Electric fans circulate air by using electricity to spin a rotor shaft attached to the fan blades. Wires wrapped around magnets inside the fan motor's housing carry electric current, turning the magnets into powerful electromagnets. Whether it's in the home or in your car, electric fans place constant demands on an electrical system that may or may not be lower than alternative air-movers.
Wattage and Power Draw
Like any other electrical device, electrical fans use a combination of voltage and amperage to operate. You can think of electricity like water coming out of a hose. Amperage is the current -- or the amount of water -- coming out of the hose; voltage is the temperature of the water. Multiply amperage by voltage and you have wattage. Decreasing the amperage (power flow) to an electric motor will reduce its power output, but decreasing the voltage will cause the motor to draw more amperage to compensate.
Electric Fan Advantages
The primary benefit of using any electric fan is that, as long as the voltage stays constant, the fan's motor will almost always turn at the same speed. This allows the manufacturer to optimize the fan blades' size and shape to work most efficiently at that target speed. This stands in sharp contrast to a mechanically-driven engine cooling fan, which changes speed in direct proportion to engine RPM. Fan blades that are large enough to move sufficient air at 900 RPM are three times larger than they need to be at 2,700 RPM. This makes the mechanical fan inherently inefficient compared to an electric one. Typically, the electric fan will offer better cooling, better fuel efficiency and more power.
Types of Electricity
There are two types of electricity, alternating current (AC) and direct current (DC). Batteries use direct current, where the electricity always flows in a single direction. Houses use alternating current, where the electrical current changes direction several times a second.
Electrical motors rely on a constantly switching signal to route power to the magnets. This isn't a problem for AC (which constantly switches anyway), but most DC motors rely on a commutator and brushes to change the signal. The DC motor's brushes can overheat and fail under constant use, which is why AC and "brushless" DC motors (which use a computer to change current flow) are almost always more reliable and powerful than regular DC motors. This is something to bear in mind when purchasing an electric fan as those which use AC and brushless DC motors are typically more expensive but can lower operating costs by reducing power consumption and maintenance costs.