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USB powered desk fan

Discussion in 'Electronic Basics' started by [email protected], Apr 1, 2007.

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  1. Guest

    It is hot in my office and for some reason I don't have any available
    power outlets near me to power a desk fan so I want to make a fan that
    is powered by USB. I bought a cheap handheld fan that is powered by 2
    AA batteries (3V) and I want to convert it to run off a 5V USB
    computer port. I need to step the voltage down from 5V to 3V. What
    type of resistor would I need to do this? It would be nice to make
    the fan have adjustable speeds so would I use a potentiometer to do
    that? What type and rating? I greatly appreciate your thoughts.
  2. Sigh, it is the first of April.
  3. Guest

    I am using this article as a reference for my design...
  4. But you can now buy all kinds of junk that plugs into USB ports merely
    to get power from the USB port. Fans, LED lights, cellphones and IPods
    so you can charge them, some things even more nonsensical.

  5. A fan?
  6. Guest

    I would rather build the fan myself because if looks like a fun
    project. I calculated from ohms law v=ir that if v=3 and i=2.8amps (2
    standard AA batteries) then r=1.07 ohms. Are my calculations and
    units correct? I went to radio shack earlier but could not find a
    1ohm resistor or potentiometer. Do I have my units off in my
    calculations? Am I thinking about this incorrectly?
  7. A fan has to move enough air to make one feel noticeably cooler. This is
    mostly based on evaporation from the skin and air flow. People who can't
    sweat don't appreciate fans. Battery operated fans normally must be held
    about 5 inches from one's face to achieve any effect. USB power limits
    would make for an anemic fan.

    This is simply April 1, which follows March madness, el-regurgitatia.
  8. Si Ballenger

    Si Ballenger Guest
  9. Tom Biasi

    Tom Biasi Guest

    Your calculations used the wrong data.

  10. A properly designed USB port only supplies 1/2 amp.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida

  11. If there are no outlets, how are you powering your computer? If
    there are no outlets, why hasn't the building inspector condemned your

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  12. Guest

    wow. lots of bird walking going on here. i just want to know if i can
    put a resistor in series to reduce 5v to 3v and what the value of the
    resistor would be. if anyone has the ability to answer this question
    please help. otherwise please leave your 2 cents in your pocket.
  13. This has nothing to do with challenges.

    If you asked "can I hook up a fan to a USB port", you'd likely get
    the same sort of answers. The fact that you are "certain" that it
    can be done is a failing of too many beginner's questions, they ask
    something they think will be a solution, leaving out the intermediary
    steps that likely are important to the ultimate solution. You've already
    gone down a path, without being sure that path is the right one.


  14. You still haven't told us how much CURRENT the lousy fan draws. Of
    its over 500 mA (1/2A) it can draw too much current and damage the
    motherboard. You know WHERE you can put your two cents.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  15. jasen

    jasen Guest

    coffee warmers, lamps.

  16. jasen

    jasen Guest

    Rather than a resistor 3 1N4001 diodes in series will be about right,
    not that this is necessarily a good idea: if the fan seizes it could
    damage your computer.

  17. Is it bird walking? Keep your 2 cents and hire a consultant.
  18. Guest

    I don't know how much current the motor draws. I bought a cheapo
    battery powered fan from the drug store. It takes 2 AA batteries to
    power it. That means 3V total and whatever the current of 2 standard
    AA batteries are. Anyone know what the current would be for 2 AA
    batteries? There is definitely a solution to this problem because we
    all know that you can buy a USB powered fan at the store.
  19. Rich Grise

    Rich Grise Guest

    Go to the battery manufacturer's web site and look up the AH (Amp Hour)
    capacity of your model of cells. Get a fresh set of cells, turn on the
    fan, and see how long it blows before its output is useless. Divide the
    AH capacity by the # of hours it ran, and that will tell you how many
    amps of current the fan draws. You might get more life out of the
    batteries if you turn the fan off for, say, 10 minutes every hour - but
    be sure and record the "run" time accurately.

    Or, you could stick an ammeter in series with the batteries and motor,
    and measure it. :)

    Good Luck!
  20. Lord Garth

    Lord Garth Guest

    Put in fresh batteries and run it until it dies, recording the time it takes
    to expend the cells OR get yourself a current meter and measure the
    demand of the fan OR just hook it up and hope for the best.

    Case in point, my Sony Vaio laptop powers an external 2.5" hard disk
    with no trouble at all yet my Dell can't run the same drive without
    resorting to the external power pack.
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