What's the Difference between AC Motor and DC Motor
When energy-efficiency costs come into play, more designers are opting for the electronically commutated motor rather than familiar AC and DC versions.
For motor applications, engineers have several options at their disposal. Typically, engineers can choose between direct-current (DC) or alternating-current (AC) motors. Machine Design has covered the difference between basic types of motors in the past.
The latest types of motors to enter the fray are those that help control the energy output and achieve higher energy efficiency. These electronically communicated (EC) motors are making strides in replacing dc and ac motors; especially with the need to achieve energy-efficiency regulations.
EC motors are DC brushless motors that are controlled by external electronic circuit board. This provides greater control and higher efficiency.
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.
According to maxon motors, DC motors are limited by their brush system and have a lifespan of 1000-1500 hours; less than 100 hours if under extreme loads. Some motors may operate to 15,000 hours under favorable operating conditions. The high speed of rotation is only limited by commutation, typically achieving up to approximately 10,000 rotations per minute.
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 induction motors use a series of coils powered and controlled by AC input voltage. The stator field is created from the input voltage, and the rotor field is induced by the stator field. The other type of AC motor is a synchronous motor that is able to operate with precision supply frequency. The magnetic field is generated by a current delivered through slip rings or a permanent magnet. They run faster than induction motors due to the fact that the speed is reduced by the slip of the asynchronous motor.
The ac motors are meant to operate a specific point on a performance curve. This curve coincides with the peak efficiency of the motor. Outside of this point, the efficiency of the motor drops significantly. AC motors consume additional energy to create a magnetic field by inducing a current on the rotor. Consequently, AC motors are less efficient than DC motors. In fact, the DC motor is 30% more efficient than AC motors due to the secondary magnetic field being generated from the permanent magnets rather than copper windings.