Connecting a capacitor across an AC inductive load

Discussion in 'General Electronics Chat' started by Clinton Brits, Aug 8, 2015.

  1. Clinton Brits

    Thread Starter New Member

    Aug 8, 2015
    I had a problem a while back where a mechanical relay controlled a motor and it caused emi that caused a bit of havoc on the controller. Changing the mechanical relay for a solid state relay solved the problem.

    In another scenario I have the inductive load controlled by a mechanical switch which causes the same problem. Given that the voltage is 220v ac, would it not be possible to connect a suitably large capacitor across the switch like what is done on the controller or is this looking for trouble?
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Looking for trouble. You need a TVS type solid-state suppressor, with maybe an RC network.

    Things that will help: move the inductive load several meters from the controller. Put the controller in a metallic (shielded) enclosure. Feed only the control signal to the relay or other power switch with a twisted pair. Even better if the power switch is opto-isolated from the inductive load side(like the SSR you got), with no common power supply connection back to the controller(separate supplies for the controller and the load/switch with no common ground).
    cmartinez likes this.
  3. MaxHeadRoom


    Jul 18, 2013
    This type of R/C snubber usually cures it for me on AC coils.
    cmartinez likes this.
  4. Reloadron

    Active Member

    Jan 15, 2015
    cmartinez likes this.