Way to slow down box fan?

Discussion in 'Home Repair' started by heathcliff, Jul 29, 2013.

  1. heathcliff

    heathcliff Guest

    Just bought a cheapo box fan, which we use in a window at night to draw in cooler outside air. However, even at the slowest of its 3 speeds, the fan is too noisy. I'd like to make it less noisy, which I think the best way would be to make it turn slower. I'm wondering if it would be possible to wire in a resistor in series with the motor to accomplish that. If so, what would be the correct specs on the resistor?

    thx, H
    heathcliff, Jul 29, 2013
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  2. You could try a regular light dimmer. It's easy to build a unit for what
    you wish to do rather inexpensively. You can use 4" conduit box,
    one with the rounded corners, a dimmer, a duplex outlet and a
    combination 4" metal box cover with a position for a switch and the
    duplex outlet. You can get a cheep three wire extension cord and cur the
    outlet end off and use it to supply power to your dimmer. You'll need a
    cord grip to attach to the 4" box. Another route is to use a
    regular handy box with rounded corners, dimmer, metal switch cover,
    cheap extension cord, two cord grips and cut your dimmer into the middle
    of the extension cord. It's very easy to make. ^_^

    The Daring Dufas, Jul 29, 2013
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  3. heathcliff

    micky Guest

    I know exactly what you mean about the noise. Almost any fan, when
    run slow enough, will be totally quiet.

    I don't know if a resistor would work, and rather than get into the
    possible problems, fire and everything, I'd recommend

    either a) getting a fan speed control and finding a box to mount it
    in, For the most part, the only fan speed controls I've ever found
    were the kind that fills the same size box that a wall switch or
    receptacle goes into. Pretty big. I did once come across, at an
    electronics flea market maybe, one about the size of a brownie, but I
    couldn't find a box the right size and ended up putting it one that
    was the right width and depth, but was 4 inches high.

    Hmmm, http://www.ebay.com/bhp/ac-motor-speed-contro The first one has
    a case and a cord l Not real attractive, but still.
    The second one I've never seen before. Only $6.50. I may switch to
    this if I ever need a sixth control.
    The two near the bottom are nice too


    has its own plastic box


    They didn't have any of this stuff 15 years ago, I think.

    Or b) getting a light dimmer, which usually comes already in a box and
    which also usually has a cord with a combination plug/receptacle, that
    you can plug the light [or fan] into and plug all of that into the

    Whenever I recommend this, I'm certain to get criticism about how
    light dimmers won't work with motors, and they are correct that they
    are not designed for the purpose, and once in a while I find a dimmer
    that will not work with a fan (probably it's the fan that is different
    from other fans, and less likely that the dimmer won't work with any
    fan.) but I have 30 years experience here, with about 12 fans and 3 or
    4 different kinds of dimmer, and I think only one fan, at most two,
    would not work with the light dimmer I tried it with. None have
    shown RF interference with the radio or tv.

    But you should never turn the speed down so low that the fan stops
    spinning. There were probably still be some current running through
    the fan motor, and if the energy in the current doesn't get turned
    into motion, it will be turned entirely into heat, with the
    possibility of a fire. (Although I seem to recall that I did test
    one combination, by turning the speed down just enough until it
    stopped, and letting it sit where it was always within my view for a
    30 minutes and feeling the fan to see how hot it was. And it was
    only a trifle warm, so I probably decided it couldn't get too hot.
    But still there is no point to turning the speed down so it doesn't
    turn, when it's just as easy to turn the fan off.

    I only use the AC about 10 days a year, fewer now that it has broken,
    so I have a fan in almost every room, even in the basement (which
    never gets that hot but on humid days, the fan feels good), and when
    the house is warm, I use them every day.

    In the bedroom I had a small table fan, and sometimes it would get too
    cold at night, as it cooled off but the fan was still on. So I took
    a thermostat from a burned-out big box fan, mounted it in a big
    plastic cap from a large aerosol can, and wired that into fan wiring
    so the fan turns off completely if it gets colder than where I set it
    while I'm sleeping.

