I have on hand two examples of charge balancing circuits, one from a handvac 14.4V rated(4-cells) and another from an supermarket "20-Volt" 5-cell battery pack. What surprises me is that the complexity is great, a dedicated >28pin IC is being used in both cases, 10's of discrete transistors, caps and resistors. No inductors were being used except to provide MCU power voltage..
But all the resistors are tiny! This seems to tell me that the actual discharging to balance currents must be small, maybe in the 40-mA range..and I was planning on using 10-ohms at 2-Watts!
I saw the spec sheet for the super charge balancer something like a 100-pin chip made by TI, which can balance something like 17 Li cells and would be in stock sometime maybe in Feb 2023.
My first impression of charge balancing circuits is that they are over-complicated, There must be a more cheap'n'dirty way to do this without significantly sacrificing battery life or fire safety.
So, at this point, my MCU basic idea to charge balance 4 to 6 cells would be to work with lower balancing current (40mA).
But when in the charging cycle to do this..while charging? Stop charging momentarily to balance? Wait for the batteries to reach a minimum low dischage level before attempting to balance? Repeat at 50% 75% 100%
? Continuously?
I have given the whole idea some thought and realize what would be an allowable mismatch between cells? And I've guessed it would be around 10% or between .33V to .42V worst case, else the battery pack would need repair or replacement.
Then, if charging takes maybe up to four to five hours at 500mA CC, and the charging current is reduced by 10% shunting of charge current with overvoltage cells, then there should be sufficient time for even a 40mA difference in charging current to balance the batteries while they are being charged.
My solution would monitor each cell voltage continuously by a MCU 10-bit A/D. This could allow a cell voltage error of no more than 15 mV( because of voltage dividers needed with the top cells in the stack). Once individual cell voltages are known, some equalizing circuit can then be developed.