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Motor speed control

Discussion in 'Sensors and Actuators' started by giser3546, Nov 20, 2015.

  1. giser3546

    giser3546

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    May 13, 2015
    I have a 1,750 RPM 110 V 1/2 HP electric motor I pulled out of an old band saw. I am hoping to use it to create a slow speed (70 RPM-ish) grinder used to sharpen woodworking hand tools. I'm trying to figure out if there would be a way to slow the motor down by means of adjusting the incoming voltage or anyway that wouldn't require a gearbox of some sort. I have a working knowledge of electronics and wouldn't be against putting something together myself to get this done.

    Any input is greatly appreciated.
     
  2. Martaine2005

    Martaine2005

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    631
    May 12, 2015
    @Minder
    Your services are required:D
     
  3. Minder

    Minder

    2,871
    594
    Apr 24, 2015
    Depends on the motor, if it is an induction motor you may be out of luck, unless it has a shaded pole, (no Capacitor).
    But 1/2 HP on a Band saw I would expect to see a capacitor run motor.
    They do not take to varying rpm well, they tend to drop out of run under load and low rpm.
    You might be better off looking for a DC treadmill motor and controller for that RPM.
    M.
     
    Martaine2005 likes this.
  4. Martaine2005

    Martaine2005

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    May 12, 2015
    I was going to suggest larger pulleys. But the RPM is quite high.
    Several pulleys would be needed. But my math is useless to work it out.
    That's why I called "the motor expert".

    Martin
     
  5. giser3546

    giser3546

    12
    3
    May 13, 2015
    I have considered a gearbox to reduce the speed to closer to 100 rpm but the final cost and effort of that will probably be higher than just purchasing a new low speed grinder ($150.00). Well shoot.
     
    Martaine2005 likes this.
  6. Martaine2005

    Martaine2005

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    May 12, 2015
    I feel your pain, but the reality is make it or buy it!
    Some prefer to make with no comprehension of cost, others buy because of cost!
    Your call...

    Martin
     
  7. Minder

    Minder

    2,871
    594
    Apr 24, 2015
    The ratio reduction could be done with two back-to-back double pulley systems, both 10:1 but would take a lot of room.
    The advantage is the torque would be increased by a factor of 20!.
    M.
     
  8. GuyfromMontana

    GuyfromMontana

    5
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    Nov 20, 2015
    Another idea would be to pick up a small geardrive motor in the right rpm range. I dig through the scrap motor box at my recycling center and finds lots of good candidates very cheap. If you want I'd look for something.
     
    Martaine2005 likes this.
  9. GuyfromMontana

    GuyfromMontana

    5
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    Nov 20, 2015
    I've also done the motor and control from a treadmill with success on drill presses and bandsaws but you really don't need that much power for what you're doing on this project.
     
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