How to control PC fans with a Pot?

Hi all;

I've got 2 PC fans (12V dc running from a 500mA rated supply). Thing is, whenever I try to use a pot to control their speed, the pot starts smoking.

This has just got to be possible, but everything I try just smokes the pot.

How can I control the fans with a 1/4 watt pot? do I use a transistor and use the tranny to control the base current, thereby avoiding the power dissipation issues?



Reply to
Markus Stone
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You're using the wrong method to control the pot.

Use a pulse width modulation system. Jaycar sell a DC motor speed control kit for about $24. It's an overkill (designed for motors up to 10A), but it will do the job. The kit number is KC-5225. Or you could use a 555 timer as a PWM, driving a transistor or a FET.


Use a 3 position switch that switches the following to the fan.

  1. 5V and 0V - low
  2. 12V and 5V - medium (the fan sees 7V)
  3. 12V and 0V - high

Reply to

"Markus Stone"

** Use an LM317 adjustable regulator IC to vary the voltage.

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........... Phil

Reply to
Phil Allison

I found this very helpful..

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I can email you a simple circuit if you like Mel


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