DIY Fan Controller for PWM Fans

I’m sure that most hardware enthusiasts are no strangers to dalliances with DIY, whether it be case modding, component modding, or custom cooling.  However, when it comes to building parts of your computer from scratch, the tally of enthusiasts who can claim this prestige most certainly diminishes.  Fortunately, this neat fan controller project requires only a little time, expense, and commitment, and the circuit is relatively easy to build and very satisfying to use!

First Things First…What is PWM?

PWM stands for Pulse Width Modulation and is, among other things, a very clever means of controlling power to electrical devices: in our case a DC (direct current) fan motor.  Although you don’t need to understand the ins and outs of PWM, it helps to have a rough idea about how PWM works, so here’s a very quick explanation.

Think of a PWM signal as if it were a beating heart.  Rather than being powered by a continuous supply of power (which would ordinarily be the case) our DC fan motor is being fed with pulses of power; it is essentially being switched on and off very rapidly.  These on-off pulses are delivered to the motor several thousand times per second, and because the intensity (or width) of each pulse can be changed, so the speed at which the motor turns can be changed.  The image below shows how different pulse widths affect the resulting power of the PWM signal:

PWM Controllers vs. PWM Fans

There are PWM controllers and there are PWM fans, but the way in which PWM is implemented in each differs greatly:  a standard PWM controller modulates the 12 V supply line of an “ordinary” 12 VDC motor. Conversely a PWM controller for PWM fans – such as the one featured in this article – doesn’t modulate the 12V supply line but instead sends a PWM signal along a different supply line (the magic “fourth wire”) to a more advanced 12 VDC motor, leaving the 12 V supply line uninterrupted.  Designated PWM fans not only have internal circuitry which differs from that of standard fans but because they are designed with speed control in mind the motors themselves are usually more advanced (and expensive).  So, PWM speed control of a standard fan is indeed very different from PWM speed control of a PWM fan…  Nidec even goes so far as to say that modulating the main supply voltage is not advisable:

Pulse-width modulation of DC operating voltage to modify fan speed is not recommended. Transients generated by that approach can irreversibly damage motor commutation and control electronics and dramatically shorten the life of a fan.

The Circuit

Here is the circuit which was originally obtained from Nidec’s website, although I found it in the overclockers forum:

Components

• 555 Timer IC (Integrated Circuit)
• Capacitors:  C1 0.01 μF; C2 680 pF; C3 10 μF; C4 0.1 μF
• Resistors:  R1 1k
• Potentiometers:  P1 100k
• Diodes: D1 & D2 1N4148

Building the Circuit

Now before you allow yourself to become intimidated by the above schematic and all these different components, make sure you are taking a calculated approach to the process of putting the circuit together.  The best thing to do is to take it one step at a time. Having done it myself (several times),  these are the steps that I find most conducive to a hassle-free workflow:

1. Plan your circuit on a piece of paper, familiarizing yourself with each component (learn what it looks like and what it does) and the layout of the circuit, and taking time to arrange it in such a way that it is clean and clear.
2. Working from your plan, carefully assemble the circuit on a breadboard.
3. Check and re-check all the connections.
4. Connect the circuit to a power source – preferably a spare power supply that is not hooked up to a PC – and check to see if it works.
5. Debug (identify problems and deal with them) if necessary.
6. Again referring to your circuit plan, assemble the circuit on a stripboard.
7. Work on the presentation of your controller – eg., put it in a project box or into a drive bay.

Step 1:  Organize Your Components and Print a Plan of the Circuit

So, now you know what each component looks like.  Once you have your components arranged spaciously on an uncluttered flat surface (as above), get your breadboard ready!

Step 2:  Breadboarding

The wonderful thing about breadboarding is that it doesn’t have to be neat or tidy…or even compact.  The point of breadboarding a circuit is to give you, the “beta tester”, easy access to each and every component and connection, allowing you to quickly sort out problems and get your circuit up and running without having to worry about making permanent connections.  Here are a few simple pointers:

• Take your time and keep your work area uncluttered.
• Make sure your hands and fingers are clean before you start.
• Use single-core wire for good connections to the breadboard tracks.
• Leave some room around each connection/component to reduce the risk of shorting.
• Remember to firmly press (but not force) the components and wires into place.

Step 3:  Check and Re-check the Connections

The reason this step is so important is that you are checking the connections solely with the power of observation; the breadboard should not be connected to a power source yet, and it is crucial that you carefully check each connection before the circuit gets anywhere near live wires.

