fechter said:
Normally you have an insulator directly against the tab on the FETs. This immediately restricts the amount of heat that can flow.
If you place the FETs directly against a copper bar (maybe even solder them) and use an insulator between the bar and the heat sink, you can get more heat flow if the surface area of the insulator is much bigger than the FET tabs. The copper (or graphite) heat spreader has to be split up into 6 sections that are electrically isolated from each other. Parallel FETs can be on the same piece of bar.
It should be possible to model this and see how much difference it would make. I would imagine for short bursts of extreme dissipation it would help a lot. More long term, you would still be limited by the overall thermal path resistance.
I can see how this would work now. Since this is a 12 fet, every 2 mosfets have the drain tabs electrically connected together. Solder those 2 mosfets down to a single section of copper that's as wide as the 2 mosfets and the full height I have in the mosfet wall. Behind the copper and between it and the mosfet wall that's where a much larger insulator would sit. The copper heat spreader would be cut into 6 electrically isolated sections...each with 2 mosfets soldered to it.
I may do this after a while if I see I need more efficient cooling. It will require isolating the screws from the shell and redrilling the shell a fair bit for more screws. I'll have the temp sensor attached under a screw directly on a mosfet tab. I'll know temps pretty accurately.
I guess the graphite insulator comes in sheets and can be cut to size.
Thanks guys, I can see how I would do this now.
Making a better heat path...
1. Use copper instead of aluminum for all that added metal I put in and on the shell to improve thermal conduction.
2. Use graphite insulators between the layers of added metal instead of thermal paste.
3. Add heat sinks to the added metal so cooling happens all along the heat path to the CPU cooler.
4. Mount the CPU cooler direct to the mosfet wall and/or use a better CPU cooler with more heat pipes and more copper in it.
5. Cut up the copper heat spreader into 6 sections and solder the mosfets to the sections.
6. Use liquid cooling.
Notes:
Number 1: Probably won't do this at all. There's already so much added aluminum, going with copper instead won't matter much.
Number 2: If/when I go with graphite insulators and cut up the copper heat spreader into 6 sections, That's when I would do this too.
Number 3:This is easy and I'll probably do that right up front by mounting a heat sink direct to the mosfet wall.
Number 4: I deliberately didn't do this due to space constraints out the side of the controller.
Number 5: We'll see...maybe later...if heat is significant or not after these other heat path mods are done and tested.
Number 6: Use a couple of liquid CPU coolers so I can cool directly at the mosfet wall and put the radiators where the CPU cooler currently mounts.