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Home Brew Forums > Home Brewing Beer > Electric Brewing > What value does a contactor add?
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Old 09-25-2012, 02:29 AM   #1
Cromwell
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Default What value does a contactor add?

I have a PID controller that accepts 110 input, and will power an SSR. I haven't bought the SSR yet, but I did buy a couple of contactors. Looking at Kal's build, there isn't a contactor in it, but I see sometimes people use them in series with the SSR. Why? Won't an SSR drive a 5500W element directly? Does the contactor lessen the current through the SSR and somehow make it last longer? A contactor is mechanical, correct? Will it have a problem with fast switching?

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Old 09-25-2012, 03:01 AM   #2
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The way I have mine wired is after the ssr. That way you can kill ALL power to that plug. Also by doing it that way you are putting a much lower load on the switch.

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Old 09-25-2012, 12:37 PM   #3
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You are normally only switching one leg of the 240V with the SSR.
The contactors used in kals setup are 2P (they switch 2 wires).

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Old 09-25-2012, 02:42 PM   #4
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Think of the contactor as an interlock.

There are 2 primary issues with SSR's:
First, when SSR's fail, they tend to fail "closed" (Hot) - Leaving you with no way to shut off your element. The contactor is a positive disconnect when you think the system is "off"
Second, SSR's never really turn off. There is always some leakage through them. The contactor in that case, gives you confidence that there is NO voltage at the element.

The contactors aren't used for fast switching - That's the SSR's job. They simply "Enable" the SSR to Element connection when the system is "Armed", for lack of a better term.

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What does the primary pressure gauge on the tank tell us? That's right, the temperature. Put it on a scale if you want to know how much is in it...
Put some duct tape over the gauge - Or better yet - Replace the high pressure gauge with a plug - High pressure gauges are useless!
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Old 09-25-2012, 02:49 PM   #5
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Quote:
Originally Posted by SweetSounds View Post
Think of the contactor as an interlock.

There are 2 primary issues with SSR's:
First, when SSR's fail, they tend to fail "closed" (Hot) - Leaving you with no way to shut off your element. The contactor is a positive disconnect when you think the system is "off"
Second, SSR's never really turn off. There is always some leakage through them. The contactor in that case, gives you confidence that there is NO voltage at the element.

The contactors aren't used for fast switching - That's the SSR's job. They simply "Enable" the SSR to Element connection when the system is "Armed", for lack of a better term.
Ok that helps, but this makes me think the contactor shuts off current to the SSR, and maybe even the PID. If the contactor is after the SSR as I see in most wiring diagrams, it's going to have to switch just as fast as the SSR, right?
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Old 09-25-2012, 02:52 PM   #6
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Ok that helps, but this makes me think the contactor shuts off current to the SSR, and maybe even the PID. If the contactor is after the SSR as I see in most wiring diagrams, it's going to have to switch just as fast as the SSR, right?
No - The contactor is controlled by a different switch. The PID drives the SSR, a switch "Enables" the contactor.

You can't move a contactor that fast - It's too much mass inside.

Placing the contactor before or after the SSR (Speaking of the high voltage side) is irrelevant. What is important is that you have the ability to turn a switch "Off", and know that there is no power at the element.

Link the diagram you're using - I can explain better with pictures
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What does the primary pressure gauge on the tank tell us? That's right, the temperature. Put it on a scale if you want to know how much is in it...
Put some duct tape over the gauge - Or better yet - Replace the high pressure gauge with a plug - High pressure gauges are useless!
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Old 09-25-2012, 04:12 PM   #7
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I designed on the side of caution. A main contactor is connected to the 50A service input to my power panel. Each of the two element legs are switched by separate SSRs and the SSR outputs are passed through a douple pole single throw relay (sized appropriately). This way, depending on my control panel switch positions, each element outlet is dead individually or with one quick slap of an e-stop switch all 240V items are dead.

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Old 09-25-2012, 04:25 PM   #8
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Sounds like you got it figured out

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Originally Posted by Ecnerwal View Post
What does the primary pressure gauge on the tank tell us? That's right, the temperature. Put it on a scale if you want to know how much is in it...
Put some duct tape over the gauge - Or better yet - Replace the high pressure gauge with a plug - High pressure gauges are useless!
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Old 09-27-2012, 08:43 PM   #9
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think of a contactor as the 20amp circuit breaker in your main electrical panel, and the SSR as the wall switch in your living room. both can turn the desk lamp on and off, but its easier and faster to use the wall switch.

(thats a bit of an over-simplification, but you get the idea...)

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