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Thread: Speed Control, Induction Motor

  1. #1

    Speed Control, Induction Motor

    Hi all,

    Got a Canadian-Taiwan mortiser (Craftex). It's a nice, heavy, well built machine but it runs 3450 RPM; too fast for my mortising. I assume I will loose torque when I reduce speed but is it safe to try it? I have a 26 amp router control that I would like to try if I will not fry the motor. Can you teach an old motor (2003) new tricks?

    Is this machine a candidate for a VFD device? Can they be used on this 1 HP induction motor (110/220)? I know nothing about them except that they offer full torque at any speed (almost) and are not regularly given away.

    Thanks,

    Tim

  2. #2
    You say "1 HP induction motor (110/220)" so I assume it's a single phase, yes?

    If so, then no, you can't add a VFD. Routers use DC motors, that's why the speed can be controlled by a small & fairly inexpensive DC voltage controller.

    Even with a 3-ph induction motor, dropping speed by 50% long-term is not advisable.

    You best bet, short of a different motor, is to change the motor pulley, if there is room.

  3. #3
    Well, that's depressing! It's direct drive. Oh well, I guess I'm in search of a motor and my good deal isn't!

    Thanks,

    Tim

  4. #4
    Technically, you can run a single phase motor on a VFD, if you can find a VFD that supports single phase output (they are available). Couple of issues that you need to watch out for:

    1. At a certain RPM, the centrifugal switch will cut in. You need to keep the RPMs above that RPM. You can hear the switch cut in so you can do some testing to determine what that RPM is. You should always start the motor at 60 Hz.

    2. Like all motors run on a VFD, you need to be concerned about heat. As you run the motor slower the fan built into the motor will move less air. You can fix that by using an external fan blowing on the motor.

    3. In general, a VFD causes the motor to provide constant torque at RPMs less than the rated RPM (3450 in your case). This is not true at extremely low RPMs but you won't be able to run those RPMs because of the centrifugal switch. HP, on the other hand, (which is the measure of work and not force) is torque times RPM times a factor. So as you run the motor slower, you'll get the same torque but less HP.

    Mike
    Last edited by Mike Henderson; 09-02-2015 at 8:46 PM.
    Go into the world and do well. But more importantly, go into the world and do good.

  5. #5
    Mike,

    Thanks for the info. I have a couple of contacts from the web that mention VFD for single phase. They're on the right coast so will have to call them tomorrow and see what transpires.
    Thanks again!

    Tim

  6. #6
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    Just curious, did they use the wrong motor, or is there something special about your mortising?

  7. #7
    I think they used the wrong motor because it is direct drive and 3450 RPM is too fast for mortising.

  8. #8
    There are a few (3) mfrs of VFDs that work for single phase motors, but not ANY single phase motor. They only work for what are called PSC (Permanent Split capacitor) and Shaded Pole (SP) motors, neither of which are the type that are used on tools. They are pump and fan motors. So don't waste your money on them.

    If you can, replace the motor with a 3 phase version. Many many small VFDs can take a single phase input and give you a 3 phase output, without de-rating the VFD (up to and including 3HP). Some will even take a 115V input and give you a 230V 3 phase output, so you would use a 230V 3 phase motor (up to and including 1HP for that feature). But either way, the MOTOR must be 3 phase 230V.

    I think they used the wrong motor because it is direct drive and 3450 RPM is too fast for mortising.
    Are you sure there isn't a planetary gear head in there and they are turning the bit slower than 3450RPM? They might do that to get more torque using a physically smaller motor.

  9. #9
    Join Date
    Jun 2010
    Location
    Upland, CA
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    1,344
    FYI, all direct drive mortisers are 1725rpm except Shop Fox advertises 3450rpm. I don't have any knowledge how that works out in actual use.

  10. #10
    Quote Originally Posted by Jeff Raefield View Post
    There are a few (3) mfrs of VFDs that work for single phase motors, but not ANY single phase motor. They only work for what are called PSC (Permanent Split capacitor) and Shaded Pole (SP) motors, neither of which are the type that are used on tools. They are pump and fan motors. So don't waste your money on them.

    If you can, replace the motor with a 3 phase version. Many many small VFDs can take a single phase input and give you a 3 phase output, without de-rating the VFD (up to and including 3HP). Some will even take a 115V input and give you a 230V 3 phase output, so you would use a 230V 3 phase motor (up to and including 1HP for that feature). But either way, the MOTOR must be 3 phase 230V.


    Are you sure there isn't a planetary gear head in there and they are turning the bit slower than 3450RPM? They might do that to get more torque using a physically smaller motor.
    While torque is important, HP is even more important. Torque is a measure of force, while HP is a measure of work. And what you want to do is remove wood, not just press against it. That takes work, not just force.

    While gearing can change the torque, it can't change the HP.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

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