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  1. #1

    Join Date
    Oct 2018
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    76

    Will a vfd control the speed of a single phase 240v AC brushed motor?

    As per the title this is for a hobby lathe running off 240v so I believe the motor which is 50hz 1420rpm is an AC brushed single phase affair.so does the AC mains 50hz frequency control the motor speed? And if so will a vfd allow the speed to be varied whilst maintaining a decent level of torque?
    Only other point for cost reasons I would need to buy a 3 phase inverter with 3x the rates motor power and just run off 1 phase would that cause problems?

  2. #2
    Registered
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    Apr 2015
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    143

    Re: Will a vfd control the speed of a single phase 240v AC brushed motor?

    If the motor is brushed (universal motor) then the answer is definitely no, frequency has little direct effect on this type of motor, they will run just as well on DC. Most speed controllers for this type use PWM. Dave

  3. #3

    Join Date
    Jan 2005
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    9826

    Re: Will a vfd control the speed of a single phase 240v AC brushed motor?

    Quote Originally Posted by men8ifr View Post
    As per the title this is for a hobby lathe running off 240v so I believe the motor which is 50hz 1420rpm is an AC brushed single phase affair.so does the AC mains 50hz frequency control the motor speed? And if so will a vfd allow the speed to be varied whilst maintaining a decent level of torque?
    Only other point for cost reasons I would need to buy a 3 phase inverter with 3x the rates motor power and just run off 1 phase would that cause problems?
    You would have to no for sure if it is brushed or not can you take a photo of the motor, most likely the answer would be no if it is brushed anything
    Mactec54

  4. #4
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    143

    Re: Will a vfd control the speed of a single phase 240v AC brushed motor?

    Quote Originally Posted by men8ifr View Post
    As per the title this is for a hobby lathe running off 240v so I believe the motor which is 50hz 1420rpm is an AC brushed single phase affair.so does the AC mains 50hz frequency control the motor speed? And if so will a vfd allow the speed to be varied whilst maintaining a decent level of torque?
    Only other point for cost reasons I would need to buy a 3 phase inverter with 3x the rates motor power and just run off 1 phase would that cause problems?
    If the speed is 1420rpm then it is almost certainly an induction motor assuming it is 50Hz supply. Brushed motors will usually run much faster than that. In principle you can use a VFD with a single phase motor but the torque drops very quickly as speed drops. You may do better changing it for a 3 phase motor which hold their torque better, fractional horsepower motors are not expensive. As Mactec noted a picture paints a thousand word, take a photo of it and the markings on it then we will know for sure. Dave

  5. #5
    Super Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Posts
    23092

    Re: Will a vfd control the speed of a single phase 240v AC brushed motor?

    If it is a brushed AC motor with rpm dependent on supply frequency then it could be a Repulsion-Induction motor, very old technology and not really seen alot these days.
    If so then there are virtually little to no options for rpm control.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  6. #6

    Join Date
    Oct 2018
    Posts
    76

    Re: Will a vfd control the speed of a single phase 240v AC brushed motor?

    Thanks for the replies so far I will take some photos and update. I was assuming it would be brushed like a cheap drill motor but I don't know.

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