    The dimmer I use the most they sold for maybe 20 years or more, but
    they don't seem to sell it, at least not in the same case now.
    It is like this one
    except the control box has square corners, is brown plastic, with a
    center plate that is brown metal, and a knob that slides up and down.
    (Perhaps a little better than a round knob when doing this in the
    dark) The only way to tell if newer dimmers work as well is to test
    one. This new one has the on/off switch built in, so that is very
    good, especially since it's not at the end of travel of a knob. You
    can turn off the fan without changing the speed, it seems clear.
    micky, Jul 29, 2013
  4. heathcliff

    micky Guest

    When the dimmer didnn't work with the fan, I mean that the fan didn't
    spin at all no matter what setting the dimmer was on. But the dimmer
    did work with other fans.

    If the fan spun at all, everything else was fine, IME.
    micky, Jul 29, 2013
  5. heathcliff

    micky Guest

    You can see this if you rolll the cursor over the slider control and
    see the enlarged picture of the dimple at one end.
    More dimmers

    micky, Jul 29, 2013
  6. heathcliff

    passerby Guest

    Small AC fans usually have shaded pole motors, RPM of which is frequency
    dependent. By cutting off part of the phase with a light dimmer you will
    just make it start even harder than it already is for this type of a
    motor. There may be *some* RPM control due to torque losses when dimmer is
    dialed down, but it's only a small percentage point around the designed
    RPM, not from 0 to the max.

    Since the actual complaint is noise, not RPMs per se, I would take the fan
    apart and try to balance the blades to deal with vibration. You know,
    disconnect the motor from power and spin the blades by hand. Mark which
    blade stops at the bottom, do it again. If the same blade stops at the
    bottom again, file some material off that blade, repeat until no single
    blade stops at the bottom repeatedly. Hard to say how effective it will be
    with lightweight plastic blades coupled to a badly constructed motor, but
    is worth a try. Not much else to do: if you have to look at the motor, you
    might as well just get yourself a new fan - motor is the bulk of the cost
    of it, anyway.
    passerby, Jul 29, 2013
  7. Ken,

    Return the fan and try another brand. If you can't find one that's quiet
    enough look into balancing the blades. That's where the noise is coming
    from, most likely.
    Forget the resistor.

    Dave M.
    David L. Martel, Jul 29, 2013
  8. heathcliff

    micky Guest

    A lof of fan noise is not caused by out-of-balance fans but by the air
    which is moving because of the fan. No matter how good the bearings
    or how well balanced the blades, if there is too much air moving, one
    can hear that. Many people may not mind or even notice, since it's
    the essense of a fan to move air, but I sure mind. Maybe that's what
    is bothering Heathcliff too.

    (My last 3 Chrysler LeBarons had 4 speed fans, and I almost always
    kept the speed on 2, almost the slowest, because that was the fastest
    speed I could not hear. After 23 years with LeBarons, I bought a
    Toyota Solara, which has 5 fan speeds. Sounds better, but only the
    lowest speed is silent. But the lowest speed moves less air than
    speed 2 (and maybe even speed 1) of the LeBaron. So I'm forced to
    use speed 2 and put up with the noise.

    (One of twenty reasons so far that the Chryslers (and the GM cars)
    were better than the Toyota.)
    micky, Jul 29, 2013
  9. heathcliff

    Bob F Guest

    Is it a lot quieter if tou hold it in the air so it doesn't touch anything else?
    If so, isolated it vibration wise, from the house structure with soft foam or
    something. Sometimes, most of the noise comes from the fan shaking the house or
    vibrating against it.
    Bob F, Jul 29, 2013
  10. heathcliff

    Nate Nagel Guest

    The real solution would be to get a quieter fan, as a resistor in series
    with the low speed will draw just as much power as the low speed does
    now, and shed all its heat into the airflow going into your house.

    I know, that's not the DIY way, but it's the truth...

    If you really, really don't want to do that for whatever reason, I would
    remove the 3-speed switch, wire everything up so the fan runs on its
    FASTEST speed, and get a triac based motor speed control so your fan now
    has infinitely variable speed.

    Nate Nagel, Jul 29, 2013
  11. heathcliff

    gregz Guest

    Newer box fans are noisy. I have an older kmart box which is very quiet.
    Many upright fans are very quiet.

    NO resistor.

