Transcript short-to-voltage

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 shortto-ground, and a short-to-voltage.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
FIGURE 4-3 An electrical switch
opens the circuit and no current
flows. The switch could also be on the
return (ground) path wire.
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CIRCUITS
Short to Voltage
FIGURE 4-5 A short circuit permits electrical
current to bypass some or all of the resistance in
the circuit.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CIRCUITS
Short to Ground
FIGURE 4-8 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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OHM’S LAW
• Ohm’s law states:
– It requires 1 volt to push 1 ampere through 1 ohm of
resistance.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OHM’S LAW
FIGURE 4-9 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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OHM’S LAW RELATIONSHIP
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OHM’S LAW RELATIONSHIP
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 4-10 This closed circuit
includes a power source, power-side
wire, circuit protection (fuse), resistance
(bulb), and return path wire.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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=IxE
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
WATT’S LAW
FIGURE 4-11 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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
WATT’S LAW
Magic Circle
FIGURE 4-12 “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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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.
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
b)
c)
d)
Short-to-voltage
Short-to-ground
Open
Chassis ground
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
b)
c)
d)
Short-to-voltage
Short-to-ground
Open
Floating ground
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
3. If 12 volts are being applied to a resistance
of 3 ohms, _____ amperes will flow.
a)
b)
c)
d)
12
3
4
36
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
4. How many watts are consumed by a light
bulb if 1.2 amperes are measured when 12
volts are applied?
a)
b)
c)
d)
14.4 watts
144 watts
10 watts
0.10 watt
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
5. How many watts are consumed by a starter
motor if it draws 150 amperes at 10 volts?
a)
b)
c)
d)
15 watts
150 watts
1,500 watts
15,000 watts
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
6. If the temperature of a conductor increases,
what will happen to its resistance?
a)
b)
c)
d)
Stays the same
Increases
Decreases
Decreases slightly, then increases
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
7. A wire was replaced with the same type and size
but is twice as long as the original. Technician A
says that the resistance will be the same as the
original. Technician B says that the resistance will
be less than the resistance of the original. Which
technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
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)
b)
c)
d)
Cannot be determined
Zero
About one-half (about 100 amperes)
200 amperes
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
9. What is the symbol for voltage used in
calculations?
a)
b)
c)
d)
V
E
EMF
I
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
10. Which circuit failure is most likely to cause
the fuse to blow?
a)
b)
c)
d)
Open
Short-to-ground
Short-to voltage
High resistance
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
END
Automotive Electricity and Electronics, 2/e
By James D Halderman
© 2009 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458