LiFePo4 and Absorption. What I learned from my previous mistakes...
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- Опубликовано: 1 окт 2024
- So this is a bit of a long story. I had some problems re-charging the battery after the last discharge. When it got fuller, some of the cells peaked and I had to manually discharge them. The more cells peaked, the more I struggled to keep the situation under control. At some point I turned charging off as I could not handle it any more. I'm not sure why the cells were so mis-balanced from the initial top balancing...
Well, I found another method online how to balance the cells without disassembling the whole pack again. So, that's what I did the whole week long. It took a while and I learned a lot about how these cells work and behave. It is all about the voltage and current. I was so wrong by just looking at the voltage...
Will the battery work after this crazy balancing procedure?
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Great work! Appreciate it. Thank you for the opportunity to study together! Best wishes from Ukraine 🇺🇦
Thank you. Take care over there!
Why not set float voltage to be the same as the absorption voltage? This will allow the BMS to continuously balance cells as well as allow solar to supply any loads without having to cycle back to bulk and absorption mode again
Yes,, that is how it have to be for grid connected batteries.
Hello. yes, the same here.
Yes, set Absorption = Float. It will be in the next video!
@@OffGridGarageAustralia yeaHHHH waiting for this Video from Spain and ready to get all hardware to copy your experience! we have a lot of sunny days as well in this country.
No, never do this (see my detailed answer elsewhere). Batteries are not capacitors, even if the amps are reading zero there are going to be eddy currents at the potential wall and overcharging above it if the charge controller is left in that state. Setting the float high enough to actually get the BMS to top-balance the cells is also high enough to overcharge the battery or greatly reduce its cycle life.
You want the charge controller to charge the battery high enough for the BMS to be able to top-balance it (e.g. bulk/absorp target minimum 3.45V/cell. 3.5V/cell is better with the absorption time set to 0), and then for both the charge controller and the BMS to both stop messing with the battery until the next charge cycle (e.g. float setting should be no higher than 3.35V or so).
-Matt
Your explanation of absorption was great, it really helped to visualize that part of the charging process! Where people can visually see there's still so much energy that can be packed into the battery even when you've reached the right voltage.
I've explained absorption before to people that it's like filling a cereal box. You can quickly fill it up to the brim but still not reach the gross weight of a full box until you kind of shake the box and let it settle some. Then you can pour in more. It isn't until you reach the right weight that you can consider the box "full" or "saturated". (The height would be the voltage, while the weight would be the current.) So the "absorption" phase is kind of like shaking the box while you pour in more cereal.
No need to put up the footage from the past 3 days if you feel this video sufficiently explains/educates people on what you learned. It's a wash of whether that could be helpful - on the one hand, people will see the entire process of how you were troubleshooting and learn along with you, but on the other hand it could actually complicate and confuse the message of what ultimately needs to be learned. With the deluge of information people face these days, I tend to think keeping things simple is better, that the value of watching you troubleshoot is negligible since you explained your thinking process pretty well here. So if you're comfortable that there's little to be gained from your footage from the past 3 days, I'd say "spare yourself the effort (and potential embarrassment 😆).
Your cereal box analogy is pretty good but it tends to apply more to flooded lead acid. In the case of lifepo4 that extra energy you're pushing in to the battery is done by fixing the voltage so that the battery cells that are already fully charged cannot accept any more because they resist this voltage but the battery cells that have not caught up yet can accept this voltage. In bulk you were charging based on fixed current but now you're charging fixed voltage. This means that the individual cells that are lower in charge are now going to be able to catch up to the ones that are already charged fully.
Why don't the more fully charged cells also continue to take a charge and end up over charging during this absorbtion stage you may ask? Because you are now keeping voltage fixed and any cell that's fully charged will resist and push back against this voltage. The only way to make them charge more fully would be to increase the voltage.
Why didn't the lower cells take more charge during bulk you ask? Because there are always slight variations between battery cells resistances.
So why can the lower charged cells accept a charge now when they didn't before? The answer is they did, but they just did so at a slower pace.. now you are giving them time to absorb this continous constant voltage over time and bring them up to the same threshold as the other cells at which point they will also start to push back against the voltage.
Think of it like teaching a class of students that vary in intelligence. The bright kids catch on quick and then sit there already educated but learning nothing new whilst you continuously repeat the same information over time untill the slow kids catch up. This repetition of information is analogous to the repetition of applied voltage over time or absorb stage as we call it.
Well i have learned a lot from him, especialy his mistakes.
@@juskarn Thank you!
The manufacturer does not take the time to fully charge, and discharge each cell to match them perfectly, it would cost you much more per cell if they did. This is your job.
You need to charge the complete battery to 100% ... 3.65v per cell, this is top balancing.
Then you need to drain the battery to the point your lowest cell reaches 2.5v, this is bottom balancing.
Then charge the battery as a whole (complete) until the highest cell reaches 3.65v, until there are 0 amps going in, this will give you your total battery capacity, this is a set value determined by the cells you got in this wonderful DYI battery lottery.
Now that this is done, you can say I will only use this much of my capacity, and only charge to 3.55v and discharge to whatever you want.
The fact is, your capacity is determined by your weakest cell only. This cell will ALWAYS charge and discharge faster.
Thanks for the info and explanations Off Grid Trucker Dude.
Amen!!👍👍 Off Grid Trucker Dude, this is the fun part in a DIY setup.
Thank you for teaching us as you learn these things yourself.
I have learned so much from your videos! There is so much to learn and you are so good at explaining the key points from your testing. Your channel is the best I have seen to truly make the complicated simple to grasp and you do it with great music and personality!!
Thanks a lot, David. Appreciate your feedback and kind words.
Hi Andy. I will give you my opinion. I made a battery with 22 LiFePo4 cells and installed without BMS on a scooter. 2 years after almost daily use I don't see any imbalance. After much reading and watching videos of experts, I opted for the technique of bottom balancing instead of top balancing. The explanation is simple. All cells have a common minimum, but not all can have the same maximum.
I unloaded cell by cell until its minimum tension and left it to rest for 2 days (the tension will naturally rise a little, being necessary to repeat). With all the cells equal at the minimum voltage, I connected them in series and connected the charger until it reached 80% of the maximum capacity. It is my safety margin and I guarantee that all cells are able to balance themselves at this voltage. LiFePo4 chemistry is very stable. It's just my opinion. Good job Andy.
Thanks for sharing. Interesting approach indeed...This method will work as you only charge to 80% capacity, that's correct. How far down do you discharge the cells during operation?
If the bus bar contacts are not good, the BMS will never get an accurate cell voltage reading which leads to unbalanced cells.
Not the best solution:
1, charge every cell separate is the best solution for balancing, that's OK. But until charge A drops to 0,05C (EVE manual !) and charge with 3,65V (EVE manual !)
2, Do NOT let BMS discharge cells separately! That breaks the balance (as you realized V does not matter so much in SoC).
3, Discharge the whole pack with a load ! Use the inverter.
I appreciate your efforts. we are all learning together.
Thank you!
