jkbms, repeated cell overcharge protection

[ajtarnas]

a friend just wired up a new jkbms to their 16s 280ah 3.2v/cell 16-cell "48v" EVE LF280K LiFePO4 battery bank.

they are having trouble. one cell keeps going over voltage. this cell has behaved fine for the last 10 months of near-continuous operation.

i suspect a bad connection either on the busbar or sensing wire or sensing wire harness entering the bms. the bank was assembled quite carefully though with nuts torqued to 6ftlb and sensing wire ring terminals carefully crimped. but my only thought is to redo thise things in the vicinity of cell 10.

anyone else experience such a thing?

i have not been present when the error occurs. this is an off-grid solar power system for a small primary residence / cabin with a victron charge controller and 6 panels at 330w each. running a 3000w wzrelb inverter 24/7.

 

[BentleyJ]

The BMS screen shots are not telling us anything. The voltage is 53.6 with a small load of 1.5A and all the cells are within a couple of mV, this is typical. Cell voltage differentials don't really start to diverge until the charge cycle hits 3.4V per cell (54.4V) Could you please post pics of the set up menus. Also a cell voltage pic when charging with constant 55.0V.

It may be that the battery needs to be float charged at low voltage for 24hrs to give the balancer time to do its job.

 

[ajtarnas]

in this case cell 10 is jumping in voltage at unusual times. i don't think it's a cell balancing issue because the bank was relatively balanced and in operation for 9+ months with an overkill bms. before installing this new jk.

the jkbms screenshots are from a moment of nominal behavior. the system log photos shows the error occuring somewhat randomly throughout the day at different battery capacities between 80-95%.

i can't post any other photos presently. i think cell overvoltage protection is set to kick on at 3.50v. and the victron was set to pre-emptively cut charging when it saw 54.9v (3.43v per cell for a perfectly balanced pack).

 

[BentleyJ]

i can't post any other photos presently. i think cell overvoltage protection is set to kick on at 3.50v. and the victron was set to pre-emptively cut charging when it saw 54.9v (3.43v per cell for a perfectly balanced pack).

54.9V for charging is fine, just takes a little longer but is easier on the cells. I'm topping up at 54.8V. I do think the OVP is too low. The electrolyte in the cells is good up to 4.2V. I would suggest OVP be increased to 3.65V min and even up to 3.80V. For short periods until the balancer has time to react I;ve never had a problem on the bench top if a cell gets that high.

 

[ajtarnas]

it appears that my theory was probably correct. my friend backed off and then retorqued all the busbar/nut connections. cell 10 is no longer showing random problematic behavior after 27hrs. time will tell.

 

[Jane]

Hello,
did you find the solution of that over charging protection problems?
I have the same problem with JK BMS.

 

[maxx-v0]

I saw this behavior on new setup. I did discharge/charge battery few times and issue gone. It was unbalanced new cells I guess.