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An Intelligent 12V Fan Controller

Does your computer make more noise than it should? It's probably mostly fan noise! Slowing the fans down will reduce the noise but if you go too far, you could end up with fricassee of CPU!

By Geoff Graham

The High Points

Control up to eight computer fans based on the measured temperature

Windows software for configuration and display of temperatures and fan speeds

Stand alone (does not need the Windows software or computer to run)

Monitor up to four temperature points

Works with most fans (2, 3 and 4 wire)

Audible alarm on fan or sensor failure

In a typical personal computer most of the noise – and it can be significant – comes from the cooling fans. That’s because they run at full tilt all the time, regardless of the temperature, inside the case or out.

You may need to run the fans at full speed when you are encoding home movies on a 40°C day but most of the time they just blow air around, creating a lot of noise.

Click for larger image
That's not a fan, that's a FAN! One out of the archives – and we're not even sure our Intelligent Fan Controller would be able to power it!

This can be especially bad if you have a Media Centre PC in an otherwise quiet lounge room or home theatre. If you would like to hear the “sounds of silence” then this project could be just what you need.

Using just two ICs and a handful of components this intelligent fan controller will regulate the speed of up to eight 12V fans. It will measure up to four temperature points and use this data to smoothly control the speed of the fans, from completely off to fully on.

There are other ways to control the speed of fans but they tend to be rather crude. That is why we called this project an Intelligent Fan Controller.

One of the crude methods, unfortunately far too common, is to simply wire the fans to 5V rather than 12V. They will then run much quieter but more importantly, they will not be able to do their job on a hot day – and you risk incurring the damage that the fans were supposed to avoid.

Another simple method of control is to wire a variable resistor in series with the fans. You can buy some fancy looking controls that will mount on your computer’s front panel; some even include a temperature display. But that requires you to be constantly monitoring the temperature inside your computer and adjusting the resistor accordingly.

You may be fortunate enough to own a computer with a motherboard that has a fan controller but even they have limitations, mostly in the number of fans that they can control.

Not just computer fans

While computer fans are the obvious target, this Fan Controller is certainly not limited to computers. Because it can run independently (without being connected to a computer) it could control the fans in a greenhouse, home brewery or just about anything else that uses small (12V) fans.

Just bear in mind the current limitations mentioned later in this article.

The details

The Intelligent Fan Controller is built on an 100 x 80mm PC board, designed to fit in a spare 3½ or 5¼-inch drive bay or any other handy spot inside your computer’s case.

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