How PC Fans Work

Enermax Apollish Electromagnets

What Makes the Fan Move?

Keeping a fan going is like pushing a merry-go-round at a playground.  The merry-go-round requires a “push” at a specific timed interval, else it will either stall or start slowing down due to friction.  In a complex electric motor, the coils in the fan hub  change polarity (the flow of electrons) at certain intervals, thus reversing the north and south poles.  This change is pretty much the same thing as the kid pushing  the merry-go-round (but now you have four kids pushing it, as most PC fans use four coils).

In a complex electric motor, this change of polarity is caused by an electrical component called a “brush”.  Brush can be a misleading term, as in this context it means “to rub against” rather than having anything to do with cleaning.  An electrical brush is a springy metal or carbon piece that rub against the contacts, changing the polarity as the brush moves.

Merry Go Round

Nearly every PC fan made today is “brushless”, and manufacturers like to tout this feature as some major engineering feat.  While a brushless design is quieter, it also makes the motor extremely simple, which reduces manufacturing cost.  Instead of each coil switching polarity, a brushless design utilizes two positive and two negative coils, set 90° from each other, which propels the permanent magnet in the fan blade in one direction.

Electric Motor Brush

You won't see brushes like these in PC fans

Have you noticed that sometimes if you stop a fan and it won’t start all by itself (requiring you to push it with your finger)?  If you reduce the voltage then the magnetic field weakens, causing the the push to be smaller, which causes the fan to spin more slowly or stall.  A fan becomes stalled when the permanent magnet in the hub gets caught between the positive and negative fields produced by the electromagnet.

Enermax Twister Fan with LED

Some fans use LEDs, such as this Enermax Twister Fan (reviewed here) with LED

Some fans have LED lighting, and LEDs have a specific tolerance to electricity.  If it gets too little electricity then they can either dim or start to pulse, depending on the situation.  Some fans separate out the LED and fan leads so that the fan speed can be reduced without pulsing, and even better fans use LEDs with higher tolerances so they won’t change with the fan speed.


There are other part of PC case fans that affect quality, noise, and airflow.  Different manufacturers will try and tell you that Fan A is better than Fan B because it uses more ball bearings, is bearingless, brushless, or the like, but the basic principle of how the fan blades move is the same.

Noctua NFB9 Fan

Noctua claims their NF-B9 (reviewed here) fan's improved blade design moves more air with less noise

The differences in most PC fans is the size and rotation speed, which has the most effect on noise and airflow.  A 120mm fan will move more air than an 80mm fan at the same rotation speed.  Because of this, larger fans can reduce their rotation speed to be quieter, and still move enough air for its designated purpose.

Thermaltake iFlash Fan

The Thermaltake iFlash Fan has an LED display

PC fan manufacturers are constantly trying to “sell” their fans by showing off some new aerodynamic design or unique feature.  Some of the more interesting features are UV-reactive plastic, LED readouts (like the Thermaltake iFlash fan reviewed here), integrated silencers and LED lighting, which are purely for aesthetics.

I hope this guide helps you to understand more about how the humble PC case fan does its job.

Alan is a web architect, stand-up comedian, and your friendly neighborhood Grammar Nazi. You can stalk him on the Interwebs via Google+, Facebook and follow his ass on Twitter @ocmodshop.