chapter 1_basic electrical principles

8/2/2019 CHAPTER 1_Basic Electrical Principles

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Chapter 1: BASIC OF

ELECTRICAL PRINCIPLES


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Atomic Structure

An atom defined as the smallest particle of an element. Atom contain particles called protons, neutrons and

electrons.

Protons and neutrons located at the centre called

nucleus of the atom. Protons contain a positive electrical charge and neutrons

add weight to the atom.

Electrons circle around the nucleus in various orbit.


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Electrical Characteristic ofElement

The outer orbit on an atom is called valence ring. The number ofelectrons on the valence ring determines

the electrical characteristics of the element.


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Conductor,semiconductor andinsulator.

Conductor Atoms that valence ring has one, two or three, the element

is classified as a good conductor, because the electrons onvalence ring move easily from one atom to another.

Conductor is a substances that allow the flow ofelectric

current or thermal energy.


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Semiconductor Atom has four valence electron, is classified as a

semiconductor.

Class of crystalline solids (germanium or silicon) withelectrical conductivity between that of a conductor and

an insulator. Semiconductors are used in the manufacture ofelectronic

devices such as diodes, transistors, and integratedcircuits (IC).


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Insulator Atom has five or more valence electrons, these electrons

will not move easily.

Insulator is a substance that blocks or retards the flow ofelectric current or heat.

An insulator is a poor conductor because it has a highresistance to electric charge flow.

Electrical insulators are commonly used to hold conductorsin place, separating them from one another and fromsurrounding structures.

Electrical insulators include rubber, plastic, porcelain, andmica.


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Electric Current Flow

When an atom lacks an electron, it attracts an electron fromanother atom.

The electrical circuit must also be complete between themassing electron and the lack of electrons.

The mass movement of valence electrons from atom to

atom in a conductor defined as Current flow .


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Electrical Circuits When the electrons flow back to where they started from,

it is called a circuit. In electrical circuits, current flows from the Positive (+ve)

terminal of the supply to the Negetive (-ve) terminal.

Any device that consumes electricity is called load.

In electrical circuit, all loads are regarded as resistance


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Automotive Electrical Circuits

In an automotive electrical circuit, one end of the wire from

each load returning to the battery is connected to thevehicle body or frame; acting as a conductor, allowingcurrent to flow through the body and back to the battery.

The body or frame is then referred to as the body ground(or earth) of the circuit.


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Voltage (V) and ElectromotiveForce (EMF)

VOLTAGE Voltage cause the electrons to move through a circuit.

Voltage is a measurement for electrical pressure differenceor potential difference.

The device that measure voltage is Voltmeter.

It is measured in volts, V

1 volt refers to the voltage that can cause 1 ampere of currentto flow in a conductor having a resistance of 1 ohm

In automotive, the electrical pressure can be provided by abattery or it can be produced by a generator


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Electric Current

AMPERES Amperes is a measurement for the rate of electron flow or

the amount of current flowing through a circuit.

It is equal to a flow of charge 1 coulomb per second or6.25 x 1018 electrons per second.


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Electric Current

Direct Current (DC) flows in only one direction. Mostautomotive circuit operate on direct current.

Alternating Current (AC) flows alternately in one directionand then in the opposite direction.

The windings in alternator stator have AC flowing in them,

but this AC is rectified to DC by the diodes in thealternator.

Therefore, DC is delivered from the alternator to the batteryand electrical components on the vehicle.


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Electric Source in Automotive

Alternator

Battery


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OHMS LAW

Ohm's law states that the current (I) through a conductorbetween two points is directly proportional to the potentialdifference or voltage (V) across the two points, and inverselyproportional to the resistance (R) between them.

I = current , V = voltage

R = resistance
http://www.answers.com/topic/electric-currenthttp://www.answers.com/topic/proportionalityhttp://www.answers.com/topic/voltage-7http://www.answers.com/topic/voltage-7http://www.answers.com/topic/voltage-7http://www.answers.com/topic/electrical-resistance-1http://en.wikipedia.org/wiki/File:OhmsLaw.svghttp://www.answers.com/topic/electrical-resistance-1http://www.answers.com/topic/voltage-7http://www.answers.com/topic/voltage-7http://www.answers.com/topic/voltage-7http://www.answers.com/topic/proportionalityhttp://www.answers.com/topic/electric-current


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Types of Circuit Primary Circuits

The first part of a two-part circuit

The switch that control the circuit must be closed before anyof the other components in the circuit will work

Open circuit

Continuity fault in the circuit e.g. broken wire, load or fuse;faulty switch

No output from the load

Close circuit

Perfect, correct functioning circuit in which the switch is closed

Output is achieved from the load

It is normal/working condition


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Series Circuit

Components connected in series are connected along asingle path.

A series circuit has these features:

1. Same current flows through all of the components.

2. The total resistance is the sum of all resistances in thecircuit.

3. The voltage drop across each load depends on the ohmvalue of that resistance.

4. The sum of the voltage drops across each load equals

the source voltage.


