand if one 2v battery goes bad I can replace that battery at $3-350, but if one cell goes bad in a 6v battery well the whole battery is done but here's the thing, whole 6v battery is $550 anyhow so not a deal breaker considering the huge reduction in bank price: ~35% less for ~20% more capacity with ~1/3rd the external connections.
What I'm asking I suppose is battery balancing easier in external 2v batteries than 6v batteries?; and secondary is, why would I accept a premium price for a 2v bank with less capcity than a ~35% less price for more capacity 6v bank?
These are all AGM batteries so I'm comparing apples with apples.
It's the chemistry. The 6V battery is most likely lead acid tech. That's exactly what you don't want. They will last only 500 cycles and you can use only half of the capacity (or they are dead within 100 cycles)
Top balance in parallel to 3,6V should do the trick.
Bottom balance method makes the most sense to me. However you still must understand that all of these problems come from the fact that a cell has an internal resistance and that resistance is different between the cells. By its very nature resistance consumes power. Whether you are charging or discharging, part of the energy is being dissipated as heat, IE is a loss. However, because each battery has a different internal resistance, the amount of that loss is different between the cells. This implies that regardless of what you do you will have drift between the cells over time. This implies that eventually you will need to rebalance.
For my money all this top balance / bottom balance / active balance / passive balance is just theater. The objective of a battery is to deliver current. Current (electrons) does all the work. When you hit the knee you are within a few percent of done charging or discharging. STOP! if you need more current get a bigger battery.
You can spend your life chasing the final couple of percent capacity or you can enjoy your limited time on this earth. Buy a bigger battery.
Its also Not save without a BMS and a working Charge Controller because These Cells will Drift over time so you can Overcharge the Cells If maybe one cell is lower
Yeah, absolutely. A BMS is a must!
i will be a top feeder...i mean balancer . ha ha ha....please dont be offended. honestly i like having a bms for my batteries. here in Montana it is far to cold for a significant time to chance damaging the expensive batteries so i dont like to ever...did i say ever? let my batteries get to zero and worry about cold temp charge problems
Right, that's a very good point. Climate could be a decision maker. Thanks for sharing.
Very good or an excellence detail how to balance your battery, think bottom balance cells win and I think BMS should stay in with the cells for just in case.
Seems like the logic method....
Thanks for the great video. In your opinion, if I am running an active balancer as well as my daily BMS do I need to top balance my batteries when I get them or can I just let the active balancer do that over a couple of cycles?
The balancer should be fine and will do the top balancing for you. You can leave the battery charged to 3.55V/3.6V and the balancer will work it out over night. Remember to only balance when cells are above 3.45V ("top balance").
I am a total novice on electricity and all that stuff. So now I have ordered a set of 4 3.6V 280 ah batteries and bms. I do not have a bench charger. Only solar panels, a charge controller, and the bms. Will I need to find a way to balance the cells or can I simply put the parts together and go from there?
Pros? Cons?
If the cells are new and you don't need the state of charge you should top balance them. If you don't have a charger or power supply, you can put the battery in series and set the charge controller to a lower value, say 3.35V. Keep measuring the voltage of the cells until they all reach that 3.35V. Slowly increase the voltage of the solar charge controller by 0.2V and monitor the cell voltages. Keep going until you hit 3.6V with all cells. It depends on the BMS how it will handle the balancing. Got a DALY BMS? Forget all the above as it won't work with these BMSs.
Alternatively you can use an active balancer (~$25 for a 12V battery) and also increase the voltage slowly as above to give the balancer time to... balance.
I'll make a video about how to do all this once the new batteries are in place.
Nobody else even got the Bert/Ernie reference?
It was very hidden ;)
you're assuming 100% efficiency on every cell. that's not possible.
while you may be charging your cells in series with 10A for 1 hr, that doesn't mean you can pull 10A for one hour from your cells.
some cells charge and hold more energy while others may not hold all of the energy that is put into it.
The LFPs here are at around 99% efficiency.
👍🏻
thanks again Andy...If i could ask a random question please
the wifi set up do you use wifi extender to the house?
i have my shed about 55mts from my house router and just looking for a suitable solution to stay connected TIA..ps... i finally received my 280ah batteries today 12 weeks...stay safe..stay charged
I'm using one of these to make the 'bridge' from the access point inside the house to the carport (shortest distance). Form there a 10m cable runs to an old router (I use it as an AP) inside the garage which provides Wifi and LAN.
www.tp-link.com/au/home-networking/wifi-router/tl-wr902ac/
@@OffGridGarageAustralia thank you so much Andy..your a champion
Is this relevant for the exam ?
