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  • single phase variable speed

    is there a simple explanation why there are no variable frequency drive systems for single phase motors?
    my shop is a beaver lodge
    steve, sarnia, ont




    1940's Craftmaster Lathe

    https://www.facebook.com/artistryinwoodca/
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  • #2

    Re: single phase variable speed

    Probably because there is no way to disconnect the start winding at a low speed. And there is very poor torque at low speed.

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    • #3

      Re: single phase variable speed

      ok so need another method of disabling the start circuit. low torque at low speeds is true of three phase too isnt it?
      my shop is a beaver lodge
      steve, sarnia, ont




      1940's Craftmaster Lathe

      https://www.facebook.com/artistryinwoodca/

      Comment


      • #4

        Re: single phase variable speed

        There are some expensive single phase variable speed motors mostly for fans but they will disappear now that vfds are available and cheap. 3 phase motors have natural torque as they have 3 sets of windings 120 degrees apart. Single phase has 2 sets in start mode then only one in run mode.
        Rob

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        • #5

          Re: single phase variable speed

          3-phase provides a genuine rotating field to move the armature along which works well across a wide range of frequencies (which govern the speed). Single phase motors exhibit very poor characteristics at slower than rated speeds with torque far worse than a 3-phase motor at the same speed and the centrifugal start switch problem is another one. Also, single-phase motors are very likely to seriously overheat at slow speeds and are not designed for it.

          There is/was a company selling speed controls for single-phase induction motors but they didn't work with just any single-phase motor and to buy the motors was very costly.

          billh
          jgarrett forsberg likes this.

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          • #6

            Re: single phase variable speed

            I posted this link once before. It looks like he is using an old Leland and simply controls speed and direction by changing the brush location https://www.youtube.com/watch?v=S5D9hL6LKM0

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            • #7

              Re: single phase variable speed

              Originally posted by tool fan View Post
              I posted this link once before. It looks like he is using an old Leland and simply controls speed and direction by changing the brush location https://www.youtube.com/watch?v=S5D9hL6LKM0
              That is not a repulsion/induction motor, it is a repulsion only motor.

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              • #8

                Re: single phase variable speed

                Originally posted by iamtooler View Post

                That is not a repulsion/induction motor, it is a repulsion only motor.
                Fair enough, but it is still single phase variable speed control

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                • #9

                  Re: single phase variable speed

                  Originally posted by tool fan View Post

                  Fair enough, but it is still single phase variable speed control
                  As is your drill! Induction motors are efficient and have no ''wearing parts'' except if there is a mechanical switch for the start windings. Note that you could use an electronic switch for that. Wound rotor motors are very expensive to build.

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                  • #10

                    Re: single phase variable speed

                    the motor in that video looks like a leland like the ones we all have on small machines.
                    but ours, i assume, are all repulse start,induction run
                    my shop is a beaver lodge
                    steve, sarnia, ont




                    1940's Craftmaster Lathe

                    https://www.facebook.com/artistryinwoodca/

                    Comment


                    • #11

                      Re: single phase variable speed

                      Originally posted by stevem View Post
                      the motor in that video looks like a leland like the ones we all have on small machines.
                      but ours, i assume, are all repulse start,induction run
                      That is exactly what I thought. I will defer to Rob, although I would like to know how he knows that it is not a repulsion induction, as the poster of the video claims.

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