Indeed we are all learning this solar together. But so rewarding ❕❕❕
Thanks Andy 👍🏼👍🏼🌞🌞🌞🌞🌞
I am sorry to sound critical, but it seems elementary to me that all things in nature need absorption, a good old soaking-in to actually achieve proper fullness. And lithium chemistry must be the same.
Just like watering a plant -- you should not just hose the ground till it looks wet. You need to soak it a bit so the next hot day doesn't quickly deplete your moisture. You'll be "recharging" the soil a lot more often with such habits and you plant will have less moisture to "discharge".
Same for battery chemistry. You can't just ram in 1C current up to 3.65v, call it full, then retreat. Ya gotta let fullness stew a bit. And worst of all are the pussies who think let's not charge all the way to 3.65 because 95% is full enough. Ffs, PhD rare-mineral chemists worked all this out over decades. Who are we to doubt their proofs in R&D with Queensland garage research.
Hi Andy! I am a novice at all this. But from my research on the internet this is what I have come up with. It is good to do an initial top balance at a very high voltage such as 3.65 per cell. A charge to this voltage will bring the cell to about 95% of its capacity. Even though you don't want your daily usage to go more than 80% as you have said. This is the way to get them balanced in the beginning. Some commenters have said that wants you achieve this initial balance they should stay in pretty close balance afterwards.
Because of the flat voltage curve you will never be able to get them balanced if you're only going to 3.5 volts.
What do you think? Maybe you could give it a try. Thanks for your videos. I appreciate all your hard work.
You rotten sod rubbing it in about your lovely weather and how we are freezing and your going in the pool to cool down !
Great episode as always. Lovely to see your frog at the end.... kept thinking of them when I saw your green battery indicator on your phone. Learnt a lot from your channel. Thanks
Thank you 🤗
You can keep your 31 degree weather. I'm going ice fishing. :)
I think I read you note... Absorb 54.4... Float was what I would expect... so, shouldn't Absorb be about 57.6v or slightly more? What have you set your time after reaching Absorb before entering float? After listening to the entire post, I heard you say "two hours". I have never understood what Absorb time should be for LFP and have seen many folks use as little as 10 minutes.
Thanks
It's true, I only have it in my system for 12 minutes maximum, two hours is for a lead acid battery.
Great Video. I've been experimenting with a Growatt 3000K 24v 8S 3.2 cells. And It is very confusing to get all the parameters rights. Your video has clear many questions regarding CC/CV, voltages and amps. I am still playing around but I think I have found a sweet spot for my setup. Thank you very much for sharing.
The way they do this at the factory seems to be: Balance to 3.4V, wait for current to drop to insignificant. Balance to 3.5V, wait for current to drop to insignificant. Balance to 3.6-3.65V, wait for current...... . For normal charging later no need to go over 3.5V/cell.
I probably only charge to 3.35V and call it, let them absorb at this stage. This is already over 95% of capacity. Everything higher just stresses me ;)
@@OffGridGarageAustralia Even charging to 3.65 volts, the cells will last well over 4000 cycles to 80% of their original capacity, which is 11 years if you fully discharge to 2.5 volts and charge them back to full every single day. Even then, after 11 years of fully discharging every single day, you still have 80% of the capacity left! You shouldn't be so afraid to charge the batteries to 90 or 95 percent. You will still get 15-20 years of service out of this pack, no problem. In 15 years, I'm sure there will be much better cells you will want to try and they also will be much cheaper to buy at that point. 10 years ago, these cells were $1000 per kwh. Now, you can get cells for close to $100 per kwh. In 10 more years, these cells might be $10 to $20 per kwh. So, don't be so afraid to charge them to 3.5v or so. Its really not going to do very much harm as far as lifespan or capacity over time.
@@catch22frubert yeah, that is probably correct...
What catch22 said. Its not so much how high you charge the cells to as it is how long you hold that high voltage after you have reached it. But yes, the typical charge profile is to charge up to a specific voltage and then immediately stop (absorption time set to 0). Typical voltage targets are 3.45V, 3.50V, 3.55V, or 3.60V (corresponds to 13.8V, 14.0V, 14.2V, or 14.4V for a 4-cell 12V battery). You can go up to 3.65V but there really should be no need. It won't change much other than stress the battery more (though not all that much, really). And the battery will still not be charged above 90%. However, if you charge up to 3.60V or 3.65V and then HOLD that voltage for a time (i.e. non-zero Absorption time setting)... that is what gets the battery all the way to 100% and that is what starts to seriously degrade its cycle life.
And, in fact, holding any voltage above the potential wall can get the battery to nearly 100%, it just might take a long time... as well as overcharge it, or cause other problems due to sloshing currents in the chemistry, which is why the Float should always be set below the low voltage side of the potential wall, never in the wall or above the wall. The low side of the wall is around 3.4V so the float should be below 3.4V (i.e. 3.2V-3.35V. 3.3V is fairly typical).
If you set the float higher than 3.4V you are effectively overcharging the battery by causing the charge controller to constantly go into bulk mode when the battery is ALREADY in a well-charged state, causing the effective charge state to cycle higher and higher. Both the float voltage and the bulk cycling will reduce the cycle life of the battery. You don't want either.
-Matt
Hi,
I also using the Same cells eve 280ah
The total battery pack is 48v 560ah
Total Solar Power 8 kwp connected to MPPT controllers,
My Setting in the Mppt are
Bulk : 54.6v
Abs time 1h
Float : 54.00v
Max charging current 140amps
This settings Works Fine for me for More than 1 year.
And in that time i Never Balanced the Cells again,
I think there is also no Need to Balance the Cells every time you charge. To 3.4v
Thanks for sharing your number of your SCC. I'll go deeper into this in the next video.
Your float is too high. 53.6V is the highest you should float, otherwise the voltage gets too close to the potential wall of the cells and can cause them to go out of balance as well as cause unnecessary wear.
There is no need to fear a high charge target voltage. If you charge to 58.4V the battery banks will still only charge up to around 90%, and still allow the BMS to top-balance the cells (which won't hurt a thing). Charging it over 90% typically requires holding the high charge target voltage for a period of time (i.e. setting a non-zero Absorption time).
If you only charge to 54.6V, that is right smack in the middle of the potential wall of the cells. The problem with doing that is that the charge controller will not be able to consistently charge the battery to any sort of percent-capacity. It could wind up charging the battery from a low state up to anywhere between 40% and 60% or so. It will be inconsistent at best. If you are seeing more capacity than that, it's because your float (at 54.0V is too high and essentially trickle-charging the pack continuously or causing extra bulk charge cycles to kick in and do the same thing... trickle-up the battery's charge state).
If you really want to conserve cycle life then you don't need to charge the battery all the way up to 58.4V, but you should at least charge it to 55.2V. That will give you a far more consistent charge state and will allow the cells to charge above the potential wall instead of inside the potential wall, resulting in a more even charge across the cells.
-Matt
@@junkerzn7312 thanks Matt. As I said in one of my last videos: if absorption voltage and float is to far apart from each other, the MPPT won't supply any power to a load once absorption voltage has been reached and the controller switches to float. It will wait until the voltage drops to float before starting a new cycle. The load will be supplied by then battery in this stage and not from solar as it waits for the battery voltage to drop to float again. I found this is a total waste of energy, the sun is out but the MPPT waits for the float voltage to be reached instead of supplying power to the load and leave the battery charged.
