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cooling fan rheostat , which one? speed control?

Discussion in 'Amps and Cabs [BG]' started by groovking, Mar 27, 2001.

  1. for cooling fan control i have a 4", 120vac, 260ma, 60hz, cooling fan, power input 22 w. does anyone know what ohmic value rheostat i should use for controlling fan speed? it now runs at max speed , and noise of 2200 rpm? any suggestions? this is an auxiliary fan. thanks all
  2. pkr2


    Apr 28, 2000
    coastal N.C.
    I don't think you'll be happy with the results of that experiment. All a rheostat does is lower the voltage that's feeding the load (the fan).

    According to Ohms law, The current goes up in proportion to the voltage going down with a given load. In other words, the fan motor would overheat if you bring the supply voltage down far enough to affect the speed.

    It would take a speed control circuit to accomplish your goal. The problem with that is that speed control circuits are very noisy and probably wont work with an induction motor. Much more expensive than just replacing the fan, also.

    Another point to consider is the fact that even if you get the speed lowered the noise from the fan would still be there because a noisy fan motor is usually a bearing prob in the motor or the fan blade is rubbing something.

    Sometimes a fan motor can be quieted down by simply getting some lubrication on the bearings. They are hard to get to though. Most of them will have a cover that blocks access to the bearing but a small hole drilled (or melted with the tip of a soldering iron) through the housing will let you get some silicon spray into the bearing. a drop of hot glue can be used to seal the hole up but isn't really mandatory cause you will eventually have to replace the fan anyway.

    This is a temporary cure, though. If the motor is noisy it really needs to be replaced.

    hope this helps, Pkr2

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