Chapter 05 Bennet

8/10/2019 Chapter 05 Bennet

1/54

Chapter 5

Fundamentals of Electricity


2/54

Objectives (1 of 3)

Define the terms electricity and electronics.

Describe the atomic structure.

Outline how some of the chemical and

electrical properties of atoms are defined bythe number of electrons in their outer shells.

Outline the properties of conductors,

insulators, and semiconductors. Describe the characteristics of static

electricity.


3/54

Objectives (2 of 3)

Define what is meant by the conventional andelectron theories of current flow.

Describe the characteristics of magnetism and the

relationship between electricity and magnetism.

Describe how electromagnetic field strength is

measured in common electromagnetic devices.

Define what is meant by an electrical circuit and the

terms voltage, resistance, and current flow.


4/54

Objectives (3 of 3)

Outline the components required to constructa typical electrical circuit.

Perform electrical circuit calculations usingOhms law.

Identify the characteristics of DC and AC.

Describe some methods of generating acurrent flow in an electrical circuit.

Describe and apply Kirschhoffs first andsecond laws.


5/54

Atomic Structure

and Electron Movement (1 of 7)


6/54

Atomic Structure


All matter is electrical in essence.

All matter is composed of atoms.

The atom is the smallest particle in a chemical

element.

The atomic structure of an element determines its

chemical and electrical characteristics.

The chemical and electrical properties of atoms aredefined by the number of electrons in their outer

shells.


7/54

Atomic Structure

and Electron Movement (3 of 7) Nucleus

In the center of every atom is a nucleus.

Protons

The nucleus is made up of positively charged mattercalled protons.

Neutrons

The nucleus contains matter with no charge calledneutrons.

Electrons

Negatively charged particles called electrons areorbiting each atomic nucleus.


8/54

Atomic Structure

and Electron Movement(4 of 7)

Electrons orbit the nucleus in concentric

paths called shells.

All electrons are alike -- AND -- all protonsare alike.

So where is the difference?

Every chemical element has a distinct identityand is made up of distinct atoms.

That is, each has a different number of

protons and electrons.


9/54

Atomic Structure


In an electrically balanced atom, the number of

protons equals the number of electrons.

This means that the atom is in what is described as a

neutral state of electrical charge. Ion

An atom with either a deficit or excess of electrons is

known as an ion.

Charge can move from one point to another.

Like charges repel.

Unlike charges attract.


10/54

Atomic Structure


Electrons (negative charge) are held in theirorbital shells by the nucleus (positive charge)of the atom.

Electrons are prevented from colliding witheach other because they all have similarnegative charges that tend to repel eachother.

A molecule is a chemically bonded union oftwo or more atoms.

A compound is a chemically bonded union ofatoms of two or more dissimilar elements.


11/54

Atomic Structure


All atoms have an electrical charge.

An atom is balanced when the number of protonsmatch the number of electrons and is said to be inan electrically neutral state.

Electricity is concerned with the behavior of atomsthat have become unbalanced or electrified.

Electricity may be defined as the movement of freeelectrons from one atom to another.

Current flow is a measurement of the number offree electrons passing a given point in an electricalcircuit per second.


12/54

Conductors and Insulators (1 of 4)

Electron movementthrough a conductor is

referred to as current.

To produce current

flow, electrons mustmove from atom to

atom.


13/54


14/54


An insulator is anonmetallic substance

that contains five or

more electrons in its

outer shell or valence. Glass, mica, rubber,

and plastic are good

insulators.


15/54


Semiconductors are agroup of materials that

cannot be classified

either as conductors or

insulators. They have exactly four

electrons in their outer

shell.

Silicon (Si) is anexample of a

semiconductor.


16/54

Current Flow (1 of 3)

Conventional theorystates that current

flows from positive to

negative.

Vehicle schematics useconventional theory

almost exclusively.


17/54


When the electron wasdiscovered, scientists

revised the theory of

current flow and called

it electron theory. The electron theory

states that current flow

is from negative to

positive.


18/54


Charge differential orvoltage is a measure of

electrical pressure. It is

referred to as:

Charge differential

Voltage (V)

Electro-motive force (EMF)

Potential difference (PD)

The greater the difference,

the greater will be the rate ofcurrent flow.


19/54

Magnetism (1 of 3)

A bar shapedpermanent magnet has

a north and a south

pole at opposite ends.

Like poles repel. Unlike poles attract.

