Plenty of overclockers use fan controllers. With each controller we sweat the Watts each channel can control, and calculate how many fans we can put on a single channel. What if we didn’t have to worry about that? That’s why Pulse Width Modulation was imported into fan control.
Introduction to PWM
Almost all motherboards can control fans with PWM, which stands for Pulse Width Modulation. A PWM fan has the normal three wires — ground, 12 V, and RPM reporting — and an additional 5 V control line. The PWM control line varies in its “duty” from zero to 100%. The intermediate settings are made with 5 V pulses that signal the circuit board of a PWM fan to tell it how fast to spin. You can emulate a zero duty state by poking a grounded wire into a PWM plug’s PWM control line. You can emulate a 100% duty state by poking a 5 V wire from the PSU into a PWM plug’s PWM control line. What you can’t do that way is produce the intermediate settings.
Motherboards can, and do, produce those intermediate settings to control PWM fan speed. If you have a heatsink with a PWM fan and you have set it to Auto you will hear the fan speed up from slow to fast as your CPU proceeds from idle to load.
Some PWM heatsinks come with PWM Y-cables that allow two fans to be controlled by PWM. Akasa makes PWM harnesses for three and five fans so you can control a number of fans with the motherboard. In the case of the Akasa PWM splitters, the power for the fans comes from the PSU via a Molex connector, so you don’t have to worry about overloading your motherboard fan header. Having such a PWM splitter would allow water coolers to have their fans respond to the cooling needs of their CPU’s. I use my PWM splitter to increase the air being fed to my CPU heatsink when it needs more. It’s really an elegant way to adjust your fans automatically.
What if you want to control your PWM fans manually? Zalman has just what you’re looking for, the PWM Mate.
Specifications & Features
(Courtesy of Zalman)
|Zalman PWM Mate Specifications|
|Dimensions||55 x 24 x 13.5 mm|
|Output PWM Duty||25-100% ± 5%|
- The World’s First PWM Fan Speed Controller – The controller modulates the PWM (Pulse Width Modulation) fan speed control signal allowing user defined PWM fan speed settings.
- Variety of Control Modes – The 3-Step Automatic Mode and a Manual Mode provide flexible customization of fan speed control according to the user’s environment.
- Convenient Controls – The Mode Switch Button, Manual Speed Dial, and Mode Indicator LEDs provide convenience and ease of use.
That articulated cover on the left is a push button. The dot to the left of the green light is a two-color LED. When you press the button, you get a blue light in the left LED that tells you the PWM Mate is pulsing at 50% duty. When you press it again you get a magenta color (blue + red) in the left LED that tells you you’re getting 75% duty. Press it a third time and the left LED shines red. Now you’re at 100% duty. Finally, press it a fourth time and you’re back to the right LED shining green, which means you’re in manual control mode. Twist that little knob on the right and you get a pulse duty range of 25% to 100%. Very simple, and it works.
Here is a fan plugged into the PWM Mate. You can see the plug that fits into a PWM fan header. That’s where you get the 5 V needed to run the PWM control. Be sure to have your motherboard’s speed control disabled.
How well does it work? I plugged the PWM Mate into an adapter I made so it can get pure 5 V and 12 V from a PSU. As best I can tell, the knob turned all the way counterclockwise delivers a 25% signal. When the blue light is lit I seem to get a 50% signal; magenta is 75%; red is 100%. Green, with the knob turned all the way clockwise is 100%. The 25%, 50%, and 75% are all approximations. All fan’s PWM runs at whatever speed they are programmed. It doesn’t have to be linear.
What surprised me is that the 100% settings are exactly 100%. My experience with motherboards led me to expect speeds that were 90-95% of what the fan gets when it is on pure 12 Volts. This little controller gave me 100%. What a lovely present Zalman has delivered! The PWM controller works exactly as advertised. I’m impressed.
Here is a PWM Mate hooked up to a motherboard’s CPU fan header:
- You can also see two fans connected with a Y-cable. Note that socket where the Y-cable is plugged in. The white wire and the wire next to it are the ground and 12 V wires. They are split at the socket, so the controller gets a ground and a 12 V power supply. But the fan or fans get the same, and their ground and 12 V supplies run directly to the fan, not through the PWM Mate. Hold that thought.
What the PWM Mate Needs
This little fan controller is great. Is anything wrong with it?
Yes. Well, no. But it needs something. It needs an adapter so it can get its power from the PSU, via Molex. That way it could power fans that draw more current than a motherboard can supply. As it stands now, you could burn out at least the fan power circuits of a motherboard if you tried to control a heavy duty fan with the PWM Mate hooked to a motherboard’s PWM header.
Okay, that thought you were holding. A fan gets its 12 V power and its ground connection without bothering the PWM Mate. So, with the right connections (sounds like New Jersey, right?) you could power a heavy duty fan, control it with the PWM Mate and leave the motherboard out of it.
Pardon the mess, but here is such an adapter:
Next to the fan you can see the Molex connectors. Swooping counterclockwise from there is the sleeving that contains the 12 V, 5 V, and ground wires. It ends where it meets the PWM Mate’s plug. Running back clockwise again is the yellow RPM wire that allows the fan to report its speed to any fan header. This adapter allows me to connect the PWM Mate to 12 V and 5 V power from PSU. With this adapter I can attach a fan that would otherwise overdraw a motherboard’s fan header.
In place of my adapter I could plug in a PWM splitter. That would allow the PWM Mate to control a lot of fans — a whole rad full of fans, for example. And because a PWM splitter draws its power directly from the PSU, a PWM Mate could control some powerful fans that would burn out any little plastic box, if they tried to draw their power there.
That’s what this little gem needs. Can’t expect everyone to make their own, and not everyone needs a PWM splitter. I understand why Zalman made it the way they did: the PWM Mate got its start as a PWM controller for one of their heatsinks. But an adapter similar to the one above makes it far more versatile.
I am mightily pleased with my PWM Mate. It works as advertised, and I recommend it.
- It’s dead easy to connect.
- The knob gives you a smooth adjustment in PWM duty from 25% to 100%.
- The button gives you 50%, 75% or 100% duty with a few quick clicks.
- This controller really does give you full speed (100%) when you want it.
With power from the PSU and a PWM splitter, the PWM Mate can be an even more useful controller. Here are five PWM fans plugged into an Akasa FP5 — a 5-way PWM splitter. The FP5 is plugged into the PWM Mate. The FP5 and the PWM Mate are plugged into the PSU. All of this allows me to get PWM variable speed control on five fans with nary a motherboard in sight.
Note to Zalman, if you are reading this: add an adapter like the one I made and your little box can control even monster fans. Not having an adapter is not really a downside. It’s a missed opportunity.