Overcomplicated IMac Cooler With 120mm Fans and PWM Speed Control

Long story short: It is inefficient but it looks cool.

I'm working on a 2011 iMac that tends to get a bit hot on the outside when it's running all day. So I designed an external cooler with spare fans I had laying around in order to bring down the temperature. The external fans can only cool the skin down so I can touch it again, but they don't do anything to the internal parts.

Why is this a silly solution?

While touching the hot surface is irritating, I only come into contact with the outer case of the computer when I reach around to unplug and switch USB devices. A simple USB hub would have also solved this.

Main Parts

1. 3x 120 mm computer fans
2. 1x Adjustable Boost Converter (example: https://www.aliexpress.us/item/3256806193593131.html)
3. 1x PWM speed controller with potentiometer (example: https://www.aliexpress.us/item/3256807025099093.html)
4. 1x USB cable

Wiring

1. 1 meter red wire
2. 1 meter black wire
3. 4x triple WAGO connectors (alternative: soldering)
4. 2x double WAGO connectors (alternative: soldering)
5. 4x crimps (alternative: direct screw connection)

Fasteners

1. 12x M3 x 30 mm fasteners
2. 6x M3 x 4 mm fasteners for PCB (alternative M3 x 6 mm)
3. 6x M3 x 8 mm fasteners for dustcaps (alternative M3 x 6 mm)
4. 4x M3 x 12 mm fasteners for wing-center connection
5. 2x M5 x 20 mm fasteners
6. 6x M5 x 30 mm fasteners
7. 4x M3 nuts

Heat Inserts

1. 24x M3 x 5.7mm threaded inserts
2. 8x m5 x 10 mm threaded inserts

In this instructable, you will see two models. One is a grey prototype and the other one is the improved silver version. I started out with the grey model and switched everything over to the silver model where I fixed some issues I had with the prototype. This might be confusing at first but it has no effect on the assembly process.

Start by printing all the parts for this project.

Install four M3 heat inserts per fan unit and two M5 inserts in the Center. Six M5 inserts go in the Backplate.

There are three frames for the Fans: Two Wings and the Center. After you installed the heat inserts, connect the Wings using M3 x 12 mm screws and M3 nuts. There are pockets in the Center where you can just drop the nuts in so you don't need to hold them. I used self securing nuts because they create friction by themselves and don't come lose with vibration.

In order to install the fans, you need to remove the connectors so you get to the bare wires. The connectors won't fit through the holes and will be replaced with WAGO connector anyway. Feed the wires through the channels of the Wings and the center until they come out in the middle. It is important that you find out exactly which wires are positive and negative and this can be difficult if all the wires are the same color. You may need to lift up the sticker or remove a cover in order to get a look at the PCB or some other type of mark that identifies the wires. In the second picture you can see a small "+" and "-" printed in white on the PCB.

I highly suggest shortening the wires once you got all your fans in place in order to save space. If you can, crimp the wires for the screw terminals as this makes installing them more comfortable.

We're using 4 triple WAGO connectors to connect the Fans in parallel. Using a short extra wire (red and black in the picture), the WAGO connectors are connected in pairs of two, one pair for positive and one for negative. Only one positive and one negative cable are leaving this compartment towards the power supply.

Now you want to install the potentiometer. First push the cables through the hole, then place the potentiometer - it can only fit one way. While we're at it, put the USB cable through both holes.

This may look complicated at first, but that is only because of the limited space. (I will add more details with an update.)

Boost Converter

At the top you see a boost converter that is held in place by two M3 screws. It boosts the voltage up to 12 Volts and can be regulated by turning the slotted brass screw on top of the blue component. This is where you use your multimeter to dial it in so it can create exactly 12 Volts from the 5 Volt USB supply.

Input:

The input is on the left (in the picture you see the little white "in" print) and it gets it's power from the USB cable. In this case I added double WAGO connectors (221) so I could solder the wires beforehand and then just clamp them together after installing the USB cable. But if you are good with soldering you can directly solder the USB cable to the Boost Converter.

Output:

The Output is on the right and leads to the speed controller terminal. The output wires are soldered to the Boost converter and then crimped.

Speed Controller

The speed controller is mounted with four M3 x 4 mm screws and can be oriented any way as it's square. I chose to place it in a way that creates the most space around the holes where the USB cable and the potentiometer cables come from. Now the speed controller has power, we can connect the potentiometer wires that we pushed through the hole in the previous step.

Input: The input comes from the Boost Converter and is already connected from the previous step.

Output: The Output is connected with two wires to the WAGO clamps that distribute the power to the fans.

Control: The Control Input is connected to the potentiometer

Once everything is connected, it's time for a test run.

Almost done! Now we close the electronic compartments with the Dustcap and some M3 x 8mm screws to make everything look nice and tidy.

Now it's finally time to mount everything with the M5 screws. Simply place the Backplate into the hole of the iMac stand and tighten the screws. The tolerances are designed to give a tight friction fit without breaking the Backplate.

As I said it does cool down the outside of the mac to a point where I can't cook an egg on it anymore but has no influence on the inside temperature of the critical components, as they don't have a thermal connection to the case. Looks like in order to really get the temperatures down I need to open it up in a future project ;)