On 3/13/21 11:47 PM, Gordon Wong via EV wrote:
My idea was to expedite the balancing process by starting at a low SOC and let the BMS stop the charge when the lower capacity cells came up to 3.6 something or whatever the BMS was set to.
That bottom balancing confused everyone. As Bill well explained, that may only worsen the problem when a BMS is dedicated to top balancing.
We don't know the details of the pack. The number of cells, the capacity of the cells, the manufacturer, the recommended voltages. We don't know what the BMS is supposed to do.
I hope the BMS is set up to top balance with resistor bypass. I hope the BMS is set up to terminate charging when a single cell goes high. If so, the BMS can eventually bring the pack into balance. If badly out of balance as your pack sounds, it may take a very many cycles. The process can be hastened by both charging only the low cells and discharging only the high cells. Something like an incandescent light bulb can be used for a single cell load. Or some other resistor.
I again recommend putting all cells in parallel and charging with a single cell charger up to around 3.45v.
I recognize that paralleling may not be feasible. The magic multi-cell charger/cycler/balancer Bill mentioned sounds wonderful but he mentioned using only with higher voltage LiPo cells rather than your lower voltage LFP. Likely, it will handle both.
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