First of all, sorry for my lack of knowledge in the subject. I have a Nidec TA450DC B35502-35 fan which I've installed in a large wooden cabinet where my computer and other electronics sit. This cabinet of course gets hot from all the electronics inside of it. The fan forces air in from the room and goes out through openings in the top of the cabinet. This fan has 4 wires: red (+12v), black (ground), and then blue and yellow. I'm using only red and black to give the fan full 12v power.

Nidec Website

The problem is since it's at max speed, it is way too loud. I have a simple toggle switch to turn it on and off. What I would like to do is replace the toggle switch with a knob to adjust the speed. I don't know how to use the other two wires to control the speed.

What kind of knob do I need to get, and how should I wire it? The minimum setting of the knob should feed the fan with its minimum required power to spin at the lowest speed possible, and the highest setting should spin it at full possible speed.

I don't have any problem with soldering a small circuit board together for this project, I just have no idea what schematic I need to put together. I've played with electronics and their components all my life but don't know nearly enough to even begin understanding how to accomplish this. It should be simple, right? Should I be using one or both of the additional wires for this, or should I use some method of adjusting the voltage?

  • \$\begingroup\$ This may not require an electronics project. Many motherboard support adjusting fan speed. Have you checked the documentation of your motherboard? \$\endgroup\$ Jun 22, 2012 at 1:23
  • \$\begingroup\$ Gotcha. Read that wrong at first. \$\endgroup\$ Jun 22, 2012 at 1:36
  • \$\begingroup\$ Not sure what happened to my comment in-between Ben's comments. But My comment was pointing out that I'm not asking about installing a fan in a computer. I'm asking about hooking up this fan to a raw power source and controlling it myself. \$\endgroup\$ Oct 4, 2014 at 0:50
  • \$\begingroup\$ Go shop for "12 volt Adjustable speed controller". Should find plenty in many styles. Shopping questions are off-topic here at EE.SE. \$\endgroup\$
    – user105652
    Jul 29, 2016 at 21:22
  • \$\begingroup\$ @Sparky256 How is this a shopping question? The core of the question is "What kind of knob do I need to get, and how should I wire it?" Also, this was asked 4 years ago and already has an accepted answer. Rules change over time. \$\endgroup\$ Jul 29, 2016 at 22:01

3 Answers 3


This should help you design a standalone PWM controller:

From Nidec

PWM Circuit

This is a simple PWM controller directly from Nidec (so I can guarantee it will work with your fan, though it's also compatible with other schematics, as long as the schematic works for a 12VDC 4-pin PWM computer fan). A 1k resistor, a 100k pot, two schottky diodes, a 555, and a handful of capacitors. Simple circuit, all you need is a +5v (so a regulator shouldn't be too hard to run off of the 12V supply you're using for the fan).

From Overclockers Forums

(The entire thread, many different schematics there for you, for different styles/applications)

You'll note they are very similar circuits. After building the circuit, you connect the fan's blue wire to the PWM Output of this circuit, then connect it to +12VDC and use a common GND with the circuit.

(Despite my constant use of Overclockers.com, I'm not trying to plug them. It's just somewhere I've seen a great how-to for how to build your own PWM controller, and the schematic is completely done out as well. I'll try to permalink it here for you.)

