How much heat sink?

[peter61]

Ok,I built my oven 72"x32"x32" it has 3 2800 watt burners the ssr I got for it is a 40amp one,heres the problem I fired it up,the burners started to get warm and then the relay blew up!The center of the relay blew out,the wires and connectors are fine,i had it mounted in a steel junction box on the side of my oven,did I need heat sink?if so how much,thanks.

[JTW37]

Cna't tell you why that happened, but here is a link to a controll box with SSR on heat sink. Pro Built.
http://forum.caswellplating.com/atta...5&d=1200853901

[ed_denu]

The 35 amps you were putting thru the 40 amp ssr is definitely to great, especially without a heat sink. 80% of maximum is normally a good target to shoot for. Here is a link to determining a proper heat sink size:

http://www.omega.com/temperature/Z/pdf/z119-121.pdf

Or do as JTW37 suggested and purchase an SSR and heatsink combination. I would recommend something larger than 40 amps based on your load.

[JTW37]

Here is a useful link I just found, thanks to ed_denu. Tells you about the heat sink your seeking.

http://www.omega.com/ppt/pptsc.asp?r...660&Nav=heac01

[rowdenboyz]

Same thing happened to me. Oven ran for a few minutes then the SSR exploded. Bought new one and installed heatsink and its fine now.

[peter61]

Doyou have a picture of the heat sink you installed?

[rowdenboyz]

I tore down an old desktop computer and took the heatsink off of the processor. I think they all have them. Just dab a little thermal paste on it and your set. The heatsink I took out even had a small fan mounted to the back, but I didn't have room for it.

[peter61]

Where is your control box mounted?Mines mounted to the side of my oven but the box is made of 16 gage metal.

[PhredAre]

I question these failures that are happening in the first few minutes of energizing the oven, and laying blame onto the lack of a heatsink. Unless the SSR is pulsing at the begining of the heat cycle it dosn't generate much heat. Further more it takes time for the heat to migrate into the heat sink and transfer into the air. My thought is the SSR is defective if it fails in the first few minutes of use, provided its not overloaded. When a new SSR is purchased with a built in heatsink we are probally purchasing a better quality device. That old saying applys ;" You get what you pay for ", Fred

[BottleFed70]

Originally Posted by PhredAre

I question these failures that are happening in the first few minutes of energizing the oven, and laying blame onto the lack of a heatsink. Unless the SSR is pulsing at the begining of the heat cycle it dosn't generate much heat. Further more it takes time for the heat to migrate into the heat sink and transfer into the air. My thought is the SSR is defective if it fails in the first few minutes of use, provided its not overloaded. When a new SSR is purchased with a built in heatsink we are probally purchasing a better quality device. That old saying applys ;" You get what you pay for ", Fred

No... the problems are due to lack of a proper heatsink.

SSR's DO generate a lot of heat. And they generate the most heat when at 100% duty cycle, not when pulsing.

If you look at spec sheets, they all say that a heat sink is reccomended for all appliacations and is required if running anything more than 20% of the SSR's rating. At more than 75% of the rating, you need a very good heat sink. Typically a large portion of an SSR's datasheet is dedicated to heat-sinking.

For the record, I also used an old CPU heatsink and cooling fan after burning up my 1st SSR due to improper heat sinking. Works absolutely perfect and the SSR doesn't even get warm anymore.