The lines of force

surrounding the

magnet are referred to

as flux lines.


20/54

Magnetism (2 of 3)

Flux lines flow in one direction. Flux lines exit from the magnets north pole

and enter through the south pole.

The flux density (concentration) determinesthe magnetic force.


21/54

Magnetism (3 of 3)

The flux density is always greatest at thepoles of a magnet.

Flux lines do not cross each other in a

permanent magnet. Flux lines facing the same direction attract.

Flux lines facing opposite directions repel.


22/54

Electromagnetism (1 of 3)

Current flow throughany conductor createsa magnetic field.

Magnetic lines of force

do not change whenthe current flow througha conductor isconstant.

When current flow

increases, the lines offorce will extend furtherfrom the conductor.


23/54


The intensity and strength of magnetic linesof force increase proportionally with an

increase in current flow through a conductor.

Similarly, they decrease proportionally with adecrease in current flow through the

conductor.


24/54


A rule called the right-hand rule is used to

indicate the direction of

the magnetic lines of

force.


25/54

Using Electromagnetism (1 of 2)

A magnetic field existswhen current flows

through a wire.

When the wire is

coiled, the magneticfield is intensified.

When an iron core is

placed in the center of

this coil, the magneticfield is further

intensified.


26/54

Using Electromagnetism (2 of 2)

Magneto-motive forceis measured in ampere-

turns (at).


27/54

Electrical Current Characteristics (1 of 2)

Direct current Current flows in one direction only.

Current flow may be:

Continuous Pulsed

DC current is used almost exclusively in

highway vehicles.


28/54

Electrical Current Characteristics (2 of 2)

Alternating current Current cyclically

reverses at high

speed.

AC current is used inalternators and by

certain sensors.


29/54

Sources of Electricity (1 of 2)

Chemical In a lead acid battery,

voltage is produced by

a chemical reaction

between lead and leadperoxide plates

submersed in sulfuric

acid.


30/54

Sources of Electricity (2 of 2)

Static electricity Thermoelectric

Photoelectric

Piezoelectric


31/54

Electromagnetic Induction

Electromagnetic induction Current is produced in a

conductor that is moved

through a stationary

magnetic field.

Current is produced whena magnetic field is moved

past a stationary

conductor.

Electromagnetic induction

is a means of convertingmechanical energy into

electrical energy.

Electrical Circuits


32/54

Electrical Circuits

and Ohms Law (1 of 5)

Ohms law describes the relationshipbetween electrical potential, current, and

resistance.

An electrical circuit must have:

Power source

Path

Load

El t i l Ci it


33/54

Electrical Circuits

and Ohms Law (2 of 5)

Voltage

Current

Resistance Circuit components

Power source

Conductors Switches

Circuit protection devices


34/54

Electrical Circuits

and Ohms Law (3 of 5) Series circuits

There is a single path for current to flow.

All of the current flows through each resistor in

the circuit. Parallel circuits

There are multiple paths for current to flow.

The resistance in each path determines thecurrent flow through it.

Series parallel circuits


35/54

Electrical Circuits

and Ohms Law (4 of 5) Electrical circuit terminology

Short circuit

Open circuit Grounds

Short to ground

High resistance circuits

El t i l Ci it


36/54

Electrical Circuits

and Ohms Law (5 of 5) OHMS law states that an

electrical pressure of 1 voltis required to move 1 amp ofcurrent through a resistanceof 1 ohm.

E = I x R I = Intensity = current in

amps

E = EMF (electromotiveforce) = pressure in volts

R = resistance =

resistance in ohms This is a mathematical

formula that techniciansMUST know.

Ohms Law


37/54

Applied to Series Circuits

All of the current flows

through all of the

resistances in the

circuit

Total circuit resistance

is the sum of all of the

resistances. Rt =R1+

R2etc

Ki hh ff L f C t


38/54

Kirchhoffs Law of Current

Current flowing into ajunction or point in an

electrical circuit must

equal the current

flowing out.

Kirchhoffs Law of Voltage Drops


39/54

Kirchhoffs Law of Voltage Drops

Voltage will drop inexact proportion to the

resistance, and the

sum of the voltage

drops must equal thevoltage applied to the

circuit.

Power


40/54

Power

The unit for measuring power is the wattusually represented by the letter P.

