I have a few thousand Lithium-Ion cells harvested from old laptops that I would like to test (measure capacity). They are mostly in 18650 form factor, but the are a couple of different ones too. I think they all charge to 4.2V though.
I have a cheap battery tester that I bought for 10 bucks which can test up to 4 cells at the same time. But as you can imagine this takes forever. I mean testing 4 cells can take like 6 hours sometimes...
So I am interested in building a custom testing device that can take 32 or more batteries at the same time. Ideally the design would allow me to easily add more, in case I decide that 32 is not enough.
From what I understand, the testing simply charges the batteries up completely and then discharges them at a constant current measuring how long it takes until they are empty to calculate the mAh (capacity).
And in the end I need a display or something to read the capacity (and maybe also the time it took to charge and the internal resistance) from. For each individual cell.
Ideally I would like to use a 12V/16A PSU that I have lying around.
Has anyone done something like this before? Or do you have any tips on how to do this?
I think the main issue that I have is that I need a PCB or multiple PCBs that on the one hand can do the testing for one or more cells, but on the other hand allow reading the data from a micro controller easily.
(Obviously I would like to keep things as cheap as possible)