Quote:
Originally Posted by jyanof
There could be a large temperature drop across that pad, especially if there's a lot of heat generation and the heat spreader (and thermistor) haven't had time to heat up. The silicon could be much hotter and having lots of margin might be desirable.
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Well said. That heat spreader is like a big dang thermal capacitor. I asked the EV Tech list about this, and Lee Hart said it was one of the classical problems of control theory. Otmar drilled holes into the back plate of the mosfets and IGBTs to get right behind the silicon to get his thermal numbers. I don't have a drill bit that skinny. That guy's crazy. haha!
Quote:
Originally Posted by jyanof
If it happens that thermal shutdown occurs, it might be better to try to reduce the thermal resistance to keep things cooler rather than adjust the threshold higher.
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My thermal shutdown code is very gradual. There is an 8 stage process, so you will definitely start to notice it gradually, rather than all at once. That's an excellent idea about reducing the thermal resistance. It wouldn't be a quick fix on your controller, though. That would be a total redesign. Maybe bolting the backs of the mosfets/diodes DIRECTLY to their own respective heat spreaders, and then isolating the 2 electrically isolated heat spreaders from the heat sink. That would require some thought.
By the way, I have a cost tally for the controller parts. We still need an enclosure, though. That's the big unknown. I was going to do the new and hopefully improved power section layout for you and Adrian, which would require a 6"x8" power section, which would fit into the largest stock build-a-box that Wherewolf found, I think. I think a metal enclosure would be much better thermally speaking than a Lexan box with a heat sink on top. Can I get your email address? You can PM me if you want. Do I already have it? I forgot!