5696395.ppt

Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OBJECTIVES
After studying Chapter 4, the reader should be able to:
1. Prepare for ASE Electrical/Electronic Systems
(A6) certification test content area “A” (General
Electrical/Electronic Systems Diagnosis).
2. State Ohm’s law.
3. Identify the parts of a complete circuit.
4. State Watt’s law.
5. Describe the characteristics of an open, a short-
to-ground, and a short-to-voltage.

CIRCUITS
• A circuit is a path that
electrons travel from a
power source (such as a
battery) through a load
such as a light bulb and
back to the power source.
FIGURE 4-1 All complete circuits must have a
power source, a power path, protection (fuse),
an electrical load (light bulb in this case), and a
return path back to the power source.

CIRCUITS
Parts of a Complete Circuit
• Every complete circuit contains the following parts.
– A power source.
– Protection from harmful overloads.
– An insulated path for the current to flow through from the power
source to the resistance.
– The electrical load or resistance which converts electrical energy
into heat, light, or motion.
– A ground (return) path for the electrical current from the load back
to the power source so that there is a complete circuit.
– Switches and controls that turn the circuit on and off

CIRCUITS
Parts of a Complete Circuit
FIGURE 4-2 The return path back to the
battery can be any electrical conductor, such
as the metal frame or body of the vehicle.
FIGURE 4-3 An electrical switch
opens the circuit and no current
flows. The switch could also be on the
return (ground) path wire.

CIRCUITS
Open Circuits
• An open circuit is any
circuit that is not complete,
or that lacks continuity.
FIGURE 4-4 Examples of common
causes of open circuits. Some of
these causes are often difficult to find.

CIRCUITS
Short to Voltage
• If a wire (conductor) or component is shorted to
voltage, it is commonly called shorted.
• A short-to-voltage is where the power side of one
circuit is electrically connected to the power side of
another circuit

CIRCUITS
Short to Voltage
• A short circuit:
– Is a complete circuit in which the current bypasses some
or all of the resistance in the circuit.
– Involves the power side of the circuit.
– Involves a copper-to-copper connection.
– Is also called a short-to-voltage.
– Usually affects more than one circuit.
– May or may not blow a fuse.

CIRCUITS
Short to Voltage
FIGURE 4-5 A short circuit permits electrical
current to bypass some or all of the resistance in
the circuit.

CIRCUITS
Short to Voltage
FIGURE 4-6 A fuse or circuit breaker opens the circuit to
prevent possible overheating damage in the event
of a short circuit.

CIRCUITS
Short to Ground
• A short-to-ground is a
type of short circuit wherein
the current bypasses part of
the normal circuit and flows
directly to ground.
FIGURE 4-7 A short-to-ground affects the
power side of the circuit. Current flows
directly to the ground return, bypassing
some or all of the electrical loads in the
circuit. There is no current in the circuit pass
the short.

CIRCUITS
High Resistance Faults
• High resistance in any circuit can cause many
problems, including:
– Slow the operation of a motor-driven unit, such as the
wipers and blower motor
– Dim the lights
– Clicking relays or solenoids

HIGH RESISTANCE
FIGURE 4-8 A dim headlight indicates high resistance in the
circuit to the device or load being tested.

THINK OF A WATERWHEEL
FIGURE 4-9 Electrical flow through a circuit is similar to water
flowing over a waterwheel. The more the water (amperes in
electricity), the greater the amount of work (waterwheel). The
amount of water remains constant, yet the pressure (voltage in
electricity) drops as the current flows through the circuit.

OHM’S LAW
• Ohm’s law states:
– It requires 1 volt to push 1 ampere through 1 ohm of resistance.

OHM’S LAW
FIGURE 4-10 To calculate one unit of electricity when the other two
are known, simply use your finger and cover the unit you do not
know. For example, if both voltage (E) and resistance (R) are
known, cover the letter/(amperes). Notice that the letter E is above
the letter R, so divide the resistor’s value into the voltage to
determine the current in the circuit.

OHM’S LAW
1. Ohm’s law can determine the resistance if the
volts and amperes are known: R = E/I.
2. Ohm’s law can determine the voltage if the
resistance (ohms) and amperes are known:
E = I x R.
3. Ohm’s law can determine the amperes if the
resistance and voltage are known: I = E/R.

