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1ph Motor start switch arc

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  • 1ph Motor start switch arc

    I have noticed arcing on the 2hp motor cent. sw. on my Jet M/D. My thought is to install a capacitor across the cent. sw. contacts. Does anyone have an idea if this will help? If so, what voltage and mfd rating would be appropriate? Thanks for any thoughts on this.

  • #2
    I think installing a capacitor across the centrifugal switch on an AC motor would act much like a short circuit, keeping power on the start winding, and leading to overheating.

    As far as the arcing goes, the switch contacts are probably designed to handle it. I'd leave it as is.


    [This message has been edited by winchman (edited 02-03-2006).]
    Any products mentioned in my posts have been endorsed by their manufacturer.


    • #3
      I installed a opto22 cube to start a motor I kept burning up points in a relay.
      Problem? electronic cube relays require low dc voltage across the terminals to turn them on.

      No spark inside a power transistor/ Mosfet.

      Each spark generates a voltage spike that emitts in all directions on the circuit. The emf can affect sensistive electronics inches away. I always try to cross controls at 90 degrees and not bundle them with controls.

      My old harley, with the mechanical regulator I was getting 3-6 months to a generator. Once I went to a electronic regulator I replaced the generator once in five years. On a low voltage system, a 1,000 volt spark does damage. Yes, transient spikes can go that high.

      When you size it, make sure to allow for the 600 percent surge going into a motor at startup.
      Excuse me, I farted.


      • #4
        A capacitor would probably be not good.

        But, a suppressor would be OK.

        Typically these are a small capacitor witha resistor in series. 0.1 uF with something between 22 ohms and 100 ohms. Must be rated for the line voltage per UL /VDE rating.

        That may suppress the arc a bit, but likely isn't needed. In general the switch can take the arc.

        The only question I would have is if the start capacitor is the corrrect value, and the hookup of the start winding correct...

        If its a dual voltage motor, (2HP is really over that level, for 120 anyhow) the start winding runs on teh lower voltage, and if the motor is on the higher, it connects across just one of teh coils....

        Too high a voltage can cause a vicious arc, and way excessive start current..... That being an import, no telling what they did........

        Keep eye on ball.
        Hashim Khan


        • #5
          A 1/4 watt 25kohm ceramic resistor soldered in across the start cap terminals will reduce the flash/arcing and extend the life of your switch gear contacts.
          I just need one more tool,just one!


          • #6
            Wierd, That would be similar to the bleed resisters we used on ref. comp. motors. Sounds like a good idea. My idea for a capcitor was like the "points and condenser" of the old ign. circuits. I'll try the bleed res. and see what happens.