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solution to soft start an ac induction motor

Discussion in 'Sensors and Actuators' started by jackorocko, Aug 18, 2013.

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  1. jackorocko


    Apr 4, 2010
    Just as the title of the thread ask, I am wondering what type of solutions I have for soft starting a 120v ac induction motor with starter coil and capacitor start? It is a 1HP. This is on a lathe so I would like to stick to 120V to avoid any extra external electronic motor controllers needed to control the direction of rotation with a drum switch.
  2. duke37


    Jan 9, 2011
    I have used a resistor, shorted out with a relay after about a second.
    The resistor needs to be a few ohms and many watts.
    The timing can be done with a rectifier, resistor and capacitor.

    I do not see how this will work with a direction switch, perhaps a current transformer could be used to reset the relay.
  3. jackorocko


    Apr 4, 2010
    I had the same thought using a resistor. I was really hoping they made something like a soft start capacitor, but as you say changing direction causes an issue because it would work in one direction and be totally negated in the opposite direction.

    Oh well, seems I might have to bide my time until I can stumble upon a 3 phase motor.


    Sep 23, 2012
    Running on 220VAC is allways better if you can.

    If you can find a 1 HP three phase motor; MC Master Carr carries a nice little electronic 869, Catalog 116: Three Phase AC Motor Speeed Controller. This unit is small, 4.5" x 6.9" x 4.4". Its variable and has reversing.
  5. Externet


    Aug 24, 2009
    Commect a 120VAC light bulb in series with the 120VAC motor.

    The lower the bulb wattage, the lower the motor speed. Want more speed, choose a larger wattage bulb.
    Relays or switches bringing the bulb(s) into/out the circuit can do a pretty and simple speed controlling.
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