Eliminate starting torque of PMAC motor

Discussion in 'The Projects Forum' started by rrenk3000, Jan 5, 2016.

  1. rrenk3000

    Thread Starter New Member

    Jan 3, 2016
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    • I'm trying to come up with a solution to eliminate the starting torque (twist) of a small 120vac 0.3amp PMAC motor. Similar, in effect, to how a start capacitor slowly starts an induction motor. Motor has a 4" fan blade attached and I want to suspend it from a flexible cord, but eliminate the twisting motion when started. Label on motor doesn't have it listed, but is approx 18watts. Alternate (compact design) ideas also appreciated.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    More details on the motor is needed, if applying full 120v then there is no wonder it exhibits high starting torque, I assume there must be a controller of some kind, if PM motor?
    The start capacitor in an induction motor is not for slow start, on the contrary, the faster it starts the better, the cap just provides a phase shift to the winding.
    Max.
     
  3. rrenk3000

    Thread Starter New Member

    Jan 3, 2016
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    Max, the motor is currently switched on/off, full 120v. I am trying to create a pendant style fan (industrial look, see picture) that hangs from an overhead track with a flexible cord, and eliminate the twisting effect when it is switched on. I understand the concept of how a start capacitor actually works, but wanted to describe the effect of the slow motor start due to others wanting to "fix" my slow starting motor rather than see that is the desired effect. I have some room in the top of the housing to work with. Thanks...
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What kind of motor if it is PMAC 1ph?
    I am just wondering how it gets phase shift, or commutation?
    Max.
     
  5. rrenk3000

    Thread Starter New Member

    Jan 3, 2016
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  6. rrenk3000

    Thread Starter New Member

    Jan 3, 2016
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    Cogging is the correct term for the twist motion from what I'm reading. The available literature seems to be associated with bigger motors.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That really appears to me to be a AC shading ring induction motor? not PM?
    If so a triac controller normally works.
    Max.
     
  8. rrenk3000

    Thread Starter New Member

    Jan 3, 2016
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    So much to learn, so little time. Doing more homework. Your time is greatly appreciated. Thank you!
     
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If you are hanging the motor from a cord there will be a continuing torque (not just a starting torque) while the motor is running, trying to twist the cord. Will the cord withstand that?
     
  10. rrenk3000

    Thread Starter New Member

    Jan 3, 2016
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    Yes, the force is nil once the motor is at speed.
     
  11. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Smaller maybe, but not nil according to Newton's Third Law. Think helicopter, need for tail rotor or other counter-torque device.
     
  12. rrenk3000

    Thread Starter New Member

    Jan 3, 2016
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    Ok, got it. Thanks
     
  13. alfacliff

    Well-Known Member

    Dec 13, 2013
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    what you need is a "soft start" to reduce the power to the motor till it gets going. or else, do away with inertia.
     
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