How to balance these cells.

[Crashcourse]

Hello, I bought 4 of these very cheap* "Elfhub" 12V 100ah LiFeP04 batteries for $480 CAD each delivered. The BMS is very basic (I googled the numbers and found nothing), no Bluetooth or monitoring of any kind. I opened the cases and installed pigtails on the BMS harness run through the outside of the case so I can monitor with a simple external LiFeP04 battery capacity checker.
After charging the first battery to 14.6V and letting rest for 3 days, the voltages are off by what I would consider to be quite a bit - 0.120mV.
"Cell" 1 3.406
"Cell" 2 3.526
"Cell" 3 3.463
"Cell" 4 3.461

When charging I monitored the voltages with my Fluke DVOM at the BMS terminals and Cell 2 hit 3.72V when the others were ~ 3.55ish then the BMS disconnected charging, so I assume it has a 3.75V disconnect. A little high but... yeah.

My DIY 48V 100ah 16 cell battery with an Overkill BMS always rests around 0.010mV.
Is there any way to properly balance these things or I'm I just going to have to charge the batteries to say 13.8 or so I can at least use most of their capacity?

Thanks for any help.

*very cheap - when I opened the cases I found that the "100ah cells" are made of 4, in series, sets of 5 20ah cells in parallel, so yeah.. you get what you pay for..

 

[chrisski]

You actually have 5p4s 20 ah cells.

How do you want to balance? Do you want to tear it down, top balance, capacity test and then top balance and then reassemble 5p4s? That may be the only way to truly do it, and that would take me two weeks at least. You'd want to group together cells.

I recommend ditching the BMS and getting one designed for lithium iron phosphate with adjustable levels. You’ve already had it out of tolerance.

 

[Crashcourse]

You actually have 5p4s 20 ah cells.

How do you want to balance? Do you want to tear it down, top balance, capacity test and then top balance and then reassemble 5p4s? That may be the only way to truly do it, and that would take me two weeks at least. You'd want to group together cells.

I recommend ditching the BMS and getting one designed for lithium iron phosphate with adjustable levels. You’ve already had it out of tolerance.

Thank you, yes 5p4s, understood.

I would love to tear them down but the 5p are frigging SOLDERED together with what I assume to be copper bus bars! All held in the cases with spray foam. Too much of a PITA to do all 4 batteries (I'm assuming the other 3 are just as bad).

I suppose replacing the BMSs is the easiest approach, would you have a recommendation on a BMS with adjustable levels?

 

[time2roll]

I add up those cell voltages and get 13.856 volts. I would reduce charging to 13.900 volts until the balance looks better. This is virtually full capacity. This should prevent the BMS shut down. When the BMS shuts down it can make the whole system have troubles.

Check cell voltages in 30-60 days and see if the balance has improved.

 

[chrisski]

Thank you, yes 5p4s, understood.

I would love to tear them down but the 5p are frigging SOLDERED together with what I assume to be copper bus bars! All held in the cases with spray foam. Too much of a PITA to do all 4 batteries (I'm assuming the other 3 are just as bad).

I suppose replacing the BMSs is the easiest approach, would you have a recommendation on a BMS with adjustable levels?

I use an Overkill BMS. This has an adjustable individual cell cutoff and same for the overall voltage and current. Also Bluetooth monitoring.

I‘d recommend a top balance of the 5p cells to 3.65 volts with a power supply, Afterwards, reassemble, and then keep the battery charged to 3.475 volts per cell, or 13.9 Volts. Charging that low will still get you 95% percent capacity and you can watch the cells throughout the day for voltage mismatch.

 

[Crashcourse]

I use an Overkill BMS. This has an adjustable individual cell cutoff and same for the overall voltage and current. Also Bluetooth monitoring.

I‘d recommend a top balance of the 5p cells to 3.65 volts with a power supply, Afterwards, reassemble, and then keep the battery charged to 3.475 volts per cell, or 13.9 Volts. Charging that low will still get you 95% percent capacity and you can watch the cells throughout the day for voltage mismatch.

I could try that. I have a variable voltage bench top power supply. I'll give it a go, thanks again.

 

[JJJJ]

I have found it helpful to charge at a slower rate. Gives the lagging cells time to adjust. Have also found it helpful to run a full cycle or two at a slower pace initially. Sometimes individual cells respond differently to storage conditions.

 

[Crashcourse]

Thank you.
When you say "charge at a lower rate" do you mean lower voltage and/or amperage? I have a 30V 10A CV/CC adjustable bench power supply.

 

[JJJJ]

Charging will only start after the charge volts are higher than the total battery voltage. Try reducing the amps.

 

[Crashcourse]

Charging will only start after the charge volts are higher than the total battery voltage. Try reducing the amps.

Thanks again.
I'm charging the 3rd battery right now so I'll reduce the amps to 5 instead of 10.
Appreciate it!