DC Motor, How it works?
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
🛠️ 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
💡Stator
💡Armature
💡Commutator
💡Lorentz Law
💡Torque
💡Back EMF
💡Series Wound Motor
💡Shunt Motor
💡Universal Motor
💡Electromagnetic Induction
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.
Transcripts
You can find DC motors in many portable home appliances
Automobiles and types of industrial equipments
In this video, we will logically understand the opperation and construction of comercials DC motors
Let's first start with the simplest DC motor possible
It looks like this
The stator provides a constant magnetic field
And the armature, witch is the rotating part, is a simple coil
The armature is connected to a DC power source through a pair of comutator rings
When the current flows through the coil, an electromagnetic force is induced on it according to the Lorentz law
So the coil will start to rotate
You'll notice that as the coil rotates, the commutator rings connected with the power source of opposite polarity
As it result on the left side of the coil the electricity will always flow "away"
And on the right side electricity will always flow "towards"
This ensures that the torque action is also in the same direction throughout the motion
So the coil will continue rotating
But, if you observe the torque action on the coil closely
you'll notice that
when the coil is nearly perpendicular to the magnetic flux
the torque action nears zero
As a result there will be irregular motion of the rotor
if you run such a DC motor
Here is the trick to overcome this problem:
Add one more loop to the rotor, with a separate comutator pair for it
In this arrangement when the first loop is in the vertical position
the second loop will be connected to the power source, so the motor force is always present in the system
Moreover , the more such loops, the smoother will be the motor rotation
In a practical motor the armature loops are fitted inside slots with highly permeable steel layers
This will enhance magnetic flux interaction
Spring loaded comutator brushes help to mantain contact with the power source
A permanent magnetic stator pole is used only for very small DC motors
Most often, an electromagnetic is used
The field coil of the electromagnetic is powered from the the same DC source
The field coils can be connected to the rotor windings in two different ways
Parallel or series
The result is two differents kinds of DC motor constructions
a shunt and a series motors
The series wound motor has good starting torque, but speed drops drastically with the load
The shunt motor has a low starting torque but it is able to run almost at a constant speed
Irrespective of the load acting on the motor
Unlike the other electrical machines, DC motors exhibits a unique characteristic:
The production of BACK EMF
A rotating loop in a magnetic field will produce an EMF according to the principle of the electic magnetic induction
The case of the rotating armature loops is also the same
An internal EMF will be induced that opposes to the applied input voltage
The BACK EMF reduces armature current by a large amount
BACK EMF is proportional to the speed of the rotor
At the starting of the motor BACK EMF is too low, thus the armature current becomes too high
leading to the burnout of the rotor
Thus a proper starting mecanism that controls the applied input voltage is necessary in large DC motors
One of the interesting variation of the DC motor is a universal motor
which is capable to run under both AC and DC power sources
To know more about it, please check the next video
Thank you
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