Latching AC Relay Circuit

Discussion in 'The Projects Forum' started by walyn, May 22, 2010.

  1. walyn

    Thread Starter New Member

    May 22, 2010
    I am having trouble with a latching relay circuit. See pump control attachment. When assemled and turned on, the relay is giving chatter. I am not sure what to do about getting the relay to stay activated. The relays that I am using are 110V AC, 10 Amp, DPDT. The completed circuit will control the filling and draining of a tank on a timer. See pump circuit attachment.

    Any suggestions would be great.

    Thanks for any help.
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    If its a latching relay, you should only be sending a pulse not constant voltage.

    Latching relays are ling ball point pens. One click and they go on, another click when your done to go off.

    What relay are you using? Model and manufacturer
  3. walyn

    Thread Starter New Member

    May 22, 2010
    The relay that I am using is a Tyco Electronics PCLH-206A1S. It is the only AC relay that I could find at Radio Shack. I don't think that it is an actual latching relay, but I am configuring the switches to make it 'latch'. I think?

    Thanks for the quick reply!
  4. walyn

    Thread Starter New Member

    May 22, 2010
    I found another thread that addresses a similar problem, except they are using DC relays and I am using AC relays. Here is the link:
    It seems that I need a component that will hold the current for a few seconds to get the relay to latch. I don't think that a capacitor will do that for me in an AC circuit. Is there something else?
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    You can get a true AC impulse latching relay from P & B. Digi-Key has a DPDT relay with a 120 VAC coil and 15 amp contacts as part #PB585 @ $47.64.
  6. williamj

    Active Member

    Sep 3, 2009

    Looking at the circuit sketch you provided and compairing it to the data sheets listed, it appears that there is a mistake. In the fill cycle the switches should be labled S"2" & S4 (not S"3") and in the drain cycle it should be S"1" & S3 (not S"2").

    Also bear in mind the proper wiring. In the fill cycle make sure it's wired to the normall "closed" terminal(s) on the float switches and in the drain cycle the normally "opened" terminal(s) of the float switches.

  7. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    It's a nasty circuit, the coil is disconnected as the relay changes state.

    A better option would be to commect the low level switch in the feed to the relay common contact, link the normally open relay contact direct to the coil feed and connect the high level switch across the contact (C to NO).
  8. walyn

    Thread Starter New Member

    May 22, 2010
    Fixed it! I changed the latching portions of the circuit to DC and used diodes and caps to control the relay bounce. Works like a charm. Thanks to all who replied.