Step 4:  Connect the Circuit to a Power Source and Test with a Fan

Connecting the breadboard to a live power source is, and always should be, the last thing you do (especially if you are a n00b, like me).  It is also advisable to use a spare/unconnected power supply, because if you happen to be so unfortunate as to cause a short circuit using the PSU that is connected to your computer, it may seriously damage the PSU and/or one of your PC components.  I can attest to this – my first attempt at a fan controller some weeks ago fried my treasured £300 Foxconn motherboard.  The PSU is fine (and has survived at least three further short circuits), however, my experience tells me that even a good PSU like mine which has commendable SCP (short circuit protection) doesn’t guarantee the well-being of your components.  You have been warned!

And remember:  This circuit uses 5v, NOT 12v.

Step 5:  Debugging

Circuits generally don’t work the first time around, so be patient and acknowledge that you will probably have to do some debugging somewhere along the line.  It’s not a big deal, and although it may involve a fair bit of work, don’t worry about it – I had to debug my circuit (and in some ways, I am still debugging it), and I had the overclockers.com forum community helping me every step of the way as I’m sure they will help anybody else who seeks assistance.  To make your life is a lot easier, get a digital multimeter if you don’t already have one.

Step 6:  Stripboard, Solder, and Sweat

When the time comes to make a proper circuit using scary grown-up tools like a soldering iron and a pair of wire cutters, it is definitely worth your while planning the layout of your circuit once again and trying to make it as compact as you can.  If you have space on your stripboard you might want to consider soldering a 4-pin fan header onto it to keep the controller tidy and practical.

The layout that I chose (above) is almost identical to the schematic of the circuit, which helped a great deal when the time came to put the circuit together and make sure all connections were made in the right place.  Stripboard has copper tracks that run along the underside of the board, so you must plan your circuit to accommodate these tracks and remember to break the tracks where necessary.  Here is a picture of the underside of my stripboard where the 555 IC is, hence the broken tracks:

Here is a picture of what is possible if components are extremely well laid out – this particular circuit was built by Martinm210 at overclockers.com forums and features a slightly different PWM generator using a 556 IC (two 555’s in one package) – see below for a schematic of this circuit:

Step 7:  Presentation

This is the icing on the cake.  You have finished your controller, but you don’t like the bedraggled morass of wires and terminals sitting beside your uber-modded and meticulously maintained gaming rig… so what should you do?  There are a number of answers, and it really comes down to what you want to use the controller for.  I use my controller for testing (well, playing with) very powerful PWM fans, so I packed it up inside a neat little project box to make it look a little more sophisticated and to make it more practical too:

Developing the Circuit

As it is, the circuit should work well with most if not all PWM fans that you are likely to find in a hardware enthusiast’s box of tricks.  If, however, like me (and a few others) you want to engage in some turbulent tomfoolery with ludicrously powerful 12VDC fans (see below), you will need to boost the PWM signal or create a different PWM generator altogether which uses a 556 timer instead of a 555.  The circuits described below are featured in this exciting thread at overclockers.com forums.

Using Two 555 Timers

Here is a schematic of the dual-555 PWM generator.  This circuit boosts the existing PWM signal using an “inverted schmidt buffer” which was suggested by bing at overclockers.com forums:

Using the 556 Dual Timer

The 556 timer is a single 14-pin package that contains two 555s.  If you would rather build the more powerful 556-based PWM generator like the ones Martinm210 and Brutal-Force put together, here is the schematic (again, courtesy of bing):

(Components are identical to the 555 circuit but are labeled differently in this schematic:  C1 = 680pF; C2 = 0.01 μF; C3 = 0.1 μF; C4 = 10 μF, polarized.  There is also an extra resistor (R2) which has a value of 10K.)

Final Thoughts and Video

First and foremost, make sure you take your time if you decide to build this (or any other) circuit for use with your system – working with electricity is hazardous (and if not for you, certainly for your hardware!) so be careful.  I’ve shorted my PC (yes, my entire system) no fewer than FOUR TIMES since I started messing around with DIY fan controllers, and unfortunately one of these shorts fried my prized Foxconn X58 motherboard.  Suffice to say, I have been more cautious since.

On the plus side, these fan controllers are a lot of fun and can be very useful if you regularly benchmark your system and require powerful cooling at the touch of a button (as I do).  Here’s a short video which shows the capabilities of the 556 circuit when paired with some seriously powerful 120mm fans…

Thanks

Primarily I’d like to thank I.M.O.G. for playing such an important role in my PWM fan controller projects (he organized the purchase and international shipping of the San Ace fans for me – top dude!) and for giving me the opportunity to write this article.  I’d also like to thank Brutal-Force for his videos and his thread which inspired me to make a PWM fan controller in the first instance, and resident electronics expert, bing, who freely shared his electronic expertise and offered valuable assistance throughout the learning process.

– Dave (LennyRhys)