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39
ELECTRICAL
FUNDAMENTALS
Automotive Technology, Fourth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
39
ELECTRICAL FUNDAMENTALS
Objectives
• The student 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.
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ELECTRICAL FUNDAMENTALS
Objectives
• The student should be able to:
– Discuss the relationship among volts,
amperes, and ohms.
– Explain how magnetism is used in
automotive applications.
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ENVIRONMENTAL AND HAZARDOUS MATERIALS
INTRODUCTION
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ELECTRICAL FUNDAMENTALS
Introduction
• Electrical system one of most important
in vehicle.
• More and more components and
systems use electricity.
• Technicians who understand automotive
electronic systems are in demand.
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ENVIRONMENTAL AND HAZARDOUS MATERIALS
ELECTRICITY
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ELECTRICAL FUNDAMENTALS
Electricity
• Background
– Universe composed of matter.
– Matter is anything that has mass and
occupies space.
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ELECTRICAL FUNDAMENTALS
Electricity
• Background
– All matter made from elements.
– Atom is smallest particle element can be
broken into and still retain properties.
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ELECTRICAL FUNDAMENTALS
Figure 39-1 In an atom (left), electrons orbit protons in the nucleus just as planets orbit the sun
in our solar system (right).
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ELECTRICAL FUNDAMENTALS
Electricity
• Definition
– Movement of electrons from one atom to
another.
– Nucleus: dense center of atom.
• Protons: positive charge.
• Neutrons: electrically neutral (no charge).
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ELECTRICAL FUNDAMENTALS
Electricity
• Definition
– Electrons (negative charge) surround
nucleus in orbits.
– Each atom has equal number of electrons
and protons.
– Number of electrons and protons
determines how electricity conducted.
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ELECTRICAL FUNDAMENTALS
Electricity
• Positive and Negative Charges
– Protons have positive charge (+).
– Electrons have negative charge (–).
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ELECTRICAL FUNDAMENTALS
Electricity
• Positive and Negative Charges
– Neutrons have no charge (neutral).
– + and – signs also identify parts of
electrical circuit.
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ELECTRICAL FUNDAMENTALS
Figure 39-2 The nucleus of an atom has a positive (+) charge and the surrounding electrons
have a negative (-) charge.
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ELECTRICAL FUNDAMENTALS
Figure 39-3 This figure shows a balanced atom. The number of electrons is the same as the
number of protons in the nucleus.
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ELECTRICAL FUNDAMENTALS
Electricity
• Magnets and Electrical Charges
– Ordinary magnet has two ends, or poles
• South pole, north pole.
• Like poles repel each other, opposite poles
attract.
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ELECTRICAL FUNDAMENTALS
Electricity
• Magnets and Electrical Charges
– Positive and negative charges within atom
like north and south poles.
– Reason that electrons orbit protons.
• Electrons repel each other, but attracted to
protons.
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ELECTRICAL FUNDAMENTALS
Figure 39-4
Unlike charges attract and like charges repel.
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ELECTRICAL FUNDAMENTALS
Electricity
• Ions
– Atom unbalanced when loses electrons—
ion.
• Lose electrons—positively charged.
• Gain electrons—negatively charged.
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ELECTRICAL FUNDAMENTALS
Electricity
• Ions
– Ions regain balance by exchanging
electrons with neighboring atoms.
– Flow of electrons during “equalization”
defined as flow of electricity.
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ELECTRICAL FUNDAMENTALS
Figure 39-5
atoms.
An unbalanced, positively charged atom (ion) will attract electrons from neighboring
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ELECTRICAL FUNDAMENTALS
Electricity
• Electron Shells
– Electrons orbit nucleus in definite paths.
– Paths form shells, like concentric rings.
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ELECTRICAL FUNDAMENTALS
Electricity
• Electron Shells
– Only specific number can orbit within each
shell.
– If too many electrons for first shell, others
orbit in outer shells.
– Up to 7 shells.
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ELECTRICAL FUNDAMENTALS
Figure 39-6 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.
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ELECTRICAL FUNDAMENTALS
Electricity
• Free and Bound Electrons
– Valence ring: outermost and most
important ring for electricity.
