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Hot Rods Question for the electrical gurus

Discussion in 'The Hokey Ass Message Board' started by Boneyard51, Jun 29, 2018.

  1. Boneyard51
    Joined: Dec 10, 2017
    Posts: 3,998

    Boneyard51
    Member

    I got a large fan in my shop that has a small 110 volt, maybe 1/2 hp,
    electric motor turning a large blade with a belt. Works great, but some times I want a little less air. Can I put a reostate or something to slow it down without hurting the motor?

    Bones
     
  2. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,146

    Rusty O'Toole
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    Not if it is AC, they are a constant speed motor. You could change the pulley or use an adjustable pulley. Or block the intake.
     
    sunbeam likes this.
  3. choptop40
    Joined: Dec 23, 2009
    Posts: 3,581

    choptop40
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    Hey hey, sure thing...a dimmer switch will do it....
     
  4. Well, it depends on what kind of AC motor it is. More than likely it's a brushless squirrel-cage type, and you'll need a frequency drive to adjust speed. These are now pretty cheap (compared to what they cost when they first came out) but will still set you back about $200. You can change a lot of pulleys for that...

    There's a remote chance it's a 'universal' motor (like what you'll find in hand-held power tools) and those can be controlled with a potentiometer (dimmer switch).
     
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  5. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,109

    gimpyshotrods
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    You can indeed control the speed of an AC motor with a variable autotransformer (aka: Variac).
     
    belyea_david likes this.
  6. Chappy444
    Joined: Jan 27, 2012
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    Chappy444
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    1. Maryland HAMBers

    sunbeam likes this.
  7. xpletiv
    Joined: Jul 9, 2008
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    xpletiv
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    from chiburbs

  8. GMC BUBBA
    Joined: Jun 15, 2006
    Posts: 3,384

    GMC BUBBA
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    I would use the dimmer light switch.....
     
  9. Sheep Dip
    Joined: Dec 29, 2010
    Posts: 1,572

    Sheep Dip
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    from Central Ca

    Now's the time to tell the wife you need a bigger shop to fit the fan!:D:D:D
     
  10. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,146

    Rusty O'Toole
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    Crazy and Gimpy are right, it is possible to control the speed of an AC motor IF it is the right type of motor, made for such use. OP did not specify, just that it was some kind of large fan with a 1/2HP motor. 99 chances out of 100 such a fan uses a common type of motor that must run at some multiple of 60 cycles per second if it is not to overheat and burn out.

    Or if you use an expensive type of controller which not many of us have lying around.

    If he said ceiling fan, then it would most likely have a variable speed motor.
     
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  11. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,146

    Rusty O'Toole
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    I'm picturing either a squirrel cage fan off an old furnace or a large industrial exhaust fan like a giant box fan.
     
  12. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,146

    Rusty O'Toole
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    Probably the cheapest solution would be to buy a pulley with graduated sizes and switch the belt to change speeds.

    [​IMG]
     
  13. I think you would need two multi-groove pulleys, or continually have to change the depth of the remaining single pulley so the belt runs straight.


    Phil
     
  14. 49ratfink
    Joined: Feb 8, 2004
    Posts: 17,689

    49ratfink
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    from California

    I'd like to help, but I am an electrical swami not a guru.
     
    46Chief likes this.
  15. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,146

    Rusty O'Toole
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    You would need to adjust the belt or put the motor on a spring loaded mount.
     
  16. Terrible80
    Joined: Oct 1, 2010
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  17. winduptoy
    Joined: Feb 19, 2013
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    Drive ratio of the driven (motor) to the driver (fan).
    If the motor has a variable pitch pulley, you can open it up. This moves the belt deeper in the pulley making it effectively smaller so it has to turn more times to one revolution of the fan. Pulls less current too.
     
  18. Jack E/NJ
    Joined: Mar 5, 2011
    Posts: 585

    Jack E/NJ
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    from NJ

    The winning suggestion!!! And 3-speeds too. 8^)
     
    Blues4U likes this.
  19. oj
    Joined: Jul 27, 2008
    Posts: 6,247

    oj
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    A lot of them have capacitive start and an internal gizmo that switches the capacitors 'Off' when the motor hits 'run' RPM, if you use a frequency drive to lower it below that RPM bad juju will happen.
     
  20. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    Member
    from Wisconsin

    There are variable pitch[diameter] sheaves available. Buy one that the od is the same as the one on the motor and open it up so the belt drops in deeper to slow the fan.
     
  21. bubba55
    Joined: Feb 27, 2011
    Posts: 316

    bubba55
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    Me thinks a dimmer light switch taint rated high enuff fer the amp / current load
     
  22. alwaysamopar
    Joined: Oct 2, 2015
    Posts: 115

    alwaysamopar

    gimpyshotrods likes this.
  23. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,839

    sunbeam
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    Last edited: Jun 30, 2018
  24. Boneyard51
    Joined: Dec 10, 2017
    Posts: 3,998

    Boneyard51
    Member

    Thanks guys, I’ve been out camping... no service. I think the answer for me is to put some hinged doors on the back of the fan to restrict the air. Is an upright shop fan about four foot blades. I built it years ago to cool the shop at the dept. Was Ok there in the big shop, just pushed it back to where I liked it, now my home shop is not that big. Thanks.

    Bones
     

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