single phase induction motor speed control

Discussion in 'Homework Help' started by eagleye, Jun 21, 2012.

  1. eagleye

    Thread Starter New Member

    Jun 14, 2012
    Hello everyone!

    I am trying to design a circuit for controlling the speed of single phase induction motor(Permanent Split Capacitor) of some table fan. I want to design these for three speed level by three switches and another for on/off.

    I want to do it by controlling voltage, in that case which type of circuit will be appropriate, I mean most efficient and cost effective for this purpose, as this is a practical project?

    Should I do it by using TRIAC circuit or just resistors?

    It would be very helpful if someone could help me with suggestions and/or circuits.
    Looking forward for your great support...
  2. crutschow


    Mar 14, 2008
    You could use a Triac (light dimmer) circuit but my experience is that causes a significant buzzing noise in the motor. I used a non-polarized film capacitor in series with the motor to control the voltage and speed of a fan I have. That's more efficient then using a resistor.

    The value of the capacitor depends upon the motor speed you want and the size of the motor. Generally it's in the range of a few microfarad for a table fan. You would need to experiment with different size caps (or connecting them in parallel) to determine the exact values you need for the various speeds.

    Make sure they are non-polarized caps and the voltage rating is sufficient (200V minimum for operation from 120VAC for example). I used some film caps designed for speaker crossover circuits from Parts Express.
    eagleye likes this.
  3. takao21203

    Distinguished Member

    Apr 28, 2012
    yes motors are inductive loads, the simple well known dimmer circuits obtain the phase signal directly, and that gets shifted obviously.

    It is also possible to build more complex circuits, which obtain the phase signal seperately. I never had a need to deal with that, but have taken a look at relevant circuits some months ago.
    eagleye likes this.