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Originally Posted by Cirrussport
i fully agree with the thermal protection idea. i have so many dead victors sitting around just because of over current. I wouldve much rather had the victor limit the current or cut out because of heat then had to replace them. Thermal protection should definately be considered.
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The thermal rise is so fast that there is no effective way to compensate for that electronically. ( it is likely that the temperature rise is fast enough that even heatsinks would not fix the problem.) At the time that the overcurrent is taking place, the branch circuit breaker was already tripping, several times. A non resetting circuit breaker would cure the damage problem but make it impossible for you to continue to compete. It is essential for teams to measure current in motor circuits while practicing in order to insure no damage to motors or to Victors. Remember that for all intents and purposes, a stalled drive motor (Chalupa, FP, or drill) looks like a dead short to the Victor. A device that is rated at 40 amps cannot sustain a 2.5x overcurrent for very long without damage. You have proved that. P=I^2 * R, with an ON resistance of .002 ohms and assuming that each FET is sharing 1/3 of the load, you have a potential for a junction dissipation of 10 watts. That little piece of silicon can't get rid of the heat fast enough.