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Old 06-01-2012, 06:56 PM   #1
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Default Power circuit design idea

I have attached a diagram for a power circuit that I'd like to get some opinions on. The diagram only shows the power components. The rest of the components that aren't shown would be wired per Kal's Electric Brewery.

This design uses only two main contactors vs. Kal's three. Instead of a main power relay and one relay for each heating element, it uses one double throw relay to select an element, and one to switch power to whichever element is selected.

This has a couple advantages. There's one less contactor which means more space in the enclosure, or a smaller enclosure. It also makes it impossible for both elements to fire at once. Even if one or both relays fail you won't get more than one element powered. And when the control panel is turned on only the 120V buses are powered. None of the 240V wiring is energized until an element is actually on.

In order to do this I had to switch the neutral on one of the relay coils. What I'm wondering is whether that's kosher, and whether the advantages I've outlined above are actually compelling.


EDIT: the image looks lousy in the attachment so I posted it here as well: http://www.flickr.com/photos/jasongetsdown/7315929586/

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Old 06-04-2012, 07:55 PM   #2
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You're going to want a relay on the rest of your components anyway so that everything doesn't turn on as soon as you plug in your power. Might as well just make that your system power relay and do it like Kal. Additionally, you can' ever fire both elements at once with Kal's setup as it uses a 3-position selector switch instead of two separate switches like yours. I'd definitely go with Kal's over this.

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Old 06-04-2012, 10:33 PM   #3
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It looks to me like your design would work, however you could accomplish the same thing with two DPST relays, one for each element. Just wire your element selector switch to switch the hot to the appropriate coil.

If you do go with DPDT relay, pay attention to the rating on the normally closed contacts. Sometimes they aren't the same as the normally open ones.
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Old 06-04-2012, 11:26 PM   #4
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Check it out.
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