Short Term Test Discharge of Cell Bank [No BMS] On Dummy Load


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Local time
12:24 PM
Mar 24, 2022
I'm replacing the old cells with new but keeping the old BMS.

Before rewelding the BMS to the new 4p X 7s cell bank I want to do a 1 minute 15 amp dummy load test to check for bad welds.

The new cells were removed from a new 7p X 10s which was used twice as a detachable range extender. It weighed too much so I downsized to 3p X 10s and slowly realized I had 40 cells left over to redo the original battery. (I'd like to say I was thoughtful enough to plan this from the beginning because it's the cheapest way to get a new battery + range extender but it was what I call a "negative unforced error.") The original 7 X 10 claimed more amp hours than what you actually get, but the cells seem to be very uniform and can take at least 2X the charge of my old cells. I can't remember the exact charge it was last spring, just less than 80%, but each new 4p is exactly 3.6 v after sitting for 6 months. The cell bank is now at exactly 36 v.

Assume some cells can discharge / take slightly more charge than other cells [the reason for BMS]. My thinking is if I only discharge from 36.0v to 35.9 v weaker 4p units might drop to 3.585 v while others would drop to 3.595 v but no cells would be getting fried.

IOW none of the 4p units could suffer much damage _even w/o the BMS_, certainly if this is just a one time short duration discharge 4 v above dead battery.