Help finding the right relay


Old 07-12-12, 01:36 PM
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Join Date: Jul 2012
Posts: 6
Help finding the right relay


I'm new to this forum and hoping someone here might have the electrical knowledge to help me.

I'm trying to find a relay that can do the following:
- Control a 120VAC circuit from a residential wall socket
- Have a coil that can be activated from a small DC battery source
- Carry up to 15A of current, which is the standard limit on my household circuit

I bought a Magnecraft relay hoping it would work

782XAXCL-120A Magnecraft / Schneider Electric | Mouser

But apparently I can operate the coil with a small battery, which is what I was hoping, since I want to control the circuit with an Arduino microcontroller.

Can anyone offer help as to what kind of relay I should look for
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Old 07-12-12, 03:07 PM
Tolyn Ironhand's Avatar
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Location: Twin Cities, MN
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There are thousands of relays out there. The one you listed has a 120v coil so it will not work with your application since your looking for something that has a DC coil

We have used many of these with very good results:
Functional Devices, Inc. - Products - Building Automation - Relays - Pilot - RIBH1C

This one will only up to 10 amps load but you can get larger ones if needed. What are you planning to control?
Old 07-12-12, 04:06 PM
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Join Date: Jul 2012
Posts: 6
I want to be able to electrically control anything plugged into my wall socket, so I could program how they work with a microcontroller. I'm doing this as a kind of learning experience.

I just went out and picked up a new relay which I'm able to switch with a 9V battery, that has similar specifications to the model you linked to. Here it is:

Now I guess an important safety question is are these just plug and play, or do I have to wire them up with resistors and/or diodes, to prevent hardware damage or overheating?

I did buy a 15 amp circuit breaker as added protection, even though I realize the wiring in my house already has breakers.
Old 07-12-12, 10:49 PM
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Join Date: Jul 2012
Posts: 6
To answer my own question, it appears a diode should be placed between the positive and negative end of the coil oriented so current flows from the negative end of the coil back to the positive end. This is to prevent voltage spikes from damaging sensitive electrical components.
Old 07-13-12, 05:02 AM
Join Date: Apr 2007
Location: Near Buffalo, NY
Posts: 4,239
That is true. The diode prevents a back-voltage spike caused by the coil.

Also, since you're powering off a microcontroller it's a good idea to use an opto-isolator as a buffer/relay driver.
Old 07-16-12, 07:42 PM
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Join Date: Jul 2012
Posts: 6
Thanks for the tip to use an opto-isolator. I had never heard of them before.

For people reading this thread that haven't heard either: An opto-isolator (optical isolator) is a small component (transistor operated using light, instead of with a physical connection) used to electrically isolate parts of a circuit. This is useful when you have sensitive electronics (like a computer or microcontroller) hooked up to devices that could potentially damage them, like an electric motor or inductor.

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