In the past few weeks, I've done a lot of searching on this topic. As I look around me at the tangle of molex connectors, piles of ruined diodes and soldering iron burns in the carpet, I thought...perhaps I could spare someone else this pain. So, I've decided to compile a short guide on how to feed your fan something less than 12 V (use of the word "controller" is a little misleading for some of these). Most of these are quite simple, and hopefully one of these will meet your needs.

Why build your own fan controller?

• You're just looking to under-volt some fans, not control the universe.
• You just found SPCR today, and you want to do something NOW!!
• You're as cheap as they come. ("Hey, is that a penny??")
• It's fun to make stuff!!

The controller's we're going to cover fall into two basic categories...simple, and dangerous. Well, perhaps not dangerous, but they might require using a soldering iron, or at LEAST use of a wire stripper. If using a wire stripper scares you, and your spouse won't let you use the other kind, then you'd better stick with the simple controllers.

Simple Fan Controllers

Here's what you'll need:

• A molex connection. You'll often find a short section of wires connecting a male and female molex connector at the end of a fan connection, basically a power pass-through. These are great for modding.
• A molex pin remover. You can either buy one, or make one. Do a google on molex pin remover and you'll find info on both. I made mine using that guide and it worked great.

With those simple ingredients, we can make our simple fan controllers. There's two we'll try.

1. The 7 Volt Mod
   
   • Good: 7 volts is a good compromise between noise and airflow for most fans.
   • Bad: It could kill your power supply (read blue caution box).
   A little explanation on the PSU problem, since this is a common question. Essentially, when you create the 7 volt molex plug, you're taking current and feeding it back into the PSU. Normally, current only goes out the 12 V and 5 V lines of the PSU. To create the 7 V plug, you're taking current out the 12 V line, and putting it in the 5 V line. In theory, if the current is low enough, the PSU will be able to handle it. Just be aware that the PSU was not designed to do this, and there is anecdotal evidence that it can kill a PSU.
   
2. The 5 Volt Mod
   
   • Good: No danger to your power supply, and a really quiet fan.
   • Bad: Not all fans start reliably at 5 volts, and you might not realize it until too late.
   
   Both mods have virtually the same process, so refer to the following links for info on both mods.
   cpemma's great guide
   Mike C's guide
   Bleedin Edge guide
   Maybe the best guide (lots of pics!)

Slightly More Complex Fan Controllers

These controllers actually give you some measure of control. You'll be able to create a range of voltages your fan can use, and some let you switch easily between them.

For some of these, you WILL have to solder. Soldering is easy to do, and low risk (as long as you have good health and property insurance). If you're a newbie to soldering, such as I am, then these guides are REALLY helpful:
A basic soldering guide
Not only is this guide from NASA, but it is all movies!!!
If PDF's are your thing...
Another great guide, complete with a first aid section!

Now that you're fully armed with soldering knowledge...we'll start off with a controller that doesn't involve any of that!

cmcquistion's Terminal Block controller

• Good: No soldering! And, gives you a wide variety of voltages to use.
• Bad: It's not very presentable, so you'll have to hide it in your PC. Also not very good for changing a fan's voltage "on the fly".

Mike C's fan speed switch

• Good: Allow for switching between two voltages. And no little magical electrical parts involved.
• Bad: Almost belongs in the simple controller section, except soldering is most likely involved here.

A PWM Controller

• Good: PWM control adds some capabilities straight voltage controllers can't.
• Bad: Not all fans respond well to PWM, and this stuff makes the Diobus seem like childs-play.

The well-known cpemma Diobus
Also shown here, thanks to Alleycat

• Good: Use a knob to switch between voltages while the fan is running. Add LED's for a visual indication.
• Bad: You should definitely understand wiring schematics for this one. And there will be soldering.

CPemma's site is excellent, by the way, for information, fan controlling ideas, etc. Highly recommended to read no matter which project you undertake.

