Question About sheet metal

[ed_denu]

Since you are looking to purchase both the PID and SSR from auber you might want to ask them this question before proceeding with your selections. The SSR you note has an input voltage requirement of 4-32 VDC while the PID only shows an output voltage of 240vac or 120vac. The PID may be capable of supplying an output DC voltage but the description doesn't state that.

I believe this is the model you need to go with the SSR you selected. It is similar but the difference is it is capable of supplying a 12VDC output voltage.

http://auberins.com/index.php?main_p...&products_id=3


Ed

[PhredAre]

Eds got it figured out, the only other thing that may develop is the fact that that SSR has no heat sink, so, you may have to detune your PID to prevent damaging the SSR when at the set point temp. The PID will pulse the SSR to maintain that set pt, generating a lot of heat in the SSR. A lot of SSRs are derated from their advertized amp rating without a heat sink. Don't forget a TC. Fred

[eclipsespeed]

Oh I didn’t even catch that. Thanks a lot. And yes I was going to get the K type TC. And I was planning on getting a Heat Sink for the SSR, but they only had them for 25A SSR's so I was going to look around a bit.

Do either of you know if the heat sinks are SSR specific, or will any 75A heat sink work. If so would you happen to have link to one you might recommend.

Thanks
Keith

[FigureLLC]

i just offered the bit about rivets for no real reason. i don't know that they offer any advantages over sheet metal screws or tack welding, etc., besides i thought they'd be faster and we don't have a welder. i used screws in some places. mainly where i couldn't fit the rivet gun. i said the part about aluminum because after i started with the aluminum, i thought i remembered reading not to use aluminum rivets in steel, but so far it seems rock solid with no warping. i said i used 1/8" because i wasn't sure what to use before i started.

[ed_denu]

Any larger heat sink should work although they tend to be rather pricey. There's nothing special about ssr's that require a unique design. I actually made one for my ssr out of aluminum stock.

[eclipsespeed]

So could i just use a heat sink with a fan off of a regular computer CPU. I have quite a few of those laying around. And how do i know if the heat sink is big enough. Is there a certain temp range im shooting for with the SSR.

Thanks,
Keith

[ed_denu]

You might be able to use a computer fan/heat sink. The problem would be adapting it to the ssr. The ssr normally wants the heat sink mounted under it, while the computer heat sink/fan mounts on top of the processor.

If you can find the tech sheet for the ssr it will list the heat range for it. I believe mine was -20 to +80C. I used an IR thermometer it check the temperature. You could also use a temperature probe.

A lot of the heat generation depends on how close to the maximum amps you are driving the ssr. Without putting it together and testing it I'm not sure how you can know for sure.

[jabe421]

This is one of those cases of "the bigger the better" the cooler you can keep the SSR the better. I had a 100watt class A amplifier that went out on me a little while ago. I pulled the heat sinks and cut one about twice the size of the SSR. It works great.

Also, I used a thermal compound between the heat sink and the SSR.

[CarWiz]

Yep, the cooler the better. Once the SSR gets over about 100*F, the load capacity drops very fast. The SSR dissipates about 1W for every Amp of load. (Closer to 1.2) So a 50A SSR dissipates about 60W at full load. That's a lot of heat. As a "general rule", you need about 3 square inches of surface area per watt. That's where a cooling fan can really help in a small space or when multiple SSRs are used. It allows reduction of surface area.

Here's the suggested heat sink for a 50A SSR as provided by Omega. Other mfgs. might vary.

[PhredAre]

McMaster sells a 50 amp relay with a built in heatsink. It would be a single pole relay rated 50 amp @230volts with a 5 to 32 vdc operating voltage. If you were to switch just one side of the elements I believe this would do what you want to do. By doing it this way the elements would be energized with a voltage of 115 when not heating, and 230 when heating. The cost is $90., but, you sure could try the relay that you were looking at with the heat sink that was suggested. Just retrofit the relay with the best heat sink you can come up with, make sure you use some good heat conducting adheasive, the fan sounds like a good idea. You might consider putting the heat sink on top(heat rises). The ssr is the most expensive single item on my oven. Fred