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7/27/2019 (31) Electrical Fundamentals.pdf
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2008 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
1
start
7/27/2019 (31) Electrical Fundamentals.pdf
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2008 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
2
Prepare for ASE Electrical/Electronic Systems(A6) certification test content area A (GeneralElectrical/Electronic System Diagnosis).
Define electricity. Explain the units of electrical measurement.
Discuss the relationship among volts,amperes, and ohms. Explain how magnetism is used in automotive
applications.
After studying Chapter 31, the reader shouldbe able to:
OBJECTIVES:
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3
ammeter amperes atom bound electrons
concentric rings conductors conventional theory
coulomb current
electrical potential electricity electrochemistry
electrons electron theory elements electromotiveforce (EMF)
free electrons insulators ion
neutral charge neutrons nucleus
ohmmeter ohms
KEY TERMS:
Continued
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peltier effect photoelectricity piezoelectricity positive temperature coefficient (PTC) potentiometer
protons
resistance resistors rheostat
semiconductors shells static electricity
thermocouple thermoelectricity
valence shell volt voltmeter
watt
KEY TERMS:
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By James D. Halderman
2009 Pearson Education, Inc.
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5
The electrical system is one of the most important
systems in a vehicle today.
Every year, more and more components and
systems use electricity.
Technicians who really know and understand
automotive electrical and electronic systems
will be in great demand.
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By James D. Halderman
2009 Pearson Education, Inc.
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6
ELECTRICITY
Our universe is composed of matter, anything that has mass andoccupies space. All matter is made from slightly over 100
individual components called elements.
The smallest particle that an element can be broken into and stillretain the properties of that element is known as an atom.
Figure 311 In an atom (left),
electrons orbit protons in the
nucleus just as planets orbitthe sun in our solar system
(right).
Continued
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Electricity is the movement of electrons from one atom to another.
The dense center of each atom is called the nucleus. The nucleuscontains protons, which have positive charge, and neutrons,
electrically neutral (no charge).
Electrons surround the nucleus in orbits. Each atom contains an
equal number of electrons and protons.
Because the number of negative-charged electrons is balanced withthe same number of positive-charged protons, an atom has a neutral
charge (no charge).
NOTE: As an example of relative sizes of parts of an atom, consider thatif an atom were magnified so that the nucleus were the size of the period
at the end of this sentence, the whole atom would be bigger than a house.
NOTE: As an example of relative sizes of parts of an atom, consider thatif an atom were magnified so that the nucleus were the size of the period
at the end of this sentence, the whole atom would be bigger than a house.
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Positive and Negative Charges Parts of the atom have different
charges. Orbiting electrons are negatively charged, protons
positively charged. Positive charges are indicated by the plus
sign
(+), and negative charges by the minus
sign ().
Continued
Figure 312 The nucleus of an atom has
a positive () charge and the surroundingelectrons have a negative () charge.
These same + and
signs are
used to identify parts of anelectrical circuit.
Neutrons have no charge at all.
They are neutral.
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In a normal, or balanced, atom, the number of negative particles
equals the number of positive particles. The number of neutronsvaries according to the type of atom.
Continued
Figure 313
This figure shows a balanced atom.
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10Figure 314 Unlike charges attract and like charges repel.
Continued
An ordinary magnet has two ends, or poles. One end is the south
pole, and the other the north pole.
If the opposite poles of the magnets are brought close to each other,
south to north, the magnets will snap together because unlike poles
attract each other. If two magnets are brought close to each other with like poles
together (south to south or north to north), the magnets will pusheach other apart. This is because like poles repel each other.
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Positive and negative charges within an atom are like north and
south poles of a magnet. Charges that are alike will repel each other,
which is why the negative electrons continue to orbit around the
positive protons. They are attracted and held by the opposite chargeof the protons. The electrons keep moving in orbit because they
repel each other. When an atom loses electrons, it becomes unbalanced. It will have
more protons than electrons and will have a positive charge. If itgains more electrons than protons, it will be negatively charged.
When an atom is not balanced, it becomes a charged particle called
an ion. Ions try to regain balance of equal protons and electrons by
exchanging electrons with neighboring atoms. See Figure 315.
This is the flow of electric current orelectricity.Continued
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Figure 315 An unbalanced, positively charged atom (ion) will attract electrons from neighboring
atoms.
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Electron Shells Orbit around the nucleus in definite paths. These
paths form shells, like concentric rings, around the nucleus. Only a
specific number of electrons can orbit within each shell.
