I've just ordered some some 3000mah Li-ion cells to build a 12ah pack[40] and I'm wondering just how important having a bms is?
Because the pack will be constructed of 10 x 4 parallel wired cells, in series, its impossible for the bms to monitor each individual cell.
If one cell was to go down, the bms couldn't tell, having 3 other cells in parallel, the voltage would remain the same.
Niether would the bms know the state of charge in each of the 4 cells in parallel, one may be 3,7v and the others 3.2v, it would only register the one with the higher voltage.
I can see it will protect against over-voltage but the charger should also do that to a point and it will cut off at low voltage which the controller also does.
As far as I can see this also applies to Lifepo4 and Li-poly packs where parallel wired cells are used.
So, other than for packs constructed of single cells in series, what use is the bms?
Because the pack will be constructed of 10 x 4 parallel wired cells, in series, its impossible for the bms to monitor each individual cell.
If one cell was to go down, the bms couldn't tell, having 3 other cells in parallel, the voltage would remain the same.
Niether would the bms know the state of charge in each of the 4 cells in parallel, one may be 3,7v and the others 3.2v, it would only register the one with the higher voltage.
I can see it will protect against over-voltage but the charger should also do that to a point and it will cut off at low voltage which the controller also does.
As far as I can see this also applies to Lifepo4 and Li-poly packs where parallel wired cells are used.
So, other than for packs constructed of single cells in series, what use is the bms?