Active balancer is not effective on such cells. The best solution is "powerwall" but not "e-bike" BMS. Batrium, or DIYBMS or something similar. Such BMSs have a normal passive balancer with significant balance currents 1 to 5 Amps, which are real Amps, ant not Chinese "promised" current. The active balancer work based on voltage difference, which in case of LiFePo4 is so small, that active balancer current is so low 0.01..0.05A. Alternative option, is to use the BMS only for safety and external passive top balancing balancer with 1-2Amps
The answer is YES!
All the more reason to design a system to operate in the 80/20 range or 90/20 if your feeling confident. Nothing wrong with a periodic combination of practices. Call it a health checkup.
Too balancing once a month by means of an active balancer then via BMS, a low limit disconnect would give you a look at the overall health. Of course with a data log. As long as you mamage the extremes, you're good. This is why bottom balance wins.
This is probably one of the best explanations I've seem on the subject. I remember when Jehu built his bus without a bms. He took some flack over that.
Thank you for your feedback and comment.
So bottom balance and the BMS without balancing option?
@@OffGridGarageAustralia yes, sorry I wasn't completely clear. Also about Jehu's van, remember they were l'ion 18650's. As in all applications, keep in mind the chemistry.
I'm an old hack from the lead acid era. The inverter chargers typically have a monthly top charge of around 15+ volts to help keep down the dendrites. On any lithium, too high of a charge voltage will help create dendrites (bad).
I've ordered my 100kw 85/20 bank last week. Need to start deciding what I'm going with on this management. Bottom balance at the 85/20 point with the previously mentioned scenario. It is for my business, wanting to beat down my $1100/mo electric bill. Keep checking for my obit to find out if it worked or not. Take care Andy. Alex
I intend to charge to 3.4 (54.4) then float at 3.4 (54.4) for 30 minutes. As you pointed out in a previous episode, this puts all cells at max capacity. I would also stop the charge if any cell hit 4.45v. Is there a problem with this? I would turn of all balancing. Do you think this would cause plating problems?
I don't think your settings will cause any problems. Are your cells not going out of sync after w while?
@@OffGridGarageAustralia still in planning stage. Thanks for your work.
Bottom
and no balancing?
@@OffGridGarageAustralia Yes - KISS
Maybe just put a balance monitor on the cells, rather than a device that try's to balance, ie turn off the balance function
Even on my 4.2v chemistry's (on ebikes usually) I bottom balance, but I also have a bms set to disconnect the pack if any cell gets above 4.1 or below 3.1. I prefer bottom balancing as at high current drains with a low SOC you have less risk of pushing a weak cell into a reverse polarity situation if it goes over the cliff..
You mention VW samba's with battery packs without a bms, well there was two... was being the important word.... apparently it was being stored in a field, and the panels were still connected but covered by a tarp, until they were not covered by a tarp..... I wont mention who fitted that 'system'.....
Yeah, very different scenario in e-bikes and other high current equipment. Also, using Li-ion is very different as the charge and discharge curves are linear to the voltage, unlike LiFePO4.
@@OffGridGarageAustralia agreed, but both have similar issues if you get to single percent soc and then something in your home current spikes like a heater/shower turns on. But I think the time has come to finally pull the trigger on a pack of batteries for the camper. I wanted to use lots of 100ah cells for an L shaped pack but looks like 300ah will be more cost effective which means going to 600ah instead of 500
Why not middle balance the cells? I know, no available equipment that do that and it is more complex when you can't just measure the voltage. But apart from that it ought to be best for the LiFePO4 cells if I'm correct?
This would only work with a precise coulomb count of Ah in and out of the battery. It is difficult to find a common spot for all cells where they have a known state to compare to. But good thinking!
@@OffGridGarageAustralia Yes. If you don't use balancing you could use your testers to find and charge all cells to their middle point of charge and then just use the bms to stop charging/discharging when the weakest cell goes high/low. Preferably at really safe voltages, this way no cell is stressed and the pack should in theory not get unbalanced.
If your use case is running on empty most of the time do bottom balancing. If usually running with greater then 50% SOC do top balancing. It is also more likely to damage cell from overcharging then overdischarging.
