280 AH lifepo4 cells lost balance

[SeaGal]

... The one was perfectly balanced as it was when I built the batteries, the other had these voltages on the cells:
Cell 1 3.22
Cell 2 3.45
Cell 3 3.45
Cell 4 3.34

Over a few years, not surprising there is an imbalance, but I'd check connections on cell #1 in particular and cell #4 to a lesser extent. 3.34V is not that low when charge is removed from the cell. 3.22V however is very low compared to the other 3.

There has been a lot of talk of balancers on here so far - but I'd use a bench top PSU to bump up cell #1 to 3.45 and then do same with cell #4.

Then check connections and float with BMS / balancer attached and see how it goes.

 

[aness]

Over a few years, not surprising there is an imbalance, but I'd check connections on cell #1 in particular and cell #4 to a lesser extent. 3.34V is not that low when charge is removed from the cell. 3.22V however is very low compared to the other 3.

There has been a lot of talk of balancers on here so far - but I'd use a bench top PSU to bump up cell #1 to 3.45 and then do same with cell #4.

Then check connections and float with BMS / balancer attached and see how it goes.

I got the 5 amp balancer off of Amazon that was recommended. It brought the cells to 3.33 for all but the one that was low it got it to 3.30 before I hooked it back up to my solar. I have the active balancer connected now and the charger looks to be floating and the cells are as follows. Cell 1 was one that was very low before the balancer.

Cell 1 3.31
Cell 2 3.60
Cell 3 3.36
Cell 4 3.36

Is 2 trying to help along Cell 1? My feeling is Cell 1 may be starting to fail? How does one know if a Cell is toast?

The system is sitting at 14.5 V right now and drops to about 13.4 if I use it to charge my ebike battery. Seems to function normally there, but I don't feel like I have the full capacity of 560 AH from the 2 12v 280 AH batteries.

Thanks for your help.

 

[Substrate]

Something I've noticed - for some reason some BMS makers think that a balance-trigger-voltage of 3.40v is acceptable. It is NOT, as much as urban mythology tries to make it. Along with "always balancing". How to fry those rice-grain resistors.

So just checking - if your adjustable bms has the balance trigger at 3.4v, that is at the bottom of the upper discharge knee. Change that to 3.5v trigger - even if that means many cycles of rebalancing afterwards to get it truly right.

 

[Berseker]

Something I've noticed - for some reason some BMS makers think that a balance-trigger-voltage of 3.40v is acceptable. It is NOT, as much as urban mythology tries to make it. Along with "always balancing". How to fry those rice-grain resistors.

So just checking - if your adjustable bms has the balance trigger at 3.4v, that is at the bottom of the upper discharge knee. Change that to 3.5v trigger - even if that means many cycles of rebalancing afterwards to get it truly right.

but some people only charge to 3.45v. am not sure 3.5v balance trigger is a good idea for unbalanced pack