Electronics > Projects, Designs, and Technical Stuff

Thermal INSULATOR Pad to Reduce Housing Temperature? (Desperate!)

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ChristopherN:
+1 for the metal foil on the outside.

We did that in one test for a product, using a metal label like this: https://www.schilder-buhl.de/produkte/metallschilder/untereloxaldruck# (random google link). The labels are available in different versions with different thicknesses, materials and so on.

Other ideas:
Use a label thats on a foam backing, there are ones that are a bit like thick double sided tape.
A third option could be a domed label, those are available in different versions as well and can add a few mm to the outside of the housing.
You could also get a plastic label that comes in form of a wave, something like this: ^^^^^. The raised spots would likely stay cooler that the rest, but I don't now if thats allowed since you can still reach the hot part if you press hard.

Can you specify the orientation the power supply must be used in? If thats the case you could specify that its only to be used with the hot spot on the bottom, that could change the heat distribution in the supply.

OM222O:
you mentioned needing to seal the box for IP rating, and it seems like active cooling is the best and cheapest bet here, so here are a few suggestions that would probably help:

is there a metal plate / bar that the PSU gets mounted to? if so, can you find empty places on the aluminum heat sink that allow it to be screwed onto the plate? this doesn't give electrical isolation, but it certainly allows for IP rating.

can you leave one of the sides of the plastic box open (only pot to the top of the aluminum plate, don't go over it and seal the entire thing) and leave the aluminum plate with the hot spot exposed to some internal part of the device, then have a fan blowing directly on the hot spot?

make the copper area around the inductor larger and use thermal vias if possible, this will increase the surface area of the "hot spot" which reduces the maximum temperature.

as a basic test, buy some non conductive thermal paste and apply it around the inductor over a "large area" (about 1 inch by 1 inch should be more than good enough) to see of that reduces the temperature at all.

I don't think insulating the hotspot is a great idea, it will only create more in different parts. just try different mounting orientations so it's not where it could be touched during normal operation. if nothing else works, you should reserve to watercooling: have a pipe in the middle, or a water block that directly contacts one of the aluminum plates and soaks the heat. another alternative would be sticking a vapor chamber to the back of the aluminum plate. they are thin and very good at conducting the heat away. that way your entire aluminum plate heats up evenly, avoiding hot spots. I'm not sure if 1mm is a large enough gap, but 2 or 3mm should be more than good enough if you can fit it between the plastic and the aluminum.

TimNJ:

--- Quote from: thermistor-guy on August 16, 2019, 01:35:33 am ---
--- Quote from: TimNJ on August 15, 2019, 06:33:52 pm ---...
Our issue is on the top of the housing. There is a small gap, maybe 1 or 2mm, between the top heatsink and the plastic housing. We've tried filling that with thermal RTV among other things. But now, at my wits end, I'm wondering if perhaps a thermal insulator on the hotspot could get us the reduction in temperature we need.
...
Any other suggestions on how to make this work?

--- End quote ---

You could try adding adhesive-backed metallic sheet (copper or aluminium foil) to the top of the housing (inside surface). The sheet reflects infra-red radiation away from the top of the housing, spreads the heat a little via conduction, plus the adhesive provides a small amount of thermal insulation. Together, these small improvements may provide just enough hotspot reduction.

Since you have 1mm to work with, you could also add a thin insulating layer between the foil and housing. This would be a cheap solution if it works. Once you get a working prototype, Parker Chomerics (http://www.chomerics.com/) may be able to help you with a professional production-ready solution.

--- End quote ---

Thanks. I really like this idea. I'm setting up the thermal chamber to give it a try now. I tried a few layers of copper foil. Will compare the housing temperature with and without.

TimNJ:

--- Quote from: ChristopherN on August 16, 2019, 11:55:50 am ---+1 for the metal foil on the outside.

We did that in one test for a product, using a metal label like this: https://www.schilder-buhl.de/produkte/metallschilder/untereloxaldruck# (random google link). The labels are available in different versions with different thicknesses, materials and so on.

Other ideas:
Use a label thats on a foam backing, there are ones that are a bit like thick double sided tape.
A third option could be a domed label, those are available in different versions as well and can add a few mm to the outside of the housing.
You could also get a plastic label that comes in form of a wave, something like this: ^^^^^. The raised spots would likely stay cooler that the rest, but I don't now if thats allowed since you can still reach the hot part if you press hard.

Can you specify the orientation the power supply must be used in? If thats the case you could specify that its only to be used with the hot spot on the bottom, that could change the heat distribution in the supply.

--- End quote ---

No, unfortuantely, cannot specify orientation, so we have to pass at the worst case. Thanks.

TimNJ:

--- Quote from: OM222O on August 16, 2019, 01:21:04 pm ---you mentioned needing to seal the box for IP rating, and it seems like active cooling is the best and cheapest bet here, so here are a few suggestions that would probably help:

is there a metal plate / bar that the PSU gets mounted to? if so, can you find empty places on the aluminum heat sink that allow it to be screwed onto the plate? this doesn't give electrical isolation, but it certainly allows for IP rating.

can you leave one of the sides of the plastic box open (only pot to the top of the aluminum plate, don't go over it and seal the entire thing) and leave the aluminum plate with the hot spot exposed to some internal part of the device, then have a fan blowing directly on the hot spot?

make the copper area around the inductor larger and use thermal vias if possible, this will increase the surface area of the "hot spot" which reduces the maximum temperature.

as a basic test, buy some non conductive thermal paste and apply it around the inductor over a "large area" (about 1 inch by 1 inch should be more than good enough) to see of that reduces the temperature at all.

I don't think insulating the hotspot is a great idea, it will only create more in different parts. just try different mounting orientations so it's not where it could be touched during normal operation. if nothing else works, you should reserve to watercooling: have a pipe in the middle, or a water block that directly contacts one of the aluminum plates and soaks the heat. another alternative would be sticking a vapor chamber to the back of the aluminum plate. they are thin and very good at conducting the heat away. that way your entire aluminum plate heats up evenly, avoiding hot spots. I'm not sure if 1mm is a large enough gap, but 2 or 3mm should be more than good enough if you can fit it between the plastic and the aluminum.

--- End quote ---

Active cooling as in a fan? This is an external power supply. Looks like a laptop power brick essentially. It does not have a permanent mounting location. It can be placed wherever the user wants...on the ground, in a corner, on a table, etc. I like your idea about using the PCB area as additional heatsinking. Maybe some fine tuning can be done there, though I think the thermal resistance from the inductor to the board is pretty high.

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