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Author Topic: Use a 5v relay to trip a 12v relay?  (Read 915 times)
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What I thought would be a quick trip to Radioshack turned into three trips and much confusion.

What I'm trying to do is use my Arduino Uno to turn on and off a 120vAC device (bedroom lamp, Christmas lights, etc).

To make a long story short, the gentleman at Radioshack did not have a 5vDC relay that would handle >1A at 120vAC and suggested I instead use a 5vDC 1A at 120vAC relay to trip a 12vDC 10A at 120vAC relay. Made sense at the time.

So right now I have:

    5vDC relay, rated 1A at 120vAC (SPDT)
    12v relay, rated 10A at 110/120vAC (DPDT)

I bought a 10ft extension cord from Walmart that I cut in half; I want to wire the relays in the middle. So my question is: how do I wire these things up? Where am I getting the 12vDC to trip the second relay? Here's a picture of the two relays and their packaging: http://i.imgur.com/hnqAb.jpg
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Well, 2 problems - the 5V relay looks to have a 50, 56 ohm resistance? Arduino can't drive that. Need a transistor to drive that.
2nd, yeah you need a 12V source.
If you had 12V and the transistor, you wouldn't need the 5V relay.
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275-0217  That's not a "12V relay".  It's a relay with a 120vac coil (!), so that's not happening in our Arduino context.
[ http://www.radioshack.com/product/index.jsp?productId=2049721 ]
Return it.  
Exchange it for a transistor or two - http://www.radioshack.com/product/index.jsp?productId=2062609
and get some resistors, too, 1Kohm (1/4W, 1/2W, whichever).
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PS,
Add a couple of 1N4001 (or 1N400x whatever they have) diodes to that list.
« Last Edit: October 27, 2012, 07:44:38 pm by Runaway Pancake » Logged

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