Continued
Figure 316
The hydrogen atom is the simplest atom, with
only one proton, one neutron, and one electron.
More complex elements contain higher numbers
of protons, neutrons, and electrons.
If there are too many electrons
for the first and closest shell to the nucleus, others will orbit in additional shells until allelectrons have an orbit within
a shell. There can be as many as seven shells around a singlenucleus.
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Free and Bound Electrons The outermost electron shell or ring,
called the valence shell, is the most important to our study of
electricity.
The number of electrons in this shell determines the valence of the
atom and indicates its capacity to combine with other atoms. If the valence ring of an atom has three or fewer electrons in it, the
ring has room for more. The electrons are held very loosely, and it iseasy for a drifting electron to join the ring and push another electronaway. These loosely held electrons are called free electrons.
When a valence ring has five or more electrons, it is fairly full. The
electrons are held tightly, and it is hard for a drifting electron to
push its way into the ring. These tightly held electrons are called
bound electrons. See Figures 317 and 318.Continued
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15Figure 317 As the number of electrons increases, they occupyincreasing energy levels that are further from the center of the atom.
Figure 318 Electrons in the outer orbit,
or shell, can often be drawn away from
the atom and become free electrons.
The movement of these drifting electrons is called current. Electric
current is controlled, directed movement of electrons from atom to
atom within a conductor.
Continued
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Conductors Materials with fewer than four electrons in their
atoms outer orbit are Conductors. Copper is excellent as a
conductor because it has only one electron in its outer orbit. Thisorbit is far enough away from the nucleus of the atom that the pull
or force holding the outermost electron in orbit is relatively weak.
Figure 319 A conductor is any element thathas one to three electrons in its outer orbit.Continued
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Copper is the conductor most
used in vehicles because the
price of copper is reasonable
compared to the relative cost
of other conductors with
similar properties.
Continued
Figure 3110 Copper is an excellent conductor of electricity because it has just one electron in i ts
outer orbi t, making i t easy to be knocked out of its orbi t and flow to other nearby atoms. This
causes electron flow, which is the definition of electricity.
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Pure water is an insulator; however, if anything is in the water, such assalt or dirt, then the water becomes conductive. Because it is difficult to
keep water from becoming contaminated, water is usually thought of as
being capable of conducting electricity, especially high voltage such as
from household 110-volt or 220-volt outlets.
Pure water is an insulator; however, if anything is in the water, such assalt or dirt, then the water becomes conductive. Because it is difficult to
keep water from becoming contaminated, water is usually thought of as
being capable of conducting electricity, especially high voltage such as
from household 110-volt or 220-volt outlets.
Is Water a Conductor?
Insulators The protons and neutrons in the nucleus are held
together very tightly. Normally the nucleus does not change.
Some outer electrons are held very loosely, and can move from
one atom to another. Some materials hold their electrons verytightly; electrons do not move through them very well.
These materials are called insulators.Continued
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Insulators are materials with more than four electrons in their
atoms outer orbit. Because they have more than four electrons, it
becomes easier for these materials to acquire (gain) electrons than
to release electrons.
Continued
Figure 3111 Insulators are elementswith f ive to eight electrons in the outer
orbit.
Insulators include plastics, wood,glass, rubber, ceramics (spark plugs),
and varnish for covering (insulating)
copper wires in alternators andstarters.
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Semiconductors
Materials with exactly four
electrons in their outer orbit
are neither conductors norinsulators; they are called
semiconductor materials.
Continued
Figure 3112 Semiconductor elements
contain exactly four electrons in the
outer orbit.
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How Electrons Move Through a Conductor If an outside source
of power, such as a battery, is connected to the ends of a conductor,
a positive charge (lack of electrons) is placed on one end of theconductor and a negative charge is placed on the opposite end
of the conductor.The negative charge will repel the free electrons from the atoms
of
the conductor, whereas the positive charge on the opposite end of
the conductor will attract electrons. As a result of this attraction ofopposite charges and repulsion of like charges, electrons will flow
through the conductor.
ContinuedFigure 3113 Current electric ity is the movement of electrons through a conductor .
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Figure 3114 Conventional theory states that current flows through
a circuit from posit ive (+) to negative (-). Automotive electric ity usesthe conventional theory in all electrical diagrams and schematics.
Conventional Theory versus Electron Theory It was once
thought that electricity had only one charge and moved from
positive to negative. This theory of the flow of electricity through aconductor is called the conventional theory of current flow.
This book uses theconventional theory
unless stated otherwise.
