110VAC relay to complete 7.5DC circuit?

Discussion in 'The Projects Forum' started by devnull1974, Jul 31, 2007.

  1. devnull1974

    Thread Starter New Member

    Jul 31, 2007
    2
    0
    Hi all,

    I'd like to create a circuit such that when a light switch is on, the 110VAC through it can fire a relay to close a circuit. That circuit will provide 12VDC to another device (whose draw is < 50mA).

    Are there relays that use 110VAC? From the (very preliminary) searching I've done on this site and elsewhere, most of the (somewhat related) relays I've found are usually driven by 12VDC and then route 110VAC.

    If anyone has a Canadian source for such a relay, I'd love to hear about it.

    Thanks,
    DN
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    There are a zillion choices. I'm in the U.S., so I have to give you a non-Canadian source. Possibly one of the easiest to use might be a Potter & Brumfield K10P-11AT5-120. It has flanges to mount it, and uses .187" quick disconnects for the wiring. Mouser has it as part # 655-K10P-11AT5-120, at $7.96.

    It is DPDT - probably more than you need. You might see if a Canadian catalog has the same part. P & B make reliable stuff.
     
  3. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    Althoug it is a little clumsy, you can use an SSR (solid state relay) opto-isolator. The reason it is clumsy is because you need to add a blocking diode (1n4004) and a a 22K ,1W, dropping resistor in series with the diode of the SSR to handle 120VAC. But, it will provide isolation and you can connect most anything to the load/contact side (within spec, of course).

    Check Digikey for the Clare PAA140S.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    The controlled voltage is 12 VDC. A SSR won't turn off with a DC voltage through it. He'll need to use a realy with mechanical contacts.
     
  5. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
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    Not with an SSR, I believe your confusing it with an SCR -- two different beasts.
     
  6. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    Standard relay with 120VAC coil. It's actually got more than just a 'coil' but not much more. They are common.

    Another choice is to find a wall wart that puts out the DC voltage you need and put connect the AC to the same circuit as the DC. ;) If you want the DC to be on all the time that will not work.

    Last combobulation is to use the wall wart to control an lower voltage relay, can be any wall wart you can scrounge and a compatible relay.

    There are SSRs that can be controlled with AC. There are so many varieties. I've even seen one very pricey one that could be controlled from 24VAC - 277VAC(?) It was an odd voltage on the high end.
     
  7. devnull1974

    Thread Starter New Member

    Jul 31, 2007
    2
    0
    Thanks for the suggestions folks...I'll follow some of these leads and see how things go!
     
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