P = I x E

1 horsepower (HP) = 746 watts

Electric Motor


41/54

Electric Motor

and Generator Principle (1 of 3)

Electric Motor and


42/54

Electric Motor and

Generator Principle (2 of 3)

DC motors

The electric motor converts

electrical energy into

mechanical energy.

Current-carryingconductors are arranged

as loops of wire in an

armature.

The armature is placed

inside a magnetic field.

When current flows

through the armature,

torque is produced.

Electric Motor


43/54

Electric Motor

and Generator Principle (3 of 3)

Generators

A generator is simply an

electric motor with its

function reversed.

AC generators produce ACcurrent which must be

rectified to DC.

Reluctor-type generators

consisting of a permanent

magnet, a coil of wire, anda toothed reluctor are used

as shaft speed sensors.

Capacitance


44/54

Capacitance

Capacitors storeelectrons.

A capacitor consists of

two conductors

separated by aninsulating material

called dielectric.

Types of Capacitors


45/54

Types of Capacitors

Power supply filter Spike suppressant

Resistor-capacitor circuits (R-C circuits)

Coils Transformers and Solenoids


46/54

Coils, Transformers, and Solenoids

Two coils are arranged so that one is subjectto a magnetic field created in the other.

The input coil is the primary coil.

The output coil is the secondary coil.

Step-up transformers have secondary coils

with a greater number of windings.

Step-down transformers have secondary coils

with a lower number of windings.

Solenoids and Magnetic Switches


47/54

Solenoids and Magnetic Switches

Magnetic switches areused so that a low

current can control a

high current.

Solenoids use thesame operating

principle, but are used

to convert electrical

energy into mechanicalmovement.

Summary (1 of 7)


48/54

Summary (1 of 7)

All matter is composed of atoms.

All atoms have an electrical charge.

When an atom is balanced (the number of protonsmatch the number of electrons), the atom can bedescribed as being in an electrically neutral state.

All matter is electrical in essence. Electricity concerns the behavior of atoms that have

become, for whatever reason, unbalanced orelectrified.

Electricity may be defined as the movement of freeelectrons from one atom to another.

Summary (2 of 7)


49/54

Summary (2 of 7)

Current flow is measured by the number of freeelectrons passing a given point in an electrical circuitper second.

Electrical pressure or charge differential is measured involts, resistance in ohms, and current in amperes.

The magnetic properties of some metals such as ironare due to electron motion within the atomic structure.

A direct relationship exists between electricity andmagnetism.

Electromagnetic devices are used extensively onvehicles.

Summary (3 of 7)


50/54

Summary (3 of 7)

Magneto-motive force (mmf) is a measure ofelectromagnetic field strength.

Its unit is ampere- turns (At).

Ohms law is used to perform circuit calculations onseries, parallel, and series-parallel circuits.

In a series circuit, there is a single path for currentflow and all of the current flows through eachresistor in the circuit.

A parallel circuit has multiple paths for current flow.

The resistance in each path determines the currentflow through it.

Summary (4 of 7)


51/54

Summary (4 of 7)

Kirchhoffs law of voltage drops states that the sumof voltage drops through resistors in a circuit mustequal the source voltage.

When current is flowed through a conductor, amagnetic field is created.

Reluctance is resistance to the movement ofmagnetic lines of force. Iron cores have permeability and are used to reduce

reluctance in electromagnetic fields.

Capacitors are used to store electrons.

They consist of conductor plates separated by adielectric.

Summary (5 of 7)


52/54

Summary (5 of 7)

Capacitance is measured in farads. Capacitors are rated by voltage and by capacitance.

When current is flowed through a wire conductor,

an electromagnetic field is created.

When the wire is wound into a coil, theelectromagnetic field strength is intensified.

The principle of a transformer can be summarized

by describing it as flowing current through a primary

coil and inducing a current flow in a secondary oroutput coil.

Summary (6 of 7)


53/54

Summary (6 of 7)

Transformers can be grouped into three categories:

isolation, step-up, and step-down.

An electromagnetic switch is used in a truck

electrical circuit to enable a low-current circuit to

control a high-current circuit. A relay is an example of an electromagnetic switch.

A solenoid uses similar operating principles to an

electromagnetic switch except that it converts

electromagnetic energy into mechanical movement.

Summary (7 of 7)


54/54

S y ( )

Solenoids are used extensively in truckelectrical circuits for functions such as starter

engage mechanisms, diesel electronic unit

injector control, automatic transmission clutch

controls, and suspension pilot switches.

Documents

Chapter 05 Bennet