LiFePO4 cell voltage difference

[ZD]

Hi all,

I am currently working on a project that uses a 5S2P 7Ah LiFePO4 battery pack. I have analysed and balance charged the pack with my hobby charger and all the cells measure fairly consistently with a capacity difference between the cells of < 1% between the cells and +/- 2 milliOhm.

I have noticed that when I am recharging the pack without a balancer, the voltage difference between the cells starts to increase a lot when it is almost fully charged, sometimes there's a difference of 100 mV between the cells. I know the voltage for LiFe cells changes rapidly at very low and high SOC so is this difference in cell voltages just due to the small capacity differences between the cells?

[NiHaoMike]

You have to do the balancing at a fairly high state of charge for that reason, 3.45-3.55V/cell tends to be a good level to do that.