How to suppress back emf in ac motor

Discussion in 'General Electronics Chat' started by gokulcircuit, Mar 21, 2013.

  1. gokulcircuit

    Thread Starter New Member

    Mar 20, 2013
    I am doing a project, where I am using voltage divider to speed control ac motor. where I am unable to control speed constantly due back emf ..
    Problem is speed controls but due to back emf speed again comes to speed before controlling..
    Pls help...:confused:
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    EMF is part of what makes an AC motor work. Suppressing it will keep motor from turning, if you could even find a way to do it. AC motors are not speed controlled by voltage, instead the are controlled by the AC frequency. Do research on VFD, variable frequency drive.
  3. BillB3857

    AAC Fanatic!

    Feb 28, 2009
    If you are simply using variable voltage, you are providing variable torque and speed is being regulated more by load due to slip than anything else. Ever notice that most motors designed to run on 60Hz have a nameplate speed of 1750-RPM and not the expected 1800-RPM. Guess where the other 50-RPM went.
    shortbus likes this.
  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    if your talking universal motors, the problem with resistance is that the load will prevent regulation without some form of feedback. A rehostat, autotrans, or phase angle control will perform better.
  5. gerty

    AAC Fanatic!

    Aug 30, 2007
    Also if the motor is capacitor start, and you run it too slowly for the centrifugal switch to open, you will burn up the motor.