Quote:
Originally Posted by Simy
On Paul's design he added some sort of fuse to blow if the circuit was draining the battery due to an open gate failure.
I figure the master can add up the cells current requirements and have the charger output that, so the output is variable and best for each one and if your design works the way I think it does the shunt of each cell can take what that battery needs. Am I understanding the theory so far?
Is it safe to assume that the highest and lowest battery should be within 1/2A of each other? Or am I missing something?
How does it balance? Does it balance the load a bit by drawing a bit more power from higher batteries and less from lower batteries, or does it discharge the higher batteries to the lower batteries?
=)
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I use a bipolar transistor to control the shunt, easier to drive than a fet. Should a shunt driver fail "on" - which is very unlikely - the cell voltage will become lower and lower and that will be picked up by the master, so I see no need to monitor the shunt states directly.
Not sure what you mean by "the cell's current requirements".
My charger produces a constant current of 16A which is the most I can get without going to 3-phase power at home. That's for its CC phase. When the current drops to less than about 20% of that, the charger does its CV phase at (no. of cells x cell max voltage) which is 162V for my 45 cell (CALB) battery. Its capacity is a little over 120 AHrs, so it takes about 8 hours for a full charge. The BMS can turn it off when a cell reaches Vmax or cut it back to only .5 amps (the shunt current) to do top balancing. (see below).
This BMS is intended for LiPO4 cells only and is not suitable for any other type. The cell modules operate from 2.2V to 4.0V only. Vmax and Vmin can be user set anywhere in this range.
Balancing is done by matching the cell voltages, nothing to do with currents. There are two ways to do it, "top" and "bottom".
Top balancing is where you stop charging cells when they reach Vmax, but keep charging all the others and bottom balancing is where you stop discharging cells when they reach Vmin but keep discharging the others.
Bottom balancing is generally safer because the "weakest" cell determines the charge in all the others so they all run out together.
Sorry if this sounds like a lecture!