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Old 03-03-2010, 08:48 PM   #3056 (permalink)
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Originally Posted by jyanof View Post
At cruising speeds, ~200 motor amps, the total calculated heat generation was roughly 300W. Roughly 2/3 of that were from the 10 mosfets, so that's only 20W per mosfet. When I went through the calculations, I think I was predicting a junction temp somewhere around 80C at these steady state conditions in the hot AZ weather. The heat generation is roughly proportional to motor amps (duty cycle has an effect too), so conceivably 400A would have twice the heat generation. Accelerations would also create excursions into higher temperatures, though they often occur after coasting or sitting still for several tens of seconds which allow enough time for the controller to cool down a little bit.
Hi Joe,
Thanks for the links, I'll check them out.

Sounds like you have a good cooling system already in need for heat pipes.

I'm a bit sleep-deprived right now but isn't the heat generated by the static resistance of a MOSFET proportional to the square of the current? That is, going from 200A to 400A would increase the power (heat) that needs to be dissipated by four times (Power = Current-squared times Resistance)?
John M.
CamLight Systems
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