Adding varible speed to an electric motor?

Discussion in 'General Electronics Chat' started by Rbeckett, Nov 9, 2013.

  1. Rbeckett

    Thread Starter Member

    Sep 3, 2010
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    I just recently acquired a new milling machine with a brand new 230 VAC single phase 1.5 horsepower motor. What do I need to build to create a variable speed set up that uses a pot to control actual speed while maintaining adequate torque to pull the bit into various ferrous and non ferrous metals and engineering materials? I know there is a correct answer, but it currently escapes my thought process before I formulate a solution... Thanks!!!

    Wheelchair Bob
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The 1ph VFD are not really a good solution, especially if the motor has a cap start only feature as motors controlled in this way tend to drop out of run at low rpm or on load.
    The alternatives would be a 3ph motor and VFD or a Quality DC brushed motor such as an ex-servo or Treadmill Motor, and using a KB or Baldor variable speed controller.
    The 3ph VFD runs off of 240v 1ph input.
    Max.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That is a Triac controller, I am assuming this would be intended for a Universal motor, it would not work on an induction motor.
    Max.
     
  4. killivolt

    Active Member

    Jan 10, 2010
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    I pulled that post in order to keep the thread clean.
     
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    What type of motor? Induction, cap start/run ....?
     
  6. tcmtech

    Well-Known Member

    Nov 4, 2013
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    If you are planning on keeping your stock peak torque at lower motor RPM's the only way you will do that is by going with a larger HP motor.

    To get the same torque at half the RPMs you will need a 3 HP motor how ever as mentioned by others the only realistic method to get variable speed is either DC drive or a VFD unit and a three phase motor.

    I have a Smithy 1340i that came with a 2hp dc motor. My brother fried it so I redid it with a 3 HP three phase motor and VFD system. Believe me the 3ph motor and VFD is the better choice for torque on a lathe or mill application.

    The other thing you can do with a VFD driven 3ph motor is run them at 2x their normal rated speeds which gives you an additional cheat for more torque being you can run faster in a lower machine gear setting.
     
    Last edited: Nov 9, 2013
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have a couple of XLO mills with 2hp spindles and I put a VFD on each and have no problem, I would advise however you pay a little extra and go with the sensorless vector for torque throughout the range.
    I don't generally use 120hz on 2 pole motors, just 4 pole, which many are, fortunately.
    Unless it is a vector rated motor, then it should be OK.
    Max.
     
  8. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    Wait what ????
    Milling machines have a speed controller on them so you don't burn up bits and etc..
     
  9. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Not all of them have variable motor speed. Though most can change speed ranges, in pretty big RPM jumps.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Many used mechanical methods, in the case of the XLO they had a vari-speed pulley system as well as a two speed G.B. Similar with B.P.'s.
    Things have changed with the later types, but if the OP has a new mill with 1ph induction motor, the odds are it is not electrically variable or possible with that motor.
    Max.
    ,
     
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