How PC Fans Work

Enermax Apollish Electromagnets

Intro

Computers and other electronics produce heat, and they need to be cooled.  Most electronics depend on fans or some other type of blower to move air and cool the system.  This cooling could be in the form of direct heat removal, as blowing air over a hot component (such as a heatsink), or ambient conditioning such as removing hot air from a closed case and introducing fresh cooler air in its place.

Regardless of why we use fans, many people don’t really know how the fan blades move.  How a fan moves its blades is actually quite simple, and its basic principle relies on electromagnetism.

This article doesn’t go over how a fan moves air, the difference in air pressure, efficiency of aerodynamics or any of that stuff.  We’re talking about the scientific principles that actually cause the fan blades to spin around a central hub.

Gelid Wing 120mm PC Fan

Basic Principles

Everyone who’s graduated elementary school knows about magnets.  Every magnet has a North and South pole; like poles repel each other and opposite poles attract each other.  This principle is used to create motion in an electric motor, and a PC fan is at its heart a very simple electric motor.

Instead of using two physical magnets, most fan designs create a magnetic field created by a several electromagnets, which act against a permanent magnet embedded in the fan blade hub.  Using electromagnets allow the fan can be turned on and off, and fan speed can be controlled by varying the voltage.

Enermax Apollish Electromagnets

You can see the four electromagnetic coils in this Enermax Apollish fan (reviewed here)

For the uninitiated, electromagnets are a series of metal coils (usually copper) that produce a magnetic field when electricity is run through it.  The positive polarity of the current produces one pole, and the negative polarity produces the other.  The pole produced is determined by the direction the wire is coiled, and which way the electricity is flowing.


Electromagnets

You can see the four copper electromagnet coils in the center of this Nonoxia fan (reviewed here)

Permanent magnets always have a magnetic field, regardless of any electricity applied.  I won’t get into the whole physics of how electricity and magnetism are really the same thing, but I’m sure you could look it up if you wanted to.

The blade speed is controlled either by a small circuit board or amount of copper in the coils.  If every fan had the same direct voltage and the exact same coil size then every fan would have the exact same rotation speed.

On the next page we discuss the scientific principles that actually make the fan blades move…