How much can I slow down a fan motor
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  1. #1
    Bill D is online now Titanium
    Join Date
    Apr 2004
    Modesto, CA USA

    Default How much can I slow down a fan motor

    Kinda off topic, but it might apply to shop fans/vents.
    I have a whole house fan which is two speed. I bought a speed control which should work on the air over Permanent Split Capacitor motor. Any thoughts on how much I can safely slow down the motor? I know it has to run fast enough so air flow going over/through the motor will cool it. Do you think I should wire the speed control to the high or low speed winding. Even at low the fan is too loud.
    Bill D.

  2. #2
    JunkyardJ's Avatar
    JunkyardJ is offline Titanium
    Join Date
    Oct 2007
    Howell Mi

    Arrow Well, most fan motors can be varied by voltage.

    I'd say there's a good chance you can vary the speed of your whole house fan pretty easily. I have a friend that plugs those big box fans into a harbor freight router speed control to cool his garage in summer. They can be slowed down to about 1/10 speed and STILL START! You can get them to spin slower, but you have to turn up the speed up first. Your house fan should be the same basic type of motor, and you can slow it down as much as you want so long as it doesn't overheat, and doesn't stall. I'd wire it for low speed, or leave the speed switch, and run it in low. Those speed controls tend to get touchy toward the bottom end, and having the motor allready in low might help with that. If nothing else, you might want to put the speed switch for the fan elsewhere so you still have the option for high speed.

  3. #3
    Damien W is offline Stainless
    Join Date
    Aug 2006
    Brisbane, Queensland


    The way I read this thread the issue was fan noise and reducing fan speed may be only one way to reduce the noise, what about an accoustic baffle? Or is it possible to reduce air flow by modifying the fan or its blades?

    My Uncle had a ventilation fan installed in the lower floor stairwell of his home so that fresh cooler air is drawn in through the windows of the house upstairs and drawn out by the fan in the stairwell. I suppose that this might be called a forced air ventilation system.

  4. #4
    Dave Johnson is offline Aluminum
    Join Date
    Oct 2007
    Pleasanton, CA


    I have a 2500 CFM attic vent over the TIG area. I control it with a fan speed control, of the proper rating. I can turn it down to the point there is no fan noise, but I can see the blades turning. But, I can also hear the motor hum. Been using it for a couple of years, without problems, but it's not on full time.

    If you never want full speed, wire it to the low speed.


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