So wouldn't you want that process to start as low as possible? Right now it's set to start at 3.8VGenerally you want to start balancing before the cells are full so you don't accidentally over charge them, even by a little bit. This also allows the cells to equal out a little faster as well.
They all seem to stay within a .15v delta from each row/grouping. So when should I have it start balancing? 3.9v?No, because then you would be wasting a lot of energy. You don't need to slow it down at the beginning of the race, you only need to slow it down as they approach the finish line.
It's possible that the one taking a charger faster (getting a higher voltage) may slow down at it reaches the upper limit, which will allow the others to catch up. All without wasting energy by burning off the "unbalanced" amount.
Take note, we're only talking a few 10's to 100 of milivolt difference. If the cells are further than that (something like 3.7V and 3.9V) consistantly, you need to find out why that slower pack is being drug down. After an initial balancing, they *should* stay pretty close. If not, you have an issue somewhere. Either a bad connection, weak cell, or a self-discharging cell or high IR in some cells. Those issues need to be fixed. A BMS is not a permanent patch for a problem.
If you had all new cells that are the same (same model, same batch), then yes.So wouldn't you want that process to start as low as possible? Right now it's set to start at 3.8V
Got it, that makes a lot more sense thank you for explaining, I'm going to have it start balancing at 4v since it should start to top some of the groups off around 4.15vIf you had all new cells that are the same (same model, same batch), then yes.
When the cells get older, or you have a mix of brands/batches (technically: different internal resistances), then voltages may rise at slightly different rates during charging, and catch up towards the end.
So if the balance start voltage is set too low, you could end up with the situation where cells #1~#6 get balanced (slowly discharged) around 3.8V, but then #7 starts to shoot ahead towards 4.1V and all the previous balancing was a total waste.
You should only ever need strong/long balancing once, after putting together the new battery. After that, _minimal_ balancing should suffice - if not, one or more cells have gone bad and needs to be replaced. High level of balancing just masks that/those damaged cell(s).
Also, there's no need for the cells to have exactly the same voltages. It's perfectly fine for one cell to cycle between 4.12v ~ 3.12v, while another cycles between 4.08v ~ 3.08v.