AC Motor at LOW RPMS, 100-200Rpms

Discussion in 'The Projects Forum' started by cmac, Jan 4, 2010.

  1. cmac

    Thread Starter New Member

    Jan 4, 2010
    6
    0
    Hi..

    Hoping someone can offer a suggestion. I need a low cost motor to run at about 100-200 RPM for 15-20 minutes at a time once a day. The motor will drive a sifting screen back and forth 4 or 5 inches to sift manure from clean bedding in horse's stalls. I tried an old single speed drill on a dimmer (which I doubted would work..it did briefly then it burned up) I then tried a 3.5 amp variable speed drill which worked great until it heated up and started smoking after a few minutes. I am assuming these motors are not meant to run at restricted RPM's for any period of time. I thought about a larger, heavy duty drill but thought I may run into the same problem. Any suggestions on a cost efficient solution? The link will take you to a short video of the machine. Your insight would be appreciated.

    http://www.youtube.com/watch?v=tcOcwWF-rSQ

    chris
     
  2. whatsthatsmell

    Active Member

    Oct 9, 2009
    102
    4
    Use an old 1750 rpm AC motor someone has laying around. 1/4 HP is plenty. Put a small pulley on it and use it to turn a shaft with a 10x larger pulley on one end (rpm now 175) and an arm on the other end to oscillate your screen.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You're trying to drive a heavy load with a small motor that's not turning fast enough to move air through itself to keep cool.

    Whatsthatsmell has the right idea.
     
  4. cmac

    Thread Starter New Member

    Jan 4, 2010
    6
    0
    Last edited: Jan 5, 2010
  5. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    They will slow your motor, but your problem will still exist. If the motor is under a load it will heat up. Most motors are self-cooled by the spinning of the shaft itself. You will get a few minutes out of it, but it will succumb to failure.

    -ed- I should add that the items you linked to (in post #3), or the reason they will not work for your application, fan blades offer little load on a motor, and routers are hi-speed, lo-torque devices. so when you loose speed, you loose horse-power. For the amount of weight you want to load the motor, is a higher torque job. By slowing the device with gearing/pulleys the motor is running at its native speed and horse-power.

    whatsthatsmell has the best idea. Pulleys or gears will allow the motor to run at the speed it was engineered for cooling it properly while giving it the speed you want. If you have an old ten speed (or more) bicycle, you can use the gears and chain off of it to achieve your desired speed.

    -rm
     
    Last edited: Jan 5, 2010
  6. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
  7. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    I prefer the worm drive reduction type motors (often seen on the motors like the Bodine you linked to) because they are compact and can deliver large reductions. This is as opposed to the pulley-belt reduction method. That said, though, the pulley-belt reduction is easy to design and implement.

    Bodine motors are well-known and well-made. I've got a little grinding wheel that's been running on a little Bodine motor for at least 50 years. It's important in using them to make sure you're not exceeding the torque rating of the motor. You can get a very rough idea of the torque needed to turn the load using a spring scale and a lever arm on the shaft that has to be turned.
     
  8. cmac

    Thread Starter New Member

    Jan 4, 2010
    6
    0
    This gear motor that is 23lb/inch torque...in laymans terms how much pull is that? Weak or strong enough? Thanks
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    If you have a wheel that is 2" in diameter and put it on a shaft, wrap string around it and hang a 23# weight off the string. Now turn the shaft to pick up the weight. You have developed 23 lb/inch of torque.
     
  10. cmac

    Thread Starter New Member

    Jan 4, 2010
    6
    0
    so it the wheel were 4 inches in diameter.... would that 1/2 or double the torque? thanks
     
  11. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    It would take TWICE the torque to lift the same load. Simple leverage.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    That little motor and reducer won't be adequate for what you're doing.

    You need something much more heavy duty.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I was thinking more like a salvaged motor and transmission from a washing machine.
     
  14. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    That is a very good idea. Boy is your mother going to be mad the next time she goes to do laundry.
    sorry. Washing machines get pretty good torque, and the transmission has an auto reversing option that could really get things shakin'.

    However, if you were getting the power you wanted out of a drill-motor, you may be able to get away with the Bodine.
     
    Last edited: Jan 6, 2010
  15. cmac

    Thread Starter New Member

    Jan 4, 2010
    6
    0
  16. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    Very good. glad to see it.
     
  17. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
  18. cmac

    Thread Starter New Member

    Jan 4, 2010
    6
    0
    I noticed the past 2 mornings When I started my "**** shaker...for lack of a better term" the 1/3 HP furnace blower motor was slow to start up....hummed a bit...pulley was turning slow....started to smoke a bit...there is really little or now load on the motor..easily turned with hand....can cold (-10 celcius) affect an electric motor? I manually helped it along a few cranks and she started running normal. then started from a standstill a dozen times..on and off after that...it has started up from a stop many times before these instances so the temperature is all I can come up with...suggestions?
     
    Last edited: Jan 12, 2010
  19. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    This forum is strictly "G" rated; we like to keep it clean for the youngsters that come in here. :)

    Does the motor have a centrifugal switch? It could be that the contacts are getting contaminated with some of the debris that are being released during the shaking. If the motor "clicks" as it gets up to speed, then it has a centrifugal switch.

    It could also be a capacitive start motor; and the capacitor may be going bad.

    I'll tell you I wouldn't want to be breathing that stuff. :eek:
     
  20. whatsthatsmell

    Active Member

    Oct 9, 2009
    102
    4
    What gauge is that extension cord you are using for your supply, and how long is it?

    You may be limiting the amperage available for startup.
     
Loading...