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single-phase motor speed control

Discussion in 'Power Electronics' started by Andrewxxd1, Jul 30, 2020.

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  1. Andrewxxd1


    Jul 30, 2020
    Hi all. I hope you can answer my concerns and that the possible answers are helpful to other people

    I am considering the possibility of controlling the speed of a single-phase motor, my question is, can all single-phase motors have speed control? Of course, there is a wide variety of single-phase motors, such as the auxiliary starting coil, capacitor starting, permanent capacitor, permanent capacitor with starting capacitor, and surplus turns.

    What would be the best option to control the speed of any of those motors?

    I know that three-phase motors can be controlled by a frequency inverter (I have).
    The issue is that I have never worked with single-phase motors and I don't know if there is any frequency inverter that works for this type of motors.

    I have seen an infinity of videos that use a dimmer "angle trigger controller with TRIAC", to control the speed of some motors, the doubt that also arises, how effective is that type of control ?, considering that it varies the input voltage but not the frequency, I tend to think that this could cause engine torque problems at low revs.

    What is the difference between controlling the speed of a motor by varying the input voltage, or varying the speed?

    In case there are frequency inverters for single-phase motors, which one do you recommend? (voltage 220v 50Hz).

    The dimmers I have seen on AliExpress say they are from 5000W to just 11 dollars, that is why I have this doubt which would be better to apply for a small business job. for example a wood cutting bench
  2. Bluejets


    Oct 5, 2014
    Single phase split phase motors such as you make reference to have their speed controlled via the number of poles in the windings and cannot be speed controlled via other external means.
    When used on lathes and such, their output can be varied by the use of differing sized pulleys via vee belt.
  3. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    AFAIK, the ONLY single-phase motor that is made to ALLOW for speed control is an AC/DC Universal Wound brushed motor, typically found in small appliances such as hand mixers. You might be able to use a variable frequency drive on a single-phase motor, but it will not be very efficient, nor will it have a very wide range of rotation speeds. Three phase motors are better suited for this because the magnetic field in the motor stator rotates in space around the rotor. The stator windings in conjunction with the rotor conductors act like a rotating transformer, with the rotation speed being a function of the stator excitation frequency.

    If all you have available is single-phase power, there are inexpensive single-phase to three-phase converters available. You could then connect this synthesized three-phase power source to a variable-speed electronic drive and a three-phase motor matched to the capabilities of the variable-speed drive. For a production wood cutting business (saw, lathe, planer, jointer, etc.) you need a reliable system, professionally installed, not something you throw together by guess and by golly.
  4. Minder


    Apr 24, 2015
    The only single phase induction motors that work with variable speed method is the type most used in fans, that is the both small shaded pole motor and the PSC, Permanent Start Cap motor, typically using Triac controllers.
    There is actually a VFD out there for larger single phase motors but they have not proved reliable, they tend to drop out of run when loaded at low rpm.
    This is why the Hobby CNC community tend to go with the 3ph motor and VFD with 1ph input.
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