Want to add speed control to attic fan

Discussion in 'The Projects Forum' started by couser, Jun 16, 2013.

  1. couser

    Thread Starter New Member

    Jun 16, 2013
    I have an attic fan that has two speeds and the low speed is still a bit noisy.

    I'd like to add a speed controller like this one at Amazon: Enerlites Fan Control . This is rated for 5 amps.

    The fan draws 4.7 amps on high and 2.4 amps on low.

    I think it's a PSC motor. I can see a cap that is wired into the motor. Likely a start cap, I don't know if there's a run cap but I could check.

    What are the ramifications of putting a speed controller on this motor? Overheating, motor life, etc.?

    Thanks in advance for your help!
  2. Metalmann

    Active Member

    Dec 8, 2012
    I think you should get one closer to 10-15 Amps.

    Here's a comment about that switch:

    "This motor speed control works well for me. I'm using it on a 1/4 horsepower fan motor and low does stall the motor, but this powerful motor isn't as capable of very low speeds as other fans may be; like ceiling fans. When set to High the fan runs as fast as it does with no speed controller. This unit is plastic and isn't heavy, but doesn't seem junky to me. If you want a really heavy duty speed controller, look at Router speed controllers."
  3. couser

    Thread Starter New Member

    Jun 16, 2013
    I'm wondering why you would go with something capable of 10-15 amps when the fan draws less than 5amps. I usually run it at 2.4 amps and that's too noisy.

  4. wayneh


    Sep 9, 2010
    A motor that isn't turning may draw 2X its running current when it starts up. You don't want to burn up your controller. If the PEAK current is truly below the controller's rating, you may be fine. But it's very hard to measure what that peak is, hence the 2X rule of thumb.
  5. couser

    Thread Starter New Member

    Jun 16, 2013
    Thanks! Great explanation.