SSR and heatsink inside control box?

I've tried searching for this, but haven't found anything that definitively (for me, at least) answers the question.

I'm planning on using a 12" x 12" x 6" plastic junction box. I've got 2 40A SSR's and heatsinks from Auber, which will send power to each leg of a 4500W ULWD element. This element will be used in a combination MLT/BK, for mash heating and boiling.

The SSR's will reside in the control box with a row of 5 DIN-rail circuit breakers (one a double pole), a row of DIN-rail terminal blocks, and the back side of an Auber PID, 5 SPST switches, a 220V outlet, and 4 110V outlets.

I understand that putting the heatsinks on the outside of the box (by mounting the SSR's and heat sinks to opposite sides of an aluminum plate with silicone grease, which is mounted in a hole in the plastic box) is the technically ideal method. However, I'd really like to keep everything within the box itself, mostly due to space concerns (and, to a lesser extent, aesthetics).

Any and all suggestions are welcome. Thanks!

How tall is the SSR\Heatsink combo? Will it fit? I would also be worried about the heat. You may need some air movement in the box.

Mounting the heatsinks inside is no problem but you'll need ventilation to draw the heat out.

My understanding is that they heat up when switching. The faster they switch, the more heat they give off. I'd second the suggestion of a fan to force ventilation probably. Heat kills electronic components.

Hermit said:

My understanding is that they heat up when switching. The faster they switch, the more heat they give off. I'd second the suggestion of a fan to force ventilation probably. Heat kills electronic components.

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+1 If you mount it in the box with no holes for ventilation or no forced cooling via a fan, don't blame us when something inside the box fails due to heat stress.

They will heatup when in a steady on state because the internal components create a small voltage drop on the load side and some of that is wasted as heat. As previously stated the heat generation is proportional to the current passing through the SSR.

Mounting them outside of the box will free up a lot of space. Seems like a big box until you start filling it up with stuff. Buy the size box you think you need then add 30-50% more space for future use and ease of working inside.

I thought as much. Like I said, I know that the proper way is mounting the heat sinks externally. I was just curious if anyone had mounted them internally without issue.

Let's not confuse the issue to much but external doesn't have to be the right way of doing it. Enclosed with forced circulation may well be better if done properly. It is about air movement across the heat sync. Just because it is out of the box doesn't mean you will get better air movement. Well, it does if you don't ventilate the box.

I agree that internal heat sinks with forced-air ventilation would be fine, but drilling holes for said ventilation would negate any water-resistance-ness, which is of a higher priority than looks.

I think I'll just cut the topmost plate off the heat sinks (opposite the SSR end), mount them on the outside, and call it a day.