Battery Pack Balancing

After around 9 months of storage of my battery packs, and following the controller auto-tuning saga mentioned previously, I began the task of balancing up the cells within each of the packs. The charger and BMS within the packs handles balancing after charging but it is less stressful on the packs to do it with an external current source. I charged each pack normally then when the BMS cut out due to a cell going to 3.9 volts (usually at a pack voltage of between 54 and 55 volts), a little external device switched to a 180mA current source. This is the same amount of current that the BMS can bypass across each cell pair. It took somewhere between 24 and 50 hours to get the packs to 58.3 volts. It took from 21st January to 12th February to balance the 12 packs. I did some work on the dashboard (yet to be blogged) during this time.

My device in the piece of black heat shrink dangling below the pack being charged.