Discovery of the electron and its negative charge led to the electron
theory, which states there is electron flow from negative to positive.
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Amperes The ampere is the unit used to measure current flow.
When 6.28 billion billion electrons (a coulomb) move past a certain
point in 1 second, this represents 1 ampere of current.
The ampere is the electrical unit for amount of electron flow just as
gallons per minute is the unit used to measure water flow.The ampere was named for the French electrician Andr
Marie
Ampre (17751836).
Continued
Figure 3115
One ampere is the movement of 1 coulomb (6.28 billion billion electrons) past a point in 1 second.
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Conventional abbreviations and measurement for amperes are
summarized as follows:
1.
The ampere is the unit of measurement for the amount of
current flow.
2.
Acceptable abbreviations foramperes areA and amps.
3.
The capital letterI, forintensity, is used in mathematical
calculations to represent amperes.
4. Amperes are measured by an ammeter (notampmeter).Figure 3116
An ammeter is installed in the path of
the electrons simi lar to a water meter
used to measure the flow of water in
gallons per minute. the ammeter
displays current flow in amperes.
Continued
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Volts The volt is the unit of measurement for electrical pressure.
Named for Alessandro Volta (17451827), an Italian physicist.
The comparable unit using water as an example would be pounds
per square inch (psi). It is possible to have very high pressures
(volts) and low water flow (amperes). It is also possible to have highwater flow (amperes) and low pressure (volts).
Voltage is also called electrical potential, because if there isvoltage present in a conductor, there is a potential (possibility) for
current flow. Voltage does notflow through conductors, but voltage
does cause current (in amperes) to flow through conductors.
Figure 3117
Voltage is the electrical pressure
that causes the electrons to flow
through a conductor.
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The conventional abbreviations and measurement for voltage are:
Continued
1. Volt is the measurement for amount of electrical pressure.2.
Another term for voltage is Electromotive force, (EMF).
3.
The letterVis the generally accepted abbreviation forvolts.
4. The symbol used in calculations is E, for electromotive force.5. Volts are measured with a voltmeter.
Figure 3118
This digital multimeter set to read DC
volts is being used to test the voltageof a vehicle battery. Most mult imeters
can also measure resistance (ohms)
and current flow (amperes).
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Ohms Resistance to the flow of current through a conductor is
measured in units called ohms, named after the German physicist
Georg Simon Ohm (17871854). The resistance to the flow of free electrons through a conductor
results from the countless collisions the electrons cause within theatoms of the conductor.
Continued
Figure 3119 Resistance to the flow of electrons through a conductor is measured in ohms.
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Conventional abbreviations and measurement for resistance are:
Continued
1.
The ohm is the unit of measurement for electrical resistance.
2.
The symbol for ohms is
(Greek capital letter omega), the
last letter of the Greek alphabet.
3.
The symbol used in calculations isR, forresistance.
4.
Ohms are measured with an ohmmeter.
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Figure 3120 A display at the Henry Ford Museum in Dearborn, Michigan, that includes a hand-
cranked generator and a series of l ight bulbs. This f igure shows a young man attempting to light
as many bulbs as possible. The crank gets harder to turn as more bulbs l ight because it requires
more power to produce the necessary watts of electrici ty.
The symbol for power is P. Electrical power is calculated as
amperes times volts: P (power) =I(amperes)
E (volts)
Watts A watt is the electrical
unit forpower, the capacity to
do work. Named for Scottishinventor, James Watt (1736
1819).
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SOURCES OF ELECTRICIY
There are several sources of electrical energy, but only a few ofthem are used in automotive electrical systems.
Continued
Friction When certain different materials are rubbed together, the
friction causes electrons to be transferred from one to the other.
Both materials become electrically charged.
These charges are not in motion but stay on the surface where theywere deposited. Because the charges are stationary, or static, this
type of voltage is called static electricity.
Vehicle tires rolling on pavement often create static electricity thatinterferes with radio reception.
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Heat When pieces of two metals are joined together at both ends
and one junction is heated, current passes through the metals. Only
millionths of an ampere, but enough to use in a temperature- measuring device called a thermocouple.
Continued
Figure 3121 Electron flow is produced by heating the connection of two different metals.
Some engine temperature
sensors operate in this
manner.
This form of voltage iscalled thermoelectricity.
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In 1823, German physicist Thomas Johann
Seebeck discovered that
voltage was developed in a loop containing two dissimilar metals,
provided the junctions were maintained at different temperatures. A decade later, French scientist Jean Charles
Peltier found electrons
moving through a solid can carry heat from one side of the materialto the other side. This effect is called the
Peltier effect.