– Number of electrons in this ring determines
valence of atom.
– Valence indicates atom’s capacity to
combine with other atoms.
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ELECTRICAL FUNDAMENTALS
Electricity
• Free and Bound Electrons
– If 3 or fewer electrons in ring, room for
more.
• Electrons held very loosely (free electrons).
• Easy for drifting electron to join ring.
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ELECTRICAL FUNDAMENTALS
Electricity
• Free and Bound Electrons
– If 5 or more electrons in ring, ring fairly
full.
• Electrons held tightly (bound electrons).
• Difficult for drifting electron to join ring.
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ELECTRICAL FUNDAMENTALS
Electricity
• Free and Bound Electrons
– Current: movement of drifting electrons
• Can be small (few electrons) or large (many
electrons).
– Electric current: controlled, directed
movement of electrons from atom to atom
within conductor.
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ELECTRICAL FUNDAMENTALS
Figure 39-7 As the number of electrons increases, they occupy increasing energy levels that are
farther from the center of the atom.
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ELECTRICAL FUNDAMENTALS
Figure 39-8 Electrons in the outer orbit, or shell, can often be drawn away from the atom and
become free electrons.
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ELECTRICAL FUNDAMENTALS
Electricity
• Conductors
– Materials with fewer than 4 electrons in
atom’s outer orbit.
– Copper excellent conductor.
• Only one electron in outer orbit.
• Orbit far enough from nucleus that only
weak force holds electron.
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ELECTRICAL FUNDAMENTALS
Electricity
• Conductors
– Copper most used conductor in vehicles.
• Price reasonable compared to other
materials with same qualities.
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ELECTRICAL FUNDAMENTALS
Electricity
• Conductors
– Other commonly used conductors:
• Silver.
• Gold.
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ELECTRICAL FUNDAMENTALS
?
Electricity
• Conductors
– Other commonly used conductors:
• Aluminum.
• Steel.
• Cast iron.
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ELECTRICAL FUNDAMENTALS
Figure 39-9
A conductor is any element that has one to three electrons in its outer orbit.
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ELECTRICAL FUNDAMENTALS
Figure 39-10 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.
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ELECTRICAL FUNDAMENTALS
Electricity
• Insulators
– Materials that hold their electrons very
tightly.
– Electrons do not move through them very
well.
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ELECTRICAL FUNDAMENTALS
Electricity
• Insulators
– Have more than four electrons in outer
orbit.
– Easier to acquire electrons than to release
electrons.
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ELECTRICAL FUNDAMENTALS
Electricity
• Insulators
– Commonly used conductors:
• Rubber.
• Plastic.
• Nylon.
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ELECTRICAL FUNDAMENTALS
Electricity
• Insulators
– Commonly used conductors:
• Porcelain.
• Ceramic.
• Fiberglass.
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ELECTRICAL FUNDAMENTALS
Figure 39-11
Insulators are elements with five to eight electrons in the outer orbit.
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ELECTRICAL FUNDAMENTALS
Electricity
• Semiconductors
– Materials with exactly four electrons in
outer orbit.
– Can be either insulator or conductor in
different applications.
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ELECTRICAL FUNDAMENTALS
Electricity
• Semiconductors
– Common semiconductors.
• Silicon.
• Germanium.
• Carbon.
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ELECTRICAL FUNDAMENTALS
Electricity
• Semiconductors
– Used mostly in transistors, computers,
other electronic devices.
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ELECTRICAL FUNDAMENTALS
Figure 39-12
Semiconductor elements contain exactly four electrons in the outer orbit.
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ENVIRONMENTAL AND HAZARDOUS MATERIALS
HOW ELECTRONS
MOVE THROUGH A
CONDUCTOR
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ELECTRICAL FUNDAMENTALS
How Electrons Move Through a
Conductor
• Current Flow
– Certain events occur if source of power
connected to ends of conductor.
• Positive charge (lack of electrons) on one
end.
• Negative charge (excess of electrons) on
other end.
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ELECTRICAL FUNDAMENTALS
How Electrons Move Through a
Conductor
• Current Flow
– Imbalance required for current to flow.
• Negative charge on one end repels free
electrons in conductor.
