Cell voltages not matching

[Joes69]

Hi all,

Just got through the winter months and have been checking on the battery health and have noticed some odd voltages.

One of the packs has been discharging to around 0.5v lower than the rest (2.9V vs 3.4V). Odd I thought, so today I have removed that pack to see if any cells are dead. Upon checking all 96 cells, around 9 of them are reporting lower voltages than the rest. The current pack voltage is 4.02V, but these 9 range between 3.2V and 3.6V.

Have you any ideas why this might be, or should I remove those cells from the pack and replace.

14S96P 18650 battery.

 

[kommando]

What cell balancer is in the mix, passive, active or non at all.

 

[Joes69]

I have a JK BMS controlling the entire system, each pack is balanced via that. I have no further balancing to individual cells.

 

[kommando]

Bring the voltage up to just over where the balancer kicks in and see if it starts to balance. Exactly which JK BMS do you have as only the latest have active balancers.

 

[Joes69]

I have a JK-B2A24S15P-CAN. Currently I am manually charging this individual pack to 4.2 volts. All the cells are connected to the central busbars, can't see any issues there, but these low volt cells aren't increasing at all. They're stationary. Confusing me a little

 

[kommando]

So its listed as having a 2A active balancer, so is the balancer kicking in at the voltage its set to turn on at.

What chemistry are the cells.

 

[Joes69]

Balancer does kick in yes. They're 18650 Li-Ion. I have tried manually balancing but they don't seem to want to increase

 

[kommando]

Check all connections and if they are still not taking a charge when the balancer is on then remove and replace.

 

[Joes69]

Yes I may have to replace them. It is very odd as these 96 cells are all in parallel so should natively balance each other, but they are not.

I have managed to charge these individual cells a little so I know they will take volts. But they are not balancing themselves while in parallel which makes no sense?

 

[kommando]

If you had the required meter you could check the internal resistance and compare it to the good ones. Maybe you could borrow one.