Quote:
Originally Posted by Volt_Ampere
Most BMS do not provide enough balance current to do the job in a reasonable amount of time with the packs we use. I designed and built my own and I use a 1 amp balance current. This causes a fairly large voltage drop in the sense lines so I don't sense the voltage during the time that the balance current is on. I turn it off for a couple seconds to measure the cell voltages. I used power resistors and gave them plenty of air cooling space because at 1 amp they are dissipating 4W each. This is why most BMS do not balance at a very high current - they don't want to deal with the heat generated.
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When I put my pack together I had 2 of the 14 cell-packs that were 50mv below the other 12. When the REC was balancing, it was bleeding down 12packs at a time through those power resistors.. The BMS is designed to stop balancing when it hits 55degC.. and that's exactly what it did. hit 55, shut off for a while until it cooled down some, then went back to work.
Since it was a one time thing (new pack), I just put a computer muffin fan on it to blow air across the case to help it out.
I have my balancing settings pretty tight as I don't let any cell go beyond 10mv of the rest.
I find it impressive that you built your own.. Not sure I'd want to invest that kind of effort into it, but if I did, I would employ multiple redundant backups for safety.