Battery help!

[22slow]

Hello, I have a 1.2k off grid system I use for back up. I have 16 280ah lifepo4 batts. I charge them with a Victron 150/35 smart charger. I use a Daly 200 amp smart bms. Here’s the question, as soon as my charger goes into absorbing, one cell tends to run away. The 15 average is 3.4 (I run 90%) but the 16 hits 3.5. when the charger drops into bulk they level out quickly. So tips , tricks, or am I fine? Thanks all

 

[sunshine_eggo]

Your battery is imbalanced. Did you top balance them prior to deploying them?

Raise cell cut off to 3.65V
Lower absorption voltage by 0.1V until the BMS stops tripping.
Raise float to 3.45V/cell
Enable balancing only above 3.40V, 20mV difference and only during charge.

Run it like that for a week.
See if you can increase the absorption voltage without tripping the BMS.

Charging to % based on voltage is folly. It's not possible without lots of trial and error. Even then, it's not consistent.

 

[22slow]

Thank you

 

[22slow]

This only happens during adsorption, under load and during bulk charge it evens out

 

[burgerking]

Either:
A. Top Balance them (requires disassembling, reassembling, disassembling, reassembling); OR
B. Use an Active Balancer and slow charge for a few days; OR
C. Manually discharge #16, by paralleling a 100W 0.5Ω~1.0Ω resistor to it until within 0.05V of the rest.

B & C should be done without discharging or you will unbalance them

This only happens during adsorption, under load and during bulk charge it evens out

During load and bulk, it is in the "very flat voltage curve". Only when the cells are in the >90% SOC and <20% will you see it deviates alot.

 

[22slow]

Either:
A. Top Balance them (requires disassembling, reassembling, disassembling, reassembling); OR
B. Use an Active Balancer and slow charge for a few days; OR
C. Manually discharge #16, by paralleling a 100W 0.5Ω~1.0Ω resistor to it until within 0.05V of the rest.

B & C should be done without discharging or you will unbalance them


During load and bulk, it is in the "very flat voltage curve". Only when the cells are in the >90% SOC and <20% will you see it deviates alot.

Really appreciate the advice. One thought though, shouldon’t the bms balance that out?

 

[burgerking]

Really appreciate the advice. One thought though, shouldon’t the bms balance that out?

You are using Daly. It can do only 20~50ma balancing. To remove just 1A of charge from #15, it will need 20~50hours.
You have 280AH cells. Maybe Daly will balance it after a year.

 

[22slow]

You are using Daly. It can do only 20~50ma balancing. To remove just 1A of charge from #15, it will need 20~50hours.
You have 280AH cells. Maybe Daly will balance it after a year.

Thank you