Well, I think this is a good start. I'll add other controller ideas as I hear about them. Also, this thread might be useful stickied in this forum for all the boneheads out there who don't know how to gather information. Otherwise, if you don't feel this post is worth keeping in this forum, then don't reply to it and it will slowly sink to the bottom of the forum and die....along with my pride

Edit: Added PWM controller link, thanks to jamesm.

I've got a cute little tip:

What to do if you're too cheap to get a Molex connector

You can rig up a "ghetto" connection to a floppy power connector. You just need to buy a roll of solid copper wire (not stranded). I think 18 guage is the right diameter, but I'm not positive. You want wire of the same diameter as a header.

Just strip off about half an inch off the end of a some of this wire, and you can push it securely into one of the PSU's floppy power connectors. Strip the other end of the wire and you can twist it with the (stranded) wire of your fan. Wrap this up with electrical tape for the complete "ghetto" look, or use heatshrink for a more professional look (while you're at it, you might want to actually use solder).

You can even make your own 4 pin floppy drive "header" using another floppy drive power connector. Strip off a length of solid copper wire. Cut it into 4 short pieces--each almost twice the length of a floppy drive power connector. Insert these 4 short pieces of wire into the sacrificed power connector. Voila! The 4 pieces of wire stick out like a 4 pin header.

So far, my mods have relied on these "ghetto" methods. No solder or heatshrink for me--just twisting wires together and electrical tape. It works for me.

I'm biased as an EE, and in my mind, this is worth keeping for the link information alone. I'm stickying it.

Woohoo! Is making a lasting contribution to an SPCR forum equivalent to making a Paypal donation?

Here's a simple version of cpemma's rotary switch fan controller which I posted a while back.

Thanks for the info. that's a better picture than cpemma's site, I think. Added it above.

Wow, all those diodes looks like a lot of work! Is there a particular reason why you can't just use a potentiometer? Obviously, you'd want one with a sufficient current rating.

To guarantee known fixed voltages?

how do you do this with a 3 pin fan? i just got a 120 mm fan and it is LOUD, my pc can be heard from 30 feet away, so i unplugged it..

You could look into getting a 3-pin to 4-pin converter. Using that, you can use the above methods of modding your own stuff.

Or you could just add a 3-pin header to your fan control circuit.

Well (and anyone correct me if I'm wrong here), the voltage terminal strip controller works just great with bare wires. Your 3 pin fan really only uses 2 of those wires.....the 3rd is for RPM measuring by the motherboard. So that means the other two wires are +12 V and GND (not sure which is which, but that info abounds in these boards somewhere).

So, snip the 3 pin connector off, separate the wires, and connect the + lead to the voltage terminal strip (just screw the bare wire on), and connect the GND wire to a GND off a molex connector.

Make sense? Or am I missing something important (sure wouldn't be the first time).

I only snipped the fan's black and red wires to connect them to the controller, and plugged the connector (with just the yellow wire still attached) to a motherboard header so that I could still get RPM readings. I heard someone say that this could damage the motherboard, but I don't see how that could happen and I've had no problems at all.

This thread is over a year old, and I'm only just now go around to checking it out lol.

Excellent link compilation you've put together here. First rate job.

Heh...well, as long as I was learning stuff, I figured I might as well document it so others could too.

I'm still willing to add more DIY fan-controllers to the original post, if anyone describes one for me. But hopefully the info that IS there is useful to ya.

That's exactly why I started the 120mm sticky thread, though naturally such a subject is far more volatile as products come and go. Simple electronics are wonderfully consistant (remarkable if we're just a product of an explosion, I know).

_Definitely_ a help. I actually have most of those linked bookmarked somewheres.... This thread will save me the agony of organizing the hundreds of bookmarks scattered over dozens of FF profiles just to find these links.

Just now looking in to the matter as my primary workstation has been a case cover-off rig, which of course allowed free, unfettered access to the inside the case whenever I wanted. Got new guts for the machine and now going cover-on, hence the rekindled desire to peruse over threads I've seen and bookmarked, but never really looked at.

A DPTP Switch or two + a few terminal strips should do the trick nicely...

