I saw Daves teardown of the Turnigy Accucel 6 LiPo charger that not only charged the LiPo batteries, but also balanced each cell voltage. I saw the schematic of the balance part of the charger and got quite confused. I have attached the balancer schematic down below and here's Dave's video:
So my question is, how does the charger balance the battery voltage for each cell. I have a few assumptions. Which one is correct? if any.
Assuming the charger is charging a 2 cell 8.4V battery. The charger puts 8.4V across the pack. Waits til one of the cells are 4.2V -
1) As soon as one reaches 4.2V, it turns on the transistor to discharge the cell, but "does not" turn off the 8.4V power supply. So, some of the current that was going to the higher cell voltage is now being turned into heat. But still some current might go into the cell and slightly overcharge it maybe?
2) As soon as one cell reaches 4.2V, it turns off the 8.4V power supply and turns on the transistor for the cell. Once both cells are at the same voltage, it turns off the transistor and starts charging at 8.4V again.
Another question I have is, why are R124, R126, R128... resistor values different? Are they not discharging each cell with 20 ohm resistor directly across them? (transistor acting as a switch) In that case, are they discharging different cells at different currents?