I read all ten pages in the
other forum, and I understand, and agree, with the notion that you can't just balance cells at the top end, and not do cell level LV protection. You might be able to get away with the latter if you charged until the lowest capacity cell was completely full, but this doesn't take into consideration the case where you simply have cells of equal capacity, but they just happen to be out-of-balance. In that case, the first cell to hit the cutoff is simply the fullest one. One solution would be to do like the RC balancers all do which is to balance to the voltage of the lowest cell, and then charge only to the point that the first cell that hits the HV point gets full. You can't just shut the charger off when that first cell hits the HVC point, as that would leave that cell less than full, but if you hold the voltage and let the current taper off, it will be as full as it is going to get, and the rest of the cells are going to be at various lesser voltages, based on capacity differences. All the cells should have roughly the same amount "gas in the tank", though, so assuming the IRs aren't too far off, and the loads aren't crazy high, they should all reach the empty point at roughly the same time.
I would still not be comfortable without cell level LV protection, though, but I can definitely see how you may not want to unilaterally cut the throttle in larger EV, like a car or a motorcycle/scooter. In a bike it is not such a big deal because you still have the pedals.
Anyway, figuring out how to make this automatic might be tricky, but doing the part where the first cell that hits the HV point starts the CV mode is pretty easy, I think, simply by using the "throttling", or PWM control of the charge current, that is in our current BMS design, but without the shunts.
-- Gary
