Comparison of Features and Differences between DC Motors and AC Motors
Electric motors are machines that convert electrical energy into mechanical energy. Definition implies that electric motors take electrical energy as input and provide mechanical energy as output. Based on input electrical energy, motors are divided into two types: DC (direct current) motors and AC (alternating current) motors. These two types are further categorized into multiple types based on design and structure. They are utilized in various fields, including industries, automobiles, medical equipment, and robotics.
When purchasing a motor, some individuals may be uncertain about their selection. This article explains the features of DC and AC motors, highlighting the key differences between them. Furthermore, it will outline the appropriate applications for each type of motor, allowing you to choose your motor with confidence.
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DC (Direct Current) Motors
DC Motors are motors that are powered by electricity flowing consistently in a single direction (direct current).
Figure1 : DC (Direct Current)
Figure2 : Principles of DC Motors
Pros of Using DC Motors
When compared to AC motors:
- For the same power rating, DC motors are more compact in size.
- DC motors have higher efficiency, especially when variable speed applications are under consideration.
- The starting torque is relatively large.
- It is easier to control DC motors for a wide range of speed curves by adjusting the voltage level.
- DC motors have a quick response time for start, stop, and acceleration.
Cons of Using DC Motors
- DC motors, regarding brushed ones, have high maintenance needs because their brushes and commutators wear out over time.
- The operation of brushed DC motors is noisier.
- For heavy-duty applications, DC motors have a higher cost because strong magnets are required for generating a sufficient magnetic field.
The Two Types of DC Motors
DC motors are categorized into brushed DC motors and brushless DC motors, based on the presence or absence of brushes and a commutator.
While brushed DC motors are simpler and lower in cost, they generate more noise due to the physical contact between brushes and the commutator, and they require regular maintenance as the brushes wear out over time.
In contrast, brushless DC motors eliminate these drawbacks by removing brushes and commutators altogether. This not only results in quieter operation but also extends the motor's lifespan, enhances efficiency, and improves performance in high-speed or demanding applications. However, the cost is higher compared to that of brushed motors of the same output range.
For more details on these motor types, view our comprehensive guide on brushed and brushless DC motors.
Figure 3 : Comparison of brushed and brushless DC motors.
(Left) A brushed DC motor uses brushes and a commutator. (Right) A brushless DC motor uses a sensor.
AC (Alternating Current) Motors
As the name suggests, AC motors are powered by AC current, which is periodic in nature and keeps switching direction.
Figure 4 : AC (Alternating Current)
AC motors come in many types, but they can be broadly categorized into two main types: synchronous motors and induction motors (also known as asynchronous motors).
A synchronous motor has coils in the stator and a rotor with permanent magnets, so the rotor rotates at the same speed as the rotating magnetic field. The speed is proportional to the frequency of the current, and this phenomenon is referred to as "synchronization."
An induction motor, also known as an asynchronous motor, is a type of motor that generates electromotive force in its coils through electromagnetic induction, causing them to rotate. While it has coils in the stator, similar to a synchronous motor, the rotor differs in that it consists of short-circuited coils. In the case of an induction motor, the rotor rotates at a speed slightly lower than that of the rotating magnetic field.
AC motors can be powered using AC signals from electricity transmitted from a power plant, or output energy coming from an inverter connected to solar or a battery.
The Pros of Using AC Motors
When compared to DC motors:
- The structure is simple and durable, with easy maintenance
- Higher efficiency for long-term use at a constant speed
- Capable of stable operation even under heavy loads
- Relatively lower noise compared to brushed DC motors
- For the same output range, AC motors cost less.
The Cons of Using AC Motors
- Difficult to control speed and torque compared to DC motors.
- Lower responsiveness in starting, stopping, and acceleration compared to DC motors.
- Relatively low starting torque.
Differences Between DC and AC Motors
The above sections in this article discuss the differences between DC and AC motors in detail. This section provides a recap and presents a comprehensive comparison between DC and AC motors.
Feature |
DC Motors |
AC Motors |
Type |
Both brushed and brushless DC motors |
Both synchronous and induction (asynchronous) motors |
Power Supply |
DC (direct current) |
AC (single or three-phase alternating current |
Input Terminals |
2 input terminals labelled as positive (+) and negative (-) |
3 input terminal |
Design & |
Brushed motors require regular maintenance due to brush wear and commutator degradation over time. |
The structure is simple and durable, with easy maintenance. |
Noise |
Brushed DC motors are prone to generating noise. |
Relatively minimal |
Armature |
The armature is on the rotor section. |
The armature is on the stator section. |
Controllability |
Capable of flexible response to a wide range of speed control. |
The controllability of the motor itself is lower than that of DC motors, and advanced controllers are required for a wide range of speed control. |
Self-Start |
Always self-starting |
Synchronous motors and single-phase induction motors are not self-starting, whereas three-phase induction motors are self-starting. |
Response Time |
Respond quickly to voltage changes. |
Respond slower than DC motors. |
Efficiency |
For applications where speed changes are frequent, DC motors are more efficient than AC motors. |
For applications that require continuous operation at a constant speed, AC motors are more efficient than DC motors. |
Main Application |
Small household appliances, precision machinery, medical devices, automotive electrical equipment, etc |
Large household appliances, industrial pumps, belt conveyors, cranes, etc |
Mabuchi Motor develops and supplies small brushless DC (BLDC) motors for demanding industrial and medical applications. Our product series is designed to deliver the reliability and precision required for automation in industrial settings and for high-performance medical devices.
View Our BLDC Series
Summary
It is important to carefully determine the necessary specifications based on the application, as DC motors and AC motors have different characteristics.
We offer a wide range of brushless DC motors tailored for various applications. If you are unsure about motor selection or would like assistance with selecting samples, please don't hesitate to contact us.
