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Old 06-28-2010, 06:54 PM   #3500 (permalink)
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Originally Posted by reissmachinist View Post
So now I had 15 batteries and 180,195
volts to the armature. It did have the higher rated mosfets, diodes and capacitors.
Dude, that's too bad! gonna think out loud now...

I'm wondering how overvoltage would play into this. What were the components rated for? There will be a voltage spike when the mosfets turn off - measurements with a scope show something like 15-20V or so at 200A or so using a gate resistor of 20 ohms. I forget, but I posted a while ago on that in this post. It gets worse as the current goes up and as the gate resistor value goes down.

Another thing to consider is that mosfet switching losses increase proportionally to votage squared (according to heat generation formulas for mosfets). So, if you increase the input voltage from 108 to 180, that's a factor of 180/108 = 1.66x. But, the switching losses will increase 1.66^2 = 2.77x! So, your mosfets may have been generating almost 3x as much heat as before! They may have heated up faster than the heat spreader could and before overtemp could kick in.
ReVolt AZ testing thread:
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