Heatsink question

[Broham1]

I'm at the tail end of my build: wiring components in the control box.

I have the Auber project box (Pbox16), the 40A SSR, and the Auber heatsink.
Can I avoid cutting the back panel and just sandwich it with the SSR on the inside and the heatsink on the outside? Does that still give the same heat dissipation?

 

[BetterSense]

What are you driving with it?

In theory, no; but you might be ok with no heatsink at all, so putting it on the outside would be fine.

 

[Broham1]

1 5500W element.

 

[ajdelange]

Can I avoid cutting the back panel and just sandwich it with the SSR on the inside and the heatsink on the outside? Does that still give the same heat dissipation?

Almost. Engineers talk of 'thermal impedance'. This is a number expressed in °/watt. If the device dissipates 10 watts and you have a thermal impedance of 1 °/watt the device will be at 10 °C above the ambient. The thermal 'circuit' starts with the actual heat dissipating device and the heat then flows through the connection between the die and the case, between the case and the heatsink and between the heatsink and the ambient air. There is a 'rise' associated with each connection. If you bolt the SSR to the inside of the chassis and the heat sink to the outside then you have introduced 2 more thermal impedances: SSR to chassis and chassis to heatsink. There will be a rise across each of those. But, in bolting the SSR to the chassis you gain conductivity to the ambient i.e. you have put the thermal impedance between the chassis and the ambient in parallel with the thermal impedance between the chassis and ambient through the heatsink. This extra conductance may more than offset the extra impedances so, in fact, the SSR may run cooler. The obvious thing to do is run the SSR on the heatsink under full load and measure its temperature (when that equalizes), attach it to the chassis without the heatsink, put it under full load and measure its temperature, being sure to abort this experiment if its temperature starts to rise fase and then finally check it when it is mounted to the chassis with the heat sink outside. It may turn out that you don't need the heat sink at all.

For best results in any of these configurations be sure to use heat sink compound at all interfaces.

 

[Broham1]

That . . . actually . . . makes total sense! I couldn't have said that before starting this build. I'm so glad I decided to build my own. My wife, however . . .

Thanks so much. I'll try these experiments.

 

[SleepyCreekBrews]

The big question in my mind at the moment is, what's the chassis material? ...aluminum would conduct heat well, while stainless(for example) would not.

 

[Broham1]

Website says 1mm thick steel, with black powder coating.

Here's a picture:

 

[alien]

You would need to remove the coating from both surfaces. If you have the tools to do that I would suggest that you might as well cut the hole.

 

[jCOSbrew]

I have seen a few designs with that box and heat sink mounted internally.
I have a similar setup for my eBIAB panel and have had no issues with the SSR getting too hot with the internally mounted heat sink.

If the SSR w/ internal heat sink gets too hot, you could add a small fan.