  • \$\begingroup\$ The Nidec link is dead. See web.archive.org/web/20130511050339/http://www.nidecamerica.com/… \$\endgroup\$
    – Dan D.
    Aug 31, 2014 at 5:27
  • \$\begingroup\$ @DanD. Updated the dead link accordingly! \$\endgroup\$
    – Shamtam
    Aug 31, 2014 at 5:43
  • \$\begingroup\$ I know it's an old Q/A, but honestly I'm getting back into this now. I've replicated this schematic in a simulation, but the square wave isn't exactly square, just an observation. I might be doing something wrong: multisim.com/content/YYhmY9mFTFKpT64NFZRYXC/… I wonder if it's because I'm not using Schottky diodes, because I cannot find it as an option on that site, so I just went with a regular one. \$\endgroup\$ Feb 6, 2018 at 1:22
  • \$\begingroup\$ @JerryDodge Schottky diodes can be more-or-less simulated by just setting the forward voltage to 0.3V. In any case, that doesn't really change the waveform. The waveform the simulator spits out is close enough that it should work fine for the application. \$\endgroup\$
    – Shamtam
    Feb 6, 2018 at 2:24
  • \$\begingroup\$ Thanks, I figured out what I was doing wrong. I was capturing the actual wave from the wrong place. Technically, still not an absolute perfect square, but close enough. \$\endgroup\$ Feb 6, 2018 at 2:25

The blue wire is a PWM control signal which can be used to adjust the fan's speed. The yellow wire is a PWM speed sense that can be used to read the speed out of the CPU.

To control the fan's speed, you need to give it PWM: a square wave adjusted to the speed you desire. This is doable with a microcontroller's PWM peripheral.

I'll direct your attention to this article:

  • \$\begingroup\$ This appears to be assuming it will be plugged into a motherboard... my fan is powered with a plain 12 volt DC adapter... \$\endgroup\$ Jun 22, 2012 at 1:56
  • \$\begingroup\$ Hmm, you're right, the linked schematic is not what you are looking for. I'll see if I can find something better. \$\endgroup\$ Jun 22, 2012 at 1:59
  • \$\begingroup\$ You have to mention a 555 timer to maximize upvotes, that coupled with a schematic gets the users whom just upvote pictures. Problems solved, upvotes acquired!(555 will run off of 12V, hint hint) \$\endgroup\$
    – Kortuk
    Jun 22, 2012 at 2:04
  • \$\begingroup\$ Heh. There might be a way to get a 555 timer to do this, but honestly I can't in good conscious recommend it. I also do not believe an analog voltage will work as I suggested in my original answer. I read the schematics wrong. A small PIC or Atmel part should be able to do this without much trouble but yes, you will have to write code for it. \$\endgroup\$ Jun 22, 2012 at 2:07
  • \$\begingroup\$ I don't mind if I ignore the 2 extra wires and just add a voltage controller... I just need to know how to add a knob which is able to adjust the speed from minimum to maximum and anywhere between. \$\endgroup\$ Jun 22, 2012 at 2:09

I hope you got that cooler fan thing figured out as its been a while but I couldn't help but see the lack of attention to the Question that these brilliant engineers gave you. I wish I had the formal training they have. I have this same fan and I'm using it for other than mfgr. intended applications as well. First thing I wouldn't put a PC inside a cabinet to keep it cool, it needs all the cool outside air it can get. **You were on the right track in the beginning, all you need is the Blk(-) and Red(+) wires in the harness. Get a Dash-pot (like a volume knob with off position, "clicks off at lowest setting") and a small capacitor to help start the motor and that's all you need to throttle the fan inside your Electronics Cabinet between the 9-12 volts, you can find new parts at local radio shack or use components from a scrape appliance (recycled parts). Note that most power adapters true output is sometimes much higher than it says due to that fact it is intended to charge batteries, of say 12volts it might actually push as much as 18 volts. A volt meter will help you there, you can put a mark on your control knob for the new 12volt while under a load setting for each perspective 12v power adapter you might use. There are many ways to manage maximum output from installing a permanent voltage meter to just getting the specs for a voltage regulator to install inline between the power source and the dash pot. That really is a nice fan, good luck.

  • \$\begingroup\$ Good answer...if a bit late. In the future please break down your wall of text into small paragraphs. It is difficult to get votes if the answer is a wall of text-people tend to skip over them and go to something else. Read some of the good answers on this site to see how it is done. \$\endgroup\$
    – user105652
    Jul 29, 2016 at 21:53

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