@@OffGridGarageAustralia You don't understand. The battery is STILL ALMOST FULLY CHARGED when it drops to a 3.35V Float. I will repeat that. The battery is still just about fully charged. You aren't saving anything by using a higher float value. Instead, you are reducing the cycle life of the battery.
The charge controller will still help supply power to the load and the battery will still remain close to fully charged at a float voltage of 3.35V.
I've said this four times now. You aren't understanding the difference between the LiFePO4 charge curve and the LiFePO4 discharge curve. They are different curves.
-Matt
@@junkerzn7312 are you getting angry now? What's wrong with you?
I had similar issues, and what worked for me was this: Charge the pack until one cell peaks. I used an 8S charger and did 8 at a time so I could see which cells were topped out at 3.65V, and which were lower. Then individually charge any cell that wasn't topped out. Then charge the pack again as an 8S pack to see which cells were still not peaking, then I charged those independently again, and after 3 rounds of that, all were very well top balanced. You can charge the individual cells with a charger while still in the pack by just using alligator clips for the individual cell. I use a battery charger for the independent cell charging because it measures the AH added, and it shuts down by itself so I don't have to watch it.
Balancers are only for maintenance, you are definitely right on that. You must balance the cells before you can even think about using a balancer, BMS balancers only work when batteries are very close to each other for state of charge. When I had one cell peaking in the 8S banks, the other batteries were anywhere from 6 amp ours, to 84 amp hours lower! I came to the conclusion that adding to the low cells was way more efficient than discharging the high cells, as that is how I started but quickly realized it was a flawed approach.
Wery interesting! Can you explain, what does it mean? I have all the time same three cells, that are higher then others for around 0.010- 0.035 mv when charging, especially higer then 3,5v and in some time after stop charging their voltege goes lower on 0.020- 0.040mv then othe cells. And balencer begins to charge them. I did paralel topbalance befor assemble. I use Daly bms and Neey 4A smart active balancer. I see that during the end of charging, that 3 cells runs up, balencer discharge them, deviation voltage goes from 0.050mv to 0,004mv, charge stops, and after that, when bettery goes in rest, voltege goes down, and that 3 cells become lower than others... They goes much lower ( near 0.080mv) under load 60-90A. Without load, they also steel lower. I set balancer to continue balance after charging to rest to until 3,330v and usually get 0.010 mv diff. But in this case next charging shows bigger then 0.040 mv different, becose other cells gets some deviation between one another. Maybe that is normal behavior? Maybe, I have to charge battary to 3.65v per cell, and then charge that 3 cells individualy with 3,65 v automatic Lifepo4 charger?
Hey! Tried this and it works! My batteries have a complex installation and I really didn't want to take them out of place for servicing. I achieved balanced cells merely by lowering the overvoltage cutoff to 3.45v as you suggested and voila! Thanks!
I ask the same question why cant you just make the absorb and float the same voltage? I suspect it may have something to do with What Comment is stated on Emily and Clark's channel, but I dont fully yet understand it.
"""I’m glad you mentioned low current overcharge of LiFePO4. So many people seem to believe that only the charge termination voltage matters, and neglect to notice that the cell manufacturers always stipulate a 0.05C charge termination rate. Charge to that voltage at a lower current and you’re overcharging.""""
Reply from Clark
"""Yes, and that can happen so easily with solar or while using your electrical system during charge.
Honestly I didn't understand this as a problem when I started this project. Solving the low current overcharge is what made this interesting to me."""
You need a full capacitive balancer 16S 6A balance current it controls the battey pack as a whole. Have a Daly Smart BMS with 20mA balancing current no good for the 280A LifePo4 cell only good to set the LVC and HVC points that all. There are Lion, LiCobalt, LiTianium and LiPo4 bats. Most charge controller on Lithium setting and will blow the cells at 3.7V. You need to know your battery chemistry and the Min and Max settings. My LifePo4 came at 3.29V 80% charge from factory and 3.20V is 20% capacity level. You will impregnate your cells if below or above the specs. Seen two case last week at my buddy's shop with pregnant 200A LifePo4 cell. Know the chemistry. I created user defined LVD and HVD points in the Inverter and in the Solar Charge Controller.
I fully agree, hence I'm doing all this testing, observation and configuration. I don't agree with the balancer though as it will hide your faulty or weak cells. They all look the same and you won't be able to identify any problems on a cell level.
Very insightful, excellent material to ponder. You have hit on an issue that I have been thinking about too. The longevity of the the batteries is greatly diminished by charging to 100%. a combination of voltage and current monitoring must be the answer. The tolerances are so tight as you point out it's so difficult to get it just right. Keep up the good work. Perhaps keep a log of the batteries that are always the highest and lowest to see if their performance deteriorates faster than the others. Keep testing to find the sweet spot! Thanks for your video
Just read a pdf paper of a BMS vendor saying...don't trust the vendors....if they mixed 280ah with 250ah batteries then it explain why some batteries need more charge than the others....
Of course the 280Ah will charge more than the 250Ah cell. That makes totally sense.
I'm snowed in but theres a lot of sunshine and its -15c so perfect solar weather
Surprisingly, yes. And the Sun is closer too.
Finally have sun today in SE Colorado after 5 days of clouds , but it’s still -4°F, good for the solar electric panels, but too cold to use the solar water heat collectors. Propane and firewood!
Good call. Just love those sunny/cold winter days.
Not well known that the power produced by solar panels is higher when it's colder due to higher voltage but the current is determined only by the intensity of the light (photons) from the sun (insolation). So for the same intensity of light in summer and winter, you will generate more power in winter.
This is what I have been saying in my comments to you for a while. You need to take the charge up to 3.5v but balance from 3.4 each charge to keep pack in balance. These cheaper cells need a fair amount of balancing. My BMS high volt cut off is 3.6
JD: Wait…what? Are you trying to take credit for that which has been common knowledge for a decade or more and revisited in this video? BTW…your voltages are a bit off, your BMS knows better. Just let it do its job after you top balance when new (and occasionally thereafter if you so desire). Also stating the obvious concerning “cheap cell” balancing issues seems a bit presumptuous from where I sit. Just enjoy the videos and absorb the wisdom.
Always a good day when I see a video from @Off-Grid Garage :)
Glad you enjoy it! Hahaha, thank you :D
So it looks there is problem at BMS. It should balance better if some cell is higher voltage it must charge less. I understand bms function like it is monitoring individual cell and control charging.
The balance current is small and if the battery still gets charged at the same time, balancing won't work. I have no changed the settings and will provide an update in a future video.
Mistake makes us to practice.
Practice makes us to perfection.
Perfection makes us fascinate.
And we can't stop thinking so there are some mistakes again... lol
That's a good summary. Success and fail are close together...
