AC Vs DC Motor Comparisons

Speed Control:

Speed can be controlled in both types of motor. AC motor velocity is controlled by the frequency of the power source. AC motors run directly off the power source and in most countries would be designed to produce a rated speed based on an input frequency of 60 Hz. However, to vary the frequency to the motor, many applications utilize specialized electronics (Variable Frequency Drives) to provide adjustable speed control. DC motor speeds can be simply controlled by varying the available DC voltage to the motor. Many control solutions exist to provide precision speed control for applications such as robotics.

 

Efficiency:

Three phase induction motors tend to offer improved efficiencies at higher power levels and rated speeds. Brushless DC motors offer better efficiencies across a broader range of performance and provide better performance at lower speeds and lighter loads. Brushed DC motors, however, have added components (brushes and commutator) that introduce some inefficiencies.

 

Maintenance:

AC motors and Brushless DC motors are preferred in most manufacturing settings since these motors require less maintenance and have longer life spans in comparison to brush DC motors, which need to be serviced more often to replace brushes or to refurbish commutator surfaces.

 

Cost:

AC motors are often the most cost-effective solution for large power applications and applications with constant speed and load requirements. Higher precision and increased load variations introduce more sophisticated control requirements. While brushless DC motors with higher efficiencies and additional control complexities may have higher initial costs, their lifetime costs are comparable to AC motors.

 

Starting Torque:

Induction motors have minimal starting torque compared with DC Motors that can be overcome with starting devices. DC motors offer higher starting torques that translate to quick accelerations. Many applications that require fast indexing and quick move and settle times require high acceleration capabilities.

 

Applications:

AC motors make up a large volume of electric motors sold worldwide and are used in many applications such as household appliances, pumps, fans, HVAC systems, and other industrial machinery. DC motors are popular for mobile applications in electric vehicles, automated guided vehicles, and submersible ROV's. They are also found in robotics, conveyor systems, packaging machinery, and many types of precision equipment.