Powering A/C Relay with DC possible?

Discussion in 'The Projects Forum' started by whiteggs, Nov 28, 2012.

  1. whiteggs

    Thread Starter Member

    Feb 15, 2010
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    The relay's rated voltage is 100/110V AC. Will it work on 100V DC?
     
    Last edited: Nov 28, 2012
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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  3. whiteggs

    Thread Starter Member

    Feb 15, 2010
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    Thanks for the link. I'll just use a 100V dc rated relay. The Omron 4pdt has an operating voltage ranging from 80V(80%) to 110V(110%) and will put a diode across the coils.
    If the relay is not used, there is still current going through it but at only 55V. This would be ok, right?

     
  4. DickCappels

    Moderator

    Aug 21, 2008
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    Probably ok, but after its run for a while, unplug the circuit from the mains and do a finger test to make sure its not over-heating.
     
  5. eblc1388

    Senior Member

    Nov 28, 2008
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    A 100V rated DC relay when operated and with 55V across it will definitely not release as the current is sufficient to hold it in the Closed position.

    For it to release, one should ensure no more than 10% of rate voltage is applied. Even 10% is kind of doggy and can result in unreliable operation.
     
  6. whiteggs

    Thread Starter Member

    Feb 15, 2010
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    What a bummer, that is exactly what happened. When I rapidly switch between 55v - 105v - 55v, the contacts is stuck and remain closed. I have to disconnect power to the relay for it to release - i.e. stay open. Is there a work around for this so it doesn't remain stuck?



     
  7. tkng211

    Well-Known Member

    Jan 4, 2008
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    You can firstly cut the 'shader ring' ( the short circuit secondary coil on the relay armature) to open the short circuit. If it still doesn't release, add a resistor about 1/2 to 1X the DC resistance of the relay coil in series with the coil, so it can make and break as required. The resistor added should be of suitable power rating. Hope you can get it done.
     
  8. eblc1388

    Senior Member

    Nov 28, 2008
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    For this special case you would need to use a DC48V relay instead.

    Put a 60V(or 48V & 12V in series if 60V ain't available) zener diode in series with the relay coil.
     
  9. John P

    AAC Fanatic!

    Oct 14, 2008
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    I promise you that cutting the shader ring, supposing you're able to do it without damaging the rest of the relay, won't make any difference. It only has an effect for AC current.

    You really should design your circuit so that the current through the relay is cut off totally when you want the relay to drop. Even a fraction of the rated current is enough to hold it energized. Is there any way you could use a resistor in series with the coil and short out the coil when you want to kill power? That would be as good as cutting the power completely, but you must be sure that the resistor can handle the power.
     
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