Tapping 12v from 48v cells with Active balancer

[georgia088]

I will probably catch flack for asking this, but if you have a bms with an active balancer on a set of cells (48v 16s prismatic cells in my case) why can't you tap off of 4 cells to get 12v if the bms is going to keep the cells balanced? I am guessing if the current draw is substantial the bms may not be able to keep up, but it should cut the bank off if the current drawn from the four cells causes them to drop below the bms programed threshold, right? So, basically wouldn't it just shut the whole 48v system down if the 12v load caused the cells to drop too low?

Thanks!

 

[BentleyJ]

Yes, you answered your own question. That type of arrangement is not recommended. Would be much better to use a low cost 48V to12V DCDC converter to produce the needed power source.

That said, if the 12V was being used for low power draw device, as in mA range and the battery pack had a 2A+ balancer it would be able to keep the cells balanced provided the absorption and/or float cycle was long enough. Still not recommended though.