Fan motors are very simple in construction. They consist of a synchronous or asynchronous electric motor, with a fan wheel of the associated shaft, and the connections for the lines. However, DC motors are used (e.g. in computers or in a car). All motors consist of a stator and contain a rotating rotor inside, which is surrounded by pole-pieces. The types and sizes of the fan motors are very different and differentiate heavily among themselves. The reason for this is the area and the performance of the engines. The higher the performance, the more complex the structure needs to be.