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Topic: Use a 5v relay to trip a 12v relay? (Read 1 time) 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.

Runaway Pancake

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.
"You gotta fight - for your right - to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"
It's "bipolar transistor" or "junction transistor" - "BJT" is stupid.
When all else fails, check your wiring!

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