One dollar variable fan controller

While trying out various computer and network gear, I quite often find the fans too loud. They are of course there for a good reason, but experience tells that the device usually works just fine with less cooling. Best case one or more fans can be removed altogether, even though that is typically not recommended. They are of course put there for a good reason..

Anyway, I have repeatedly found myself looking for an easy solution to control the speed of regular 12V fans. Something that is just plug-and-play. Ideally also cheap or even free.

Going through a 7805 data sheet for other reasons, I suddenly realised that a 7805 set up in variable voltage configuration (figure 4 in the data sheet) should work great as a fan controller. These 12V fans usually run just fine down to 5-6 volts, but at lower rpms, and thus quieter. Just what was needed!

The circuit is quite basic:

The circuit is pretty clever – by shifting the ground to a higher level than the common ground/0V level, we get the voltage regulator to output between ca 6V and 10.5V. The component values were ones I had in my junk box, making a point of only using scavenged parts (don’t forget a heat sink for the 7805!) plus a little piece of strip board, the cost for me was actually zero. Nice!

A possible drawback of the design is the fact that a linear regulator like the 7805 will get rid of all (well… most anyway) excess energy as heat. A proper heat sink is thus definitely needed. An option would be to use some kind of low drop-out voltage controller (to get the upper limit closer to 12V), but it would have the same issue with heat dissipation. A better/easier option is probably to use one of the many PWM fan controller ICs available (here is Maxim’s list, there are plenty others too), it deals with at least some of the heat waste issues. You might be able to get some free samples too if you just want to play around with them. Most of them are not too expensive though.

All working well thus, and the story could have ended there.. However, a week or two later i was pulling apart an old PC when I found a couple of Zalman Fanmate 2 controllers… Too much of a coincidence not to see what made them tick.

After pulling one apart it turns out it is using exactly the same circuit as above! They did go a bit cheap and skipped the smoothing caps though, seems to work fine anyway – the fans won’t care much about some noise on their power line.

Also, the heat sink seems quite small and the controller is only specced to 6W, which is half of what the 7805 should be able to handle (it can handle 1A, so 1A*12V = 12W max power, with a proper heat sink).

Interestingly enough the Zalman controller costs ca USD 7 – not a huge amount of money, but one dollar to buy the components of your own (or even zero!) is a lot better..

Some additional shots of the Zalman controller: