DC Motor, How it works?

Lesics

22 Sept 201404:49

Summary

TLDRThis video script offers an insightful look into the operation and construction of commercial DC motors, which are widely used in portable home appliances, automobiles, and industrial equipment. It explains the basic components, including the stator, armature, and commutator rings, and how they work together to produce motion. The script delves into the principles of electromagnetic force and the Lorentz law, highlighting the importance of the commutator in maintaining torque direction. It also discusses the role of additional loops and highly permeable steel layers for smoother operation. The script further explains different types of DC motor constructions, such as shunt and series motors, and their respective torque and speed characteristics. A unique feature of DC motors, the production of back EMF, is also covered, along with the need for a proper starting mechanism to prevent motor damage. The video concludes with a mention of universal motors, which can operate on both AC and DC power sources, inviting viewers to explore further in the next video.

Takeaways

🔋 DC motors are found in home appliances, automobiles, and industrial equipment.
🛠️ The simplest DC motor consists of a stator providing a constant magnetic field and a rotating armature coil.
⚡ The armature is connected to a DC power source through commutator rings, inducing electromagnetic force that rotates the coil.
🔄 The commutator ensures the direction of current flow and torque remains consistent, allowing continuous rotation.
⚙️ Adding more loops to the rotor and separate commutator pairs smoothens motor rotation and enhances performance.
🔧 Practical motors use armature loops in slots with highly permeable steel layers to enhance magnetic flux interaction.
📈 Spring-loaded commutator brushes maintain contact with the power source, while larger motors use electromagnetic stators.
🔌 DC motors can have field coils connected in parallel (shunt motors) or series (series motors), affecting starting torque and speed regulation.
⚖️ Shunt motors maintain almost constant speed regardless of load, while series motors have high starting torque but speed drops with load.
🌀 DC motors produce BACK EMF, which reduces armature current and prevents rotor burnout, necessitating proper starting mechanisms.
🔄 Universal motors can run on both AC and DC power sources, offering versatility in various applications.

Q & A

What are the common applications of DC motors?
-DC motors are commonly found in portable home appliances, automobiles, and various types of industrial equipment.
What is the basic construction of a simple DC motor?
-A simple DC motor consists of a stator that provides a constant magnetic field and an armature, which is the rotating part, typically a simple coil connected to a DC power source through a pair of commutator rings.
How does the Lorentz law relate to the operation of a DC motor?
-The Lorentz law states that an electromagnetic force is induced on a current-carrying conductor in a magnetic field. In a DC motor, this force causes the armature coil to rotate when current flows through it.
Why does the torque action on the coil change direction as it rotates?
-The torque action changes direction because the commutator rings are connected with the power source of opposite polarity, ensuring that the torque is in the same direction throughout the motion and allowing the coil to continue rotating.
What is the issue with torque action when the coil is nearly perpendicular to the magnetic flux?
-When the coil is nearly perpendicular to the magnetic flux, the torque action nears zero, which can result in irregular motion of the rotor.
How can the problem of irregular motion be overcome in a DC motor?
-This problem can be overcome by adding more loops to the rotor, each with a separate commutator pair, ensuring that the motor force is always present in the system and providing smoother rotation.
What role do the armature loops and highly permeable steel layers play in a practical DC motor?
-In a practical DC motor, the armature loops are fitted inside slots with highly permeable steel layers to enhance magnetic flux interaction, improving the motor's performance.
What are the two different ways field coils can be connected to the rotor windings in a DC motor?
-The field coils can be connected to the rotor windings in two different ways: in parallel or in series, resulting in two different types of DC motor constructions known as shunt and series motors.
What are the characteristics of a series wound motor compared to a shunt motor?
-A series wound motor has good starting torque but its speed drops significantly with the load. In contrast, a shunt motor has a lower starting torque but can run almost at a constant speed regardless of the load.
What is the unique characteristic of DC motors known as BACK EMF?
-BACK EMF is a unique characteristic of DC motors where an internal electromotive force (EMF) is induced in the rotating armature loops that opposes the applied input voltage. This BACK EMF is proportional to the speed of the rotor.
Why is it necessary to control the applied input voltage during the starting of a DC motor?
-It is necessary because at the start, the BACK EMF is too low, which results in a high armature current that could lead to the burnout of the rotor if not controlled properly.
What is a universal motor and what makes it special?
-A universal motor is a variation of a DC motor that is capable of running under both AC and DC power sources, making it versatile for different applications.

