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Discussion Forum

Dimmer Switch on Blowers????

Mooney | Posted in General Discussion on December 8, 2005 03:20am

My fireplace inserts blowers are to high speeded . Id like to turn them down several notches.

Ive looked in the shop and have come up with a light diller switch?

That work ?

Tim

 

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Replies

  1. User avater
    RichBeckman | Dec 08, 2005 03:59am | #1

    Please don't take my word on it. I'm just guessing that the answer is yes as long as the dimmer is sufficiently rated.

    Rich Beckman

    Another day, another tool.

  2. sawdust58 | Dec 08, 2005 04:16am | #2

    You must be careful to use a dimmer rated for a motor, a dimmer used on a paddle fan would do if the amperage draw of the blower is not to great.  A lighting dimmer will burn out very quickly

  3. IdahoDon | Dec 08, 2005 04:19am | #3

    I'm pretty sure it depends on the type of motor used in the fan as not all motors are suitable for easy speed control.

    Unfortunately, I haven't remembered enough to help identify your motor, or to recite which types of motors are easily controled.

    Best of luck,

    Don

  4. Ray | Dec 08, 2005 04:38am | #4

    If the motor has brushes, look for a speed control used for tools (drills, routers).  That would be more in line with motor control than a lamp dimmer.  Sorry, can't tell you where to look, I haven't seen one for years.

     

  5. DanH | Dec 08, 2005 05:01am | #5

    The motor is almost certainly a shaded pole induction motor.  The best fit would be a ceiling fan speed control, but use of one could shorten the life of the motor.  It would not be unsafe, though.

    A simple light dimmer should not be used.

    If ignorance is bliss why aren't more people

    happy?

    1. Mooney | Dec 08, 2005 05:35am | #6

      Sorry every body , I know better than to ask a question without enough information.

      Big Dummy me.

      It looks like a very small turbin fan which already has a variable speed switch. 1 1/2 inch by about 9 inches long. That the right name for it ? Same as a blower motor in heat and air but miniture.

      Cant see the ratings of the dadgum thing and besides its black in there . <G>

      Cant see how to pull it either.

      Tim

       

      Edited 12/7/2005 9:36 pm by Mooney

      1. DanH | Dec 08, 2005 05:44am | #7

        It would be helpful to find out how the variable speed switch works -- whether there are multiple windings on the motor, or the switch just switches resistors in and out.
        If ignorance is bliss why aren't more people

        happy?

        1. Mooney | Dec 08, 2005 06:24am | #8

          Im supposed to be snowed in tomorrow .

          Ill work on it if thats the case.

          Thanks,

           Tim

           

  6. pah51 | Dec 08, 2005 09:11am | #9

    Most small AC blower motors I've seen are designed to run either single speed or multi speed. The multi-speed motors are usually controlled by switching the windings in and out.
    I would not use a lighting dimmer to control the speed of a motor. The standard dimmer that I have used controls voltage through an electronic semiconductor device called a triac but does not simultanously alter the frequency which is necessary to vary the speed of a standard single speed AC motor. To run a single speed AC motor variable speed, you will probably need some kind of electronic drive that will vary the frequency as well as the voltage (VF drive) but in addition, the motor needs to be designed to withstand the exrta heat that is generated at slow speeds. You may want to contact the motor/blower supplier to see if yours can be operated VS and if so, do they have a controller to drive it. Good Luck.

    Edited 12/8/2005 1:33 am ET by pah51



    Edited 12/8/2005 1:35 am ET by pah51

    1. DanH | Dec 08, 2005 03:53pm | #12

      Actually, induction motors are not synchronous but always experience some degree of "slip".  Varying the voltage WILL vary the speed, within a significant range.  Ceiling fans are induction motors and do fine with variable voltage.

      Interesting thing about an induction motor is that it's really a DC motor with an inductive (non-contact) commutator.  You can actually turn a DC motor into an induction motor by removing the brushes and shorting the commutator contacts together, then just supplying juice to the field winding.

      The max speed of an induction motor is limited by the AC frequency, however, and it loses torque rapidly as the voltage is reduced.  The loss of torque isn't a major problem in fan applications, however, as torque varies with speed.

      The hazards with an induction motor under variable voltage controls are simple overheating and overheating due to the hysterisis losses caused by the electronic control.  Presumably a ceiling fan control would be designed to cause lower hysterisis losses.  It's hard to predict whether a given induction motor will tolerate this heating.
      If ignorance is bliss why aren't more people

      happy?

  7. DavidThomas | Dec 08, 2005 09:47am | #10

    pah51 has got it right. Light dimmer switches reduce the voltage. Reducing the voltage to an AC induction motor will simply cause it to run hot. Or not at all.

    You need to reduce the frquency which a much more complication endeavor. Also available off-the-shelf, but it won't fit in a light switch, 2x4" junction box. Also, it won't cost $10.

    I'd first look at getting a replacement electric motor with the same frame size, shaft size, voltage, and rotation (CW or CCW) but of a different speed. Then it could be plug-n-play. Look at Graingers first.

    Blower that have multiple speeds have multiple wires to access the different combination of windings. In a DC motor, a resistor (or triac-reduced voltage like a modern dimmer switch) will work. Like the defrost fan in your car.

    David Thomas   Overlooking Cook Inlet in Kenai, Alaska
    1. User avater
      maddog3 | Dec 08, 2005 02:45pm | #11

      I am thinking that the motor is only ####shaded pole with a squirrel cage fan.......the speed control would be quite easy to find...
      like you said ......Grainger ...or any small motor shop would have a 5A rheostat....<$20Mooney needs to make sure that the blower is ALWAYS turning though...to provide air circ. over the motor .....if the motor stalls it WILL overheat and eventually fail

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