Why wouldn't you set your charge controller to push max amps for as long as possible - why would you taper off the amps half way through the charge cycle - that makes no sense... I don't buy a 20 amp wall charger and only use 10 amps to charge. I charge with 20 amps (way below safe max amps) until the battery is full, near full and I let the BMS and its micro balance function do its job over night, if the battery needs a top off, I top it off; and whalla - a full charged battery. People do not understand this and think that if you set the charge controller voltage higher then the battery BMS cut off voltage, it is somehow dangerous - for lead acid, maybe, but for modern batteries with good BMS - this is not the case, you can push the volts higher then the pack cut off voltage and be totally fine, you are NOT overcharging the battery. Unless your BMS is useless and all you are using is an active balancer, but you are not - you have one of the best BMS on the market - let it do its job, and max out your charging amps by telling your charge controller to use a higher voltage ceiling... Of course there is a limit to how high you should go, and you are probably one of the only people who has the equipment, skills and knowhow to run the tests properly - if you don't understand this, then you are like the rest of the planet - because everyone is confused about this, and its really sad.
3.65v i think cut of charging voltage is right thing to do.....
Or capacity balancing ....add missing capacity with small cells...
try looking at this ausy.. HBPowerwall he's just fantastic. runs his house on 48v solar
@DIY Projects Professor Andywho.. there are so many
please witch one???
@@toneault7499 I'm sure he is not a witch.
I watched a few of his videos and it's very interesting. I just think this is now all 'old school technology' and many people prefer the large capacity cells now to build powerful batteries. It's just too much work with these small cells building large battery banks. For small projects, yes (like my gate opener) but to power a building, nah...
I'm catching up on your videos so I'm probably being a bit repetitive, but here is what is going on:
Your Absorption voltage of 3.4V is way too low and the Float voltage of 3.375V is way too high. Remember that the charge curve and the discharge curve are very, very different. When you charge you need a voltage above 3.4V. Really, 3.45V is the minimum charging voltage you should be using. Otherwise you wind up right smack in the middle of potential wall for the cell and that can definitely lead to mismatched currents going into the cells. Very slight differences between the cells will get magnified when the Bulk/Absorption voltage is that low. For 80% charge, the Bulk/Absorption voltage should be around 3.5V per cell.
Then when you discharge, remember that no matter how charged the battery is (above 3.4V that is), the cell voltages will nearly instantly drop to 3.4V. You do NOT want your float voltage to be anywhere near 3.4V (!)(!). You just don't. That's cutting the line too fine. Slight deviations in cells and measurement error will result in the charge controller potentially charging the battery at the float voltage... overcharging the battery really. I will repeat that. A float voltage that high will charge the cell up to 90% over time and possibly even start overcharging individual cells in the battery bank.
The Float voltage must be somewhere south of that, like 3.3V or 3.35V. This guarantees that the float won't overcharge something and reduce the cycle life of the battery. When discharging, a cell voltage of 3.3V still means that the battery is at least 80% charged, and 3.35V still means that the battery is at least 85-90% charged. You aren't losing any real capacity by setting your float at 3.3V or 3.35V (assuming that the charge controller goes back into bulk very shortly after going below the float voltage, that is).
Again, remember that there are measurement errors that have to be accounted for, and also that cell variances get magnified inside the potential wall of the chemistry. The potential wall is around 3.35V to 3.40V for a cell. Something like that. Don't set ANY charge controller parameter to a voltage in that range for any reason.
-Matt
What’s a potential wall? 🤓🤷♂️💜
@@serversurfer6169 The potential wall is the non-linear portion of the voltage/current curve around 3.40V for LiFePO4. The chemistry forms a potential wall where a voltage below this value, even if above a cell's nominal charged resting voltage, is unable to push any significant amount of energy into the battery, while voltages above this value can charge the battery up to nearly full given enough time.
This is also why the typical Float voltage of 3.35V - 3.375V will not charge the battery much at all, even from empty, will not trickle-charge a half-full battery, and will certainly not overcharge the battery. Even though its above a full cell's resting voltage, it is still too low to overcome the potential wall. (i.e. exactly what you want for a float voltage setting).
And yet, even a voltage like 3.42V can charge the battery to 90% given enough time. Even 3.40V itself will charge the battery somewhat, albeit at an extremely low rate, but it isn't a voltage you want to use because depending on cell age you could very easily push charge into some cells and not into others in a series-connected pack... i.e. the pack will go out of balance more easily. You don't want your charger charging the cells right on the knee of the voltage/current curve.
This is why 3.45V is about the lowest bulk / absorption target that you want to set for LiFePO4. 3.45V - 3.55V is typical. Up to 3.65V (the typical BMS cut-off point) if you really want to charge the battery up to 100%. But that's only at a decent charge rate of 0.5C. At lower C-rates you have to be more careful to avoid over-charging the cells. But you still don't want to go below 3.45V so you can wind up between a rock and a hard place if charging at e.g. 0.1C for example. The only way to figure out the state of charge of the battery at rates that low is to count watt hours going in and out of the battery.
--
You can experiment with a small 12V LiFePO4 battery (one of those cheap < 10Ah ones) to see this in action. If you discharge the battery and then put a current limited power supply on it set to 13.40V (3.35V/cell) you can see how quickly the current falls to zero with the battery remaining mostly discharged. If you then bump it up to 13.60V (3.40V/cell) you will see it trickle-charging the battery but the current again quickly falls to very low values (though probably not zero). If you then bump it up to 13.80V (3.45V/cell), the current will double and not drop off as quickly. If you bump it up to 14.0V (3.50V/cell) the current will double again (or more). Etc.
Hence why 13.80V is the minimum charging voltage you would want to use. Also, the BMS probably won't go into balancing mode unless the voltage hits 3.50V/cell (14.0V for a 12V battery), so keeping the battery healthy long-term (over several years) can be a challenge if your charging capability is below 0.2C.
-Matt
@@junkerzn7312 Ha! It never occurred to me to buy some low-capacity cells for experimentation. I’d been worried about ruining a pricey rig while learning the ropes, but this’ll let me get started immediately. 💜🤓👍
What’s a nice, configurable charge controller that I can plug into the wall? I assume I’ll need a BMS before I can wander away from the longer experiments? Any recommendations there? 🤓🤔🤷♂️
This is interesting. I just switched to Lifepo and in all my research I didn’t see this information at all.
Best video so far. Thumbs up.
And thanks for sharing the new app release.
Thanks John, much appreciate it.
Hi good morning, I think unless you top balance the battery to 3.6/3.65V the imbalance might happen again. I think the voltage from 3.55-3.65V is the necessary absorption, as you said it's 99% charged at 3.5V, the remaining seems to be required Absorption. And Setting 3.6/3.65 absorption and 3.4/3.5V float might be better for maintaining a balanced battery. Just my opinion. Thanks.
he top balanced before. he just needs to let the BMS balance his cells as they are charged and discharged. perhaps his BMS is not doing what he wants exactly but all cells with spread out from each other a bit as they are charging and discharging.
I can absorb at 3.3V, right? It just takes longer...
@@pilgrimvalle Yes, I know Andy did at battery build 2 video, but I am just suggesting coz the pack seems unbalanced now.