Aeh, I think it's the other way around, cells damage very quickly at under 2.5V while overvoltage can go up to 4.2V with these cells. 3.65V is the max recommended voltage.
My battery rarely gets under 40% so I'm staying rather in this 2nd half as well.
@@OffGridGarageAustralia
You can take a cell down to 1v if you recharge it soon after. If left in over-discharged state for long time (days) it will grow lithium metal dendrites that can short out cell. This is why you should initially charge from over-discharge at low rate. If it has dendrites, the cell voltage will not rise and the low current charge will avoid overheating on cell. Electrolyte will breakdown below 0.2v (or above 4.3v) assuming cell is using most common electrolyte. (lithium hexafluorophosphate LiPF6 ‘salt’ , with Ethylene Carbonate C3H4O3 'solvent'),
Most damaged cells on the forums are the result of over-charging where the electrolyte breaks down and puffs up the cell with gases released from decomposed electrolyte. The other by-products from electrolyte breakdown coats the anode and cathode surfaces, clogging them up and reducing ion flow in to and out of the electrodes increasing cell impedance.
The 2.5v spec is based on no significant capacity is achieved below 2.5v and if left at or above 2.5v for long time it will not grow damaging dendrites.
Thank u" Battery man" up up and balancing lolll 😂😂😂😂😂👍👍👍👍
No worries
Good Job. I have more idea on top, bottom and balancer. Thanks so much.
Thank s for your feedback!
Do what works for you and your battery bank. Any bank is only as good as your worst cell. Old batteries do not even charge at the same rate. In your example a 280 ah battery with 100 ah in it will not ever come to 3.6 volts so your bank voltage will be made up with more voltage from the weak cell.
we like everything, meat , fish if a reason for a new video! science is a great religion
I'm bidding on a 29kw hour battery, so all this is going to come in handy, after I deconstruct it and re-assemble I'll need to buy six matching cells for a 40KwH battery!!!! Talk about life changing for a 100% off grid solar guy! I can run an entire week off it if the battery is good!
If it was boring it's because it didn't have enough frogs in it.
Arghhh, they are all in winter deep-sleep
Bottom balanceing is ideal but there aren't any bms's that do anything but top balance so I don't know how useful it is and as far as active balancers they are not quite that smart they can only move energy over 1 cell I think what would work better is taking a high voltage cell and boosting to the whole pack voltage and dumping it there and taking power from the whole pack to charge an undervoltage cell and just do that for one cell at a time I think would be fine but I don't think they over cycle the battery because it is mostly doing it during charging so instead of like 10 amps it's getting like 9
Well, if you bottom balance, you would not need a BMS with balancing capabilities at all then. This would just destroy your initial bottom balance. Same for a balancer.
@@OffGridGarageAustralia but I mean cells are probably going to drift but if you are not planning on having any balancing what difference does it really make if you had them top balanced or bottom balanced they are going to drift just the same
I don't know about balancing by capacity it seems to me that you're relying on your ability to measure how much capacity you took out and how much capacity you put back in the shunts are pretty accurate but I don't know if they're quite accurate enough
All balancers take the cell voltages as measurement. As long as there is a difference, they keep either burning off energy or shuffling into other cells.
A coulomb count through a shunt may work but is not 100% accurate either as it would need several other parameters as well (current, temperature, SOC) to make an accurate decision.
Seems like it, we cannot really find the perfect solution.
Or you could balance it around 50% SoC and cut use of the pack on weakest cell reaching higher and lowest voltage. BUT with flat curve batteries like LFP it's close to impossible because you would need a hard to achieve precise charging at 50% SoC for every cell before top balancing AND a long time (> week ?) top balancing because of the low voltage differences...
Thumbs up - thank you for sharing all your experiences and explaining the "religious" topics from a scientific and mostly neutral perspective! btw: the active balancer was in fact a boost Konverter, wasn't it? 😉
Und auch ein großes Dankeschön für die tägliche Seifenoper! Bin langsam schon ganz neidisch auf Eure Flächenverhältnisse in AUS...
Danke Dir, Dirk. Ja, das war ein Booster 😉
Es ist alles sehr viel groesser hier. I'm moment im Lockdown aber was macht das schon bei 30.000qm land. Guck mal auf Living Down Under fals du das noch nicht kennst ;)
7:10 Yet on spec sheet for EVE 280K, that busbar should be shorter.
