How much heat sink?

[BottleFed70]

Originally Posted by ed_denu

I considered doing this awhile back, but I couldn't come up with an acceptable way of providing dc power to the computer fan. I first thought about building my own internal dc power supply using a transformer, bridge rectifier, etc. then I looked at a transformerless power circuit. Finally I considered adding a 120vac receptacle to the control panel and using a pre-made plug-in ac to dc adapter.

How did you accomplish this?

I put a 120V AC to 12V DC wall adapter inside my control box. It's powered on the same circuit as the elements so that it's only on when the elements are.

[CarWiz]

Originally Posted by BottleFed70

I put a 120V AC to 12V DC wall adapter inside my control box. It's powered on the same circuit as the elements so that it's only on when the elements are.

That may not be such a great plan. The PID can pulse the heaters quite often. (Sometimes at a rate in seconds.) Not only is this hard on your power supply but also won't purge heat built up in the heat sink if your fan never gets to full speed. Having the fan come on when main power is applied won't substantially increase your cost to operate. And your power supply will like you more for it too.

[BottleFed70]

Originally Posted by CarWiz

That may not be such a great plan. The PID can pulse the heaters quite often. (Sometimes at a rate in seconds.) Not only is this hard on your power supply but also won't purge heat built up in the heat sink if your fan never gets to full speed. Having the fan come on when main power is applied won't substantially increase your cost to operate. And your power supply will like you more for it too.

Yeah it pulses them fairly often. The AC adapter is rated such that it could power 5 of those fans without a problem. So I don't think the pulsing will hurt it much. The fan keeps spinning for a while with no power applied, so it keeps spinning between pulses.

I think the CPU heatsink without any fan would be more than enough for proper cooling. I just decided to use the fan because it was easy, and I was a little paranoid after my 1st SSR blew up.

The oven has approx 50hrs on it, so far the fan hasn't shown any signs of giving up. If it does fail, I'll make sure to post here.

[damfast]

im haveing this exact same problem...what sis ya find out..Ive been through 2 40 amp ssrs and they were on a heat sink that came with them...I have 3 2600 watt burners and am guessing i need a larger ssr... It blows in the first min or two.

[CarWiz]

Originally Posted by damfast

im haveing this exact same problem...what sis ya find out..Ive been through 2 40 amp ssrs and they were on a heat sink that came with them...I have 3 2600 watt burners and am guessing i need a larger ssr... It blows in the first min or two.

You're over the limit with a "good" heat sink.
"...they were on a heat sink that came with them" What does the heat sink look like? If you're talking about that little metal base of the ssr, that's NOT a heat sink!

[CarWiz]

Originally Posted by BottleFed70

The AC adapter is rated such that it could power 5 of those fans without a problem. So I don't think the pulsing will hurt it much.

The rating doesn't mean a thing. It's the flashing power up cycle that will kill the power supply.

[damfast]

yeah it is a real heat sink...i ordered a 75 amp today so what percent usage will i be at now?

[ed_denu]

Originally Posted by damfast

yeah it is a real heat sink...i ordered a 75 amp today so what percent usage will i be at now?

32.5 amps on a 75a rated ssr = 43%

[damfast]

thanks for your help...should i run a 40 amp breaker then?

[ed_denu]

Originally Posted by damfast

thanks for your help...should i run a 40 amp breaker then?

Yes - with appropriate 8 awg wire.

You still need a heat sink also.