Fan pinouts PC 3 pins 4 pins

If you want two or more fans in your computer and have only one header on the motherboard, you've got to figure out how. I tend to forget details so I wrote them down, hope they help you too.

About fan connectors

  • Fan connectors come in three pin or four pin variants.
  • Their (maximum) voltage is 12 V
  • The maximum current is in general 1 Ampere per header
  • Wire colors below are often seen but can be different

So If you have two fans of 0.44 A each, you are save with 2 * 0.44 = 0.88 A < 1 A.

Difference between 3 and 4 pinouts

3 pinout

Pin 1

"Ground"

Black

Pin 2

"Voltage"

Yellow

Pin 3

"Signal"

Green

The way a three pin fan works: Signal from pin 3 represents the fan speed and is send to the motherboard. Based on that and how much heat needs to be dissipated, the motherboard offers a voltage on pin 2, ranging in theory from 0 to 12 V.

4 pinout

Pin 1

"Ground"

Black

Pin 2

"Voltage"

Yellow

Pin 3

"Signal"

Green

Pin 4

"PWM"

Blue

The way a four pin fan works: The voltage on pin 2 is always 12 V. As with a 3 pinout, signal from pin 3 represents the fan speed and is send to the motherboard. Based on that and how much heat needs to be dissipated, the motherboard offers a PWM signal to the fan. With the PWM signal as input, the fan electronics determine the fan speed.

Trivia

  • The PWM signal on pin 4 is 25 kHz
  • The signal on pin 3 has a frequency of two times revolutions per second.
  • Can you connect a 3 pin fan to a 4 pin header? Or connect a 4 pin fan to a 3 pin header? Often yes, you'll probably get a fan running at full speed.
  • Obtaining exotic PWM fans can be done on the known Asian sites where brands with a good reputation are for example Delta and Sunon. A warning: They may be used. Pay attention to screw holes without traces of screws, discolouration of wires and scratches.

Connecting multiple fans to one header

With this knowledge it is easy to plan wiring when multiple fans need to be connected to one motherboard header. The motherboard can only analyse one signal per header, so only one fan signal can be used (pin 3). Based on that, voltage on pin 2, or, PWM on pin 4 is regulated. For that reason you should always use similar fans when combining them parallel.

In short, whether 3 pins or 4 pins, combine fans parallel but offer the motherboard only one signal (pin 3) as shown.

Two_fans_one_molex_connector.svg

This is equal for a 3 pin configuration, the blue wiring is simply not available.

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