chap31 pps Automotive technology at University of Cambridge

start
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

1

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


OBJECTIVES:
After studying Chapter 31, the reader should
be able to:

• Prepare for ASE Electrical/Electronic Systems
•
•
•
•

(A6) certification test content area “A” (General
Electrical/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.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

2

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458

KEY TERMS:
ammeter • amperes • atom • bound electrons
concentric rings • conductors • conventional theory •
coulomb • current
electrical potential • electricity • electrochemistry •
electrons • electron theory • elements • electromotive
force (EMF)
free electrons • insulators • ion
neutral charge • neutrons • nucleus
ohmmeter • ohms

3

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ

NJ07458
07458


KEY TERMS:
peltier effect • photoelectricity • piezoelectricity • positive
temperature coefficient (PTC) • potentiometer • protons
resistance • resistors • rheostat
semiconductors • shells • static electricity
thermocouple • thermoelectricity
valence shell • volt • voltmeter
watt

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

4

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ

NJ07458
07458


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.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

5

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458

07458


ELECTRICITY
Our universe is composed of matter, anything that has mass and 
occupies space. All matter is made from slightly over 100 
individual components called elements.
The smallest particle that an element can be broken into and still 
retain the properties of that element is known as an atom.

Figure 31–1 In an atom (left),
electrons orbit protons in the
nucleus just as planets orbit
the sun in our solar system
(right).

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

6

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall

Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


Electricity is the movement of electrons from one atom to another. 
The dense center of each atom is called the nucleus. The nucleus 
contains 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 negative­charged electrons is balanced with 
the same number of positive­charged protons, an atom has a neutral 
charge (no charge).

NOTE: As an example of relative sizes of parts of an atom, consider that 

if 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.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

7

©©2008
2009Pearson
PearsonEducation,

Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


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 ().
These same + and  signs are
used to identify parts of an
electrical circuit. 
Neutrons have no charge at all. 
They are neutral.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

Figure 31–2 The nucleus of an atom has
a positive () charge and the surrounding
electrons have a negative () charge.

8

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


In a normal, or balanced, atom, the number of negative particles 
equals the number of positive particles. The number of neutrons 
varies according to the type of atom.

Figure 31–3
This figure shows a balanced atom.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

9

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


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 push 
each other apart. This is because like poles repel each other.

Figure 31–4 Unlike charges attract and like charges repel.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

10

Continued

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


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 charge 
of 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 it 
gains 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 31–5. 
This is the flow of electric current or electricity.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

11

Continued

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


Figure 31–5 An unbalanced, positively charged atom (ion) will attract electrons from neighboring
atoms.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

12

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


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.
If there are too many electrons
for the first and closest shell to
the nucleus, others will orbit
in additional shells until all 
electrons have an orbit within
a shell. There can be as many

as seven shells around a single 
nucleus. 
Figure 31–6
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.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

13

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


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 is 
easy for a drifting electron to join the ring and push another electron 
away. 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 31–7 and 31–8.
Continued
14
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458

07458


The movement of these drifting electrons is called current. Electric 
current is controlled, directed movement of electrons from atom to 
atom within a conductor.

Figure 31–8 Electrons in the outer orbit,
or shell, can often be drawn away from
the atom and become free electrons.

Figure 31–7 As the number of electrons increases, they occupy
increasing energy levels that are further from the center of the atom.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

15

Continued

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle

SaddleRiver,
River,NJ
NJ07458
07458


Conductors  Materials with fewer than four electrons in their atom’s outer orbit are 
Conductors. Copper is excellent as a conductor because it has only one electron in 
its outer orbit. This orbit is far enough away from the nucleus of the atom that the 
pull or force holding the outermost electron in orbit is relatively weak. 

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

Figure 31–9 A conductor is any element that
has one to three electrons in its outer orbit.

16

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle

SaddleRiver,
River,NJ
NJ07458
07458


Figure 31–10 Copper is an excellent conductor of electricity because it has just one electron in its
outer orbit, making it easy to be knocked out of its orbit and flow to other nearby atoms. This
causes electron flow, which is the definition of electricity.

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.

17

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice

PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


Is Water a Conductor?
Pure water is an insulator; however, if anything is in the water, such as salt
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.

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 very 
tightly; electrons do not move through them very well.
These materials are called insulators. 
18

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

©©2008
2009Pearson

PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


Insulators are materials with more than four electrons in their 
atom’s outer orbit. Because they have more than four electrons, it 
becomes easier for these materials to acquire (gain) electrons than
to release electrons.
Insulators include plastics, wood, 
glass, rubber, ceramics (spark plugs), 
and varnish for covering (insulating) 
copper wires in alternators and 
starters.
Figure 31–11 Insulators are elements
with five to eight electrons in the outer
orbit.

19

Continued

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


Figure 31–12 Semiconductor elements
contain exactly four electrons in the
outer orbit.

Semiconductors
Materials with exactly four 
electrons in their outer orbit
are neither conductors nor 
insulators; they are called 
semiconductor materials. 

20

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


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 the 
conductor 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 of 

opposite charges and repulsion of like charges, electrons will flow 
through the conductor.

Figure 31–13 Current electricity is the movement of electrons through a conductor.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

21

Continued

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


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 a 

conductor is called the conventional theory of current flow. 
Discovery of the electron and its negative charge led to the electron 
theory, which states there is electron flow from negative to positive. 
This book uses the 
conventional theory 
unless stated otherwise.

Figure 31–14 Conventional theory states that current flows through
a circuit from positive (+) to negative (-). Automotive electricity uses
the conventional theory in all electrical diagrams and schematics.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

22

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458

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 André Marie 
Ampère (1775–1836). 
Figure 31–15
One ampere is the movement of 1 coulomb (6.28 billion billion electrons) past a point in 1 second.

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

23

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458

07458


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 for amperes are A and amps.
3. The capital letter I, for intensity, is used in mathematical 
calculations to represent amperes.
4. Amperes are measured by an ammeter (not ampmeter).
Figure 31–16
An ammeter is installed in the path of
the electrons similar to a water meter
used to measure the flow of water in
gallons per minute. the ammeter
displays current flow in amperes.

24

Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson

PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458


Volts The volt is the unit of measurement for electrical pressure. 
Named for Alessandro Volta (1745–1827), 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 high 
water flow (amperes) and low pressure (volts).
Voltage is also called electrical potential, because if there is 
voltage present in a conductor, there is a potential (possibility) for 
current flow. Voltage does not flow through conductors, but voltage 
does cause current (in amperes) to flow through conductors.
Figure 31–17
Voltage is the electrical pressure
that causes the electrons to flow
through a conductor.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

25

©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
SaddleRiver,
River,NJ
NJ07458
07458