• Positive charge on other end attracts
electrons.
• Result is electrons flowing through
conductor.
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ELECTRICAL FUNDAMENTALS
How Electrons Move Through a
Conductor
• Current Flow
– Imbalance required for current to flow.
• Result is electrons flowing through
conductor.
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ELECTRICAL FUNDAMENTALS
Figure 39-13
Current electricity is the movement of electrons through a conductor.
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ELECTRICAL FUNDAMENTALS
How Electrons Move Through a
Conductor
• Conventional Theory Versus Electron
Theory
– Conventional: electricity has one charge;
moves from positive to negative.
– Electron: electrons flow from negative to
positive.
– Most automotive applications use
conventional theory.
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ELECTRICAL FUNDAMENTALS
Figure 39-14 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.
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ENVIRONMENTAL AND HAZARDOUS MATERIALS
UNITS OF
ELECTRICITY
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Amperes
– Unit used throughout world to measure
current flow.
– Named for French electrician, Andre Marie
Ampere (1775–1836).
– 1 ampere = 6.28 billion billion electrons (1
coulomb) moving past point in 1 second.
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Amperes
– A and amps are acceptable abbreviations
for amperes.
– Capital letter I (intensity) used in math to
represent amperes.
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Amperes
– Amperes do the actual work in circuit.
• Without amperage, device will not work.
– Measured by ammeter.
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ELECTRICAL FUNDAMENTALS
Figure 39-15 One ampere is the movement of 1 coulomb (6.28 billion billion electrons) past a
point in 1 second.
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ELECTRICAL FUNDAMENTALS
Figure 39-16 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.
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Volts
– Unit of measurement for electrical
pressure.
– Named for Italian physicist, Alessandro
Volta (1745–1827).
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Volts
– Comparable to psi (pounds per square
inch).
– Possible to have very high pressures (volts)
and low flow (amperes).
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Volts
– Possible to have high flow (amperes) and
low pressures (volts).
– Also called electrical potential.
• If voltage present in conductor, potential for
current flow.
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Volts
– Voltage causes current (in amperes) to flow
through conductors.
– Electromotive force (EMF) another way of
indicating voltage.
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Volts
– V generally accepted abbreviation for volts.
– Symbol used in calculations is E, for
electromotive force.
– Measured by voltmeter.
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ELECTRICAL FUNDAMENTALS
Figure 39-17
conductor.
Voltage is the electrical pressure that causes the electrons to flow through a
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ELECTRICAL FUNDAMENTALS
Figure 39-18 This digital multimeter set to read DC volts is being used to test the voltage of a
vehicle battery. Most multimeters can also measure resistance (ohms) and current flow (amperes).
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Ohms
– Resistance to the flow of current through a
conductor.
– Named after German physicist, George
Simon Ohm (1787–1854).
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Ohms
– Results from collisions electrons cause
within atoms of conductor.
– Unit of measurement for electrical
resistance.
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Ohms
– Symbol is Ω (Greek capital letter omega).
– Symbol in calculations is R, for resistance.
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Ohms
– Measured by an ohmmeter.
– Resistance depends on material used as
conductor.
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ELECTRICAL FUNDAMENTALS
Figure 39-19
Resistance to the flow of electrons through a conductor is measured in ohms.
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ELECTRICAL FUNDAMENTALS
Units of Electricity
• Watts
– Electrical unit for power, or capacity to do
work.
– Symbol is P.
– Calculated as amperes times volts:
P = I × E.
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ELECTRICAL FUNDAMENTALS
Figure 39-20 A display at the Henry Ford Museum in Dearborn, Michigan, which includes a handcranked generator and a series of light bulbs. This figure shows a young man attempting to light as
many bulbs as possible. The crank gets harder to turn as more bulbs light because it requires more
power to produce the necessary watts of electricity.
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ENVIRONMENTAL AND HAZARDOUS MATERIALS
SOURCES OF
ELECTRICITY
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Friction
– Certain different materials rubbed together,
become electrically charged.
– Charges not in motion, but stay on surface
where deposited.
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Friction
– Called static electricity.
– Vehicle tires rolling on pavement often
create static electricity.
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Heat
– Two different metals joined at both ends.
