To heatsink or not heatsink... That is the question!

Hey guys,

Been doing a lot of work on the environmental chambers at work and I noticed that not one of the SSRs is on a heat sink and they are all rated about double their switching load (ie 20a SSR switching 10a). I ran this by one of the EEs at work (since I'm just a dumb mechanical guy...) and he said if an SSR is mounted to a metal frame it will disipate most of the heat away. He also said that as long as you are under the switching limit the current going thru the SSR doesn't really matter that much. That 75% of headroom is no better than 25% headroom.

This begs the question: Do we need heatsinks? I think its probably the best practice but may not be entirely necessary.

Thoughts?

McC

Heatsinks become more necessary as the power level increases in the equipment. It also becomes more important as the cheapness of the SSR construction increases. I have some really nice 45a OPTO22 SSRs that can take it, but I just ordered some Fotek SSRs that I doubt would take kindly to any overheating. I think that if you're running a 20 or 30a circuit, you would be wise to include sinks to improve the SSR longevity.

I'm using 40A SSR's with my setup. Technically speaking I could have used 25A SSR's for my build. The heatsinks are mounted outside the control box and they get pretty hot. Without heatsinks the SSR's would be dead. If I was using a metal control panel I'd be concerned that it would be very hot and dangerous to use. Not part of the build I'd skimp on, nor would I get cheap with any of the electronic parts.

When I was in college, I saw a team of EE's semester-long project fizzle in approximately 10 seconds because they didn't use heatsinks on their SSRs.

McCuckerson said:

...he said if an SSR is mounted to a metal frame it will disipate most of the heat away. He also said that as long as you are under the switching limit the current going thru the SSR doesn't really matter that much. That 75% of headroom is no better than 25% headroom.

This begs the question: Do we need heatsinks? I think its probably the best practice but may not be entirely necessary.

Thoughts?

McC

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Yeah, I've seen this a lot in the industry, and it usually works fine. I would be concerned, though, as well. Did you feel the metal frame around SSR? If it's hot to the touch (as opposed to just warm), then yes you need heatsinks. I agree that it's best practice to always use heatsinks. Would it be difficult to install them?

weirdboy said:

When I was in college, I saw a team of EE's semester-long project fizzle in approximately 10 seconds because they didn't use heatsinks on their SSRs.

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LOL! Man that had to suck, poor EEs... Point well taken, I will use heatsinks....

weirdboy said:

When I was in college, I saw a team of EE's semester-long project fizzle in approximately 10 seconds because they didn't use heatsinks on their SSRs.

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EarthBound said:

Yeah, I've seen this a lot in the industry, and it usually works fine. I would be concerned, though, as well. Did you feel the metal frame around SSR? If it's hot to the touch (as opposed to just warm), then yes you need heatsinks. I agree that it's best practice to always use heatsinks. Would it be difficult to install them?

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No, not hard at all. In fact, I planned for it in my CP. Just caught me funny when he said you really don't need them. Although it sounds like you do.

I wonder if its because in industry, you just let purchasing know when you need a new SSR instead of buying another with your own money.

It depends on the specifications of the SSR. Some are made to run cooler. Most of the cheaper ones are not. The datasheet is the easiest way to figure it out. If you have enough surface area on your panel you may be able to use it as a sink, but you need to consider surface area, personel safety, and ambient air temp and airflow. I would heatsink it just to be safe though. They're cheap if you look around.

SgtB said:

They're cheap if you look around.

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Yep! It should be easy to get it for free from an old computer. That's what I've done several times.