From Diversity to Unity: The Classification of DC Motors

June 28, 2024 Luciano Bertene

In the complex field of electrical engineering, where innovation and precision come together, the humble DC motor is a symbol of diversity and unity. These machines, from compact to colossal, power our world with remarkable efficiency and versatility. Hidden within their rotating cores is a rich variety of types, each tailored to specific applications, but together forming a harmonious symphony of movement. This exploration embarks on a journey from diversity to unity and addresses the systematic classification of DC motors. As we step through the intricate nuances of their design, purpose and performance, we reveal the threads that weave these disparate entities into a cohesive force that drives industries, technologies and aspirations toward a shared future of progress.

Performance and functionality

The classification of DC motors is based on several factors, including design, electrical configuration, and operating characteristics. Understanding the operating principles behind these classifications is crucial to effectively using DC motors in a variety of applications. Let's delve deeper into how the main types of classified DC motors work.

Similar to generators, DC motors are also divided into three types according to field winding connections. They are

Shunt Motor
Series wound motor
Composite winding motor
Brushed DC Motors
Brushless DC Motors

Shunt Motor

Uma classificação sistemática de motores DC

In a shunt motor, the field winding is connected in parallel to the armature winding; As shown in the figure, the current through the shunt field winding and the armature is not the same. In this type, the field windings are designed to produce the required mmf through a moderately large number of turns of high resistance wire. As a result, the current in the shunt field winding is less than the armature current.

Prerequisite for maximum efficiency in direct current machines

Series wound motor

In series motor, the field winding is connected in series with the armature as shown in the figure. The series field winding therefore carries the armature current. In a series motor, the current flowing through the field winding is equal to the armature current. Series field windings must be designed with significantly fewer turns than shunt field windings with constant mmf. A series field winding therefore contains a comparatively small number of turns of thick wire and can therefore have a low resistance.

Composite winding motor

The compound winding motor has two field windings, one in series and the other parallel to the armature. As with generators, there are two types of compound motor connections. Since the shunt field winding is directly connected to the armature winding terminals as shown in the figure, it is called the short-circuit terminal. When the shunt winding is connected, it connects the series connection of armature and panel in series as shown in the figure and is called long circuit connection.

Generally, compound machines, whether motors or generators, are designed to produce flux through a shunt field winding. Thus, the shunt field composite machine is generally the dominant factor in generating the magnetic field in the machine.

DC motors with brushes

Brushed DC motors consist of a rotating armature (the rotor) and a stationary set of magnets (the stator). The rotor is connected to a commutator and brushes that transmit electrical current to the armature windings. When electric current flows through the armature windings, a magnetic field interacts with the stator magnetic field. This interaction creates torque that turns the rotor and generates mechanical energy.

Brushless Motors

BLDC motors offer precise speed control, making them suitable for applications that require precise and constant speeds. Speed control is achieved using sophisticated electronic switching methods such as sensor-based or sensorless control. Sensorless control uses the motor's back electromotive force (EMF) to determine rotor position, while sensor-based control uses Hall effect sensors or encoders for accurate feedback. BLDC motors have excellent torque-to-weight ratios and power densities, allowing them to deliver high torque despite their compact size. This feature makes them suitable for space-limited applications that require a high power-to-size ratio.

Classification criteria

Speed control: Some DC motors maintain a constant speed, while others are designed for variable speed applications.
Starting torque: Motors with high starting torque are essential for applications that require heavy starting loads.
Control Methods: DC motors can be controlled using various techniques such as armature voltage control, field flux control, or a combination of methods.
Efficiency and energy consumption: Different types of motors have different efficiencies, which affects energy consumption and operating costs.

Forms

Due to their simplicity and efficiency, PMDC motors are used in small appliances, tools and toys.
Series wound motors are suitable for drive systems and cranes that require high torque.
Due to their constant speed, shunt motors are often used in conveyor belts, lathes and fans.
Composite winding motors are suitable for applications that require speed and torque.
Separately excited motors are widely used in industries where precise control is required, such as robotic systems and machine tools.

Conclusion

Each classification offers unique benefits and capabilities, from timeless brushed DC motors to innovative brushless DC motors. Thanks to their simplicity and reliability, brushed DC motors continue to be the workhorse in countless applications. On the other hand, brushless DC motors are gaining popularity in modern industries due to their efficiency, precise speed control and maintenance-free operation. We also look at the characteristics of series, series, and compound DC motors, each with different features and applications. DC shunt motors offer speed control and relatively constant torque-speed factors, while DC series motors offer high starting torque and are used in high load applications. Compound DC motors combine the best of both worlds, offering better speed control and torque characteristics.