@@OffGridGarageAustralia Hmm, in my opinion 3.3V could be too low for an absorption voltage. I think the basic idea with absorption will be when the cell voltages increases with very less current input. That happens in the 3.6V range I think. And I also guess the SOC of each cells can't be determined accurately with the constant voltage unless it is in the 3.6V range.
Yeah, I hear you. But if you charge with CV to say 3.3V only, the absorption time would be very long and the voltage could not rise above that voltage.
I once charged a cell to 3.25V only with CV and it stopped taking current after a long time. Rising the voltage just slightly got it charging again. So from that, I think absorption is happening at any point of time. More testing under way.
Good work, my suggestion is to get in touch with Dacian from Electrodacus...he truly is a wealth of knowledge about all BMS things and battery chemistries.
He will definitely answer your questions...
Dacian is the best
I have learnt a lot about solar batteries from your videos. Im building a 8s , 3,2x120Ahs, 24volt system: The BMS I could lay my hands on is PWOD LiFe Po4 8S 24v BMS. Im kind of lost as I donot know if I can get purformance data from this BMS. Is it worth anything or I should just forget and get a different BMS brand?
you're the best ! I literally want to go to Australia specifically to hangout with you 😊. I enjoy learning with you and appreciate your fun attitude to figuring out problems 👍
By the way I am in the middle of this exact issue you encountered here . Just did a single cell to 3.5v taper to < 0.1amp for each cell..I then paralled em and did the same thing.
Waiting for some load testing equipment to re-test. Fingers crossed
Did you top balance all the cell in parallel before you series them?
Yes he did, you should catch up on his other vids, all the progress is documented
You don't really have to do that. If they're reasonably close in voltage, you can assemble the pack and then balance charge it at a moderate current, say, .1 or .2C. The charger's balance circuit will set the cells to the same voltage.
One thing that may be happening with your cells since some are newer than others is the potential for some variation between manufacturing batches. Another thing I have noticed with my smaller cylindrical LiFePO4 cells that are all new and from the same batch is that they seem to have a wake-up period of a few cycles after being stored for a while (1-3 months) where they don't pull full capacity and then after being cycled a few times they come back. Not sure why that happens but it seems to be a thing. I wonder if since those batteries have such a large internal surface area, it just takes a long time for them to fully saturate.
I have an active balancer on my pack that will balance at 2 amps so I set the float to happen around 2 amps so that the batteries are allowed to balance. I have the balance voltage of the BMS set to 10mv below the setting of the active balancer. When they were out of balance at the beginning I would see balancing happening on the active balancer during bulk and float but now they are usually all fairly well balanced during the absorption stage so the active balancer only comes on when the BMS isn't able to balance which is now fairly rare.
Very true, think of it as if you were filling a drum with foam peanuts. Once full, you tap it a few times more electron settle themselves, and you add more til your full. A good balancer will do this an as you say it takes a few cycles to reach steady state.
Interesting comments. Thanks!
There is always one cell that is lowest and one that is highest :)
I don’t know why you are trying to reinvent the wheel. Victron have presets in the charge controller for lithium.
I have a 400amp 12 volt battery. Using 200amp prismatic cells. Set up in 2p 4s configuration. I use my Daly 250amp BMS to control the voltage of the cells. I have set it up to charge cells to 3.55 volts and then the BMS stops excepting charge. At the lower end I have the disconnect set at 2.8 volts per cell. It gives me approximately 360 amps. I did a capacity test prior to doing alterations. I discharged at 0.25C and the battery was at 11.98 volts and amps total was 418.
I also have a temperature sensor and auto disconnect at 2 Celsius.
I have set my victron inverter to shut off at 12 volts.
My batteries after charge is complete are at 14.2volts. After approval 1 hour that sit at 13.4volts. When discharging the sit on 13.3, 13.2 volts for 400 amps then it starts to drop off.
The preset LFP profile in Victron is not great I found. Also I want to learn and understand...
Thanks for sharing your settings, that's really interesting. So why do you set your charge controller to 14.2V and not to 13.4V? The cells will fall back to that voltage anyway so why force them into a higher voltage which causes just more stress? Just interested about your thoughts about that...
I use the recommended settings from Will Prowse solar forum.
At the end Sparky the Frog, yes!!! Hm, I am little bit confused, I was expecting that 3.55V is already on the steep part of the voltage curve, but maybe because of the huge capacity of your batteries this is also relative. The problem ist that you can not measure the current at a cell level(but I think this is obviouse by now). The question is how to overcome the slightly difference in the charging/discharging behaviour of the cells. I'm afraid that the only way will be, even if you don't want to hear it, sorry for that, the usage of an additional active balancer or to determine the cells with simmilar behaviour and put them together with their own BMSs. Any other ideas?
As nelo says, active balancers can do max 10amps, but if you put 10 balancers in parallel they could do 100amps.
I think the solution is in not charging to high and let the cells absorb for longer. So I'll do some testing with 3.35V max charge (~95%) and let them absorb until the current is low. I'm freaking out if cell voltages go higher...
@@OffGridGarageAustralia Settle petal, just assume the position & say hummmmm. Get 16 hi/lo volt audible alarms, 1 on each cell & charge/discharge each cell manually with all the spare time you have. I have just ordered an active balancer so I don't have to freak out when my pack is finished. Cheers Scotty
This is why voltage is an unreliable way to judge soc. Current draw is better.
From the video, I understood him explaining to us why you need to use both V and I.
@@MiniLuv-1984 yep. But I'll leave the comment up.
I do feel there is a slight misunderstanding about the way bms works tho.
@Yoda B.at1 the misunderstanding is...?
You been my teacher and I've learned a lot from you.. I'm using sealed wet cell and I know If I took my batteries and disconnect from my system, the solar power of 1000 watts would just take over and maintain my 12 volt / 1000 watts requirement. I really think you very close on solving this.. I live in sunny southern California and my generation has been excellent. If you can master using your batteries banks with the solar system and normal load usages at the same time, then I will upgrade to lithium lifepo4. Thank you for teaching us !!
Excellent detective work there...
It's even harder to build an understanding when you have experience that needs to be forgotten because it no longer applies.
It would be interesting to see what the settled voltages of each cell were, after you carefully saturated each one.
Perhaps they each have a different saturation voltage... This would explain why the voltage based balancers can cause trouble!
0 mins absorption. Bulk only settings in charge controller. Float same voltage as bulk.
So you just turn off charging when the overall voltage is reached? Not looking at absorption and give individual cells time to catch up?
@@OffGridGarageAustralia yes, but in practice due to system loads current will go in and out of battery slowly giving time for absorbtion. I found after a few days of cycling the BMS was able to sort out the balance and the cells stayed in balance enough that the bms doesn't cut current. When nearly charged last few ah I constantly have 13-14 of my 16 cells balancing. The longer the balancer is working the closer to balance it will stay. Obviously if all cells are balancing than the overall effect is lost, so up to 15 cells is ideal. Also I have multiple charge controller a and can taper current near top by using slightly different endpoints, however this only works when we are not drawing much current in the house.
Very interesting, thanks. Do you set the balance threshold just above the absorption or the same? What numbers are you running?
