Does polarity matter for a 12VDC relay?

Discussion in 'General Electronics Chat' started by Johnnyb60, Jan 24, 2015.

  1. Johnnyb60

    Thread Starter Member

    Sep 6, 2013
    30
    0
    I bought a 12VDC/10A DPDT Plug-in Relay from RadioShack, but all I got was the socket so far. I want to start wiring for it now because I can just plug in the relay later when it gets here.

    The problem is that I don’t know which of the coil terminals 7 or 8 is positive or does that even mater?
    Not sure if the polarity would change the direction of the relay coil.
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,421
    3,357
    Polarity does not matter.
     
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  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,509
    2,369
    Some relays have a BEMF diode and/or a signal LED, if yours has neither then it should not matter, IF they are fitted then polarity matters..
    If no BEMF diode fitted, one should be wired across the coil terminals and then the correct polarity should be observed, +ve to cathode.
    Max.
     
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  4. Johnnyb60

    Thread Starter Member

    Sep 6, 2013
    30
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    Well I don’t believe there is a BEMF diode in the Radio Shack relay, but I’m actually soldering a Bridge Rectifiers to the coil input because I have 12VAC supply and I can’t find a small AC relay to use.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I just mentioned it to cover the bases, I am not sure of R.S. products anymore, they pulled out of Canada about 20yrs ago!!.
    Max.
     
  6. Johnnyb60

    Thread Starter Member

    Sep 6, 2013
    30
    0
    You know, now that I think about this particular relay I should have known this because it’s only an electro magnet pulling the contacts down. For some reason I was thinking if the poles were reversed the contacts would want to move away, but in this case the contacts aren’t magnetic. :oops:
     
  7. snav

    Active Member

    Aug 1, 2011
    100
    10
    The armature is magnetic but not a magnet so polarity is not important.
     
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