Mercury contactor vs. SSR

burglar · Jan 24, 2011

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?

Walker · Jan 24, 2011

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.

ScubaSteve · Jan 24, 2011

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.

stevehaun · Jan 24, 2011

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.

gunner65 · Jan 24, 2011

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.

ClaudiusB · Jan 24, 2011

stevehaun said:
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.

gunner65 said:
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.

Cheers,
ClaudiusB

Hermit · Jan 25, 2011

ClaudiusB said:
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.

burglar · Jan 25, 2011

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.

stevehaun · Jan 25, 2011

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.

Mercury contactor vs. SSR

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