This has probably been done before, and maybe there's a better way - but as a n00b i read the usual sticky post on balancing & in parallel it was going to take AAAAAGES for a 24v 300AH pack at 3.6v
So i thought about it & have a really simple way to do it much faster.
The issue is that you need the biggest voltage difference (charger vs battery pack) to push current when charging, when you put all cells in parallel - this is the lowest voltage drop you could possibly have. A full pack in series is the highest voltage drop.
So here's the process...
- Get yourself a hobby battery charger that can do LiFe chemistry, they're soooo cheap!!! & can use a 12v computer PSU, and have awesome (1.5A) balancing, and big current capacity. Drones, remote control whatever... that type of hobby charger.
- Connect up the battery bank in series, connect all the balancing & start the charge, lets say its a 24v 8s pack
- 1 cell will hit high voltage, remove that cell from the pack & re-assemble the pack - its now a 21v 7s pack
- Set the hobby charger to 7s cells, connect all balancing & charge
- the next cell will hit high voltage, remove it from the back & re-assemble - a 18v 6s pack
- .... repeat
All cells will be removed 1 by one when they hit peak voltage, and you've kept the highest charge current at all times, you've had balancing & safety on - so its all "safe". There is NO BMS!!! so not completely safe, you need a good charger that stops when it hits full voltage, which is easy enough for a hobby battery charger.
Feel free to point out any errors or problems, or link to a better way/information if there is any. The biggest downside is the removal of the BMS, so watch like a hawk & make sure you KNOW that the charger disconnects & stops when it should on the voltage.
Hope that helps any other n00bs & speeds up everyone's balancing.