Hi all:
I am interested in charging individual LiPO or LiFePO cells when they are connected in series. Most LiPO chargers (that I have seen) simply charge the entire series string of cells, then discharge any cell(s) that get overcharged. I would like to implement some way of charging each cell individually, without needing to discharge any overcharged cells.
The big problem as I see it is that while it is simple to wire-up a charger to one cell, any subsequent cell will be referenced to the same ground (or reference) and therefore present a short to the first cell.
Is there any way around this without resorting to some kind of relay to provide isolation between cells?
I am interested in charging individual LiPO or LiFePO cells when they are connected in series. Most LiPO chargers (that I have seen) simply charge the entire series string of cells, then discharge any cell(s) that get overcharged. I would like to implement some way of charging each cell individually, without needing to discharge any overcharged cells.
That sounds potentially (pun intended) dangerous. Surely the whole point of balance charging is to even out the voltage of cells without any of them becoming overcharged at any time
By the way, I don't think that your description of how balance chargers work is correct as the ones that I have used do not take a cell above its rated top voltage then discharge them back to the rated top voltage. Instead they reduce the charge to individual cells that are above the voltage of other cells being charged and/or discharge them slowly down to the voltage of other cells to achieve a balanced charge
Remember too that LiPo batteries are charged in 2 phase, constant voltage and constant current
A non-trivial project, with quite a bit to go wrong and the project\battery ending up in flames. A good and thorough understanding of how to charge LiPos is essential.
Why do you want to build one, commercial ones are not expensive ?
schmarduino:
Most LiPO chargers (that I have seen) simply charge the entire series string of cells, then discharge any cell(s) that get overcharged.
Incorrect. They do not ever "overcharge" cells.
Balance chargers constrain the voltage to individual cells which reach the "target" voltage and drop that voltage to the level at which they do not charge further. Not to be confused with "discharging" cells, it is the lower voltage at which there is simply negligible charging current.