Like Tree1Likes
  • 1 Post By SMurf

Slowing Down a Fan (not in a computer)

This is a discussion on Slowing Down a Fan (not in a computer) within the Tech Board forums, part of the Community Boards category; Hello, Recently I bought an 18-inch desktop fan, ready for the summer. It has a rotary switch on it for ...

  1. #1
    Registered /usr
    Join Date
    Aug 2001
    Location
    Newport, South Wales, UK
    Posts
    1,266

    Question Slowing Down a Fan (not in a computer)

    Hello,

    Recently I bought an 18-inch desktop fan, ready for the summer. It has a rotary switch on it for three speed settings, but even the lowest setting is a lot like the back of a hovercraft.
    The whole point of my buying a largish fan was that it could run more slowly and quietly, while still moving a decent volume of air.

    With this in mind, I would prefer not to crack the control unit open in case I still want to return it for a refund.

    Is it possible to in some way constrain the AC (110-230V, 50/60Hz) input so that it runs more slowly? Or would I need to work on the DC side?

  2. #2
    Master Apprentice phantomotap's Avatar
    Join Date
    Jan 2008
    Posts
    4,415
    O_o

    I'm not much of an electrics guy so I don't even know if you could reasonably do this on the AC side without spending more than what a new fan would cost.

    That said, I think it would be safer to operate on the DC side in any event so that has my vote.

    Soma
    “Often out of periods of losing come the greatest strivings toward a new winning streak.” -- Fred Rogers
    “Salem Was Wrong!” -- Pedant Necromancer

  3. #3
    Registered User
    Join Date
    May 2010
    Posts
    2,919
    You could use a reostat to control the voltage to the fan, thereby reducing the velocity. Or you could use PWM to reduce the duty cycle. But probably the least expensive approach would be to return the fan for a smaller, lower velocity fan.

    Jim

  4. #4
    Registered User
    Join Date
    Dec 2006
    Location
    Canada
    Posts
    3,183
    It depends on the design of the fan. If it uses an AC synchronous motor, there's not much you can do. They run at a fixed ratio of the AC line frequency, and you can't change the frequency easily (short of moving to Japan). Decreasing the voltage will just make the fan run rough/noisy/break.

    If it's a DC motor decreasing the voltage may or may not work. It may not work because if the fan has a closed loop regulator it will just draw more current at the lower voltage to get the same voltage to the motor, and spin at the same speed.

    In short, there is probably no easy way.

  5. #5
    Registered User
    Join Date
    Mar 2011
    Posts
    500
    A smaller fan is probably your best solution.

    Multispeed fans typically use various taps on the field winding to select speed. Each tap effectively
    provides the fan with a motor of a different horsepower.

    A light dimmer type control reduces the effective voltage supplied to the load. There is a couple
    problems with that. If the horsepower is reduced below some certain value, the fan motor will
    be running in an overloaded condition, and will overheat. Also, dimmer type controls have a high
    frequency component in the power supplied to load. It is not a sinusoidal voltage, and fan motors
    are not typically designed to handle this high frequency voltage.

    -

  6. #6
    Registered User
    Join Date
    Oct 2006
    Posts
    2,590
    Chances are it's just a typical AC induction motor - the most common type of AC motor. Synchronous AC motors are actually quite uncommon. even 3-phase motors are much more common. With an induction motor, you can reduce the voltage and it will run at a lower speed. Look for a 5-amp variac on ebay. That would work really well for your purposes. Set the fan on high, and then use the variac exclusively to control the speed.
    Code:
    namespace life
    {
        const bool change = true;
    }

  7. #7
    Registered User
    Join Date
    Jun 2011
    Posts
    2,706
    Perhaps the simplest (safest, cheapest) solution would be to mount a vent to the front of the fan...

  8. #8
    Registered User
    Join Date
    Jun 2005
    Posts
    6,657
    Quote Originally Posted by cyberfish View Post
    It may not work because if the fan has a closed loop regulator it will just draw more current at the lower voltage to get the same voltage to the motor, and spin at the same speed.
    Drawing more current doesn't produce the same voltage at the motor. It simply means the motor will draw the same power (and hence spin at comparable speed).

    In any event, it would probably be easier and safer to get a fan that meets the need, rather than trying to coerce a fan to behave differently. Also easier to check the fan in operation before buying it.
    Right 98% of the time, and don't care about the other 3%.

    If I seem grumpy or unhelpful in reply to you, or tell you you need to demonstrate more effort before you can expect help, it is likely you deserve it. Suck it up, Sunshine, and read this, this, and this before posting again.

  9. #9
    Registered User
    Join Date
    Dec 2006
    Location
    Canada
    Posts
    3,183
    Quote Originally Posted by grumpy View Post
    Drawing more current doesn't produce the same voltage at the motor. It simply means the motor will draw the same power (and hence spin at comparable speed).

    In any event, it would probably be easier and safer to get a fan that meets the need, rather than trying to coerce a fan to behave differently. Also easier to check the fan in operation before buying it.
    Unless it has a switching regulator, that will give the motor the same voltage, and the motor will draw the same current when it sees the same voltage.

  10. #10
    Registered /usr
    Join Date
    Aug 2001
    Location
    Newport, South Wales, UK
    Posts
    1,266
    It is an AC induction motor. 50 Hz.
    I am itching to open the control box, because I would be interested to see what the rotary switch is doing to the circuit.
    Sebastiani likes this.

  11. #11
    Registered User
    Join Date
    May 2010
    Posts
    2,919
    Probably just switching to different "taps" of the motor windings, thereby changing the resistance of the windings to chang the speed of the motor.

    Jim

Popular pages Recent additions subscribe to a feed

Similar Threads

  1. Forums slowing down again?
    By VirtualAce in forum General Discussions
    Replies: 2
    Last Post: 05-16-2010, 01:06 PM
  2. Slowing down programs
    By Da-Nuka in forum Windows Programming
    Replies: 7
    Last Post: 12-27-2004, 03:50 AM
  3. Slowing down game
    By Superfrog in forum Game Programming
    Replies: 2
    Last Post: 09-29-2004, 06:31 AM
  4. Need help on slowing program down
    By zz3ta in forum C++ Programming
    Replies: 2
    Last Post: 11-23-2003, 09:39 PM
  5. slowing a program...
    By major_small in forum C++ Programming
    Replies: 4
    Last Post: 08-19-2003, 09:56 PM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21