But in reality it is LONGER!
No engineer would design is system to operate at the extremes, we analyzed the system extreme precisely so that we can avoid them and yeah what are we doing here? Discharging the battery clear down to 2.5 volts. Charging the battery clear up to 3.65 volt. Those are the extremes which we are supposed to stay well away from. And for what purpose? So that we can store a miniscule amount of extra current. Makes no sense to me. I will operate from knee to knee. If I am so desperate for more power that I need to operate beyond that, I will buy another battery.
When the battery is operating in the steep part of the curve it is struggling to provide or store more power. When the battery struggles it is being damaged. STOP. You don't suddenly start damaging the battery at 2.49 volts or 3.66 volts. You are already damaging it and the damage gets worse the further down the slope. And why? For a few more milliamp hours of storage? When you hit the knee, STOP. Order another battery.
Just my humble opinion of course.
Thank you John. That is great advice. So what are your settings for your battery? 3.1-3.4V?
Before we get Into what voltage, we need to discuss Equalization. By connecting all the batteries in parallel for some period, the batteries will equalize. Equalization is not the same as balance. Balancing is voltage State, Equalization is charge state. Once Equalization is accomplished, put cells in series . Set the BMS to cut off charge and discharge when any cell enters the knee. You Are done. Enjoy the battery. Just know that in a year or two or three, you might have to equalize again. Unlike balancing however Equalization is quick and easy.
@@jwcolby54 So you let the BMS control your battery charging/discharging?
That would involve a better control system as many have where the BMS controls the SCC as well as the load and inverter.
To be pedantic about balancing...
1) check voltage to group in sets of four that are close (ideally within 1/10v)
2) with 4s bms wire in series
3) charge each 4s with 12v until BMS shuts off
4) unwire battery(s)
5) check voltage of each cell and any that are 1/10v or more different charge to close enough to others
5) rewire cells all in parallel
6) charge to 3.6v until current is negligible
7) unwire battery, rewire in desired configuration
The balancer size needed is not determined by the size of your battery but by the size of your charge and discharge currents.
How do people feel about extending pv cables by soldered splice and marine shrink wrap? I ask, as I need to extend some existing cables, and there is little room in the conduit for anything else. Otherwise I have to spend £100 for new cable. Would the soldered join act as a resistor? The cable is 4mm2, 1000v . I intend to run around 1kw at @98v down these wires.
So long as the splice solder is thicker than the wire then no issue.
Hey, Chris, there is no problem with that. I have done it numerous times. If the solder connection is solid, no problem.
@@OffGridGarageAustralia thanks all, this is todays job.
What if my 8 cells I just got in are all reading exactly the same voltage 3.29v all 8 cells do I need to still do a top balance ?
Looks like really nice bus bars. I guess Al need around 50-60% larger cross area to get same resistance as Cu and the thickness of these looks like 2x the one that follow batteries, so it should be quite a lot better. :)
Yes, you are right.
Hahaha loved your Scottish accent lol but I still say one day of bad weather doesn't compare lol
Probably not, it's still warm here, even in winter 😊
@@OffGridGarageAustralia hahahahahaha we'll were having our week of sun now 😂😛😛😛
Up to 11.2k subs now, congrats! Thumbs up and subscribed and 🍺$! Nice wildlife!
If your bottom is not balanced, dann wirste doch schief man.
Genau!
Please more fart sounds
I used that 5 amp active balancer to bottom balance my 8s pack while still hooked up in series with BMS. I did n't dare redo the nuts on these cheap flimsy cell terminals again. I could feel these cheap terminals moving when I put it together the last times. the buss bars and holding the =/- cables while tightening the nuts prevents movement. runit down to low cell shut down, then wait for balance, then run it down till a low cell cutoff again and waited for balance again. each time the cell difference got less . till they all run out the same time.
I use the technique described by Jack Rickard and recommended by @Helder Pereira. Before anything, I bottom balance the cells to 2.75 by discharging them down to 2.65, and let them set overnight. Because the voltage climbs back up a little, I discharge them 1 more time and they settle between 2.70 and 2.75 Volts. Now the cells can be put in series and are ready to be charged.
What about the BMS and charge control settings?
@@OffGridGarageAustralia I turn off the balancing in the BMS and just use it for protection. I like to charge up to 80% so the charge controller is set with an absorption of 53.2V and slightly less for float.
@@SpeakerKevin Thank you.