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Speed!!

Discussion in 'Misc Electronics' started by D O'Reilly, May 14, 2004.

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  1. D O'Reilly

    D O'Reilly Guest

    I have an electric fan in my bedroom when even on its slowest setting
    is far too
    powerful,can anyone tell me how to adjust the fan with some sort of
    device or switch to lower the rpm's,your help would be most
    appreciated.

    Dave.
     
  2. Patch

    Patch Guest

    Is this a ceiling fan or a stand alone fan?
     
  3. Zak

    Zak Guest

    The simplest is probably a light bulb in series. The lower the wattage,
    the slower the fan will run.


    Thomas
     
  4. D O'Reilly

    D O'Reilly Guest

    It is a desktop fan that runs from a 240volt mains supply.
     
  5. John Fields

    John Fields Guest

    ---
    Connect the fan to the mains through a zero-crossing solid state
    relay.

    Use an optoisolator as a zero-crossing detector across the mains,
    divide its output by two to get nice sharp edges, and use the output
    of the divide-by-two to gate a counter.

    Shine an IRLED through the fan blades and place an IR phototransistor
    in the beam on the other side so that when the fan is rotating it
    chops up the beam and turns the phototransistor on and off.

    Use the output of the phototransistor to clock the counter which is
    being gated by the divide-by-two.

    Connect the counter's Q outputs to the inputs of D type flip-flops,
    and use one of the divide-by-two's edges to simultaneously clock the
    accumulated count into the D flops and clear the counter.

    Connect the "A" set of data inputs of a magnitude comparator to the
    outputs of the D flops and the "B" set of data inputs to the outputs
    of a manually operated binary coded switch.

    Connect the B>A output of the magnitude comparator to the control
    input of the solid state relay.

    Turn on the fan and adjust its speed by changing the setting of the
    binary coded switch.

    Or use a µC... ;)
     
  6. Mjolinor

    Mjolinor Guest

    Or chop every other blade off the fan :)
     
  7. John Fields

    John Fields Guest

    ---
    Gross...

    An odd number of blades will make the fan vibrate right off the table.

    Schematic at abse...

    Enjoy!
     
  8. Mjolinor

    Mjolinor Guest

    I could agree with that, pretty gross :)
     
  9. Mjolinor

    Mjolinor Guest

    I think that with careful selection of blades it should still be possible to
    statically and dynamically have a balanced blade if you remove an odd number
    (possibly 3), one at one side and two several blades apart at the other.
    Could still be cheaper, more reliable and easier going for your option
    though.
     
  10. Guest

    Guest Guest

    get a dimmer switch,

    blow the fan at a wall
    so you get the reflected blast.
     
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