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Old 02-03-2010, 12:52 PM   #2924 (permalink)
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Join Date: Feb 2008
Location: Maricopa, AZ (sort of. Actually outside of town)
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Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000
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Hi Jack, do you mean the contactor for the controller? or the bms above? For the controller, the contactor is disabled while pin 13 is high. If the software sets it low, then that turns on the LED in U9, which causes the gate of Q1, (which is normally pulled high to battery 12v), to suddenly be shorted to about 0.3v, which turns on the p channel fet (Q1), which connects 12v to the coil.

I haven't heard much about the mini-bms. A couple concerns I have is that it continuously draws "less than" 10mA, which could mean 9mA. hehe. people that leave their car parked for too long or sent in for repair could destroy their batteries. It would take a pretty long time though. It also can only shunt 0.75amp for a little while, rather than continuously. I think it shuts off the charger if one of the shunts gets too hot, so the rest of the cells may not have a chance to balance. I'm also not sure how it will work in a noisy environment. Some people have had problems with this sort of thing under heavy acceleration I think.

Mine (from Fran's ideas haha) will use like 1uA (1 millionth of an Amp) when not in use, shunt any amount of current you want (continuous) from 0amp up to 2 amps away from each cell for as long as you want, causing anywhere from 2amp down to 0amp go through the battery until the rest are completely balanced (the programmer can have that 2 to 0amp be whatever he wants based on the "topping off" profile). This shortens the time necessary during the balancing phase. Each 25w power resistor is off board, on aluminum. Also, the charger and controller will know the exact voltage of every single cell, so you can output it to a laptop or something and watch the state of each and every battery while charging or discharging. Also, because CANbus is used, the communication will be very noise tolerant. ya!
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