Hello everyone,
I have a problem with my battery: there’s a persistent imbalance between the cells. The maximum voltage of a cell is 3.68V, while the minimum voltage is 3.33V.
Currently, the maximum charging voltage is set to 55V. I first reduced it to 54.6V, then to 53V, but the imbalance persists. Lowering it to 52.4V eliminates the imbalance, however, the state of charge (SOC) no longer increases.
Does anyone have a solution to this problem?
You need balance the cells. Does your BMS have a built-in balancer? If yes, is it “strong” enough?
An active balancer, like a Neey 4A, would most probably solve your problem permanently.
You should only start this balancing when the first cell will reach ~3,45V.
Then you reduce the charge current to e.g. 2A only, and let the balancer work. This might take many hours as there is a big inbalance.
In best case, once this balancing is done properly, this could hold you cells in balance for a long time again. Depending on the differences in the cells.
Some bms programming allows a fairly big gap.
What batteries batteries do you have?
What is the manufacturer recommended charge voltage and absorb time?
How old are they?
Last weekend I have partly balanced a 16 kwh 16 cell battery, 2 cells are off by 150mv at 100% soc.
It took 14 hours of balancing to go from 150mv to 60 mV difference (2A balancer).
So another 12 hour it should be done…
350mV difference (at 100% soc?) will take a looong time of balancing.
Wow with a 2A balancer. That is crazy long. But i sounds like you may bave big cells or a bunch in parallel?
Setting the system to keep batteries charged and leaving them there at the max charge voltage (with no voltage cap) is the way.
314 ah, Multi Rs, and it was my first time, the second time it should be faster., 2 cells are off by 150mv btw.
I use a lithium battery, a BSL BATT
Thanks , I’m going to try that
Active balancers are very, very slow. They only do one operation at a time (charge or discharge) and on one cell at a time.
A BMS with passive balancing can balance multiple cells simultaneously. It can usually balance half of the cells (all even or all odd cells) at the same time.
But existing passive balance BMS’ had a balancing current of 50mA - 200mA, far too small for Chinese Aliexpress-grade LiFePo4 cells with capacity above 100Ah.
So then the market was flooded by “active balancers” with 1A - 2A balance current and these became the “standard”. Not because active balancing is better, just because the existing passive balancers were completely inadequate.