Download Basic Electrical

Electrical
Fundamentals
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What is Electricity?
A good technical definition of
electricity is:
The flow of electrons through a
conductor.
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ATOM
 Made up of three parts:
Protons–positively charged particles
Neutrons–particles with no charge
Electrons–negatively charged particles
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Structure of an Atom
 Protons and neutrons combine to form the nucleus
 Since opposite charges attract each other, the
negatively charged electrons tend to remain in orbit
around the positively charged nucleus
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Valence
 The valence is the outer electron band of an atom
 The number of electrons in the valence determines
whether that element makes a good conductor, insulator,
or semi-conductor of electricity.
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Conductors
A Good Conductor Has
Less Than 4 Electrons In
The Valence
 Allow the flow of electricity
 Contain atoms with free
electrons
 one to three electrons in the
outer orbit
 Free electrons are not
locked in orbit around the
nucleus
 electrons can be forced to
move from one atom to
another
 Copper, gold, and silver
are good conductors
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Insulators
A Good Insulator Has
More Than 4 Electrons
In the valence
 Resist the flow of
electricity
 Contain atoms with
bound electrons
 five to eight electrons
in the outer orbit
 Bound electrons will
not leave their orbit
around the nucleus
 Plastic, rubber, and
ceramics are good
insulators
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Semiconductor
Semiconductors Have 4
Electrons In The Valence
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 Substance capable
of acting as both a
conductor and an
insulator
Wire Size
 Determined by the diameter
of the wire’s metal conductor
 Stated in a relative
numbering system, called
gauge size
 Wires become smaller as
gauge numbers increase
 When replacing a wire,
always use wire of equal
size or greater
smaller wire could
overheat
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Characteristics
of
Electricity
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Electrical Principles
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Electrical Terms
 Three terms are
used in the study of
electricity:
 current
 voltage
 resistance
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Current




Flow of electrons through a conductor
Measured in Amperes (A)
I is the abbreviation for current
Conventional (current) theory
 states that current flows from positive to negative
 Electron theory
 states that electrons flow from negative to positive
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Voltage
 Electrical pressure that causes electron flow
 Measured in Volts
 V (voltage) or E (electro motive force) is the
abbreviation for voltage
 Higher voltage increases current flow
 Lower voltage decreases current flow
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Resistance
 Opposition to current flow
 Measured in ohms ()
 R is the abbreviation for resistance
 High resistance reduces current
 Low resistance increases current
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Resistance Factors
Resistance of a conductor is determined by a
combination of four factors:
 Atomic Structure (number of free electrons)- For
example, copper vs. aluminum wire.
 Length of the Conductor – The longer the conductor,
the higher the resistance.
 Width (cross sectional area) – The larger the cross
sectional area of a conductor, the lower the resistance.
For example, 12 gauge vs. 20 gauge wire.
 Temperature – For most materials, the higher the
temperature, the higher the resistance.
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Predicting Resistance
 Sometimes you can
predict that high
(unwanted) resistance is
present in a circuit by just
looking at one of the
electrical connections for
the component, or by
inspecting the component
itself. You can expect
high resistance if the
connection is discolored,
corroded, or loose.
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Ohm’s
Law
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Ohm’s Law
One volt can push one amp of current
through one ohm of resistance
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Using Ohm’s Law
 Formula for
calculating voltage,
amperage, or
resistance when two
of the three values
are known
 Resistance = voltage
divided by current
R = 12 Volts
6 amps
R = 2 ohms
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Ohm’s Law
 Here are four very important electrical
facts to learn form ohm’s law
 Assuming that resistance stays the same:
oIf voltage increases, current increases
oIf voltage decreases, current decreases
 Assuming that voltage stays the same:
oIf resistance increases, current decreases
oIf resistance decreases, current increases
 Notice that current is determined by
voltage and resistance. Current cannot
change on its own
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Work Sheet #1
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The
Complete Electrical
Circuit
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Complete Electrical
Circuit
 Power source
battery, alternator, or
generator
 Load
electrical device that
uses electricity
 Conductors
wires or metal parts that
carry current between
power source and load
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Power Source
Battery voltage
depends on the
number of cells
Open circuit cell
voltage is 2.1 volts
12 volt battery has 6
cells - open circuit
voltage 12.6 volts
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Load Device
 A load device is anything that is powered by, or
consumes electricity. Such as the following:
o
o
o
o
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Lights
Radio
Motors (starter, door locks, windows, etc.)
Fuel Injectors
Insulated Conductor
The battery Positive
terminal is connected to the
supply or “hot” side of the
circuit
All circuits need an
insulated conductor to carry
voltage to a circuit from
Positive battery terminal
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Ground Conductor
 On a vehicle, the negative
battery post is ground
 All electrical circuits on a
vehicle lead back to a ground
connection somewhere on the
chassis of the ground
 The chassis serves as a
common ground which
connects all individual ground
connections back to the
negative battery post.
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K-I-S-S Means…
Keep It Simple!
