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Old 12-02-2012, 09:44 PM   #1
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Default SSR Heat Sinks on the Inside of the Box

I am looking at this single PID box from Auber and it looks like they have the SSR heatsink on the inside of the box. Is this simply screwed into the casing?

Does the heatsink not heat up the box?

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Old 12-02-2012, 09:53 PM   #2
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We run 5 SSRs with heat sinks in a our system with two cooling fans in the box. Even without the fans the SSRs do not get overly warm in PWM settings where you would think they would warm up so I doubt the box you show will heat up much.

With the fans in our system on there is very minimal noticeable heat on the sinks or in the exhaust air. This is all running 4500 and 5500 W elements. A photo of our layout follows, in the lower right of the box there is a fan pulling air in, just to the left of the DIN heat sink row there is a fan exhausting air out (hard to see).

Hope this helps.

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Old 12-02-2012, 09:58 PM   #3
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I don't know what kind of magic the master above is using, but the heatsink will get hot. If it is inside the box without air flow, the whole box will get hot. This might not be a problem for you, but there are lots of situations where it might be.

I had the heat sink inside the box at one time and I had problems with the heat affecting my PID, specifically thermocouple readings.

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Old 12-02-2012, 10:21 PM   #4
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A metal box will dissipate heat to a degree and an oversized SSR won't put out as much heat as one running closer to its limit. Also, that Auber box has some vents on the back and little rubber feet which allow some air flow underneath.

It might be fine but I think it's better to mount to an external heat sink. It doesn't hurt to go larger on the heat sink either. I used a huge one that I had and it doesn't even get warm that I can tell.

I've seen a number of people here with it set up exactly like that picture-same Auber stuff, so maybe they'll chime in with how things are holding up.

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Old 12-02-2012, 11:19 PM   #5
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Quote:
I don't know what kind of magic the master above is using
makes laugh... PFM if you know the acronym...

On a more serious note the SSRs will create heat and lots of it if running near capacity. I was not clear. We are using over sized SSRs, the cost is little to do so and we do used oversized units.

We tested with SSRs rated for just above the load for a 5500 W element and the sink does get hot but we never had problems with excessive heat even with fans powered off. But.. this said we have two huge holes that I would guess allow lots of air flow due to convection even without the fans running.

I do not know the exact PID you are using, but I would guess the reason you had problems with the PIDs is that you are getting the overall PID over temp or getting the cold junction (if thermocouple used) temperature out of the PIDs capability when your SSRs heat up the enclosure.

Brewing up some more MAGIC now!!...

Cheers
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Old 12-02-2012, 11:38 PM   #6
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I use an Auber PID and Crydom SSRs.

PWM is what my PID uses to modulate the power. Set frequency, variable duty cycle. I thought that's how all of them worked.

Yes, the cold junction in the PID was getting warmer than the connector for the thermocouple, and this did cause problems. That's when I moved the heat sinks outside the box. Problem solved. RTD/thermistor sensors are resistive and immune to this problem.


Quote:
Originally Posted by brewmastercontrols View Post
makes laugh... PFM if you know the acronym...

On a more serious note the SSRs will create heat and lots of it if running near capacity. I was not clear. We are using over sized SSRs, the cost is little to do so and we do used oversized units.

We tested with SSRs rated for just above the load for a 5500 W element and the sink does get hot but we never had problems with excessive heat even with fans powered off. But.. this said we have two huge holes that I would guess allow lots of air flow due to convection even without the fans running.

I do not know the exact PID you are using, but I would guess the reason you had problems with the PIDs is that you are getting the overall PID over temp or getting the cold junction (if thermocouple used) temperature out of the PIDs capability when your SSRs heat up the enclosure.

Brewing up some more MAGIC now!!...

Cheers
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Old 12-03-2012, 12:04 AM   #7
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Good solution?
External Mount Heat Sink for 40A SSR
Problem solved.

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Old 12-03-2012, 03:57 AM   #8
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Obviously the external mount will work the best, but I'd like to use the smaller box. I'm assuming that I'll be alright if I just mount it to the interior.

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Old 12-03-2012, 05:00 AM   #9
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Quote:
Originally Posted by Chugmaster View Post
Obviously the external mount will work the best, but I'd like to use the smaller box. I'm assuming that I'll be alright if I just mount it to the interior.
You can use the Auber box (if that's what you mean) and mount an external heat sink.

http://www.homebrewtalk.com/f170/sug...ml#post2998542
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Old 12-03-2012, 01:48 PM   #10
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There are ways to adequately ventilate an SSR/heat sink combination in a box, but as mentioned above it requires fans and holes in the enclosure. I prefer to keep the heat sink outside because:

(1) You no longer have a NEMA 4/12 or IP65 water resistant / water proof box because you had to install a fan. (There's no way to way make a fan water resistant from the very nature of what a fan is). Make sure your box is as far as possible from any water sources. Accidents happen.

(2) Fans don't last forever. Out of all the devices you may stick in a box, they have likely the lowest lifespan. Use a good industrial fan if you can (rated for thousands or tens of thousands of hours), not some cheap $5 one you stole from one cheap desktop PC. Use a finger guard too (like in the picture above). If you do use a fan I'd recommend something with a control line that doesn't allow the box to be used if the fan has died.

(3) Dust. When using a fan you're moving air continously through the enclosure to cool so you'll get dust build-up. Dust is a great insulator which causes things to run hotter so if you use a fan open it up once and a while and give it a good cleaning (just like you do with a desktop PC).

(4) Component lifespan. With an SSR inside the box, you need to make sure that you ventilate adequately not just for the SSR/heatsink in question for but everything else in the box. This is true of regardless how you build your box (heatsink inside or out). Electronics will last longer if run cooler. While manufacturers of parts will have temperature ranges within which their stuff is intended to be used, generally speaking the cooler you run electronics, the longer it lasts. In the home theater forums I visit I often see people post that as long as a certain product is running within the manufacturer's ambient recommendated range, that it's ok. Not true. Run that amp/receiver/PS3 (or whatever) at 70F ambient instead of 100F ambient (because you enclosed it in a cabinet) and it may last 10 years instead of 5. The biggest issue is electrolytic caps which dry out over time. They dry out regardless, it's just a question of how fast. Heat speeds up this process.

Your needs may be different so some of these "cons" may not matter. Always weigh your own needs against what you intend to do and see if there's any "gotchas" that affect the way you like to brew.

Kal

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