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Old 04-07-2009, 09:19 PM   #801 (permalink)
MPaulHolmes
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Michael's Electric Beetle - '71 Volkswagen Superbeetle 500000
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OK, so it isn't a complete failure. I have been worrying for the last couple hours that it was just going to be a big hunk of junk once tried on a larger motor. By the way, the hardware current limit comes on at 500 amps, and keeps the mosfets off until about 478amps, so the actual current limit probably averages out to around 485 amps or something.

If you feel like it's starting to lose power, it's because the thermal cutback is kicking in. The micro-controller is continually measuring the temperature, and starts to limit current when the copper heat spreader reaches about 70 degC.

At 70 degC, the software current limit is 7/8*478 amps, at around 71 or 72 degC, the software current limit is 6/8*478 amps, ... all the way until 80 degC, at which point the software current limit is 0/8*478 amps (which, by the way, is 0 amps! hehe).

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