How to control PC fans with a Pot?

[Markus Stone]

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?

Thanks

-Markus

 

[swanny]

Markus Stone wrote:

everything I try just smokes the pot.

really?

 

[dmm]

On Wed, 1 Jun 2005 21:23:21 +1000, "Markus Stone" <markusm@alphalink.com.au> wrote:

Hi all;

How can
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.

You're using the wrong method to control the pot.

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?

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.

OR

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

Thanks

-Markus

 

[Phil Allison]

"Markus Stone"

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?

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

http://www.hw.cz/data_ic/lm317.pdf



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

 

[NormL]

I found this very helpful.. http://www.cpemma.co.uk/index.html


"Markus Stone" <markusm@alphalink.com.au> wrote in message
news:429d9ac0@news.alphalink.com.au...

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?

Thanks

-Markus