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SSR or EMR

SSR or EMR

(OP)
We have a big Washer in our Heat Treat room. There is a 100amp relay or contactor that is turning on and off every minute. Yeah I know, but that's the way the machine came brand new. They also sent a replacement contactor because they said it would go out in 6 months. I am looking into a different setup. I replaced some other contactors with a mercury style that are still working on another machine that was cycling a lot also. The problem with an SSR is that if the SSR goes out they usually go out shorted and the contactor is running heaters, which would not be good. Anyone have a different idea?

RE: SSR or EMR

IRstuff, time proportional on-off control of heaters to control temperature is very common. A one minute cycle time is also common when using mechanical contactors. 5 or 10 second cycle times are more common with solid state relays.

Deetz, use an SSR for temperature control in series with a contactor for over temperature control. Can you still even buy mercury contactors any longer? Environmental regulators have been very aggressive in removing mercury from commerce wherever possible.

RE: SSR or EMR

Use an SSR controlled by a simple controller, and back it up with a contactor energised through a supervisory overheat stat with a manual trip reset. No wear and tear on the contactor, and protects against the shorted SSR problem. I think this may be what Compositepro was alluding to.

RE: SSR or EMR

Yes, Scotty.

RE: SSR or EMR

I totally agree with Compositepro.

Ditch the mercury contactor.

Reinstall the original contactor.

CORRECTLY install a Solid State Relay rated at 100 or 120A.

Purchase and install a second device called a "process alarm" used as an over temperature monitor that only controls the original contactor, dropping it during an over temperature event.

Here's some examples, some of which are 3phase and some are single phase and would, of course, require three.


http://www.thyristorscr.com/product/three-phase-solid-state-relays_id16.html

Digikey SSR search

Keith Cress
kcress - http://www.flaminsystems.com

RE: SSR or EMR

Quote (IRstuff)

Ok, but what was the manufacturer's recommendation? Is that what they did in the original installation, and if not, why?
Because its cheaper to just use a single contactor and even give the customer their "first" replacement for free..
Then on top of that they get a revenue stream from all the replacement contactors they sell to their customers over the years of use.. 2thumbsup

RE: SSR or EMR

You are as cynical as me.

Well, almost. wink

RE: SSR or EMR

2
A graphic of what ScottyUK describes:



A limit controller needs to be manually reset after it trips (on high temp); its output drives the contactor which interlocks the energy going to the heater.

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