Home Theater Cooling Fans

Thread Starter


Joined Sep 17, 2007
I'm trying to assemble a cooling system for me home theater cabinet. I've seen systems consisting of a 120mm 12v fan with a couple of thermocouples, and a power supply. Price is about $300. I'd like to put my own together using computer cooling fans, a controller, and power supply.

I've found the fans, some have thermocouples attached, there's also controllers that allow you to control the speed, temperature via thermocouple. These would typically fit into a computer bay.

I believe the fan and controller use 5 and 12 V. The power supply I found has 5 and 12 V with a 4Pin Mini DIN connector.

The fans and controller use molex and 3 pin connectors, which I assume I can find on the net.

The big question is where does the ground wire come from? Any help on this project would be appreciated.


Joined Sep 16, 2007
Are you looking for the ground wire of the fan or from the powersupply? either way it is normally a black wire (of course) and the red wire as a rule is generally for 5V, the 12V should be a yellow wire. Then if its a standard power supply, the remaining 2 wires may be black and brown most likely they are both ground. However, all of this should be verified via DMM. Hope that helps.


Joined Jul 17, 2007
Since the ATX form factor came into being, computer fans have speed sensors (tachometers) built into them.

If your fans have three (or more) wires, they have this tach lead. You can use this to your advantage.

The tach lead is an open-collector output, and thus needs a pull-up resistor in a range from between 1k and 10k for it to provide an output signal. There are two pulses per one complete fan revolution.

Armed with this additional information, you can design your setup to monitor the performance of the fans vs the temperature of your equipment vs the ambient room temp.

For example: When a fan is brand new, it's bearings are fresh and the blades are smooth and spotlessly clean. For a given applied voltage (current), your fan will rotate at a given speed.

As the bearings wear, the RPM's will decrease with the additional friction.
Dust/dirt on the fan blades will also slow the fan, along with significantly decreasing the airflow due to air friction.

If the path of air through the fan becomes blocked by an obstruction (piece of paper, snoozing pet, etc.) the fan speed will actually increase, as the flow drops off and the temp of your equipment rises.

If the speed of the fan is near maximum, or the current output if your supply is at maximum, your equipment needs to be shut down before it can be damaged by overheating.

As temperatures increase, the density of air decreases.
As humidity increases, the density of air decreases. (shocking, but true!)

How much time and effort you wish to put into all this is up to you. It's your equipment.

Have a look at this website:
That's where the specifications for PC's come from.
Under the Motherboard Form Factors, click on the FlexATX link, and select
FlexATX Thermal Design Suggestions v1.0 (it's an Adobe Acrobat .PDF file)

Lots of information on planning a cooling system for electronic equipment; in this case, computers - but directly applicable to your project.

Thread Starter


Joined Sep 17, 2007
Thanks to everyone responding. First off I'm no electrician so the "formfactors" are way over my head.

I did call the power supply company and he said the ground is the metal shield on the din connector. If I just cut off the din connector he said I'd probably find the ground is a braided wire like a coax cable. If so I could run a lead off that. Here is the spec from the web site (www.powersupplydepot.com/productview.asp?product=16246+PS):

MODEL: NU25-22120-140
Input: 100-240 VAC 50/60Hz
Output #1: +5V @ 1.5A #2: +12V @ 1.5A
Specifications/Features: Removed from New Equipment Desktop switching supply. Over current protection. Std. IEC 3 wire input connector. 4ft. output cable with 4Pin Mini DIN connector. UL/canada/usa/VDE/CE Listed.
POWER CORD: Order Stock # 7378-WI
L: 4-1/2" W: 2-1/8" H: 1-1/2" WT: .64

The fan controller (www.xpcgear.com/llfanctrlsil.html) list the following:
3.5” Lian-Li Aluminum Multi-Function Fan Controller with LCD Thermometer, Alarm, Time Display: PC-TR3A (Silver)

• Time setup and display
• Fan speed control and detection
• Available for Centigrade and Fahrenheit
• Icon display for Power on / HDD access
• Icon display for fan speed
• Monitoring temperature of CPU, HDD and SYS (SYS-r / SYS-f stands for two sets of wire connecting to individual fan for status control)
• Available for speed detection and control for 3 fans
• Alarm for fan error.
Product Specification:
Drive Bay: 3.5" Drive Bay
Fan RPM Speed detection and control for 3 fans
Unit of Measurement Centigrade and Fahrenheit

The fan I'm looking at (www.xpcgear.com/d12sl12o.html) states:
20mm NEXUS Yate Loon D12SL-12 SuperSilent PC Case Cooling Fan (120x120x25mm, 3 Pin and 4 Pin Pass-Through Connectors, Orange/Black)
Product Specification:
Model Number

D12SL-12O (Compare to NEXUS D12SL-12)
Size 120x120x25mm
Rated Voltage (V) 12
Operation Voltage: 6.5~13.8 Volts
Input current: 0.30 Amp Max
Operation temperature: -10 to +65 C
Storage temperature: -40 to +70 C
RPM: 1350 +/- 10%
CFM: 47
dB: 28dba
Connector 3 Pin and 4 Pin Pass-Through Connectors

So the big question is, if I cut off the din plug and attached a 4 pin molex that plugs into the controller (5V/grnd/grnd/12V), and the fans plugs into the controller with the 3 pin plug would this whole contraption work?

Thanks again for the help


Joined Sep 16, 2007
Sounds good to me. Just make sure all power is disconnected to the power supply for atleast 5 -10 mins before you go snipping off the connector, that could be nasty :) If you need anything else just ask. There are very qualified people on here to help you. I am not one of them, but they are here somewhere. lol