60V battery only charges to 63.5V instead of 67.5V

[CrossRoads]

I have multiple 60V batteries and have tested the charger on the other battery, which charges up to the expected 67.4 / 67.5 just fine, so i know the issue is with the battery, not the charger. Just wondering what this could be indicative of. A problem with the BMS? unbalanced cells?

 

[HumanPerson]

could be BMS could be bad cells could be bad cell group...

 

[ElHegpah]

Should be 67.2. 16 x 4.2. Explain this discrepancy.

 

[smutboy]

Should be 67.2. 16 x 4.2. Explain this discrepancy

with it being off by 4 volts less. sounds like its got a bad cell in the battery pack.

 

[ElHegpah]

He is off by 0.2/0.3, much less than 4 volts, and it is an overcharge.

 

[smutboy]

He is off by 0.2/0.3, much less than 4 volts, and it is an overcharge.

he said one is only going to 63.5V and the other one goes to 67.5

 

[ElHegpah]

Sorry, you are correct. I did not bother reading the headline, just checked the post.

 

[smutboy]

Sorry, you are correct. I did not bother reading the headline, just checked the post.

its already even the first few times i read the OP it took me a second to realize part of the info was in the post head line and not in the post its self.

 

[CrossRoads]

OP was not well formated. my apology. Indeed, it is under by about 4 volts, about the voltage contribution of one cell. It's a 20Ah battery, which should be 16s8p. If indeed one cell is damaged there should be 7 more to do the job, but would one cell being dammaged cause the whole parallell group to not be charged by the bms? I.e., does the bms notice something is wrong with that group and cut the charging supply voltage? I'm just wondering how this bms stuff works.

 

[ElHegpah]

BMS detects voltage of all P groups. High groups are bled down, during charge, very slightly.

A single low cell could drag down the whole P group, possibly absorbing the entire charge load dangerously. A single cell at 0 volts could trigger an end of charge, or a total shutdown. A bad connection to a single P group could leave that group with a charge detected, but no output to the main battery.