Thread: Low cost BMS
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Old 12-13-2013, 06:51 AM   #116 (permalink)
arber333
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Quote:
Originally Posted by Astro View Post
I started thinking about using the cell top BMS to load the higher voltage cells at the start of the charging process after i read post by harlequin2. Harlequin2 mentioned that some people had balanced their cells by leaving them in reduced charge current state for a few days. That was probably an extreme example but it made me think, the low current period of cell balancing is burning up kwh's whilst possibly waiting for just one cell to balance.
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I see the logic behind this...
For now my BMS uses either one large 3W/5W resistor or two of the variant for maximum balancing 4A if the mosfet would hold. BUT in reality i see some glitches while balancing for prolonged time at 2A. Possibly heat is interfering with PIC12F... I recommend single 5W 3R3 resistor or dual 3W 4R7 for 1A balancing.
I see that now when cells are equal even 0,5A would work ok.

If you want to balance early you would have to change the code for charger off condition and program PWM so you would only partially open shunt at 3,5V and then at 3,65V balance fully.
Though it is of no use; now i charge at 45A and i see cells riding at 3,5V almost all the time. Only in the end one or two runs ahead. It would be very difficult to balance at high amps without measuring internal resistance. But this is simple BMS... I opted to just reduce charger down to 10A when one module starts to balance - o/p1 of the master. It works for me now...

A
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