a) DC "Waterproof Cooling Fan" is to provide the use of a DC power supply: DC motor star and rotor of two parts, there is a star poles (winding or permanent magnet), the rotor winding, energized, the rotor also forming a magnetic field (magnetic poles), there is an angle between the star and rotor poles in the stator and rotor magnetic fields (N and S poles between) attract each other, the rotation of the motor. Change the brush seat, you can change the angle between the star and rotor poles (assuming the angle between the star pole starting side, the rotor poles to the other side, the "Waterproof Cooling Fan" rotor store magnetic pole pointing direction is the direction of rotation of the motor) direction, thus changing the direction of rotation of the motor.
b) exchange "Waterproof Cooling Fan" is to provide the use of alternating power supply: single-phase AC motor has only one winding, rotor squirrel cage of.