OHM’S LAW RELATIONSHIP

Ohm’s Law Applied to Simple Circuits
• Using Ohm’s law, we can calculate the number of
amperes that will flow through the wires and the
resistor.
• Remember, if two factors are known (volts and
ohms in this example), the remaining factor
(amperes) can be calculated using Ohm’s law.

Ohm’s Law Applied to Simple Circuits
I = E/R = 12 V/4 Ω
The values for the voltage (12)
and the resistance (4) were
substituted for the variables E
and R, and I is thus 3 amperes
(12/4 = 3).
FIGURE 4-11 This closed circuit
includes a power source, power-side
wire, circuit protection (fuse), resistance
(bulb), and return path wire.

WATT’S LAW
• Electricity can also be expressed in a unit of power
called a watt and the relationship is known as
Watt’s law, which states:
– A watt is a unit of electrical power represented by a
current of 1 ampere through a circuit with a potential
difference of 1 volt.
W = I x E

WATT’S LAW
FIGURE 4-12 To calculate one unit when the other
two are known, simply cover the unknown unit to
see what unit needs to be divided or multiplied to
arrive at the solution.

WATT’S LAW
Magic Circle
FIGURE 4-13 “Magic circle” of most of the formulas for problems involving Ohm’s
law. Each quarter of the “pie” has formulas used to solve for a particular unknown
value: current (amperes), in the upper right segment; resistance (ohms), in
the lower right; voltage (E), in the lower left; and power (watts), in the upper left.

SUMMARY
1. All complete electrical circuits have a power
source (such as a battery), a circuit protection
device (such as a fuse), a power-side wire or path,
an electrical load, a ground return path, and a
switch or a control device.
2. A short-to-voltage involves a copper-to-copper
connection and usually affects more than one
circuit.
3. A short-to-ground involves a copper-to-steel
connection and usually causes the fuse to blow.
4. An open is a break in the circuit resulting in
absolutely no current flow through the circuit.
5. High resistance in a circuit is a common type of
circuit fault.

REVIEW QUESTIONS
1. List the parts of a complete electrical circuit.
2. Describe the difference between a short-to-
voltage and a short-to-ground.
3. Describe the difference between an open and a
short.
4. State Ohm’s law.
5. Explain what occurs to current flow (amperes) and
wattage if the resistance of a circuit is increased
because of a corroded connection.

CHAPTER QUIZ
1. If an insulated wire rubbed through a part of the
insulation and the wire conductor touched the
steel body of a vehicle, the type of failure would
be called a(n) _____.
a) Short-to-voltage
b) Short-to-ground
c) Open
d) Chassis ground

CHAPTER QUIZ
2. If two insulated wires were to melt together where
the copper conductors touched each other, the
type of failure would be called a(n) _____.
a) Short-to-voltage
b) Short-to-ground
c) Open
d) Floating ground

CHAPTER QUIZ
3. If 12 volts are being applied to a resistance of 3
ohms, _____ amperes will flow.
a) 12
b) 3
c) 4
d) 36

CHAPTER QUIZ
4. How many watts are consumed by a light bulb if
1.2 amperes are measured when 12 volts are
applied?
a) 14.4 watts
b) 144 watts
c) 10 watts
d) 0.10 watt

CHAPTER QUIZ
5. How many watts are consumed by a starter motor
if it draws 150 amperes at 10 volts?
a) 15 watts
b) 150 watts
c) 1,500 watts
d) 15,000 watts

CHAPTER QUIZ
6. High resistance in an electrical circuit can cause
_____.
a) Dim lights
b) Slow motor operation
c) Clicking of relays or solenoids
d) All of the above

CHAPTER QUIZ
7. If the voltage increases in a circuit, what happens
to the wattage if the resistance remains the same?
a) Increases
b) Decreases
c) Remains the same
d) Can not be determined

CHAPTER QUIZ
8. If 200 amperes flow from the positive terminal of a
battery and operate the starter motor, how many
amperes will flow back to the negative terminal of
the battery?
a) Cannot be determined
b) Zero
c) About one-half (about 100 amperes)
d) 200 amperes

CHAPTER QUIZ
9. What is the symbol for voltage used in
calculations?
a) V
b) E
c) EMF
d) I

CHAPTER QUIZ
10. Which circuit failure is most likely to cause the
fuse to blow?
a) Open
b) Short-to-ground
c) Short-to voltage
d) High resistance

END

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