3.4 balance, 3.4 charge 3.6 BMS cutoff. No absorbtion time. Bulk, float and absorb all same voltage.
Trying to get that last little bit from 3.5v to 3.65v is only about 1% of total capacity anyway. Get them up to 3.5. and forget them. You'll be fine.
Thank you, that is correct. I did heaps more testing in future videos with amazing battery testers and I show all the graphs and data. Learned so much from that...
@@OffGridGarageAustralia Nice, I'll take a look :)
I had a similar problem, this worked for me.
Have you tried setting the BMS to balance off line. That way you can leave your charge controller running. The BMS will turn off charging while it balances then turn it back on once done. Once balanced it does not need to come on very often.
Go to Function settings, turn off charge balance. (This is on the previous version of the software. On a n even earlier version this was in settings, balance mode, static balance. )
Thanks for your videos.
Dave
Thanks, Dave, good suggestion!
Now wait for all the comments that you will destroy your charge controller when turn off the battery while still connect to solar.
@@OffGridGarageAustralia I did that to a victron 150/35, same model you have. It doesnt care. Just don't connect solar first. Thats what kills them. I also had the same problem as you did, cells racing to 3.6V while others were still at 3.45. Shoved 10A into them at 8 volts until they reached 3.5 and then topped them off with a buck converter at 3.55V. They are now balanced up nicely.
@@OffGridGarageAustralia The disconnect is only the charging internally, not the feed to the charge controller. Look on your parameters view, you have two switches, charge and discharge. These are also on the new dashboard. Turn off your solar input, turn off charging on dashboard, charge controller still has power. Simples...
@@muddy11111 Great suggestion. How accurate is your set up? I've got a 24V 8S battery within .025mV @ 50% I want to dial in before I install it in my RV. Am I being greedy? Thanks again for the idea.
@@matthewburgaAre you sure ? 0.025mV.... You can set the balance differential in the software. Currently my 12v8s is sitting at 100% and 0.002v or 2mV, that should be good enough for anyone.
Please excuse me if this has already been mentioned. You appear to have a few mismatched cells. Some of the China resellers are not sending out capacity matched cells. If one cell has lower capacity, then that cell will reach a higher voltage sooner. Same for higher capacity cells will not come up to voltage as fast. Maybe test each cell individually for capacity, then get new cell or cells from seller with requested capacity. Make sense? Correct me if I'm wrong.
I think this is exactly what happens to me. I have three different delivers, so each of these shipings should have been matched. It seems they are not, so I'm doing all the testing and observation now to find out how, why and what happens.
YEP!!! a foot+ of snow on the solar panels here!!!
Wow! Stay warm and get this snow off the panels!
I had the same problem with my 12v lifep04 battery installed a 5a active balance board. That's sorted the problem took couple of days but it got the job done. The board was like £10 from AliExpress
god bless brother keep up the great videos iim learning alout thank you
I appreciate that
I think ideally you want your batteries to reach full charge every day (let the solar panels do the work). you do not want the individual cells to go under 2.5 volts on discharge. 3.55volts is 99 percent full. to go to 3.6 or 3.65 volts should only be done once when you initially did the top balance. the purpose of the BMS is to prevent the cells from being charged too high, or discharging too low. both cause permanent damage and decrease the life span. the charging with solar panels is great for the LiFePO4 chemistry as it charges at a low C rate. and normally you will use the stored energy at a low C rate. both of these will prolong the LiFePO4 battery cells' life span. yes, it is a big learning curve to get your mind to wrap around the likes and dislikes of a LiFePO4 battery bank. if I only want my cells to be charged to 90 percent SOC I can set that in the Electrodacus. my Electrodacus SBMS0 is set to charge up to 3.55 volts which is 99 percent. when any cell goes to 3.55 volts for too long it will turn off the Electrodacus DSSR20's(the solar chargers) so the LiFePO4 does not get overcharged. then the inverter load or my direct dc loads use some of the battery power and will allow the DSSR20's to charge some more. solar is a slow but reliable charging system. mine is 24-volt Lishen 16cell 272Ah per cell build. I have 2 of these LiFePO4 batteries functioning like clockwork in a 2P8S configuration. love your videos. they will be very helpful to all solar DIY people. keep up the good work. it is 25 degrees below zero Fahrenheit this morning in South Dakota USA at my pilgrim valley farm. solar panels like the cold - I have to only go out about 10 minutes with a lot of clothes to dislike it. cheers 😎😎😎
Great feedback and comment, Michael. Thank you very much. I cannot use the Electrodacus BMS as I have a 48V system but I'm very keen to try it out. They offered me a sample to check out here on my channel, so the next build will be a 24V system, I guess, with an Electrodacus system. It seems to be very thought through and can be customized as per user needs.
Stay war over there in SD!
Great video! I'm a believer too! Sometimes, I feel like a solar monkey... Thanks for sharing all your trials and tribulations. The experiences and the data - all very helpful. I downloaded the newest XiaoXiang app - Thanks! The Play store only has 1014. Battery balancing is indeed a daunting task. I'm still looking for the sweet-spot where it can all run unmanned. I only have 8 cells in a 2P, 4S, 12V configuration.
Thanks for sharing, Peter. I will probably only charge to 3.35V eventually to stay save and don't charge the cells too high. The balancing and testing takes a long time but that's where I learn the most.
Jeez, you'd think someone named Peter would know it's spelled Monkee. 😜
Just don't over-Tork your bolts!
I understand only wanting to go to 3.4v, I would like to charge to that point only too, but you will not get measurable differences in cell in-balance until after 3.4v.
Would it be worthwhile to top balance ~3.65v for maintenance, then dial it back and cap your “daily”charge cycles ~3.5v, to stay in the healthier SOC zone for normal operation? 🤓🤔🤷♂️
@@serversurfer6169 probably although the difference between 3.5 and 3.65 in % is less than 1%.
I'm glad I'm not the only one who got the "I am a believer reference" at 16:17. 👴
Great insights there. Thanks for sharing with us! You learn when you jump in the deep end - if you were mucking around with cheaper, lower capacity or fewer cells, you wouldn't worry about these subtleties as much.
So true! It all looks easy when you watch other videos but building a battery yourself is more challenging than expected. Ot at least, it can be...
I'm watching your video 3 years after you made it. Today I am still pulling my hair out about Lifpo batteries: the lack of info about basic stuff that should be obvious. The lack of hardware choices, etc. This is not hobby equipment like it might have been ten years ago.
Even a total D.S. could pop a lead acid battery in his greasy car. This morning I am looking at lifpo prismatics at 310 amps and I want to get my 1c charging and 1c discharging out of terminals that look like they will melt at half that amps. Why Why Why? Home power backup is still in infancy.
Hi Andy, great job from you as always. Can i kindly ask for your help. I use BMS JBD AP21S001 and facing problem with drying of my LiFePo4 battery during nigh when my inverter (Axpert King II) are in bypass mode. In application (blue small elefant logo from Xiaoxiang) i see 0,8A consumption every 2-3 seconds. Look like BMS is doing something and finally drying my battery a lot. Can you guide me what to check and how to adjust BMS option accordingly? Many thanks and have a nice day. B.R.