– If one junction heated, current passes
through metals.
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Heat
– Current very small (millionths of an
ampere).
– Enough current to use in a thermocouple.
– Called thermoelectricity.
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Heat
– Used in some engine temperature sensors.
– Peltier effect: electrons moving through
solid can carry heat from one side to the
other.
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ELECTRICAL FUNDAMENTALS
Figure 39-21
Electron flow is produced by heating the connection of two different metals.
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Light
– Some of light energy is transferred to free
electrons in metal.
– Breaks electrons loose from surface of
metal.
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Light
– Electrons can be made to flow through
conductor.
– Called photoelectricity.
– Used in light-measuring devices such as
automatic headlamp dimmers.
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ELECTRICAL FUNDAMENTALS
Figure 39-22
Electron flow is produced by light striking a light-sensitive material.
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Pressure
– First explained in 1880 by Pierre and
Jacques Curie.
– Called piezoelectricity.
– Used by engine knock sensor to create
voltage signal for engine computer.
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ELECTRICAL FUNDAMENTALS
Figure 39-23
Electron flow is produced by pressure on certain crystals.
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Chemical
– Two different materials placed in
conducting, reactive chemical solution.
– Create a difference in potential, or voltage.
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Chemical
– Called electrochemistry.
– Basis of the automotive battery.
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Magnetism
– Electricity produced if conductor moved
through magnetic field.
– Also produced if moving magnetic field
moved near conductor.
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Magnetism
– Used in many automotive devices.
• Starter motor.
• Alternator.
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ELECTRICAL FUNDAMENTALS
Sources of Electricity
• Magnetism
– Used in many automotive devices.
• Ignition coils.
• Solenoids and relays.
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ENVIRONMENTAL AND HAZARDOUS MATERIALS
CONDUCTORS
AND RESISTANCE
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ELECTRICAL FUNDAMENTALS
Conductors and Resistance
• All conductors have some resistance to
current flow.
• If conductor length is doubled,
resistance doubles.
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ELECTRICAL FUNDAMENTALS
?
Conductors and Resistance
• If conductor diameter is increased,
resistance is reduced.
• As temperature increases, resistance of
conductor also increases.
• Materials used in conductor have
impact on its resistance.
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ELECTRICAL FUNDAMENTALS
Chart 39-1
Conductor ratings (starting with the best).
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ENVIRONMENTAL AND HAZARDOUS MATERIALS
RESISTORS
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ELECTRICAL FUNDAMENTALS
Resistors
• Fixed Resistors
– Resistors represent electrical load, or
resistance, to current flow.
– Resistors used to limit and control flow of
current.
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ELECTRICAL FUNDAMENTALS
Resistors
• Fixed Resistors
– Can be made from carbon or other
materials that restrict flow.
– Available in various sizes and resistance
values.
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ELECTRICAL FUNDAMENTALS
Resistors
• Fixed Resistors
– Most have series of painted color bands.
– Color bands are coded to indicate degree of
resistance.
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ELECTRICAL FUNDAMENTALS
Figure 39-24
This figure shows a resistor color-code interpretation.
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ELECTRICAL FUNDAMENTALS
Figure 39-25
A typical carbon resistor.
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ELECTRICAL FUNDAMENTALS
Resistors
• Variable Resistors
– Two types of mechanically operated
variable resistors used in vehicles.
– Potentiometer: three-terminal variable
resistor.
• Wiper contact provides a variable voltage
output.
• Used in throttle position (TP) sensors, sound
system controls.
Automotive Technology, Fourth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
39
ELECTRICAL FUNDAMENTALS
Resistors
• Variable Resistors
– Rheostat: two-terminal unit.
• Current flows through movable arm.
• Used in dash light dimmer control.
Automotive Technology, Fourth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
39
ELECTRICAL FUNDAMENTALS
Figure 39-26
A three-wire variable resistor is called a potentiometer.
Automotive Technology, Fourth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved
39
ELECTRICAL FUNDAMENTALS
Figure 39-27
A two-wire variable resistor is called a rheostat.
Automotive Technology, Fourth Edition
James Halderman
© 2011 Pearson Education, Inc.
All Rights Reserved