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Motor Speed Control

Discussion in 'Sensors and Actuators' started by Emesine, Jan 11, 2018.

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  1. Emesine

    Emesine

    12
    0
    Jun 19, 2017
    I currently have a Baldor KL1205a motor installed on a machine. This is a 1/3 HP 230VAC single speed motor with a start capacitor on a centrifugal switch.

    I need to convert this to a variable speed motor. What is the easiest way to do this?

    I can access the wires to the start capacitor phase very easily. My first thought is to wire the start phase to a separate power supply, then turn on this phase during only the first 500 ms of starting up the motor. Then control the speed there-after using a simple triac controller (Nimbus, made by control resources, is what I have in mind.)

    Thanks!
     
  2. duke37

    duke37

    5,343
    753
    Jan 9, 2011
    This is a messy way of doing it and is likely to be unsucessful. An AC motor is designed to run at a certain speed depending on the mains frequency. Throttling the input may involve extra current and poorer cooling.

    The modern way is to use a three phase motor driven with a variable frequency and voltage. Convertors will operate from single phase.
     
    Emesine likes this.
  3. Minder

    Minder

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    623
    Apr 24, 2015
    Agree, 1ph cap start induction motors tend to drop out of run at low rpm and/or on load.
    Especially a Triac controller would not cut it.
    You could go with a DC T.M. motor and controller, although being much larger, torque wise, it would be physically smaller than your 2pole 1/3rd HP motor.
    Another alternative is a smaller DC motor and one of the Really cheap 555 based PWM DC motor controllers on ebay.
    M.
     
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  4. Emesine

    Emesine

    12
    0
    Jun 19, 2017
    Thank you both, you've answered my question.

    In order to find a replacement for this motor, I need to look at the frame type and the mount type, is this correct? I'm attaching the data sheet for the currently mounted motor for reference. 56c frame F1 mount, I believe.

    thank you again for your help,





     

    Attached Files:

  5. Minder

    Minder

    2,948
    623
    Apr 24, 2015
    Also shaft size is sometimes an issue, another option is to get another face mount motor and make up a mounting flange to suit.
    M.
     
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