Full Saturation = 0.05C at the cell level.
See Spec Sheet for your particular cell.
100AH cell 1C=100A, 0.5C-50A, 0.05C=0.5A
YOUR PROBLEM = Unmatched BULK Cells.
If they were properly Matched & Backed (Like the cells are in YOUR TESLA) they would not deviate through the range as they do. A GOOD Active Balancer compensate somewhat provided it is correct for the "Cell Size" meaning Enough Amparage transfer capable.
If you have Properly Matched & Batched then you would not need any real "balancing beyond passive".
You are also not using the term Absorption properly, your misunderstanding of the terminology only confuses you and your viewers. Too many assumptions as to meaning , intent & purpose.
EDited to correct typo.
Hello. I think 0.05c is 5A?
Cheers.
@@hommerdalor6301 fixed typo
So Steph, do not spoil us, enlighten us with your knowledge! What is absorption then?
That's why the flat voltage feature of LFP is just garbage compared to non flat curves like LTOs. When the curve is flat, it's so INACCURATE to fully use the full capacity of a battery and to correctly measure the battery capacity. You need external measuring equipments to GUESS the capacity, but you CAN'T measure it appropriaply
thank you for doing all this, saving me much brain pain. keep the froggies coming
Will do! Thank you Dirk!
I built a 4s pack, and when I first got the cells, I found one which was low and charged it separately for a while. Big mistake. Because I had added several AH to it compared to the other cells, it was always high and the pack cut out before the others balanced.
Even with a 1A balancer board, it would start balancing... and then cut out, charger would shut off and I'd have to manually restart it.
What I ended up doing was taking a small 5A adjustable power supply, and setting it to 14.0/14.1V. Enough to keep the per-cell voltage above the 3.4V needed for balancing, but not high enough that the highest cell would hit 3.65V and cut out. Left it that way for 24 hours as (effectively) the balancer board kept balancing as the supply kept it topped up. Now, it's all nicely balanced, and I disconnected the balancer board and haven't needed it since.
Finally pleae at what voltage to set for 1. Absorp vol 2. Constant vol 3. Float vol. Thanks in advanced.
3.55 at begin of absorption and 3.55 at the end. "the voltage not change". this is impossible for physic . ohm law. The voltage change but you dont see. maybe change from 3.55002 to 3.55245. you think not change. but change. the same on discharge. people say lifepo4 dont drop voltage for 30% discharge . not possible! voltage change , but some like 0.0004v and you dont see.
According to this author
nordkyndesign.com/charging-marine-lithium-battery-banks/
The maximum charging voltage depends on the relationship between the voltage and the current and can be different (probably will be) on every single charge. It is a linear relationship.
IOW, the voltage to stop charging at is not a number that can be preset.
If I read him correctly, the linear relationship is y = [(.05-.033)C] / (3.65 - 3.37)V](x)- 5.63 (C) where y is relative current in C and x is the cutoff voltage.
I have 13 PCs 3.2v Lithium Phosphate Batteries 280Ah & I have 6 PCs 3.2v Lithium Phosphate Batteries 200Ah “ my issues are my inverter is 48v = 15 PCs needed 3.2v but I’ve got 13 - 3.2v 280Ah what’s you’re idea on using 2 PCs of the 200Ah in Parallel which will keep me at 3.2v but I’ll be at 400Ah what I’ve read & heard the 280Ah will make the 200Ah work harder to try to keep up with the 280Ah because of the 80Ah Less ! Where I’ve got the extra 200Ah batteries if I have to replace the 200Ah batteries I have 6 of them so where I need to use 2 of them I can replace them each 2 more times next to using the 400Ah and making the 280Ah batteries keep up with the 400Ah ! The price for the 280Ah batteries have gone up over the past year $ 40.00 + each , 2020 I paid $ 119.00 each 280Ah and now they cost $ 159.00 each 2021 ! Better to have to replace what I have next to having to buy another 13 Batteries at more then $ 159.00 each I kinda Answered my own Question thanks !
052223 Recycling videos. Twenty years experience. ..
✌️👨👍
Hey?
Batteries are all like this.
Voltage and capacity don't often Equate.
The voltage can rise quickly, but that's nothing to do with capacity. I think the old rule was reach the voltage and then 20% later is the capacity.
Lipo are constant voltage and constant current charge. The end of the charge is the current drop. Thats 0.2 per cell just incase anyone needs to know.
A battery takes current (amps) not volts. If you go by volts then you would get around 15% charge.
I bought a new battery, 12.65v it was about 40% capacity but people were claiming they were sold fully charged., I think that may work with tiny single cell batteries?
My charger only works by current.
It sets the voltage and then measures the current flow and then when it drops off it stops charging. It doesn't care about the voltage when charging (within reason... Sometimes)
Anyhow, you're charging voltage at 3.4 is 0.25 lower than max, 3.65.
Which should be the charge voltage.
I float at 27.4, I charge at 29.2, I equalise at 30.2.
This depends on cilic or not as I sometimes don't use power and can run from the over product of power. So I set the charge I want on the basis of use (known power removed) which is usually counted by the voltage.
So if I drop to 25 or less then it's a full charge cycle. If it's been around 26 or above then it's not..but it's this area that will cause the batteries to go all over the place.
(What you are seeing and have said in this video)
Because you're using what would be the surface charge. This imbalance will more likely be down to resistance at each cell.
The best way to deal with it is to discharge down to 70% and then bring them back up using a full cycle charge.(correctly done).
Make sense??
Hope that helps with the issue.
PS I use the light bulb to do balancing. I look at the power and how much I need to shift and then do it that way, but if I make too much power it can't be done. It just makes a lot of heat
.. as you found out...
You could lower the input current, this aids in balance charging. Sounds counter productive, but it's what I've seen happen.
I just got a new Victron 100/50 to handle 500w of solar on my RV. I have a 412ah prismatic battery that I built last spring. It is 8-206ah cells in a 2p4s configuration. The issue I am having is this. When my battery is say 50% charged on a sunny day, the charger is running on bulk and then changes to absorption and then to float even when it still is only 60% charged. I am not utilizing sunlight well at all. I have the controller set up in the lifep04 pre-program (#7 on the rotary wheel). Why is it going to float when still a long way from fully charged? Even when I put a heavy load on it (microwave for refer), it stays in float. I expected this charger to stay in bulk, then absorption until the battery was nearly full, and then to float when essentially full. Anyone know what is going on? Should I change to "User" defined and extend the absorption time? Any other thoughts or ideas? I replaced an Epever 40A BN series with the Victron because it also did this. Did I waste my money on this Victron?
If you have a charge controller further away from the battery like I do. I noticed when you set the mppt charge parameters to say charge your battery to say 90 percent (for longevity) you end up undercharging I'm guessing due to voltage drop. It seems the charger sees higher voltages than at the battery while charging. So would I need to increase the parameters to get it closer to 90 percent at the battery terminals?