    Some motor speed controllers are only for brushed devices. A heavy duty
    dimmer will probably work, but may introduce buzzing.

    gregz, Jul 30, 2013
  12. heathcliff

    micky Guest

    Not a bad idea, except there's no need to remove the 3-speed switch.
    He can just set it to the highest speed. Then, if he or the next
    user ever stops using the speed control, he'll still have a 3-speed

    However, my experience is that sometimes it's better to use the
    external speed control with the lowest speed. Frankly, I forget
    why, but it might have been this: Say the knob and the rheostat is
    such that one can set the control to any one of 200 physical
    positions. If the fan has natural speeds of 400, 800, and 1200,
    then at the low setting, one can control the speed in increments of 2,
    (2 x 200 = 400) but at the highest speed setting, he can only control
    the speed in increments of 6. If he's going to use a speed below 400
    anyhow, he'll have more control over the speed when the fan is set at
    400. (I'm not saying 400 or 1200 what, revolutions per something or
    other. I don't know what actual speeds these fans run at.)
    micky, Jul 30, 2013
  13. My suggestion was about a low cost experiment. I built a variable
    voltage box using a triac, pot, trigger diode, capacitor, single 120
    volt 15 amp outlet, cord, cord grip and sloped project box. I was able
    to use it for all sorts of things including shaded pole motors, light
    bulbs and universal AC/DC motors. If he uses a triac type dimmer, it
    should work. A dimmer using an SCR might not work very well. The link
    below is about LED dimming but shows the waveform output of a triac type
    dimmer. ^_^



    The Daring Dufas, Jul 30, 2013
  14. Dang, I forgot all about the dimmer already built on to the cord. The
    only thing I don't know about them is whether or not they use a triac.
    Perhaps one made to dim LED lamps would work better but those may use
    SCR's instead of triacs. I'm so use to building things I forgot about
    the ready made dimmers on a cord. o_O

    The Daring Dufas, Jul 30, 2013
  15. I have an 89 full sized Dodge van that's older than the girls I chase.
    The poor old guy makes all kinds of noise. I'm looking for a vehicle
    manufactured in this century like a small SUV and I'll keep the old van
    since it carries a lot of stuff and has a ladder rack. ^_^

    The Daring Dufas, Jul 30, 2013
  16. heathcliff

    micky Guest

    LOL. This reminds me of when I wanted to build a lid for lidless
    frypan, but you all convinced me to buy one meant for another pan or
    pot. (I had to go to 8 thrift shops, but it took only about 5 minutes
    each and was a lotl easier than making one.)
    micky, Jul 30, 2013
  17. heathcliff

    micky Guest

    Good plan.

    When I was in college my 80-year old cousin gave me his '50 Olds, in
    1968, I noticed a similar car and left a note trying to buy his
    back-up lights. He wouldn't sell but we became friends. He was 30 or
    35 and would drive his '50 olds around campus, saying he thought the
    college girls might find the car interesting. I'm sure none did, but
    I didnt' tell the guy since it seemed to be his whole social life.

    He had two models of the 50 Olds, or a 50 and 51, and he had a whole
    townhouse stuffed full of electronic parts, etc. on the first floor at
    least, that he bought in bulk at auctions. He lived somewhere else.

    Later, when my brother went to Viet Nam, he gave me his '65 Pontiac
    Catalina convertible, and when I left town 18 months after that, I
    couldn't take both. I didn't want to but I gave my Olds to my friend,
    so he had three!
    micky, Jul 30, 2013
  18. Man I wish I still had my 1981 Dodge Aries station wagon. It was a neat
    little car with bucket seats and four on the floor which was unusual for
    those funky little cars especially in a wagon. I got the roller cam from
    a later model 2.2L engine and it bolted right in and improved
    performance but the other thing that really helped was getting the
    clutch and flywheel off a turbo version of the 2.2L engine and it was
    a direct bolt in too. The friction surface and disk took up the whole
    flywheel which gave me the ability to lite up the front tires without
    any clutch slippage. Darn, I wish I still had the little critter. ^_^

    The Daring Dufas, Jul 30, 2013
  19. heathcliff

    Nate Nagel Guest

    For "Small SUV" I don't think anyone will ever top the Jeep Cherokee or
    early Grand Cherokee... everything since has either been too big or not
    capable enough.

    It'll be a sad day when mine dies but I'm hoping to postpone that day as
    long as possible.

    Nate Nagel, Jul 30, 2013
  20. Yea, I was thinking about an older Jeep Cherokee with the straight 6 in
    it because I loved my Slant Sixes in my Mopars. I even built a 170cid
    Slant Six with a 3/4 race cam. It was a real hoot to wind that little
    sucker up but I kept blowing the stock muffler off of it at high rpm. ^_^

    The Daring Dufas, Jul 30, 2013
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