I am using SSR's for the first time. One for the boil element and one for the HLT. I have a 12x12 PVC box to mount everything in. Do I NEED to vent the box? How much heat do these things generate?
SSR cooling
- Thread starter lschiavo
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SOB
Well-Known Member
They can get pretty hot...I am assuming you are putting heat sinks on them? If you mount them in the box you need some kind of air circulation. You could always mount the SSRs in the box with the heat sinks out of the box.
Heat sinks won't do much if they are inside the box.
I had a metal box of about the same size. I mounted the SSRs right to the metal box. It still got hot as hell. The heat affected the accuracy of the Auber thermocouple measurements by at least 10F. So, I would answer yes, you need heat sinks and they need to be outside the box. If you do it this way, you do not need to vent the box. My toolbox is unvented.
I had a metal box of about the same size. I mounted the SSRs right to the metal box. It still got hot as hell. The heat affected the accuracy of the Auber thermocouple measurements by at least 10F. So, I would answer yes, you need heat sinks and they need to be outside the box. If you do it this way, you do not need to vent the box. My toolbox is unvented.
OP
OP
I dont really want the sinks hanging out of the box. The heat sinks are meant to mount on DIN rails so I assume they are meant to mount inside an enclosure. I guess I will put in a computer fan and vent. Will they actually fail from excessive heat?
missing link
Well-Known Member
The heat will most definitely cause them to fail and when they fail, mine have failed in the on position. This also cooked a heating element when powering my system since the pumps hadn't primed.
Linc
Linc
I think it also depends on the size of the enclosure and backplate. My box is larger (16 X 20). I have two 40 amp SSRs mounted on generous heat sinks which are in turn mounted on the backplate. I have no air circulation or ventilation. My enclosure never even gets warm. My enclosure is metal and this will also conduct heat which aids in dissipation.
If you use a fan and vent the box you'll probably be OK. I was stating that if you put the heat sinks inside the box without ventilation, then you'd have a problem.
OP
OP
Yeah, a PVC box is a good insulator. If I had a metal box, I think with proper mounting, I would be ok. I probably will put in a fan/vent.
OP
OP
Right. I understand. I guess that is the route I will take.
Thanks for the help guys.
FYI, all AC SSR's dissapate about 1.5W per amp current (this is probably worst case, but best for calculations).
Heat sinks are rated in °C/W. For example, my heat sink is 0.7 °C/W. This is without forced air.
My element draws 23A. So, the SSR will need to dissapate 23*1.5 or about 35W. The resulting temperature rise (over ambient temperature) will be 35W * 0.7 °C/W or 25C.
The SSR is rated for maximum temp, so you want to be mindful of this.
Heat sinks are rated in °C/W. For example, my heat sink is 0.7 °C/W. This is without forced air.
My element draws 23A. So, the SSR will need to dissapate 23*1.5 or about 35W. The resulting temperature rise (over ambient temperature) will be 35W * 0.7 °C/W or 25C.
The SSR is rated for maximum temp, so you want to be mindful of this.
OP
OP
Good info. Thanks. I need w calculator to get to F though. My ssrs came straight from some Guy in China with no specs. There should be a sticky on ssr's.
