Quote:
Originally Posted by MPaulHolmes
I only used a copper heat spreader on Joe's I think. And maybe Adrian's. Perhaps aluminum is just fine? I haven't heard of any thermal problems from anyone. I just don't know what the difference in performance is. I'm inclined to think that aluminum is fine for most people. Bill is in Phoenix, Arizona which is another name for the fires of heck! I'm sorry for that terrible language! The only part that determines the power board is 1" or 0.75" wide.
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i was curious about the impact of heat spreader material and width, and I happened to have my work computer at home, so I did a quick thermal model to see what happens.
Keep in mind this was done super quick with ballpark numbers and the results probably don't represent reality, but rather give insight into each configuration's performance relative to the others.
The model consisted of a 11" heat spreader on 1/4" aluminum plate. There is 250W of heat generation on the upper portion of the heat spreader on both sides to represent losses from both the mosfets and diodes. 500W total heat generation would be consistent with a current output of 300A, based on the normal calculations for mosfets and diodes. There's a tad of thermal resistance at the spreader/plate interface. Also, there's convection to 22C air applied to the bottom of the plate to represent a finned heatsink. The hole looking thing in the middle isn't a hole, but where the final temperature was read once everything reached steady state.
I ran 4 models; the two different materials and the two different widths.
Al/0.75": 86C
Cu/0.75": 78.5C
Al/1.0": 81C
Cu/ 1.0" 75C
I think the differences are significant but may not matter depending on the application. For a more demanding application that requires a lot of current output and thus, increased controller losses, going with wider copper may help the controller last longer and/or take more time to reach thermal cutback.
However, a wider heatspreader means the diodes and mosfets are farther apart, which could lead to more parasitic inductance and higher voltage spikes/noise etc.
Ah, tradeoffs...
