I done some search about "bottom balancing". All that can be read on the various debates confirms what I though : I really don't see any advantage of bottom balancing !! On the contrary, there are severe disadvantages :
- You need to discharge all cell at the LVC, it's a waste of energy and it's exactly the opposite of the prefered method for lithium chemistry, charge them even if they are not empty, to increase their lifetime
- You also need to cutoff the charge when the first cell reach the HVC, because they will not reach the same full voltage in same time if cell are not completely identical (capacity, internal resistance, temperature ...), and they are not.
- When discharging the pack, you also need to check the LVC on each cell, because cell cannot be identical, even if same amount of Ah have been entered in all cell, the cell with higher internal resistance will reach the LVC before the other.
- With bottom balancing, you completely discharge all cell, thus at the next charge, you cut off the charge when the lower capacity cell reach the HVC, but at this time the higher capacity cell are not completely charged and their voltage is not at full voltage, thus your pack is not at full voltage. Thus when discharging, for a given power you will need higher current...
In fact, I cannot understand why there is a debate between top or bottom balancing, because I cannot see any advantage of the bottom balancing method
If anyone has a link to an explanation about the advantage of bottom balancing I am interested !!
Anyway, in my opinion, balancing is not really mandatory, the global pack capacity will alway be in any case the capacity of the lower cell. Just cut charge when the first cell reach the HVC and cut the discharge when the first cell reach the configured LVC and your pack will alway be healty, because no cell can be over discharged or overcharged.
But an intelligent top balancing (balancing during charge and not at the end) can add an advantage, have the maximum of cells at their top voltage at the end of charge, to maximize the global voltage of the pack.