Cell Balancing Question

[brclark82]

I have a new Chins LFP battery that needs the cells top balanced. The BMS does have cell balancing but is either very slow or isn’t working.

My first charge hit OVP on cell 1 at 3.65 while the other were at 3.45ish

Let it sit overnight and the cells range from 3.574 to 3.411.

BMS won’t start charging again until cells are 3.50 or under.

I plan on discharging this afternoon and testing capacity but was curious the best method to top balance cells in an assembled battery.

I only have a Victron Smart Solar MPPT for charging but am in the market for an external charger if that would help and you have a recommendation.

Thanks

 

[12VoltInstalls]

curious the best method to top balance cells in an assembled battery

Charge at 14.2V on a voltage controlled charger until current drops to zero. Even 13.8V will work but it takes a little longer and some say it’s not as effective.
I think it’s fine

 

[mikefitz]

Use your Victron MPPT charger set to absorbtion volts 13.8 with a long absorption period. If you don't encounter BMS shutdown increase the charge voltage in 0.1 volt steps .
If you are charging at a low current compared to battery capacity then reaching 14 volts will be almost fully charged

 

[dragonzzr]

i am kind of in the same boat here. only difference is that my preassembled battery has balancing function but seems to not be able to keep the cells balanced, even when charging with controlled power supply at 14.00 volts.

 

[dragonzzr]

quick update...just tested to discharge about 10ah and now strangely all cells are balanced within 4mv deviation

 

[mikefitz]

Discharge about 10ah and now strangely all cells are balanced within 4mv deviation

That's normal, the cell inbalance will only show up when the cell volts are in excess of 3.4 volts. It's above this voltage that most BMS start to balance. It will take some time, so if possible arrange the charge volts and current so balancing is taking place but BMS protection is not occurring. Several hours in this condition should show an improvement.
Once the cells reach over 3.45 they are practically fully charged.
Just using the battery as normal with a reduced charge voltage ( so protection is not occurring) is a practical approach. Eventually the cells will become more in balance. Charge voltages over 13.8 will charge OK.

 

[dragonzzr]

Thanks for your explanation.