Two dollar variable fan controller

Well – given current exchange rate, AU 2.59 = USD 2.33.. So it’s not quite a two dollar product, but pretty close. And “2.33 dollar fan controller” did not make for a nice subject line…

After the earlier post about variable 12V fan controllers, it might be worth looking at what is available on Ebay. Turns out you can get a variable controller delivered anywhere in the world for USD 2.33 – pretty amazing! It looks deceivingly like the Zalman Fan Mate 2 too:

Zalman Fan Mate 2 (left, USD 7) and eBay ditto (right, USD 2.3)
Zalman Fan Mate 2 (left, USD 7) and eBay ditto (right, USD 2.3)

The eBay controller only has one 3-pin male connector (where the fan connects), and then a soldered in wire with a 3-pin female connector, for attaching to the PC or other equipment.

The Zalman on the other hand has a 6-pin male connector on one end, a special Y-cable (it comes with the Fan Mate 2) is then needed to hook up the controller to fan and PC. Both variants of course work, the Zalman approach is maybe slightly better, as it allows the controller to be mounted closer to an inside corner, without the cables being in the way. Not a major difference though.

Looking inside the eBay controller, it is obviously different from the Zalman. For starters, it has a NEC B772 P PNP medium effect transistor in there, rather than a voltage regulator. I could not find a datasheet for that particular NEC device, but I am pretty sure it is more or less identical to ST’s 2SB772.

There is also a TL431 adjustable voltage regulator in there, together with a second SOT23 transistor market J6, it might be a S9014 NPN transistor (or equivalent).

So, in essence the eBay controller is also a linear regulator, but based off an adjustable regulator (rather than the fixed-voltage 7805 that the Zalman uses), with an extra power transistor to boost current. The extra transistor is needed, as the TL431 can only sink 100 mA on its own.

All good so far. But when reverse engineering the eBay controller, the schematic just doesn’t add up. Below is what the eBay controller looks like, with the above assumptions on components – and this is not a working circuit, as far as I can tell (or is it? Feel free to add your expertise in the comments!).

eBay variable fan controller - except that the circuit is a bit weird.. Need to re-check those PCB traces!
eBay variable fan controller – except that the circuit is a bit weird.. Need to re-check those PCB traces!

So…. either I made incorrect assumptions regarding what SMD components are used in the eBay controller, or I just didn’t check closely enough how the PCB traces were connected. Time to bring out the multimeter to check those traces – more to come on this topic.

One dollar variable fan controller

2013-08-09_22-06-40_copyWhile 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:

7805 based variable fan controller
7805 based variable fan controller

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/easiesr 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.

Zalman Fan Mate 2, variable fan controller
Zalman Fan Mate 2, variable fan controller

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: