Are heatsinks necessary for my temperature controller build?

[Derp]

Please save me from over-engineering my Raspberry Pi and Arduino-based chest freezer controller.

I have a 15 cubic foot chest freezer that uses a 50-watt reptile heater as a heat source. I decided to use a couple of cheap 25-amp SSRs to control the heating and cooling outlets. I figured that the freezer would draw up to 10 amps for a few seconds while starting up, before dropping to an amp or so. I mounted the SSRs to some heavy duty velcro on the inside of the thick plastic enclosure and figured that would be good enough. Then paranoia set in: what if the tiny bit of heat generated by the SSRs eventually loosened the velcro's adhesive and they fell into the box and managed to arc and spark and burn my house down?

So I decided to remove the velcro and install external heatsinks. I gained a lot of respect for the velcro's adhesive, as it was so sticky that I managed to separate one of the SSRs from its plastic housing. Oops.

I had a couple of nice 40-amp SSRs sitting around after an aborted electric brewing controller build, so I've decided to use them in place of the 25-amp cheapies for this build.

Here's my question: Can I just screw the SSRs to the large plastic enclosure and call it good? I don't think much heat will be generated while operating the freezer and I've just realized what a pain it will be to mount the SSRs and heatsinks through the enclosure. The best idea I could come up with would involve a metal plate and a lot of cutting and drilling.

Will it be safe to just mount the SSRs to the plastic enclosure without any heatsinks? Please either reassure me, or tell me that it's a stupid idea. Thanks!

 

[Smellyglove]

I'd use a DIN-rail. I have one SSR in my pretty small controller enclosure (comparing to what many here are rockin'), it sits on a heatsink, which is DIN-rail compatible. Inside the box, no extra ventilation or such, doesn't get warm. It's a 25A SSR, and I pull about 13,5A @220ish volts = just below 3000W

 

[Derp]

I'd use a DIN-rail. I have one SSR in my pretty small controller enclosure (comparing to what many here are rockin'), it sits on a heatsink, which is DIN-rail compatible. Inside the box, no extra ventilation or such, doesn't get warm. It's a 25A SSR, and I pull about 13,5A @220ish volts = just below 3000W

13.5 amps at 220 volts? Is that for a chest freezer or an electric brewing setup?

 

[Smellyglove]

13.5 amps at 220 volts? Is that for a chest freezer or an electric brewing setup?

It's for an electric brewing setup. But the point was that that amount of effect works fine within my closure. A chest freezer does not pull anyway near that amount.

 

[Derp]

My main question is whether it is safe to mount the SSRs flat to the enclosure wall without a heatsink. I know that the amount of heat that will be generated will be small, but I'm hoping that someone can confirm that a chest freezer doesn't need any heatsinks at all.

 

[rkhanso]

I don't know the answer to your question.....

but - I would not screw an SSR to a plastic mount/housing regardless of how much current I thought would flow and a guess on how much heat that would create. If something unforeseen happens, that plastic could melt and there goes your mounting and sparks/fire starts.

I'd err on more safety than less. What happens when there's a problem with the freezer and the draw is too high and it suddenly does create a lot of heat in the SSR? Or if the SSR itself goes bad and somehow creates a lot of heat. I'd prefer to mount it to a metal housing at the least, but preferably a proper heat sink.

I tend to live dangerously in other areas of life, but for something like this - I'd try to keep more to standard safe practices.

 

[Smellyglove]

My main question is whether it is safe to mount the SSRs flat to the enclosure wall without a heatsink. I know that the amount of heat that will be generated will be small, but I'm hoping that someone can confirm that a chest freezer doesn't need any heatsinks at all.

Right, sorry. I'd still use an DIN-rail though, because thats more "proper" way to do it. Get at least some air in between there. Or if you mount it straight onto the chasis You'd use the whole cabinet as a heatsinkt, which is better, but I don't find that that's a "proper" way to do it. So my answer would be "no" . I don't think a dedicated heatsink should be necessary at all for a freezer though. But I like to do it "over-safe"

 

[Derp]

I would not screw an SSR to a plastic mount/housing regardless of how much current I thought would flow and a guess on how much heat that would create. If something unforeseen happens, that plastic could melt and there goes your mounting and sparks/fire starts.

I'd err on more safety than less. What happens when there's a problem with the freezer and the draw is too high and it suddenly does create a lot of heat in the SSR? Or if the SSR itself goes bad and somehow creates a lot of heat. I'd prefer to mount it to a metal housing at the least, but preferably a proper heat sink.

It's an indoor/outdoor junction box that says it's rated for 194F ambient temperature, so I doubt there's any way that I could get it to melt with the heat generated by two SSRs. I think the rule of thumb is about a watt per amp, so even at 10 amps it's not a lot of heat. The freezer is on a 15-amp circuit, so it would blow before the SSR got too hot. That said, I guess I'll mount it on a rail just to be safe. The SSR doesn't have a DIN mount, but the heatsink does. That'll mean mounting the whole thing inside the box and it'll make things a tight fit, but I'll make it work somehow. Thanks for your suggestions.