How do you deal with batteries off specs? Do you try to single them out before putting into an EV?
Cheers madires
In the case of the Solar EV racing cars, because we push our cells to the absolute limit, our matching method is very strict.
We are supplied with pre-matched cells, 1-2 passes, and test data (mainly Internal impedance curves). We check, sort and
make up "modules", usually ~5-7 in parallel (the current car will have 21 in parallel !!) Then we run 3 conditioning cycles,
both TOP and BOTTOM matching, then check the BM graphs. All "modules" need to be MAX +-25mV from median, usually 10mV.
If so, we know ALL single cells in ALL "modules" are tightly matched. We rarely ever find any that drift after that, even years later.
In the EV packs, we're no where near as strict. Basically, IF you have more than 1 set of parallel "modules" your BM simply
needs to do an accurate voltage tracking, at all current levels. If they are within +-10-25mV, then you can be CERTAIN that
ALL the individual cells are still matched. There is also one Temperature sensor per "module", BUT THAT can depend on air flow,
air eddy currents etc, so we don't place as MUCH weight on it.
For a Single parallel bank, we sense the current for each cell / battery. OFTEN it's just the bridge cable, so no complex wiring
is needed. 1-2mR x100 fixed gain amp, is plenty to work with.