A Peltier effect device is often used in portable coolers to keep food
items cool if the current flows in one direction and to keep items
warm if the current flows in reverse.
Continued
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Light In 1839, Edmond Becquerel noticed that shining a beam of
sunlight over two different liquids developed electric current.
When certain metals are exposed to light, some light energy is
transferred to free electrons of the metal. This excess energy breaks
electrons loose from the metal. They can be collected and made toflow in a conductor.
Photoelectricity is
widely used in light-
measuring devicessuch as photographic
exposure meters andautomatic headlamp
dimmers.
ContinuedFigure 3122 Electron flow is produced by light str iking a light-sensitive material.
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Pressure The first demonstration of a connection between
macroscopic piezoelectric phenomena and crystallographic structure
was published in 1880 by Pierre and Jacques Curie. Whensubjected to pressure, certain crystals, such as quartz, develop
a
potential difference, or voltage, on the crystal faces. This current is
used in phonograph pickups, crystal microphones, underwaterhydrophones, and certain stethoscopes.
Figure 3123 Electron flow is producedby pressure on certain crystals.
The voltage created is called piezoelectricity.
Some automobile engine control
sensors, such as the knock sensor(KS), use piezoelectricity to create voltage or to vary resistance and control a computer input signal.
Continued
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Chemistry Two different materials (usually metals) placed in a
conducting and reactive chemical solution create a difference in
potential, or voltage, between them. This principle is calledelectrochemistry and is the basis of the automotive battery.Conductors and Resistance All conductors have some resistanceto current flow. Several principles of conductors and their resistance
include the following:
If the conductor length is doubled, its resistance doublesThis is why battery cables are designed as short as possible.
If the conductor diameter is increased, resistance is reduced
This is the reason starter motor cables are larger in diameterthan other wiring in the vehicle.
See Chapter 7 for further details on wiring sizes. Continued
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As the temperature increases, the resistance of the
conductor also increases This is the reason for installing heat
shields on some starter motors. The shield helps protect theconductors (copper wiring inside the starter) from excessive
engine heat and reduces resistance of starter circuits. Because a
conductor increases in resistance with increased temperature,the conductor is called a positive temperature coefficient
(PTC)
resistor.
Materials used in the conductor have an impact on itsresistance Silver has the lowest resistance of any conductor,
but is expensive. Copper is the next lowest in resistance and it
is reasonably priced. See the following chart for a comparison of materials.
Continued
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CONDUCTION CHART
1. Silver
2. Copper3. Gold
4. Aluminum
5. Tungsten
6. Zinc
7. Brass (copper and zinc)
8. Platinum9. Iron
10. Nickel
11. Tin
12. Steel
13. Lead
Starting with the best
See this chart on Page 323 of your textbook.
Continued
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2008 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
38Figure 3124 This figure shows a resistor color code interpretation.
Resistors Resistance is opposition to current flow. Resistors
represent an electrical load, or resistance, to current flow.
Continued
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2008 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
39
Most electrical and electronic devices use resistors of specific
values
to limit and control the flow of current.
Resistors can be made from carbon or from other materials that
restrict the flow of electricity and are available in various sizes and
resistance values. Most resistors have a series of painted color bands around them.
These color bands are coded to indicate the degree of resistance.
Continued
Figure 3125 This figure
shows a typical carbonresistor.
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2008 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
40
Variable Resistors Two types of mechanically operated variable
resistors are used in automotive applications. A potentiometer is a
three-terminal variable resistor where the majority of the currentflow travels through the resistance of the unit and a wiper contact
provides a variable voltage output.
Continued
Potentiometers are most commonly used as throttle position (TP)
sensors on computer-equipped engines.
Figure 3126 A three-wire variableresistor is called a potentiometer.
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2008 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
41Figure 3127 A two-wire variable resistor is called a rheostat.
Another type of mechanically operated variable resistor is the
rheostat. A rheostat is a two-terminal unit in which all of the
current flows through the movable arm. A rheostat is commonlyused for a dash light dimmer control.
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2008 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
42
SUMMARY
1. Electricity is movement of electrons from one atom to another.2.
Automotive electricity uses the conventional theory of current
flow (electricity flows from positive to negative).
3.
The ampere is the measure of the amount of current flow.
4.
Voltage is the unit of electrical pressure.
5. The ohm is the unit of electrical resistance.6.
Sources of electricity include: friction, heat, light, pressure,
and chemical.
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