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Basic Understanding of DC Motors

Updated: Mar 26

Electrical energy can be transformed into mechanical energy by an electrical machine called a DC motor. A DC motor uses direct current as its electrical input, which is converted into mechanical revolution.

DC motors are favored over other kinds of motors because they can precisely control their speed, which is essential for industrial machines. The ability of DC motors to start, halt, and reverse quickly is crucial for managing the functioning of manufacturing machinery.



Construction of a DC Motor

The following six components make up a DC motor:


Yoke:

The outer frame of a DC motor is called a yoke, and it is a hollow cylinder composed of rolled or cast steel. The yoke fulfills the following two functions:

  • It functions as a protective cover for the machine and supports the field pole core.

  • It gives the magnetic flux generated by the field winding a way.


Magnetic Field System:

A DC motor's magnetic field system is its stationary component. It generates the majority of the magnetic flux within the motor. It comprises a field winding looped around the pole core and an even number of pole cores fastened to the yoke. The salient poles of a DC motor are its inwardly projecting poles, and each pole core has a curved pole shoe. The pole shoe is used for two things.

  • It supports the field coils.

  • By expanding the magnetic circuit's cross-sectional area, it lowers its resistance.


Armature Core:

The pole cores consist of thin sheet steel laminations that are isolated from one another in order to minimize the loss of eddy current. In order to create alternating north and south poles when current passes through the coils, the field coils are linked in series with one another.


Armature Winding:

The armature core's slots are occupied by the insulated conductors. The connections between the conductors are appropriate. Armature winding is the term for this interconnected configuration of wires. Wave winding and lap winding are the two forms of armature windings that are employed.


Commutator:

A commutator is a mechanical rectifier that changes the direct current input from the DC source into an alternating current in the armature winding of the motor. The commutator is composed of wedge-shaped copper segments that are covered in mica sheets to provide insulation from the shaft and from one another. Every commutator segment is linked to the ends of the armature coils.


Brushes:

The armature windings get current injection from the DC source through the brushes, which are fixed on the commutator. The carbon brushes are held up by a brush holder, which is a metal box. Springs are used to regulate and keep the pressure that the brushes provide to the commutator at a consistent level. Through the carbon brushes and commutator, the current travels from the external DC source to the armature winding.


Working of DC Motor


As seen in the illustration, consider a two-pole DC motor. The DC motor's field coils are excited, producing alternate N and S poles, and current flows through the armature windings when it is linked to an external DC supply source.


All armature conductors under the N pole carry current in a single direction, say into the paper's plane, whereas all conductors under the S pole carry current in the opposite direction, say out of the paper's plane. Every conductor exerts mechanical stress on itself since it is in a magnetic field and carries current.


Applying Fleming's left-hand rule reveals that the armature is prone to moving in an anticlockwise manner due to the force applied to each conductor. The armature rotates as a result of the torque produced by the combined force acting on each conductor. The current in a conductor is reversed and simultaneously subjected to the next pole of opposite polarity when it goes from one side of a brush to the other. The force applied to the conductor stays in the same direction as a consequence. The motor is spinning in the same direction as a result.


Types of DC Motor

DC motors convert electrical energy into mechanical energy by using DC current. Using this has the primary benefits of having speed control and being smaller.


The DC motor comes in four main varieties. They are as follows:

  • Series DC Motor

  • Shunt/Parallel DC Motor

  • Compound DC Motors

  • Permanent Magnet DC Motor


A permanent magnet DC motor generates field flux through the use of permanent magnets. The electrical connections that exist between the rotor and stator determine how the other three kinds are categorized. They all have different torques and speeds.


Separately Excited DC Motor

The field coils of an independently excited DC motor are powered by an external DC supply.


Self-Excited DC Motor

The field winding in self-excited DC motors is linked to the armature winding either in series or parallel.


Permanent Magnet DC Motor

A permanent magnet is utilized in these kinds of DC motors to produce a magnetic field. In this case, there is no input current used for excitation. These are utilized in air conditioners, wipers, car starters, and other devices.


Shunt DC Motor

In this instance, the field and armature windings are linked in parallel, or via a shunt. Because the shunt field may be energized independently of the armature windings, it can be employed to provide much simpler reverse control in addition to higher speed regulation.


Series DC Motor

Here, the field is wound with a few turns by a long wire carrying the whole armature current. Although there is no way to control the speed, this type of motor produces a lot of starting torque. If they are operated without any load, harm might occur. These aren't the best choice for situations requiring varied speeds.


Compound DC Motor

They feature a shunt field that is activated independently. Although they offer a strong torque at startup, they may not work well in applications with fluctuating speeds.


Short Shunt DC Motor

The sole connection between the shunt field winding and the armature winding in this instance is a parallel one. The series field coil is divided into the armature after being fully exposed to current.


Long Shunt DC Motor

The armature and series field coil in this instance are linked in series with the shunt field winding, which is connected in parallel.


Differentially Compound DC Motor

The flux generated by the shunt field windings in this kind of compound-wound DC motor lessens the impact of the main series windings.


Cumulative Compound DC Motor

The flux generated by the shunt field windings in this instance amplifies the impact of the main field flux generated by the series winding.


Brushed DC Motor vs Brushless DC Motor

In contrast to brushed DC motors, synchronous DC motors, commonly referred to as brushless DC motors, lack a commutator. An electrical servomechanism that can sense and modify the rotor's angle takes on the role of the commutator in a brushless DC motor.


The commutator of a brushed DC motor produces torque in a single direction by reversing the current every half cycle. Even through brushed DC motors are still widely used, more and more have recently been replaced with brushless types, which are more energy-efficient.


Applications for DC motors


Computer equipment

Drive motors for CD-ROM drives and HDDs are among the applications for CPU cooling fans. In order to minimize dust emissions caused by the motor's commutator and brushes wearing out, brushless DC motors are frequently used in these applications.


Audio and video equipment

Audio CD, DVD, and Blu-ray players are among the devices in visual and audio equipment that employ DC motors.


Home appliances

DC motors are utilized in small electric fans, electric toothbrushes, and shavers, as well as in radio-controlled versions such as the little 4WD. These kinds of products employ tiny DC motors that run at low voltages-about 9 volts.


Automobiles

  • Power seat, power window, and wiper motors are just a few of the many uses for DC motors in automobiles.

  • Showcase the role of DC motors in automotive power systems, including power seats, windows, and wipers.


Industrial machinery and medical equipment

  • Industrial robot servo motors are made up of numerous DC motors. Applications for fan motors in medical equipment include oxygen concentrators and respirators.

  • Additionally, they are utilized in construction and agricultural gear.

  • Emphasize DC motors as essential components in industrial machinery, serving as actuators in diverse applications.

  • Highlight the use of DC motors in medical equipment and industrial robots, showcasing their versatility.



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