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Old 01-24-2011, 05:31 PM   #1
burglar
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Default Mercury contactor vs. SSR

This will be my first in a long line of questions for my build.

I see that almost everyone uses SSRs to control their elements. At my work we use mercury contactors quite often because of their long life.

As a mechanically minded guy, I'd feel safer using one of these over an SSR. Any reason not to use one?

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Old 01-24-2011, 09:31 PM   #2
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If you can get them with low voltage DC coils, then they should work fine and a PID could control it exactly like they control SSRs.

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Old 01-25-2011, 01:10 AM   #3
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Sorr y for being devils advocate, but won't they wear out being switched so frequently? Also, wouldn't the sound get annoying? It seems most people around here use a combination of the two to keep things safe.

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Old 01-25-2011, 03:25 AM   #4
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My PID is set up on 1 sec cycles. I don't think a contactor would last very long being switched once a second. I use contactors for a hard on/off and SSRs for control.

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Old 01-25-2011, 04:04 AM   #5
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He is not talking about a mechanical relay he is talking about mercury contacts.

http://www.plasticservices.com/techtips/contactors.htm

We use them in our lab for high voltage lightning surges. For brewing simple I would stick with an SSR.

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Old 01-25-2011, 04:53 AM   #6
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Quote:
Originally Posted by stevehaun View Post
My PID is set up on 1 sec cycles. I don't think a contactor would last very long being switched once a second. I use contactors for a hard on/off and SSRs for control.
1 sec cycle time does not mean the PID is continuously switching ON/OFF every second.

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Originally Posted by gunner65
We use them in our lab for high voltage lightning surges. For brewing simple I would stick with an SSR.
I have used them on molding machines and the single and dual coil versions I have start at $85.00.
The SSR is a better choice for us hombrewers, cheaper and not so bulky.

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Old 01-25-2011, 05:39 AM   #7
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Quote:
Originally Posted by ClaudiusB View Post
1 sec cycle time does not mean the PID is continuously switching ON/OFF every second.
You want to maintain a steady boil. I do stove top. If I turn my control down to 90% the off cycle is noticeable. A one second duty cycle is reasonable. Think 50% to 70% power depending on element size and boil size. You would be turning off once a second. I have NO idea on your design parameters. Just throwing this into the thought process.
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Old 01-25-2011, 12:49 PM   #8
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Thanks guys, I'm looking at the manual for the Auber and it reccomends a 2 second cycle time for an SSR and a minimum of 20 seconds for a mercury relay on manual mode. Big difference!

The SSR will give me much finer control of the boil.

Lesson learned: don't try and reinvent the wheel.

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Old 01-26-2011, 02:48 AM   #9
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When I run my PID in manual mode, SSRs switch on/off once a second. I have it set up on a one second cycle. If I run on 90% power, the SSR is "on" for 0.9 sec and "off" for 0.1 sec. If I run my PID on anything longer than a 2 sec cycle, I can see the boil surge and stop when the SSR is "on" and "off". If I run the PID to control to a defined temp, then the SSRs do not switch on/off once a second.

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