How do direct-current motors differ from alternating-current motors?

Direct-current (DC) motors and alternating-current (AC) motors differ primarily in their power source, construction, and speed control mechanisms.

Direct-Current (DC) Motors

DC motors rely on a direct current supply. A defining feature of many DC motors is the commutator, a mechanical switch on the rotor shaft that reverses the current direction in the armature coils to maintain continuous torque.1
* Speed Control: Speed is typically proportional to the supply voltage. By adjusting the field current or armature voltage, these motors offer precise control over speed and direction, making them ideal for robotics and industrial machinery.1
* Components: They utilize stationary magnetic fields produced by permanent magnets or field coils.1

Alternating-Current (AC) Motors

AC motors, such as the synchronous motor, operate on alternating-current power.
* Speed Characteristics: Unlike DC motors, a synchronous AC motor runs at a speed directly proportional to the frequency of the power source, allowing for constant speed operation.2
* Operation: The rotor’s magnetic field aligns with the rotating magnetic field generated by the stator's multi-phase currents. They are often favored for high-efficiency industrial applications or devices requiring precise, constant timing, such as clocks and timers.2