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
    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


    Jul 18, 2013
    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.
  3. MaxHeadRoom


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

    Active Member

    Jan 10, 2010

    I pulled that post in order to keep the thread clean.
  5. Alec_t

    AAC Fanatic!

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

    Distinguished Member

    Nov 4, 2013
    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


    Jul 18, 2013
    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.
  8. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    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
    Not all of them have variable motor speed. Though most can change speed ranges, in pretty big RPM jumps.
  10. MaxHeadRoom


    Jul 18, 2013
    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.