Difference Between AC Motor and DC Motor

Aside from the obvious difference of voltage source, the significant difference between AC and DC motors is structural, and is directly related to voltage source.

Typically, DC motors (and generators) are built with the field windings incorporated into poles built into the inside of the stator housing, while the armature windings are built into the rotor and connect to the outside through the commutator, commutator slots and brushes.

On the other hand, AC motors are built with a slotted stator that houses the armature windings and the field windings are installed on the rotor. With synchronous motors, the field windings are wired to slip rings and brushes to that the field windings can be energized, but with induction motors, the rotor sis built with a squirrel cage that is energized by the rotating magnetic field of the armature windings.

The reason the armature windings of the AC motor are in the stator is primarily because of magnitude. AC motors are built to handle more voltage, more current and more load than DC motors, and that voltage and current works in the armature winding. If the armature windings were built into the rotor, the rotor would become impractically large and heavy as the windings became larger and heavier to handle the higher voltage and current.

With the armature windings in the stator, the AC motor can handle more voltage and current with bigger and heavier wires without loading down the rotor with more conductor and insulation, and can do more work with less weight and materials.

Here is an answer I wrote on AC vs DC generators, and generators are basically motors that are operated in reverse: fed mechanical energy to produce electrical energy. Maybe it will give you some additional insight, or at least another perspective.

CONCLUSION

DC motors are usually seen in applications where the motor speed needs to be externally controlled. AC motors work best in applications where power performance is sought for extended periods of time. All DC motors are single phase, but AC motors can be single phase or three phase.

AC and DC motors use the same principle of using an armature winding and magnetic field except with DC motors, the armature rotates while the magnetic field doesn’t rotate. In AC motors the armature does not rotate and the magnetic field continuously rotates.

In some applications today, DC electric motors are replaced by combining an AC electric motor with an electronic speed controller, known as variable frequency drive. DC electric motors are replaced with an AC electric motor and an electronic speed controller because it is a more economical and less expensive solution.

DC electric motors have many moving parts that are expensive to replace, and DC electric motor repair is usually more expensive than using a new AC electric motor with an electronic controller.

So as far as maintenance is concern, AC motors are used most as easy availability of AC supply DC motor has constant maintenance problem.

DC motor advantages:

1. The starting and speed regulation performance is good, the speed regulation range is wide and smooth, the overload capability is strong, and the electromagnetic interference is small;

2. DC motor has good starting characteristics and speed regulation characteristics;

3, DC motor torque is relatively large

4, the maintenance is relatively cheap;

5. DC of DC motor is more energy-saving and environmentally friendly than AC.

DC motor disadvantages:

1, DC motor manufacturing is more expensive, there are carbon brushes;

2. Compared with asynchronous motors, DC motors have complex structures, are inconvenient to use and maintain, and require DC power supplies;

3. The complicated structure limits the further reduction of the volume and weight of the DC motor, especially the sliding contact between the brush and the commutator causes mechanical wear and sparks, which makes the DC motor have many faults, low reliability, short life and maintenance. The maintenance workload is large.

4. The reversing spark not only causes the electric corrosion of the commutator, but also a radio interference source, which will have harmful effects on the surrounding electrical equipment. The larger the capacity of the motor and the higher the speed, the more serious the problem. Therefore, the brush and commutator of the ordinary DC motor limit the development of the DC motor to high speed and large capacity.