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    Ac motor speed control

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    Hai friends,
    In my project I have to control speed of AC230V,50HZ,4A,single phase motor.I tried TRIAC BT136 with optocoupler 3041 but it switching on when the PWM is high but in low pulse its not working.....Then removed the optocoupler it working fine.
    Then used IRF540 but it always in ON condition.Its not responsible with PWM.


    Please provide suggestion to control the motor speed by using PWM controls

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    Re: Ac motor speed control

    MOC3041 is zero crossing detector device, use MOC3021.



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    Re: Ac motor speed control

    For starters..... you don't trigger a Triac with PWM. You trigger it with phase control.

    Phase control is a trigger delay from zero the zero crossing.
    Additionally, not all single-phase motors are suitable for speed control. They are limited mostly to shaded pole ones.
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    Re: Ac motor speed control

    Quote Originally Posted by FvM View Post
    MOC3041 is zero crossing detector device, use MOC3021.
    MOC3021 with BT136 is suitable for speed control or have to change any other TRIAC also..?



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    Re: Ac motor speed control

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    This is my circuit used to control the speed of the motor.
    But I not working...Motor is either switching ON or OFF condition only....

    I can't control the speed of the motor by using the PWM pin..
    PWM is working fine,i checked it by connecting an LED with PWM pin which used for control the speed of the motor.

    - - - Updated - - -

    Quote Originally Posted by schmitt trigger View Post
    For starters..... you don't trigger a Triac with PWM. You trigger it with phase control.

    Phase control is a trigger delay from zero the zero crossing.
    Additionally, not all single-phase motors are suitable for speed control. They are limited mostly to shaded pole ones.
    No already speed of the motor is controlled by an mechanical switch...



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    Re: Ac motor speed control

    Hi,

    as schmittt trigger already mentioned: don´t use PWM. It won´t work.

    Read basics about phase control.
    In short: You need to detect zero cross of line voltage --> Then use a variable delay (the shorter the delay, the higher the speed) --> then trigger the Triac with the use of MOC3021.

    Klaus
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    Re: Ac motor speed control

    Quote Originally Posted by KlausST View Post
    Hi,

    as schmittt trigger already mentioned: don´t use PWM. It won´t work.

    Read basics about phase control.
    In short: You need to detect zero cross of line voltage --> Then use a variable delay (the shorter the delay, the higher the speed) --> then trigger the Triac with the use of MOC3021.

    Klaus
    If we SWITCHED the TRIAC using delay function means controller have to do that work only,because it will comes under infinite while loop.
    To avoid this one I need PWM control..

    Is their any other way to control the speed of the motor by using the PWM control..?



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    Re: Ac motor speed control

    Variable delay doesn't necessarily mean software delay loop, it can also use zero crossing interrupt and hardware timer.



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    Re: Ac motor speed control

    Hi,

    A microcontroller PWM usually is not aligned (synchronized) to an external signal.

    But for phase control you need the mains zero cross as timing reference.

    --> any free running PWM (like a PWM usually works) will not work as phase control.

    *****
    Maybe you think the correct way, but in my eyes the phrase "PWM" is not useful (at least: misleading) for phase control.

    Klaus
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    Re: Ac motor speed control

    Quote Originally Posted by venkates2218 View Post
    If we SWITCHED the TRIAC using delay function means controller have to do that work only,because it will comes under infinite while loop.
    To avoid this one I need PWM control..

    Is their any other way to control the speed of the motor by using the PWM control..?
    No
    It is not synchronized with the zero crossing.
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    Re: Ac motor speed control

    you have to check for zero crossing signal and switch on the triac with a delay from 0-10 ms . 0ms full on and 10ms full off



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    Re: Ac motor speed control

    i used to work at a shower company where they controlled the speed of an AC motor (for the shower water pump) with just with a TO220 triac and a isolated
    Triac driver.
    It was very very rough, and noisy, but it worked.
    They were using PWM.
    They just kept occasionally turning the driver off for varied intervals.....WHEN on , they just kind of kept the drive on so that the triac didnt always turn off when the mains
    went back through zero.

    It was very noisy...some customers used to complain about the noise, but it was cheap.



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    Re: Ac motor speed control

    They were using PWM.
    I am not so sure. Most of the simple controllers use use a phase delay control. Most use a RC circuit to generate the delay from the zero crossing. PWM is much more messy.

    The noise is due to the controller? My kitchen fan makes noise like a jet engine but it does not have any regulator.

    By the way, phase control (in some sense) is same as PWM (except that the waveform is not rectangular)...
    Last edited by c_mitra; 20th October 2018 at 16:12.



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    Re: Ac motor speed control

    The noise was from the motor



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    Re: Ac motor speed control

    The noise was from the motor
    The noise in my exhaust fan is (my guess; no study) is due to (i) unbalanced blades (ii) resonance and (iii) airflow turbulence.

    Noise due to blade unbalance is not going to change with speed (but the frequency and perception will change);

    Resonance will peak at a particular speed and appear to reduce both above and below (the resonance speed);

    Turbulence noise (airflow) perhaps depends on the geometry.

    AND this may perhaps be the case in your motor too.



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