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Topic: Use a 5v relay to trip a 12v relay? (Read 2048 times) previous topic - next topic


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


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.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


Oct 28, 2012, 02:36 am Last Edit: Oct 28, 2012, 02:44 am by Runaway Pancake Reason: 1
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).
*** *** ***
Add a couple of 1N4001 (or 1N400x whatever they have) diodes to that list.
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

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