If you are having fun doing this then I say enjoy.......but what I'm doing to avoid ALL this is 1st buy grade A cells. And 2nd limit the charge discharge to the flat part of the curve. 3.0v at bottom 3.4 at the top... been running no bms for almost ten years now....a good top balance would be my next move if I started having this trouble
May be my issue with my ampere time 24v 100ah is that internally they are not balanced.
Going to do a 4hr absorb at 27.6V highest amps i can do on solar and have a bench charger coming to do a deep charge.
When i do a 50-60amp draw my battery dips WAY down. BMS shutsoff
ruclips.net/video/QxAtVbu_-Zg/видео.html
Andi I got the same issue, but I use chins 100 Ah batteries in series/parallel for 48 volts, and then I use some old LiOn batteries for a 36 volts system, but on the 48v battery bank 2 of the batteries went down approx 14% capacity IAW my capacity tester so I adjusted the high and low voltage cutoff to avoid interruptions during charging and discharging, but since those 2 batteries are lower in capacity I will have that issue until I replace them with new batteries, which are coming next week. I'll use the 2 lower ones plus another one for the 36 volts bank and call it done, at least for some time when I'll have to do it all over again. Seems like keeping things simpler is harder with today's technology, HEY?
Thats a normal process for nearly all battery technologies! Thats why your charge current is reduced massively when reaching cut-off voltage of your battery. And thats also the reason why the voltage will drop, when stopping the charging process. First fast - than slower and slower and then settles somewhere between 3.5 .... 3.4 V (for LiFePO). The main problem with balancing is that you have probably not very good matched cells! Some have higher, some lower capacity, some have more, some less IR, some have higher self discharge than others and your Balancer is too weak to equalize them and maybe not accurate enough.
No one ever mentioned that:
bulk = cc
absorption = cv
...you'd think someone over the decades would have said it.
But, that would require that someone knew it, first.
Which nobody does.
Because everything is stupid now.
Thanks!
CC charging reaching 3.35volts and stopping a charge..... You will measure a voltage drop as soon as the charge is stopped. CC-CV is always the standard. Check battery university for the best understanding of battery charging
frankenstein it !
OK! 🤖
Sir, tell me the complete settings for my mppt hybrid solor inverter, if i use four pack of 100 Amp lithium Ion fosforce battery in series
48 volt 5.2 kV mppt hybrid inverter . I don't want to charge on AC power because electricity bill is not efordable
Hey, I just got me some lifepo4 EVE cells, 8 of them but 2 of them won't charge pass 3.36, what's causing that and can I fix that issue?
I think, this is that problem what some people saying about, with LiFePo4 cells, connected in series.
That when you do not charge LiFePO4 to full state then you don't know exactly if it's balanced or not.
how to make Daly bms make absorption !??.. when a cell reaches the calibrated voltage it's directly switched off !!!>> then the voltage dropped while a balancer starts working .
I disagree with the fact that balancing only works with no current going into the battery.
Even if you’re charging with 50A and the balancing current is 0.2A, this means that the high cell will charge with a net 49.8A and all the others will charge at 50A. It doesn’t matter if 0.2A is much smaller than 50A, it’s still being balanced the same way as if the battery were in standby because there is still a 0.2A draw
You are doing great things.
Thanks for being you.
🐸
Thanks so much 🐸
Thank you very much for this crucial info :):):)
Hey, Andy! Great video! The problems that are the most difficult are also the ones that will teach you the most. You already made great progress and learned a lot. I have no doubt you will find the settings for the charge controller and bms that work for what you want. Good luck my friend.
Thank you.
Hi Andy. I could be wrong, but after watching your video up to 3:15, it seems obvious to me that you have at least 3 different connections (2 different busbars and one flexible conductor) connecting the terminals of your cells. I really believe that these variations in conductors between different cells causes that a certain cell charges faster than others and also discharges faster than others. Reason why?
I noticed this phenomenon in my own battery, where I had the first four and last four cells connected with standard iron, but between cells 4 and 5 I had a different wire (as you have between cells 7 and 8). Then I wondered what is wrong with cell 5 as it always charges faster and also discharges faster. When I then made the change so that there is a standard iron between all the cells, the problem disappeared. In my view, even a small variation in the resistance of the conductor between the poles makes it impossible to achieve balance.
I understood that at FLOAT stage there is no current going into LifePO4 battery, not in mine..... it still charges at FLOAT
I do not understand this guy!! I start watching his videos but it doesn’t make sense!!! One day no need to compress the cells, next video you have to, next video no need balance, next video why is important to balance oh my god I do not know what to think off!!!😂
my 12 v 16 a lfp battery appears to have failed-instead of reading apx 12 v i'm getting 3.5 v. wth happened? any way to revive it?
If you set absorb voltage 55.2 and you have your absorb time to 1 hour. What happens if you haven’t reached the 55.2.
Dear Andy, love your humor and most practical demo of solar system building.
Just went back to watch your first episode from very beginning. Love it and enjoy it.👍
Wow, thank you!
That's not "Frankenstein" it's a real "Churchstone". :D
Now you are on the right way !
You have made no change in configuration, so it's now time to make a video of discharging, if there are the same sh...y cells contact your dealer for exchange this cells which are out of spec! hand walter
edit2: you draw the line of charging ; next step is to draw the line of discharging then your cellspeccurve is complete
Wait for the next videos... ;)
@@OffGridGarageAustralia Don't lick the frog ! 8D
I think this was one of the best episodes for learning and conecting things in my brain !
when i test lead acid batterys i have this system, i charge and leave on float for 3 days to let all the energy absorb, i stop the charge then i test the voltage after an hour and then after 24 hours another voltage test and a 50A load test and then i choose the batterys closest to each other to put in a battery bank for solar, it's just the way i do things after years of charging used batterys and resurecting them for solar powerbank use but after watching this vid it clicked, somone else has similar thoughts ! differant chemistry i know but cool to see a similar thought process in somone elses head !I really really enjoyed that one, i love learning alongside you ! keep it up :)
Thanks for the feedback. I've got this effect all the time and step by step things make starting sense... Then I need to test and confirm that new learned, so it all takes time...
I do not understand why you would take any power out of the batteries with a BMS. I will do lots of testing without a BMS and hopefully show everyone they don't need a BMS. I could be wrong but I do have to see myself. I do know clean buss bars that make the best contact is needed. I will also charge each cell up in a series then each before setting up.
Why are un unable to use the load if not charging/discharging the battery ? Most inverters support this (panels to load directly).
you dont know why note this difference during charging the cells. Is for different IR , because not top quality cells
Get yourself a decent active balancer
I was about to say it too, add a active balancer.
Active balancers will just hide the problem. You will never find out if you have faulty or weak cells in your pack. They should only be used for maintenance purposes.
@@OffGridGarageAustralia if there's one weak cell in the pack, will the active balancer drain down all the others to match the weak cell? Or do they operate only during charge and bypass charging current on the good cells, delivering it to the low cell?
Would a larger capacity BMS say 10A also solve this problem ?
Hello sir quick question What type of BMS and charger controller you using ?
You should not have this problem if you start with balanced batteries to begin with and if the cells are matched well. I thought you stated you did start with balanced cells, go figure.