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12 volt Fan help needed

Discussion in 'Misc Electronics' started by L W, Dec 6, 2003.

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  1. L W

    L W Guest

    Hello:
    Kid has me building a "snow-machine" for a school play, it will blow
    white confetti out of several pvc tubes, However......... it is about
    twice as strong as we need for a realistic effect, we used a standard 2
    terminal 12 volt auto heater/defroster blower fan, Any ideas what size
    resistor paralelled in the hot lead might cut the power/speed to about
    half???
    Thank you & Happy Holidays!!!
    J.
     
  2. CWatters

    CWatters Guest

    A resistor will probably dissipate a lot of heat. Here are two other ways to
    do it that avoid the problem..

    1) Try a 6V battery if you can find one.

    or

    2) If the motor has a rating label that gives you the wattage (eg 100W) try
    connecting car headlamp or other bulbs with a similar rating in series with
    the motor. Bulbs of the right size are likely to be easier to get than
    resistors and you might even have spares in your car. The bulb will get hot
    so you need to take car. Mount it in the airflow?
     
  3. Mark

    Mark Guest

    Make the tubes twice their diameter, or cut some holes with a sliding collar
    to get the required pressure.
     
  4. The resistor will have to be a very high wattage one, and it is
    connected in SERIES, not parallel to drop the current through the
    motor. The value of the resistor would be hard to calculate, because
    the torque of the motor would be reduced, and the mechanical load may
    not be constant all the time.

    You need to lower the voltage, not put a series resistor. See if you
    can get a varible supply, or see if you can have a 6 Volt source for
    it. This should drop the speed.

    Or use an AC fan. These mostly all come with a speed control. You can
    get a big floor fan, and just throw the confetti in front of it. In
    the TV studio we use about 6 to 10 of these fans when we do the stage
    shows that need confetti. We get a bunch of people to throw the stuff
    in front of the fans, and it goes all over the place! If we want to
    have the look of snow, we throw the white stuff from up in the
    lighting grid.

    In the black and white days when I was starting out, when we wanted
    the look of snow, we used to use cornflakes. It was funny. The stage
    hands were eating the cornflakes while throwing them down to the floor
    to make the snow. Occasionaly the people on the set would grab some
    and start eating them when they were off camera. With colour TV, and
    the quality of TV today, cornflakes would not look very good for snow.
    For large flakes we used to use popcorn. The actors were sweating
    under the hot lights in the studio, because they had to be dressed
    like out in the winter.

    Yea... I am getting on in years.


    Jerry Greenberg
     
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