Low voltage in one P group

[jai134]

I have one P group that is between 0.130 and 0.2V lower than the other groups and I wonder if it could be a bad cell or is it just unbalanced?
I also wonder how I can find one bad cell in a pack built with copper/nickel sandwich method? I know which group it is

 

[amberwolf]

I have one P group that is between 0.130 and 0.2V lower than the other groups and I wonder if it could be a bad cell or is it just unbalanced?

By definition, a cell group that is different from the others is "bad" *because* it's different characteristics (capacity, internal resistance, etc); unbalanced is just another term for the same thing.

If it's a just-built pack and the cells were not charged to the same state of charge (and voltage) before assembly, but hte cells were all tested to be identical characteristics, then it's "unbalanced" in that the voltages are just not the same, and charging everyt group to the same capacity will make them the same voltage.


If it's already been cycled and that group has dropped in voltage over only a few cycles, but was previously tested to be identical to the others, there could be a BMS balance channel stuck on, constantly draining that group.


If the cells were not tested to be identical before assembly, then it's possible that group just has some of the worst cells in it (other groups could also have "bad" cells and also be low in voltage, etc).

 

[Bandit1961]

The only way is with a thermal camera

 

[docw009]

It would seem that .10 volt isn't much, but for a 15P using 3AH cells, that might represent 4AH less?

Look at it when the battery is fully charged, and then when it's discharged to your typical low level. Maybe it goes away or maybe not important for a 45-50AH battery.







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[jai134]

Here is when it was assembled in januari this year.

 

[jai134]

I had a Daly BMS last months because of the registration. Now, when my motorcycle is street legal I returned to my JBD BMS. It balances the cells which the Daly doesn't do.
If you say that the difference isn't alarming I let it be like this for some time. Could a balancing card be a good idea to have or is it good enough with the JBD?