DrCR

I used Mike C's switches in my rig, patching together two swiches, one of the exhast and gpu fan, the other for my intake and cpu fan. When I was looking to do some gaming, I'd flip that switch and my Solo went from whisper to jet engine. Worked great though and everything stayed cool as a cucumber when it needed to.

I'm moving into a p182 for the extra HDD space and want something a little more nuanced, so I sold out and went with the zalman 6 channel fan controller.

I feel like a quitter, but the last time I soldered I burned the holy hell out of myself and my wife said she wouldn't let me pick up the soldering iron ever again because of the smell.

I have a couple articles on my website regarding fan control. Maybe someone will find them useful?

• Fan Jitsu
• Thermostatic Fan Controller

Just as I was about to delve into the wonderful world of PWM, mobo mfgrs started putting PWM fan control onboard. I haven't built a fan controller since.

I liked the idea of the tri-cool switches (Low-Medium-High settings) at the back of my P182 so I just modded the wiring so I can plug my 2 SlipStreams (or any other fans).

It is a very simple circuit : all you need is 2 (1watt) resistors by fan. Soldering is an option, you can just tie the resistors with the wires. Dont forget to always use electrical tape around every connections.

The wattage of the resistors depends of the current consumption of your fan.

I ran all the wires to the back of the case so nothing seems unusual.

First off this stuff is great, thanks. Second, I want to try and build something a little more powerful. I was wondering if I could run the 12v power from one of the three pin fan connectors on the motherboard to a transistor to control 8 120mm fans in series(4 pin molex of course). This way I could control all of them with speedfan. Any ideas or a point in the right direction would be great!

Why would you want to run them in series? The voltage (and hence) speed would drop with each fan in the link. You wouldn't really know what any of the fans were doing at any given time (except the first). I think you meant running them in parallel which would output the same voltage to all fans at once.

You do NOT want to run any more than 1 or 2 (maybe) 120mm fan on a motherboard header. You will blow the output by drawing too much current. You need a bay controller or two.

Why do you need 8-120mm fans? That's an awful lot of fans, I don't even know a case that will fit that many.

Running a couple fans in series is sometimes done by us, specifically to reduce the voltage and speed. For example, two identical fans in series connected to 12v will each see 6v. However, I don't like to do this because it tends to produce a "pulsing" effect. The resistance of a fan isn't constant, but varies. As a result, the two fans will interact with each other in a weird way.

Still, running 8 fans in series is pretty crazy. Even if the load were constant, 12v would only supply 1.5v to each fan (few fans reliably start at that voltage).


In parallel? Yes. Multiple fans in series, in contrast, would actually draw less current. For example, putting two fans in series will double the resistance, and thus halve the current.

Okay, how about in parallel? there are 8 120s on two water cooling units(4 on each). Plus there are a few more fans in the case. I know the 3 pin header can't handle much, that is why I wanted to build a unit with a transistor to control the 12v soure(4 pin molex CONTROLLED by the 3 pin fan controller with a transistor).

This is what I was thinking of, sorry but I'm not much of an artist. There probably has to be a resistor in there somewhere to limit the current on the base or something. Maybe an optoisolator instead of the transistor?

A really basic circuit, that one will heat up. It is more suitable for small or low power fans. You may notice that I used a small SMD resistor, so I only need 2 wires on this transistor:

I found and built this controller: http://www.modding-faq.de/index.php?artid=510

It's in German but the project is very simple, if someone needs translation, just ask. This controller also features a capacitor in case fan needs a high starting voltage. If you choose a beefy transistor it can power several fans. It works very well and is very small.

If you could provide a basic translation I would most appreciate it, had a look in google translate and while most of it makes sense, a couple of bits have me confused.

Thanks in advance.

Sure, although I'm no electronics expert. This is only for valtage controlled fans, no PWM. I built it for two Noctua 140mm fans and it works very well.

If there is a specific question, ask. I assume you can read the electronic schematic on page one. Just be careful to copy the wiring correctly. The cap will probably explode if wired incorrectly, so cover your eyes or the board before trying it out.
By the way, fourth column of the table, which shows the needed parts has part numbers for a german shop.

