Control Relay from AC Source

Discussion in 'General Electronics Chat' started by yoyom, Jun 1, 2013.

  1. yoyom

    Thread Starter New Member

    Mar 6, 2013
    I have a 5-Pin 30A relay, which I want to control from an AC 240V Source.

    I have a transformer, 240 to 12VAC and this DC converter.

    Problem is when I switch the power on, relay turns on and when I switch off its goes to back position, but on switching the power again the relay does not work. I have to remove the wires and then connect the wires, again it starts working.

    What could be the problem? Relay works perfectly fine but only for the first time.
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    Can you post a picture of the relay or what model number it is?
  3. crutschow


    Mar 14, 2008
    You didn't specify the relay's coil voltage rating and whether the coil is AC or DC.
  4. yoyom

    Thread Starter New Member

    Mar 6, 2013
    Its a local made 12V DC Coil Relay.
  5. strantor

    AAC Fanatic!

    Oct 3, 2010
    I suspect that your DC converter is ill-equipped to handle the inrush current of the relay. It works when you disconnect the wires because when you do this, it allows the caps in your DC converter to charge and when you connect the wires again, these caps discharge and overcome the switching current requirement, and then whatever is left over is enough to maintain the holding current requirement, but when you try to do it from the starting line, the DC converter is trying to charge the caps PLUS deliver the switching current, which over-exerts it, and thus FAIL. Maybe try a better "DC converter."

    - disclaimer - I don't know what I'm talking about.
  6. vk6zgo

    Active Member

    Jul 21, 2012
    Forget about the DC converter & use a bridge rectifier followed by an electrolytic capacitor.

    Without the cap,your DC relay will "chatter" as it tries to follow the ac ripple on the rectified DC.

    The capacitor value is a bit "select on test",as too big a value will affect the release time (& to a lesser extent,the operate time) of your relay.
    Too small a value,& your relay will "chatter" as described above.