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Older Headway and A123 16s Voltage differences

Posted: Nov 06 2017 10:26am
by energyi
ES: Simultaneously breaking down two older LiFEPO4 plug-in-hybrid packs from higher voltage to nominal 48V's 16s configurations. I need some Endless-Sphere help in reconciling why the same charger>BMS will have different end voltages? The A123's ends at 59.4 volts and balances the cells nicely. The Headway 40152 SE cells end at 57.0 volts and thus doesn't balance the cells. There are no circuits other than the Ping 5 amp charger and generic BMS. Can anyone suggest a reason why the Headway's stop at the lower voltage? Supposed to be 3.65 charging voltage, for 16s that is 58.4 volts. Again, all cells are old, temperatures are the same. Thanks in advance for any perspectives.

energyi

Re: Older Headway and A123 16s Voltage differences

Posted: Nov 06 2017 11:36am
by dustNbone
Sounds like one or more cells hitting full charge before the rest, check them all with a volt meter when it seems to stop charging, and any that are severely undercharged you could try individually charging. The BMS might still be balance charging at a low enough rate that the charger shows "charged", depending on how low the low cells are (and the balancing current of the BMS) it could take a really long time for them to balance through the BMS.

Re: Older Headway and A123 16s Voltage differences

Posted: Nov 06 2017 3:46pm
by energyi
dustiNbone:
Thanks for the reply. I think you are right, I have two cells that are higher voltage than the rest of the pack. Instead of removing these two, which would be difficult would it be OK if I use a 100-watt resistor on each of them to reduce the voltage while they are still in the pack? The 16s would be disconnected from everything else while I drain a little from each of these strong cells. Thanks in advance for any safety suggestions.

Best,

energyi