From Diversity to Unity: The Classification of DC Motors

August 18, 2023 Jessica

In the intricate realm of electrical engineering, where innovation and precision intersect, the humble DC motor is an emblem of diversity and unity. These machines, ranging from the compact to the colossal, power our world with remarkable efficiency and versatility. Within their spinning cores lies a rich tapestry of types, each tailored for specific applications, yet collectively forming a harmonious symphony of movement. This exploration embarks on a journey from diversity to unity, delving into the systematic classification of DC motors. As we navigate through the intricate nuances of their design, purpose, and performance, we unveil the threads that weave these diverse entities into a cohesive force that propels industries, technologies, and aspirations toward a shared future of advancement.

Performance and Functioning

The classification of DC motors is based on various factors, including their construction, electrical configuration, and operational characteristics. Understanding the working principles behind these classifications is crucial for effectively utilizing DC motors in different applications. Let’s delve into the working of the main types of classified DC motors.

Similar to generators, DC motors are also classified into three types by the connections of field winding, and they are

Shunt Wound Motor
Series wound Motor
Compound Wound Motor
Brushed DC motors
Brushless DC motors

Shunt Wound Motor

A Systematic Classification of DC Motors

In the shunt wound motor, the field winding is connected in parallel with the armature winding; as shown in Fig., the current through the shunt field winding and the armature will not be the same. In this type, the field windings are designed to create the needed m.m.f by a moderately large number of turns of wires with high resistance. As a result, the current in the shunt field winding is smaller than that of the armature current.

Condition for Maximum Efficiency in DC Machine

Series Wound Motor

In the Series wound motor, the field winding is connected in series with the armature, as shown in Fig. Thus, the series field winding carries the armature current. In the Series motor, the current passing through field winding is the same as that of the armature current. Series field windings should be designed with abundant fewer turns than shunt field windings for constant m.m.f. As a result, a series field coil contains a comparatively tiny range of turns of thick wire and, therefore, can possess a low resistance.

Compound Wound Motor

The Compound wound motor has two field windings, one connected in series and another parallel to the armature. Like Generators, there are two types of compound motor connections. Once the shunt field winding is directly connected across the armature winding terminals, as shown in Fig, it’s referred to as a short-shunt connection. When the shunt winding is connected, it shunts the series combination of the armature and series field, as shown in Fig, and it’s referred to as a long-shunt connection.

Generally, compound machines, either motors or generators, are designed so that the flux is created by shunt field winding. Thus, the shunt field compound machine is the usual dominant factor in producing the magnetic field in the machine.

Brushed DC Motors

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, which transfer electric current to the armature windings. As electric current flows through the armature windings, a magnetic field interacts with the stator’s magnetic field. This interaction generates a torque that rotates the rotor, producing mechanical power.

Brushless Motors

BLDC motors offer precise speed control, making them suitable for applications that require accurate and consistent rotational speeds. Speed control is achieved through sophisticated electronic commutation methods like sensor-based or sensorless control. Sensorless control utilizes the motor’s back electromotive force (EMF) to determine rotor position, while sensor-based management employs Hall effect sensors or encoders for precise feedback. BLDC motors exhibit excellent torque-to-weight ratios and power densities, allowing them to deliver high torque outputs despite their compact size. This characteristic makes them well-suited for applications with space constraints requiring a high power-to-size ratio.

Classification Criteria

Speed Regulation: Some DC motors maintain a consistent speed, while others are designed for variable speed applications.
Starting Torque: Motors with high starting torque are crucial for applications requiring heavy initial loads.
Control Methods: DC motors can be controlled using various techniques such as armature voltage control, field flux control, or combined methods.
Efficiency and Energy Consumption: Different motor types exhibit varying efficiency levels, impacting energy consumption and operational costs.

Applications

Due to their simplicity and efficiency, PMDC motors are used in small appliances, tools, and toys.
Series-wound motors are suitable for traction systems and cranes demanding high torque.
Due to their consistent speed, shunt-wound motors are prevalent in conveyor belts, lathes, and fans.
Compound-wound motors are adaptable for applications requiring both speed and torque.
Separately excited motors, like robotic systems and machine tools, are common in industries needing precise control.

Conclusion

Each classification offers unique advantages and capabilities, from the timeless brushed DC motors to the innovative brushless DC motors. With their simplicity and reliability, Brushed DC motors continue to serve as workhorses in numerous applications. On the other hand, brushless DC motors, with their efficiency, precise speed control, and maintenance-free operation, have become increasingly popular in modern industries. We also delved into the characteristics of shunt, series, and compound DC motors, each with distinct features and applications. The shunt DC motors provide speed regulation and relatively constant speed-torque factors, while series DC motors offer high starting torque and find use in heavy-load applications. Compound DC motors combine the best of both worlds, offering improved speed regulation and torque characteristics.