Altering Relay coil pick-up

Discussion in 'General Electronics Chat' started by arudzki, Jul 3, 2012.

  1. arudzki

    Thread Starter New Member

    Sep 25, 2011
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    I'm pretty sure I know the answer to this but I wanted to ask anyway.

    If I add a resistor in parallel to a relay coil, do the rules for resistance in parallel apply? I'm looking to switch in a resistor to alter the current required to pick up the relay.

    Will this work?

    Thanks all.
     
  2. #12

    Expert

    Nov 30, 2010
    16,304
    6,814
    Yes.......
     
    arudzki likes this.
  3. crutschow

    Expert

    Mar 14, 2008
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    Why do you want to increase relay pickup current (the pickup voltage stays unchanged, of course)? :confused:
     
  4. strantor

    AAC Fanatic!

    Oct 3, 2010
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    yes, the rules for resistance in parallel apply. Therefore, your relay coil will draw the same amount of power as it did before, plus additional power through the resistor. Your circuit will draw more power than before and your relay will function the same.

    I think what you want to do is put the resistor in series with the coil to lower the current. But, really, I don't think you even want to do that. Relays are designed a certain way for a certain reason. If they draw 100mA, it's because 100mA is what needs to be flowing through the coil for it to function properly. If you start meddling with it's current, it probably won't engage fully, allowing arcing and bad contacts.

    That being said, it takes less current to hold a relay than it does to switch a relay, so there are RC circuits which deliver ample amps to switch it, then limit the current afterwards.
     
    Last edited: Jul 3, 2012
  5. arudzki

    Thread Starter New Member

    Sep 25, 2011
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    0
    Strantor, thanks. My situation is this. I have a wire with a 16V 60 Hz voltage on it that I am monitoring with a current transformer for breakage. The output of the CT has a load resistor across it and I want it to hold a relay energized. Now, there is a chance that the wire will be replaced with one that is much longer, and the electrical characteristics will be the same. So my issue is that I would like to use a switch that would allow the relay to drop out at approximately the same voltage with either wire length installed. The switch would be labeled something like short and long.

    Does that make sense? Or is there a better way to do this?
    Thanks
     
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Your current transducer isn't going to care about how much voltage is present across the wire. It only cares about current.

    If you expect the current in the long wire to be less because increased resistance then I follow. Perhaps you could do some testing to define your requirements.

    Have you tested any of this? does it work so far? What kind of amps are we dealing with and how much current does your c/t put out for those given amps?
     
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