This design starts the fans at almost 12V for a second due to the capacitor. After that it uses the speed you set. There are two controls, one is speed the other is minimum speed. The first is supposed to be external (if you want that) but the second should prevent the fans from stopping if you turn the first control too low.

Speed signal isn't touched, just it connect directly to the fans. The controls are potentiomenters, I used smaller trimmers for both since I don't adjust the speed after initial setup anymore, and I can hide the controller inside my case.

The T1 transistor 2N3055 is OK (alternatively TIP 34A and maybe BD643), and alternatively comes in a more compact TO-220 package, which needs a heatsink. In the picture they used the larger package. This larger one only needs a heatsink if you have a lot of fans.
On page two they show the pin assignments for the transistor package, the pins are not exactly in the middle. One pin is the case itself.

The fuse is about 2A fast acting. If you have a lot of fans, again you can use a higher rated one. As small as possible should be the goal of course.

I salvaged fan adapters for the connectors between fans and board, but you can buy them as they show.

I will definitely have to try this, Looks like awesome mod for my rig.

Super-simple PWM-to-3pin-fan adapter

Note that this is absolutely as KISS as it gets. Particularily, you can kiss your RPM readings goodbye on anything other than 100% speed.

If you want better, Tealc's http://forums.overclockers.co.uk/showthread.php?t=18421145 is for you.

Note to future readers with 3pin fans & 4pin headers: Before you do anything else, check if your BIOS has a setting for 3pin/4pin control. If it does, you can probably just set it to 3pin and stop reading now.



Things you need

1. A resistor package suitable for your fan, Zalman's package should handle most everything with its beefy 56 ohm resistor (7v operation)
   
2. A nice big N-channel MOSFET. 3 amps or bigger and you don't need extra cooling. Minimum 20V throughput. The max Gate voltage can be between 6--20 volts, but don't go bigger than that or the 5V PWM pin feed becomes too low to open the MOSFET properly.
   My TV repair shop gave me an IRF630 which is complete overkill.
   Your best bet is to get hold of a logic-level input MOSFET that still has enough throughput.
3. Steal one connector from your PC chassis.

My version drives my Zalman 9700 CPU fan from 40% PWM up to 100%, resulting in about half of max speed due to the resistor. The action sounds sort of linear-ish, which probably means it isn't. (Sound level increases exponentially with RPMs)

If you like, you can short out the resistor entirely for full range action. Be aware however that your fans will start spinning at 10-15% PWM and that the curve is pretty aggressive. You'll be going fairly high on RPMs at 60% already. This means that standard BIOS fan controls will likely drive fairly high RPMs, so you might want to be able to tune the PWM curve yourself (via e.g. SpeedFan)... unless you simply want high RPMs, of course.


About the RPM monitoring: no, there is no way to get working RPM monitoring with this few components, you can forget it. With 3 (and switching the MOSFET for a P-channel in high-side driver configuration) you might be able to get it working. But don't take my word for it. Perhaps with a 10-100uF capacitor parallel with the fan? Unknown & untested. One definite caveat is that the heatsink goes +12V live.

Caveats:

• Your BIOS will likely "F1 to continue" you in the face with this adapter on the CPU fan because it can't see RPM readings. Disable the monitoring in the BIOS!
• Tools like ASUS Fan Xpert will probably hate you too for the same reason. SpeedFan works!

Wins:

• You can actually turn your CPU fan completely off!

I have a related question, I'm not very electronics minded, though I can solder, heatshrink etc no problems (used to install car audio).

I have an amplifier with a noisy 80mm, 24 volt fan. Was wanting to replace with a 120mm Sycthe 500rpm 12v fan. (current draw 0.07amps).

Would just wiring it up to this suffice? http://www.jameco.com/webapp/wcs/stores ... 1_51334_-1

And if so, which wires would connect to which post - + and - for the fan, + and - for the fan power supply in the amp?

If heat regulation is an issue that's no prob, I can screw it to the amp's heatsink.