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Series Circuit

In a series circuit, the components (switches, bulbs,fuses etc.) are all connected so that the current flowsfirst through one and then through the next

There are no branches; the current doesn't split intomore than one route

Disadvantages

If one component fail, the system will revert to opencircuit

Unable to control the operation of load separately

Each load receive different voltage due to voltagedrop


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Series Connection

The combined resistance Ro in this circuit is equal to the sum of individualresistance R, and R2.

Therefore, the strength of current I flowing in the circuit can be found asfollows:


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Application of Ohm's Law

To determine the current (I) value.


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Application of Ohm's Law

a)To determine the voltage (V) value. b) to determine resistance (R) value.


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Voltage drop/divider When current flows in a circuit, the presence of a resistance in

that circuit will cause the voltage to fall or drop as it passesthrough the resistance.

The resultant difference in the voltage on each side of theresistance is called a voltage drop.

When current I flows in the following circuit, voltage drops V, andV2 across resistances R, and R2 can be determined as followsfrom Ohm's law. (The value of current I is the same for both R,and R2 since they are connected in series.)


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1.Voltage drop is the difference in voltage across aresistance when current flows through the resistance.

2. Voltage drop/divider,

V1= I x R1

or

V1= Vsource x R1

R1+R2+R3

Voltage drop/divider


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1. Total Resistance,RT= R1+R2+R3

2. Voltage drop,

V1= I x R1 (Vsource)

orV1= Vsource x R1

R1+R2+R3

3. Voltage

Vsource=V1+V2+V3

4.Current

I=Vsource

RT

Series Circuit


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Quiz 1

1. Calculate the total resistance in the circuit.2. What is the value display of the Ammeter, A?

3. Find the value of voltmeter V1,V2,V3 and V4.

V1

V2

V3

V4

1


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Solution:


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Parallel Circuit.

The components are connected separate path for currentflow.

The amount ofcurrent flow through each load depends onthe amount ofresistance in that part of the circuit.

Equal full source voltage is supplies to each load.

The total resistance is always less than ohm value of thelowest resistor in the circuit.


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Parallel Circuit.

1. Current flow,

2. Total/effective resistance ,RT

1 = 1 + 1 + 1

RT R1 R2 R3


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ELECTROMAGNETISM


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Magnetism A phenomenon by which materials assert an

attractive/repulsive force or influence on other materials Magnetic flux travels from N to S


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Magnetism

A permanent magnet has an invisible magnetic fieldsurrounding the magnet.

Arrow on the line that represent the field show the directionof magnetic flow, or flux.

Basic magnetic principles, as below figure;


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Electromagnetism

A phenomenon by which magnetism properties arestrengthened by an electric current

Right-hand rule

When currentflows in the direction of the travel ofa right-

hand . screwas it is being screwed in, a magnetic flux is

generated in the direction of the force that turns the screw


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Electromagnetism What happen to the magnetic flux when we have a circular

wire rather than a straight wire???

When a straight wire is bent, it becomes a circular coil andcreates a much larger, more powerful flux. When current

flows in a coil, the direction of the magnetic flux is suchthat Nand S poles are created in the coil


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Electromagnetism When a conductor is wound in a tubular-shaped coil, it is

called solenoid. S pole is created under the solenoid and Npole above it.

The number of magnetic lines of force increases as thenumber of turns of the coil increases


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Electromagnetism

An electromagnet is manufactured by winding a coil of wirearound a metal core.

An iron core become concentrate of the magnetic field.

The strength of an electromagnet is determined by;

1. The number of turns on the coil.

2. The amount of current flow through the coil


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Electromagnetic Force

An electromagnetic force is a force that acts on a conductor when

current flows in the conductor within magnetic field.

There are a smaller number of magnetic lines of force above the

conductor since the direction of the magnetic fluxes created by themagnet and the direction of those created by current oppose eachother.

In contrast, there are a larger number of magnetic lines of forceunder the conductor as their directions coincide.

The direction of an electromagnetic force can be determined fromFleming's left-hand rule

Direction of electromagnetic force


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Fleming's left-hand rule

The index finger is the direction of the magnetic flux The middle finger is the direction of the current

The thumb is the direction of the electromagnetic force


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Application Electromagnetism

Application in automotive; RELAY - is an electrically operated switch, which use a small

current to control large current.

A simple electromagnetic relay consists of a coil of wiresurrounding a soft iron core, an iron yoke which provides a

low reluctance path for magnetic flux, a movable ironarmature
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Application Electromagnetism

Application in automotive; STATER SOLENOID are designed to handle the

exceptionally large current which are required by startermotors.

When the ignition switch is turned on, a small electric current

is sent to the starter solenoid. This causes the starter solenoid to close

a pair of heavy contacts, thus relaying a

large electric current to the starter

motor, which in turn sets the engine

in motion.


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Test and measuring instruments

Current Measurement Measuring current using an ammeter in series with the rest

of the circuit component.


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Resistance Measurement

Measuring resistance of a component which has beendisconnected from the electric circuit using ohmmeter.


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Voltage measurement Measuring voltage using a voltmeter connected across a

component whilst it is in circuit with the current flowing.


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THE END

Any question?
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chapter 1_basic electrical principles

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