DIY PC Fan Controller





Introduction: DIY PC Fan Controller

This instructable should help you build a simple 3 speed fan controller for any 12v dc computer fan. I couldn't find a decent tutorial on fan controllers so i've made this simple one. This is my first Instructable so I hope it's alright :)
Please comment

I can't be held responsible if you break stuff, i have tried to describe things as thouroghly as possible but if stuff breaks it's your fault not mine . None of my stuff broke

The 3 speeds will be off, half speed and full speed
Being able to turn case fans off helps you keep your computer quiet when you don't require the extra cooling, the two fan speeds allow you to turn the fans up when necessary and dow to keep the system quiet while still cooling

You will need:

DC fans - I used 2 i bought on Ebay for about £1.50 each from China, they came with 2 wires for power(+/-) Not PWM 3 pin/wire type and a molex plug so they would run at 12v constantly (Loud)
I don't reccommend LED fans, mine were LED and the change in voltage from changing the speed makes them go dim, not a massive issue but you might not want that
An On/Off Switch
A SPDT switch (3 pins underneath on/on)
Some bits of wire
Soldering iron and solder
Electrical tape or Heat shrink
A computer or computer powersupply to give the fans power
Maybe a screwdriver to open your PC case

Step 1: Chop Chop Chop

First Chop the molex plug off the end of the fan wires,get as close as you can as it will give you more wire to work with later.

So then you should have a fan with a red wire and a black wire coming out and nothing on the end of them.

My fans had pass through molex connectors so you can connect several fans using only one molex outlet on your PSU, if yours does also then clip the end off like in the picture, you want as much wire as possible on the end we're keeping to make soldering easier

Step 2: Solder Stuff Up

Soldering starts now, so plug in your iron.

If youre using more than one fan join the connectors together, all of your fan + wires should be joined (Usually Red) and all the - wires should be joined together (Usually Black).

Add an extension bit of wire to make soldering to the switches easier, thats the blue wire in the picture.

Tape or heatshrink your soldered wires to insulate them.

Step 3: On Off Switch

Take your Negative wire you just soldered up and soler the free end to the on off switch NOT the SPDT switch.

Get your molex plug we saved earlier and twist the two black wires in the middle together and solder them to the other side of the on off switch with some wire.

Step 4: High and Low Speed Switch

So the speed change will be because of the switch between the two volages a molex plug provides.

Yellow is 12V (Full speed)
Red is 5V (Half-ish Speed)

Solder the yellow molex wire to one of the outside pins on the SPDT switch and the red one on the other side, extend if you need to, i'd reccommend adding some extra wire in as other wise you may struggle when fitting into your case.
While youre soldering the switch solder another wire onto the middle pin and leave the end free for the next step.

Step 5: Next Step

Now solder the middle switch pin wire to your + Fan wires (Red)

The electronics bit is done now apart from testing

Step 6: Testing

If you have an old PSU, use that!

Once again it's not my fault if you break something (Including yourself) during this stage or any other .

If you don't have an old/separate PSU I reccommend removing your PSU from your PC to test this. A fried PSU is better than a fried PC.

Unplug the PSU from the mains.
Unplug the leads into your motherboard and drives, un screw the PSU and it should lift out of the case.
There are loads of youtube videos that will help you with this so i'm not going to go into any more detail than that.

Now it's removed, find the green wire in the big bunch that went to the motherboard It's pin 16 (See picture)
Then get a small pece of wire and connect Pin 16 (Green) to pin 15 (Black)
This makes your PSU think it's attatched to a motherboard, otherwise it won't turn on
Now turn the PSU on and connect the Fans (Plug it back into the mains don't forget)
Turn your PSU on, the fans should come on when you throw the fan switch to on, and should be fast and slow when you use the other switch

Disconnect everything and put it back in your case

Step 7: Mount in Your Case

It's up to you how you mount the switches into your case, you can use empty drive bays or just put them in the case roof. If you add enough wire theres no reason why you cant have them in an external box on your desk or something

Hope ths is useful to you,
I'll be glad to hear your comments



    • Casting Contest

      Casting Contest
    • Oil Contest

      Oil Contest
    • Clocks Contest

      Clocks Contest

    We have a be nice policy.
    Please be positive and constructive.




    2 years dead but...JelleW1's post pointed out the main problems.But there is more to point out here.

    Learn-Count-Draw-Build-Test-Use, do not skip...

    Do not bild blindly....understand it...

    Also I would not use the same PSU again in my main station after this "cripling" short- circuit trick.....

    Could you swap out the switch for a variable resistor for more control

    1 reply

    if you lower the 12V with a potentiometer (or something like that). it would be possible. be aware to check the Datasheet of your fan itself, since most fans can not go below 7V. Also fans have start up problems on low voltages. If you get a to low voltage and your fan does not start up it could burn though and set on fire. -Electrician

    [*Also as a disclaimer I'm not responsible for what you do]

    Sorry didn't mean to comment twice

    Could you swap out the switch for a variable resistor for more control

    Hey g199 I was wondering when you said solder the negatives to the on/off switch to which on/off switch do you mean? The computer on/off switch? Figured I had better ask before hand even if it is a stupid question. Thanks!

    1 reply

    Nope I think he means the extra ON/OFF switch that you place between the
    fan wires and the SPDT ON/OFF switch output wire and molex ground wires. If I'm not mistaken, you could use an SPDT ON\OFF\ON switch instead of adding the extra ON\OFF switch. Also I've read that certain fans will not start from 5V so this might not always work in which case the resistor method could be a valid alternative.

    Nice and easy instructable g199 :)

    But i have 1 QUES g199,
    since last few days i have browsed almost as many as possible various diy fan controller projects and most dem had some kind resistors and capacitors and heatsinks etc involved in their projects. Stating it to be useful to use it with diff.. variety fans

    That is the reason i hesitate moving further referring those projects coz i was looking for some think simple and effective like u have shown.

    SO, i wanted to know is it ok not to use all resistor and capacitor etc... for dis project?

    2 replies

    If you're using 12v fans then there is no need for a resistor in this circuit :)
    Because the amp draw of pc fans is pretty low you don't need to worry about using relays or anything for the switch
    It's a simple idea and it works, so i don't really see the need to add more components because that adds more expense.
    Adding a potentiometer is quite a good fan modification, then you can turn the fan speed up and down to any value with a dial type adjuster, but it's a bit more complicated and costs a bit more.
    Hope this answered your question :)

    tnx G199 now i feel free to proceed with dis diy project tnx again for the reply :)

    nice work.... ive done something same but haven't used the 5 volt rails... just running the fans on 12 volt rails.. plus have mounted them on an acrylic sheet.. i also have added some leds... but am not able to power them up without blowing them :(

    7 replies

    here is an image :D its kept upsite down though :P


    If your LEDs are blowing use a rail with less voltage and/or use a resistor, i hope that sorts your problem :)

    ya i know i need to use resistors.. but idk what rating resistor to use for a particular led... i currently have 10 of each red, green, blue and white....


    you can work it out quite easily, just google "led resistor calculator", you'll need to know the voltage rating of the LEDs you're using, if you don't know what they're rated to then assume it's 3V, if they're really dim with 3V try 5V, if 12V is blowing them then they probably aren't 12V or above

    hey i got the blue and white leds to work on the 5volt rails :D


    Looks good, nice work :)

    ty man will do that for sure... btw m using the 5 volt rail for the led :)

    Interesting. Thanks for sharing!