Firstly, DC motors rely on carbon brushes and a commutation ring to switch the direction of the current and magnetic field polarity in a rotating armature. This interaction between the internal rotor and fixed permanent magnets induces the rotation of the motor.
DC motors have a high efficiency rate, but suffer from specific losses. They lose efficiency due to the initial resistance in the winding, brush friction, and eddy-current losses.
AC motors consume additional energy to create a magnetic field by inducing a current on the rotor. AC induction motors use a series of coils powered and controlled by AC input voltage. The other type of AC motor is a synchronous motor that is able to operate with precision supply frequency.
The AC motors are meant to operate a specific point on a performance curve. Outside of this point, the efficiency of the motor drops significantly. Consequently, AC motors are less efficient than DC motors.
