How to control speed of single phase induction motor

Discussion in 'The Projects Forum' started by asjadullah1, Feb 28, 2016.

  1. asjadullah1

    Thread Starter New Member

    Feb 28, 2016
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    0
    Hi guys,

    I have 50 W single phase induction motor, need to control its speed. I wish to control the speed using the ordinary fan speed controlleres (regulators) available in the market.

    But I am facing a trouble that the motor does not start until the regulator has been turned to full speed position.

    Can anyone help me in correcting me,
    what mistake I am making,
    Is there an economical and better solution than this,


    Your help will be greatly appreciated.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Split phase Capacitor motor or shaded pole?
    Max.
     
  3. asjadullah1

    Thread Starter New Member

    Feb 28, 2016
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    Split phase capacitor motor.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Then I suspect that the start winding current is not sufficient at low level turn on, Especially if the motor is under any kind of load at turn on.
    Max.
     
  5. asjadullah1

    Thread Starter New Member

    Feb 28, 2016
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    Yea bro, thats what I am suspecting. Any suggestions?
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Capacitor start/run motors do not control well with Triac or other means such as VF, this is why you do not see many (any) successful VFD's for 1ph motors. Which tend to be bad low rpm starting or dropping out of run on load etc.
    The Triac type is usually confined to either 1ph shaded pole or Universal motors.
    Max.
     
    asjadullah1 likes this.
  7. tranzz4md

    Member

    Apr 10, 2015
    139
    28
    Well, youre not telling us much about your load, and we know that you dont actually need to control and vary the speed of a motor; you wish to control the movement of a load.

    Strangely enough, you can get good and adjustable control of a load using a 3 phase motor fed from a single phase supply using VFD, in unusual instances. I merely point this out to highlight the wide variety of options and approaches to dealing with individual applications.
     
  8. Johann

    Senior Member

    Nov 27, 2006
    190
    30
    The speed of an induction motor is proportional to the frequency of the supply voltage and always tries to attain synchronous speed, however, it is limited by what is called "slip". The speed control the Chinese employ in their fans, make use of stalling techniques such as limiting the current with inductors with taps or tapped windings on the motor stator. This method is limited to small fans etc which are very light loading on the motor's rotor.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The exception of course is the shaded pole induction motor which will operate using reduced power, (Triac control) and mainly fan applications.
    Max.
     
  10. Johann

    Senior Member

    Nov 27, 2006
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    It is still an induction motor and frequency dependent. They are impedance protected and will withstand abuse such as forced lower speeds by introducing either inductors or resistors in series to choke the current, thereby starving the motor so to speak.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Mine are just using phase angle Triac control!;)
    Shaded pole induction motors, Ceiling fans and air exchanger blowers.
    Max.
     
    Johann likes this.
  12. Johann

    Senior Member

    Nov 27, 2006
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    Yes, they work alright! As long as they are lightly loaded such as in a fan application.
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    We are right back to post #6 then!:confused:
    Max.
     
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  14. asjadullah1

    Thread Starter New Member

    Feb 28, 2016
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    0
    Yes my induction motor is 50 W, and lets say I want to operate it at no load, with varying speed.

    The ultimate solution is to use VFD, but I want an economical solution, with readily available products.

    How about installing a capacitor in series to the winding, that would improve the pf and lower the starting current lag angle, once started we can regulate the speed by Triac and Diacc configuration.

    Your comments
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Either use a small shaded pole motor, or use a small DC motor and one of the $5.00 PWM controllers on ebay.
    Max.
     
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