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Old 04-06-2009, 10:49 AM   #768 (permalink)
MPaulHolmes's Avatar
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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Heating issues:

I used a big fat commercially pure (C110) copper heat spreader instead of aluminum. Also, my mosfets are more efficient than the ones Ian is using. Mine have an RdsON typical of 8 mOhms, and his is 17 mOhms. So, my mosfets will have 1/2 of the heat loss. He found the more efficient mosfets after already building his, so I used them instead.

In version 2, I have a way to bolt the heat sink to the copper heat spreader with much much more pressure (not tapping into the copper heat spreader), which will allow more efficient heat transfer from the heat spreader to heat sink.

I'll have larger switching losses because I'm using larger gate resistors at first, just to be safe, to keep down the voltage spikes. I can improve that later.

My design uses hardware current limiting, and so is bullet-proof in the sense of it being impossible for the current to get so high that the mosfets burn up.
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