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24 volt ac relay chatter in parallel to doorbell

Discussion in 'General Electronics Discussion' started by esoundinvestment, May 13, 2014.

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  1. esoundinvestment

    esoundinvestment

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    May 13, 2014
    Hello all, this is my first post. I have wired a relay in parallel to my doorbell. im using the relay to trigger a camera event on my cctv dvr to send me a picture when it is pressed. The problem i have is that when its pressed the doorbell ring is cut a little short and the relay starts to chatter. The button is led lit and i think there is some residual current causing it. Would a diode or something in series do? thanks for and suggestions.
     

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  2. shrtrnd

    shrtrnd

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    Jan 15, 2010
    It's possible the doorbell LED is causing a problem with your circuit, but first things first.
    Are you sure you have the appropriate relay (coil) for your circuit. AC vs. DC? It should be marked on the relay itself.
    You're powering your relay coil from what source? A traditional transformer that powers a doorbell circuit?
     
  3. esoundinvestment

    esoundinvestment

    2
    0
    May 13, 2014
    Yes the coil is 24v AC. I have it wired to the traditional 24v AC doorbell transformer in parallel with the doorbell. I need to have the doorbell ring and relay trigger together. Thanks
     
  4. shrtrnd

    shrtrnd

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    Jan 15, 2010
    I'm trying to visualize that. Are you somehow accidentally short-circuit wiring something there?
    Are you sure that what needs to be wired in parallel or in series, is wired that way?
    It sure sounds like your LED doorbell might be causing the problem. I'm just wondering if you can
    eliminate your wiring scheme as a potential cause.
    The relay coil needs to be energized with 24VAC when the doorbell push-button is depressed (a series circuit), and the
    contact closures on the relay should then trip your camera trigger, (however that circut is wired).
    I know you're getting relay contact chatter. That can easily be solved with a diode or MOV (metal oxide varistor) across the coil.
    My understanding of your post may not be correct. Can you just touch the two wires across your doorbell contacts to complete the circut?
    (temporarily eliminating the LED in doorbell from the circuit altogether for this test), and see if you're still getting relay chatter.
    Something just doesn't sound right to me about this, but I may not fully understand the problem.
    Good luck.
     
  5. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    Does the power supply hold up at 24V with both things in parallel?

    You cannot put a diode across a AC relay.
    The relay can be made more sensitive if fed with DC. You could try a bridge rectifier but take note of the power dissipation.
     
  6. shrtrnd

    shrtrnd

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    Jan 15, 2010
    duke37 is right that a single diode across an AC relay coil is not correct. A single diode is often used with a DC relay coil. What is normally used for suppression of voltage spikes on an AC relay coil is called a 'snubber' which is basically a resistor in series with a small capacitor across the relay coil. I normally use an MOV (a varistor) across the coil in AC relays to prevent chatter (back emf from coil discharge), and in-rush current spikes, which acts essentially, electrically, like back to back diodes.
    Good call on correcting my mis-statement in my post, duke37.
     
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