Outlines

00:00

🛠️ Basic Operation and Construction of DC Motors

This paragraph introduces the ubiquity of DC motors in various applications and sets the stage for a detailed exploration of their operation and construction. It begins with the simplest form of a DC motor, highlighting the role of the stator in providing a constant magnetic field and the armature as the rotating coil. The paragraph explains how the interaction between the current flowing through the coil and the magnetic field generates the electromagnetic force that causes rotation, as described by Lorentz's law. It also touches on the role of the commutator rings in maintaining the direction of the current flow, which is crucial for continuous rotation and overcoming the issue of torque variation when the coil is perpendicular to the magnetic flux. The addition of extra loops with separate commutator pairs is suggested to ensure a constant force and smoother operation. The use of highly permeable steel layers and spring-loaded commutator brushes is also mentioned to enhance performance. The paragraph concludes with a brief mention of different types of DC motors, including shunt and series motors, and their respective characteristics regarding starting torque and speed under load.

Mindmap

Keywords

💡DC Motor

A DC motor, or direct current motor, is a type of electrical motor that is powered by direct current electricity. It is the main focus of the video as it is used in various applications from home appliances to industrial equipment. The script discusses the operation and construction of commercial DC motors, highlighting their importance in different sectors.

💡Stator

The stator is the stationary part of the motor that provides a constant magnetic field. It is a critical component in the functioning of a DC motor, as it works in conjunction with the armature to create the necessary conditions for the motor to operate. In the script, the stator's role is to maintain a steady magnetic field against which the armature can interact.

💡Armature

The armature is the rotating part of a DC motor, typically consisting of a coil of wire. When connected to a DC power source, the armature experiences an electromagnetic force that causes it to rotate. The script explains that the armature's connection to the power source is facilitated by a commutator, and its rotation is fundamental to the motor's operation.

💡Commutator

A commutator is a mechanical switch that periodically reverses the direction of the current in the armature windings. This reversal ensures that the torque is consistently applied in the same direction, allowing the motor to continue rotating. The script describes how the commutator works with the power source to maintain the flow of electricity and the direction of torque.

💡Lorentz Law

The Lorentz law describes the force exerted on a charged particle moving through a magnetic field. In the context of the video, it is the principle that explains how an electromagnetic force is induced on the armature when current flows through it, leading to the rotation of the coil. The script uses the Lorentz law to explain the fundamental physics behind the motor's operation.

💡Torque

Torque is the force that causes rotation in the motor. The script discusses how the torque action is maintained in the same direction throughout the motion of the motor, which is crucial for the continuous rotation of the armature. The concept of torque is central to understanding how a DC motor produces mechanical work.

💡Back EMF

Back EMF, or counter electromotive force, is a voltage induced in the armature as it rotates within the magnetic field. This internal EMF opposes the applied input voltage and is proportional to the speed of the rotor. The script explains that back EMF is a unique characteristic of DC motors and has implications for the motor's current and speed control.

💡Series Wound Motor

A series wound motor is a type of DC motor where the field coils are connected in series with the armature. The script mentions that this configuration provides a good starting torque but causes the speed to drop significantly with an increase in load. It is one of the two different kinds of DC motor constructions discussed in the video.

💡Shunt Motor

A shunt motor is another type of DC motor construction where the field coils are connected in parallel to the armature. According to the script, shunt motors have a lower starting torque but can maintain a nearly constant speed regardless of the load. This characteristic makes them suitable for applications requiring a stable speed.

💡Universal Motor

A universal motor is a versatile type of motor that can operate on both AC and DC power sources. The script briefly mentions this variation of the DC motor and suggests that viewers watch the next video for more information. Universal motors are interesting because they offer flexibility in power source usage.

💡Electromagnetic Induction

Electromagnetic induction is the process by which an electric current is induced in a conductor moving through a magnetic field or by a changing magnetic field around it. The script refers to this principle to explain the generation of back EMF in the rotating armature loops of a DC motor, which is a key factor in the motor's operation.

Highlights

DC motors are commonly used in portable home appliances, automobiles, and industrial equipment.

The video explains the operation and construction of commercial DC motors.

The simplest DC motor consists of a stator providing a constant magnetic field and an armature that is a rotating coil.

The armature is connected to a DC power source through a pair of commutator rings.

Lorentz law induces electromagnetic force on the coil when current flows through it, causing rotation.

The commutator rings ensure that the torque action is in the same direction throughout the motion.

Adding more loops to the rotor with separate commutator pairs helps maintain a constant motor force.

Practical motors have armature loops fitted inside slots with highly permeable steel layers to enhance magnetic flux interaction.

Spring-loaded commutator brushes maintain contact with the power source.

Most DC motors use an electromagnetic stator pole powered by the same DC source.

Field coils can be connected to the rotor windings in parallel or series, resulting in shunt and series motor constructions.

Series wound motors have good starting torque but speed drops with load.

Shunt motors have low starting torque but run at a constant speed regardless of load.

DC motors exhibit a unique characteristic: the production of back EMF.

Back EMF is proportional to the speed of the rotor and opposes the applied input voltage.

At motor start, back EMF is low, leading to high armature current and potential rotor burnout.

A proper starting mechanism is necessary to control input voltage in large DC motors.

Universal motors are a variation capable of running under both AC and DC power sources.

The video concludes with an invitation to learn more about universal motors in the next video.