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Controlling the speed of a Delta fan via PWM? Answered

First off, i would like to state i am a beginner in this area of whatever this area may be considered to you (Not a complete beginner, i know one or two things...). With that being said, i may need things explained to me to a certain level of extent. 

The way i learn is hands on, and having a goal. Since i want to learn the basics of Pulse Width Modulation, i started looking around for a project, and had found one after my brother, a person who works in the International part of Technology (IT Guy.) gave me a project to work on, The project being, to control a 12 volt,  4 amp, 48 watt delta fan and the speed it spins at. His reason being, "I have two delta fans that do a wonderful job at cooling my ridiculously overkill of a computer. My problem, is that the amount of noise they make is too loud, and i would like to be able to adjust the speed of them in order to reduce noise." Since his motherboard cannot control the speed of the fans, he is looking of a manual way of doing it, sticking some sort of device in between the ATX power supply, and the input for the fan(s). The fans have three cables: Red(Positive) Black(Negative) and Blue(With minimal research, i believe this is a censor for the CPU to know at what speed the fan is running at. I also heard it is used for speed control? Someone please clarify.) Looking into methods of reducing speed, adjusting the Pulse width looked like the best idea. Now, for my question. How would i make a device capable of controlling the PWM of such device listed above? I would like to adjust speed via a potentiometer.

Thank you for your time and support,
-RocketPenguin/Nicola Tesla/LinuxJunkie


First off, PWM fans control the speed not by changing the voltage (well, they kind of do), but by changing the width of the pulse (hence the name pulse width modulation). Basically the controller sends a pulse of certain length (variable) and voltage (constant) to the fan which determines its speed. Imagine this as a switch being turned on for a certain amount of time, then being turned off, and this repeatedly in certain intervalls. Because the voltage is constant, hooking a PWM fan to a potentiometer will only result in it either being off or running at full speed. Wikipedia has a good article about PWM.

Now for your brother's problem:

I could not decipher if he's against front panel fan controllers in general or because the mentioned one just wouldn't withstand the given wattage.

In the latter case, check out the Lamptron FC-9. It allows easy control over up to four 50W fans. Sadly not even the manufacturer states if 50W includes the 4amp limit (as this is not a given), nor if it's PWM-compatible. Best bet would be writing them a mail. Still, this seems like the most comfortable solution.

In the former case and to accomodate your intent to learn about PWM:

Again, potentiometers don't work for PWM fans directly, you'd need a few more parts to pull that off. Overclockers has an article about building a PWM fan controller, but it will probably be a challenge to design the circuit and all parts to work with 4amp/50W.

I can also tell you that 4W potentiometers are not that cheap by comparison, and the second you exceed 4W (which for security reasons you probably should do) it gets quite expensive. At least this was the case when I was looking for sturdy potentiometers around here. I highly suggest you get yourself a smaller PWM fan to learn about PWM with.

But at least you now have a project to start out with.

Never said i was going to use a pot; I already know how PWM works and why a pot wouldn't do the same thing. Its not all as much about learning PWM as building it. Yes, i would learn in the process of designing one, but more over, i would get the job done. He cannot use a front panel device because there is simply no room for one, even with his massive case. It would interfere with the hard drive bay, and thus a front port cannot be used. In the above link you posted, that looks like it may work, and i may write them. Still the issue persists of it being in the way of the hdd bay. I have done past pwm projects, such as: LED dimmers via arduino and via chip and a pot, i have also made a pwm based plasma speaker, and a few other projects involving sound and light. I have a grasp on pwm, would like to learn more, but moreover, solve my brother's issue in this case.

Thanks for your response!

I'm sorry, I must've misread a couple of lines while skimming over the posts. I thought one of your questions was for an explanation of PWM.

But back to business:

Usually the fan control panels are quite a bit shorter than CD drives for instance, so they should not really interfere with a drive rack behind it.

If the front panel slot cannot be used as there are too many drives inside the case I'd say things are looking bleak. Any type of control circuitry will need some space, especially if you wish to access it from the outside.

Altough not the optimal solution, you could still go with the drive bay, build an external enclosure for it and mount it next to the case.

Otherwise I'd suggest to switch out fans for larger diameter ones as those would reduce the RPM/noise while maintaining the CFM.

With a case that fits 13 drives there must be several 200mm fan mounting options, he should make use of those.
Just in case, could you supply more information about his rig? Used case, drive bay loadout, front panel loadout, etc.? pictures of its inside might prove to be helpful. I might think of some other solutions given more information.

He is using a Cooler Master Cosmos II, size specifications and pictures can be found here: http://www.newegg.com/Product/Product.aspx?Item=N8...

Switching out fans would work, or even using smaller ones. But, that isn't the question, nor is it really much of an option in this case unfortunately. (He like to overkill everything, and already has two delta fans, and doesn't want to purchase other fans when he already has two turbines that he could use, with of course, this slight modification i am looking for.)

Thanks for replying!

Yeah, I kinda know that feeling. After my last PC overheated too often I built a monster myself, though compared to your brohters' it looks like a tame kitten. I did transfer all my 8 data HDDs to a NAS system though so I don't have that much to think about cooling-wise, there's a good airflow due to lack of drives in my case. And I can still access my files with 50MB/s over LAN, which should be good for just about anything. I'm really trying to understand what kind of profession warrants a 13-bay monster like that.

Anyway, unless he has 3 BluRay/DVD/CD drives or otherwise blocked the slots, he should have room for a panel. And if he does, he might have to think about the redundancy really being worth it. The reson I am insisting on this point is simply because it's the easiest, most elegant solution.

But if there really isn't enough room, then either you have to look for some in-line DIY PWM fan controller that you can tuck away somewhere deep within the bowels of this monster or build some external controller and slap it to the case.

Or as suggested before build an enclosure for the given Lamptron FC-9, use cable extensions and have it sit on his desk so he can control it easily. For better aesthetics you can even use some sort of cable canal.

I really do not see any other solutions.

The 3rd wire is reporting the RPMs for the motherboard to read. You won't need that wire to control the speed. There are a large array of chips that will give you PWM. It's all a matter of finding one that will support the power need of the fan.

A better project for playing around with PWM would be to control the brightness of an LED. Using a micro controller like an Arduino will give you experience in PWM as well as programming micro controllers.

IMHO your brother should buy a fan controller for his system. Then he would have a nice panel in a 3.5" or 5.25" bay that would give him easy access to the controls.


Cool beans! Thank you! Thats what i was looking for.

Have a nice day, and thanks for replying!

That fan controller would burn out very quickly considering that the OP stated 4A / 48W Delta fan. My guess is that it is probably the PFB1212UHE-F00. That fan is a behemoth of a fan boasting 252 CFM airflow!!! (and very loud at 66 dB)

Twenty minutes after replying, my brother also pointed this out to me, that it would burn out very fast. (EACH fan being 50w) Also, he added it cannot stick out of the device because it would get in the way of the 13 slot hdd bay... And about starting on an LED or using arduino. Already did both. I get the idea, but would like to try something harder, such as the project enstated above.