Manual Fan Control on Laptops With Uncontrollable Fan

This Instructable is about how to let your computer’s fan run at full speed (refer to the Principle down below) and return fan control to the system or motherboard when you want to. This is especially useful if your computer isn't supported by any fan control software, and you want your fan to spin faster than your fan control firmware asks it to prevent your CPU from overheating.

If you are in a hurry, just skip to the Principle. Below is just some talk about the CPU and the fan.

So I have an old gaming laptop, which has one significant problem. When it’s CPU overheats, the frequency drops from 3.2GHz to 2.4GHz, causing performance drop.

Another problem is that when it’s overheated, the fan doesn’t run at full speed (I will talk about it later), it simply just run at a higher speed.

Both Speedfan and NBFC (2 major fan controller apps) don’t support my laptop, which means I can’t control the fan from application layer.

But! The fan is powered and controlled via PWM cable. The PWM has 4 wires, 1 for power, 1 for speed control, 1 for speed feedback, and 1 for ground. If I cut the speed control wire, the fan stops receiving signal from the motherboard, and boom! The fan just starts wooshing loud and fast, faster when the CPU is overheated, and the fastest ever. This method increases the performance at a significant level, for it makes the CPU less likely to overheat.

However, it’s also obvious that…it’s too noisy in some situations, like in a library. You are not going to connect the wire back each time before you go to the library and cafes, right?

Supplies

Soldering Iron, 1 normally closed reed switch (normally open reed switch is also ok, but NC is better), spare wire, 1 magnet, 1 multimeter if possible, and a screwdriver.

Step 1: Principle

A large amount of computer fans are controlled via 4 PWM wires, one of it is for fan speed control.
Cutting the speed control wire makes the fan run at full speed, in which mine is faster than it is when my CPU overheats. This indicates that your fan might haven't reached its limit like my fan, too.

But...

It is kind of noisy, especially if you plan to take your computer to somewhere people might complain about noise from time to time, like libraries and cafes.
And it accumulates lots of dust on your cooling system, making dust cleaning more frequent.

So,

Instead of just cutting the control wire, we are going to connect a reed switch to it.
A normally closed (NC) reed switch goes "ON" in normal conditions but goes "OFF" and stops current from passing through it when a magnet is near it. For a normally open (NO) reed switch, it just goes vice versa.
So that when we want the fan run at full speed, we can place a magnet near the switch, and when we want it quiet, just take the magnet away and return control to the firmware.

WARNING:

See if your PWM wires are near your HDD. If so, placing a magnet near the reed switch might damage your HDD and cause data loss!

Step 2: Open Your Computer With Your Screwdriver

Step 3: Locate the Fan and the PWM Wires

Generally, the red wire is for power, the black one is for ground. So rest 2 wires are for speed control and feedback. For my laptop, the yellow one is for speed feedback, the red brown one is for speed control. If you are not sure which one is what we wanted, just randomly cut one, start up your computer and see if your fan goes loud!

Step 4: Connect the Reed Switch to It!

So just cut the wire and go for some soldering!

My reed switch has 3 pins, one is normally closed, and one is normally open, as shown in the image. I did some testing with my multimeter to find out which is NC and which is NO.

If you are new to soldering, just watch some tutorial and do some practice with your spare wires. It takes a little bit of skill, but patience pays back! Also, safety first! Soldering irons are super hot…

After that you can do some test with your multimeter if your soldering is successful.

WATCH OUT:

If your PWM wires are distant from your computer case, controlling the switch with a magnet might be difficult. Consider extend your speed control wire and stick the reed switch to the case.

Step 5: Find a Spot to Place Your Reed Switch

I put my switch to somewhere fits just right for it, as shown in the image.

Be careful! If your reed switch is too close to your hard drive, your HDD might be damaged and data might lose when you put the magnet near your switch and your HDD.