Balancing the Batteries

I was able to replace the failed battery without trouble, however, due to that misbehaving battery, the rest of the batteries were no longer in sync – meaning some had a lot more charge than others.  I tried bringing the new battery down to the rest of the pack level using a 0.4 ohm resistor (50 feet of 16 gauge wire) – doing this for 5 minutes at a time.  It came close, but when charging, the rear half of the pack reached top charge before the top half.

So, after some consultation with battery experts at work, I realized that if I did a REALLY slow charge (2.3A at 110v), then the resistors on the BMS would be able to discharge as fast as I was charging, thus allowing ALL cells to reach that same point.  Please note that I have 108 cells, so I had to do some math.  2.3A * 110v = 253W.  108*3.4 = 367v.  253W / 367v = 0.69A.  So I’m pushing 0.69A through the pack…ok, resistors can handle that…  V = I*R, or I = V / R.  Resistor on the BMS is 4.7 ohm.  3.4 / 4.7 = 0.723A.  Easy.  🙂

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