Motherboard Fan Connectors: What They Are and How They Work

Motherboard fan connectors provide fans the small amounts of power they need to keep spinning and, in some cases, offer user control of fan speed. Here's everything you need to know about motherboard fan connectors.

What Is a Motherboard Fan Connector?

A motherboard fan connector is a small three or four-pin connector located on the motherboard. The fan will have one set of cables (bundled together) that will connect into the connector on the motherboard.

The motherboard fan connector is a Molex KK connector. It’s part of a family of computer power connections engineered by the Molex Connector Company, which also created other internal computer power connectors like the larger 4-pin Molex used by older hard drivers and the motherboard power connector.

Today, the Molex name is rarely used. Motherboard manuals more frequently use the terms “SYSFAN” and “CPUFAN” when referencing these connectors. SYSFAN and CPUFAN are technically the same connector, but SYSFAN is used to connect PC case fans, while CPUFAN is used for the fan attached to the CPU heat sink. If you've never used these connections before, don't worry. They are easy to use and nearly impossible to connect incorrectly. The most difficult time you might have is getting your hands and fingers into the area you need to be.

How Does a Motherboard Fan Connector Work?

Power delivery is a motherboard fan connector’s job.

A three-pin motherboard fan connector usually has black, red, and yellow wires on the PC fan’s side, but those colors can vary depending on the manufacturer and sometimes even the model. The black wire is the ground, the red wire carries power, and the yellow wire provides a reading of the fan’s current speed back to the PC.

A four-pin motherboard fan connector enables a feature called Pulse Width Modulation (PWM). PWM can cycle power on and off extremely rapidly. This allows fan speed control.

If a fan is set to run at 50 percent of its maximum speed, PWM will cycle the power such that the fan only receives power half of the time. This happens too quickly to perceive, so it seems as if the fan is running at a constant 50 percent of its normal maximum speed.

The motherboard fan connector will also include a plastic guide that extends from the connector beside the pins. This fits into a notch on the PC fan’s connector. The guide ensures you can’t reverse the connector.

How Do I Connect Fans to My Motherboard?

As typical motherboard fan connector is a three or four-pin connector attached to the end of a PC fan’s wire. This is attached to the three or four-pin fan header on the motherboard.

There’s no trick aside from lining up the notch on the connector with the guide on the header. Align each side, gently press the connector into the header, and then examine the connection to make sure it appears secure.

A secure connection should see the fan connector’s end flush with the motherboard header. It should not appear or feel loose. The connector does not include a latch to keep it secure, so the motherboard fan connector is easy to remove by pulling it straight out.

How Many Fan Connectors Does a Motherboard Have?

This depends on the motherboard in your computer. Most motherboards are have at least two connectors. One will be used for the processor, while the second is used for a case fan. High-end motherboards may support six fans or more.

Can I Plug a 3-Pin Fan Into a 4-Pin? 

Yes, you can.

However, this will disable PWM (Pulse Width Modulation) support. That means you can’t control the speed of the fan through PWM. It doesn’t matter if the motherboard header or fan connector lacks the fourth pin. PWM won’t work if it’s missing on either.

You may still be able to control the speed of the fan. Motherboards often include the ability to control fan speed by changing the voltage sent to the fan. This does not require the fourth pin. Your motherboard manual can tell you which fan control modes are supported.

PWM is the preferred method of fan control. A typical PC fan will have a minimum required voltage that must be supplied to keep the fan spinning at all. This leads to a limit on the minimum possible fan speed. PWM can support very low fan speeds without issue which, in turn, can reduce noise.

Conclusion

A motherboard fan connector does exactly what it says it will do: it connects the fan to the motherboard. Its simplicity is refreshing next to more complex connectors like GPU power connectors. The connector has remained unchanged for decades, too, so an old fan should happily work with a new motherboard (and vice versa).