chapter 8b - dc motor_intan.ppt

8/11/2019 Chapter 8b - DC Motor_Intan.ppt

1/17

ELECTRICAL MOTOR:

DC MOTOR


2/17

Types of Machines


3/17


4/17

How DC Motor Works?

A DC motor works by converting electric powerinto

mechanical work. Current flows through a coil and

producing a magnetic field that spins the motor.

The simplest DC motor is a single coil apparatus


5/17

Basic DC Motor

In Figure 8.1a shows the field winding is one long coil of wire

that has been separated into two sections.

The top section is connected to the positive pole and bottom

negative pole. The current flow in this direction makes the top

coil the north pole of the magnet and the bottom coil the south

pole of the magnet.electromagnet condition

The permanent bar magnet represents thearmatureand the

coil of wire represents the field.The arrow shows the clockwise

direction of the armature's rotation.

Figure 8.1a


6/17

Basic DC Motor (cont..)

The north pole of the armature comes closer to the south pole of the

field, and the south pole of the armature is coming closer to the northpole of the field. (Figure 6.1b).

When the opposite poles are at their strongest attraction, the armature

will be "locked up.

Problem - For the armature to continue its rotation, the armature's

polarity must be switched. Since the armature in this diagram is apermanent magnet, it would lock up during the first rotation and not

work.

Idea - If the armature is an electromagnet, its polarity can be changed

by changing the direction of current flow through it.

Figure 6.1b


7/17

Basic DC Motor (cont..) One commutator segment is provided for each terminal of the

magnetic coil. DC current flowing through it to becomemagnetized.

A stationary set of carbon brushes is used to make contact to

the rotating armature. The brushes ride on the commutator

segments to make contact so that current will flow through the

armature coil. In Figure 6.1c you can see that the DC voltage is applied to the

field and to the brushes.

Figure 6.1c


8/17


Since negative DC voltage is connected to one of the brushes,

the commutator segment the negative brush rides on will also

be negative.

The armature's magnetic field causes the armature to begin to

rotate.

A commutator is used to reverse the direction flow of current.

The current flows in opposite directions in the wires which also

switches the polarity of the armature coil's magnetic field at just

the right time so that the repelling and attracting continues.

Figure 6.1c


9/17


Motor as having just two essential components as in Figure 6.2:

1. There's a permanent magnet (or magnets) around the edge of the

motor case that remains static, so it's called the stator of a motor.

- (the field magnet could be an electromagnet as well, but in most

small motors it isn't in order to save power)

2. Inside the stator, there's the coil, mounted on an axle that spins

around at high speedand this is called the rotor. The rotor alsoincludes the commutator.

Figure 6.2c: Basic diagram of DC motor


10/17

DC Motor Rotation

Figure 8.3 show the operation of DC Motor Rotation


11/17

HOW IT WORKS

In 0 degree to 90 degree rotation In the 0 degrees, the brushes arein contact with the voltage sourceand current is flowing.

Current through wire segment C-D interacts with the magnetic fieldand the result is an upward force.

Segment A-B has the sameinteraction, but the force is in the

downward direction.

Both forces are of equalmagnitude, but in opposingdirections.

Figure 6.4:DC motor rotation from 0 degree to 90 degree

Figure 6.5: Plot graph DC from 0 degree to 90 degree


12/17

In 90 degree to 180 degree rotation

In the 90 degree diagrams, thebrushes are not in contact withthe commutator and the current

stops flowing through the coil -noforce is produced.

However the coil keeps turning

because of its own momentum.Figure 6.6:DC motor rotation from 90 degree to 180 degree

Figure 6.7: Plot graph DC from 90 degree to 180 degree

How it Works Cont.


13/17

How it Works Cont.

In 180 degree to 270 degree rotation In the 180 degrees, the brushes arein contact with the voltage sourceand current is flowing.

Current through wire segment A-Binteracts with the magnetic field andthe result is an upward force.

Segment C-D has the sameinteraction, but the force is in the

downward direction.

Both forces are of equal magnitude,but in opposing directions.

Figure 6.8:DC motor rotation from 180 degree to 270

degree

Figure 6.9: Plot graph DC from 180 degree to 270

degree


14/17

We can increase the turning force (or torque) that the motor

can create in four ways:

1. More powerful permanent magnet

2. Increase the electric current flowing through the wire

3. Make the coil so it has many "turns" (loops) of very thin

wire instead of one "turn" of thick wire

4. The closer together the permanent magnet and the coil, thegreater the force the motor can produce

How it Works Cont.


15/17

DC Motor Application

Photo 8.1: The main parts inside a medium

sized electric motor from a coffee grinder. Photo 8.2: An electrician repairs an electric motoronboard an aircraft carrier. The shiny metal he's

using may look like gold, but it's actually copper.

Although copper doesn't conduct electricity quiteas well as gold, it's much less expensive.
http://www.explainthatstuff.com/gold.htmlhttp://www.explainthatstuff.com/copper.htmlhttp://www.explainthatstuff.com/copper.htmlhttp://www.explainthatstuff.com/gold.html


16/17

Residential and commercial: Clocks, timers, toys, cars,

fans, pumps, medical equipment.

Industrial: steel and paper mills, conveyors, textile

machines, printing presses, packaging machines,

extruders, material handling, mining, marine generationand propulsion.

DC Motor Application Cont.


17/17

Fan

Hoist

Compressor

Conveyor

chapter 8b - dc motor_intan.ppt

Documents