No matter how complicated the circuit is
that you are trying to fix, always
remember that in order to make a
complete circuit, four things are needed
 Voltage Source
 A Complete Conductive Pathway
 Load Device
 Ground
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Series & Parallel
Circuits
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Series Circuit
Rules for a Series Circuit
 There is only one path for
current flow
 Current flow is the same at
every point in the circuit
 An open anywhere in the
circuit stops current flow
 Individual resistances add up
to the total resistance
 The sum of the individual
voltage drops of all the
resistors, or load devices,
equals the source voltage
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Parallel Circuit
Rules for a Parallel Circuit
The voltage applied to each
leg, or branch, of the circuit
is the same as the source
voltage
Total resistance is less than
the lowest of the individual
resistances
Total current in the circuit
equals the sum of the
branch circuits
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Calculating Resistance in a
Two Branch Parallel Circuit
If there are only two branches,
use the following formula
Rt= R1 x R2
R1 + R2
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Work Sheet #2
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Work Sheet #3
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Introduction
To Digital
Multimeters
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The Digital Multimeter
 The DMM comes in
many different forms,
but they all perform
the same basic
functions.
 The DMM is capable
of reading both AC
and DC amperage,
both AC and DC
voltage, and Ohms
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The Digital Multimeter
 Electrical values are often
very small or very large and
sometimes it can get very
confusing working with these
small and large values
 Electrical calculations are
done using metric values to
simplify the readings.
 The metric values are Mega,
Kilo, Milli, and Micro
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Mega (M)
 Mega (M) stand for one million. So if a circuit has
one million ohms of resistance, you can write it
two ways as shown below.
1000000. Ohms
or you can move the decimal over to left six places:
1.000000
with the decimal moved, we can rewrite this number as:
1 Megaohm
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Kilo (K)
 Kilo (K) – Kilo stands for one thousand. Let’s say
you have a 12,000 volt voltage source. Again this
can be written two ways:
12000. Volts
Or you can move the decimal over to left three places:
12.000
With the decimal moved, we can rewrite this number as:
12 Kilovolts
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Milli (m)
 Milli (m) – Milli means one thousandths. It’s very
useful for small measurements. So, let’s say you
have circuit that has 0.015 amperes of current. This
can be written two ways:
0.015 Amperes
Or you can move the decimal over three places to the right:
015.
With the decimal moved, we can re-write this number as:
15 Milliamperes
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Connecting Black Lead
 The black lead is
called the “common”
lead.
 You plug the black
lead into the input
terminal that says
COM
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Connecting Red Lead
 The red lead you actually measure
with and will be plugged into
different jacks depending on what
you are measuring
 Voltage – connect red lead to
terminal marked with a “V”
 Resistance – connect red lead to
terminal marked “Ω”
 Amperage – connect red lead to
terminal marked “A”, however there
may be several terminals
depending on the maximum
amount of current you will be
measuring
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Work Sheet #4
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Voltmeter
 A voltmeter is used to measure voltage
potential…
Always
Never
Units:
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place in parallel with device
place in series with device
Volts (V) and Millivolts (mV)
Voltmeters
 Always Remember
A voltmeter always measures the differences
in electrical potential (or electrical “pressure”)
between two points
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Voltage Drop
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Voltage Drop
 Voltage drop is the difference in voltage
between two points due to a loss of electrical
pressure as current flows through resistance
 Any resistance in a circuit opposes the flow
of electrons and there is a resulting loss of
voltage through the resistance
 A circuit that has only one load device in a
circuit “uses up” all the electrical pressure
(voltage) in the circuit
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Ohmmeter
 An Ohmmeter is used to measure Resistance…
Always – place across the device
Never – test while power is applied to circuit
Units – Ohms (Ω) 1.0
Kilo-ohms (KΩ) 1,000
Megaohms (MΩ) 1,000,000
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Measuring Resistance
Keep the following points in mind:
 Always disconnect the section of the circuit
you’re testing from the power source
 You can check the resistance of anything
 Measure between two points in the circuit
 When testing devices you should
disconnect them from the circuit to prevent
false readings
 40 ohms is too much resistance for many
circuits to operate properly
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Ammeter
 An Ammeter is used to measure current flow:
Always – place in series with the device
Never – place across the device
Units – Amps (A) and Milliamps (mA)
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Measuring Current
Keep the following points in mind:
 If the current flow exceeds the rating of the
meter fuse, the fuse will blow since the current
flows through the meter (the meter is like a
jumper wire)
 Never place the meter leads across the
component when measuring amperage
 When measuring current in a circuit, always
start with the red lead of the DMM in the Amp
input (10A fused)
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When Using Multimeters
 Always test meter to confirm meter is
operating correctly
 Always make sure the leads are
connected properly to the meter for a
given test
 Always make sure the meter is set to
the right scale for the test being
conducted
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Work Sheet #5
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Work Sheet #6
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Electrical
and
Magnetic
Components
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Magnet Basics
A magnet is any object that attracts iron
and steel and certain other materials
Three basic types of magnets are:
Natural
Man-made or permanent magnets
Electromagnets
A magnet has two poles; we call these
north and south poles
Like poles repel; unlike poles attract
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Magnetism
Electricity can be used to produce magnetism
A starter motor uses electrical energy form the
battery to create electromagnetism, which it uses
to produce mechanical energy for cranking the
engine
Magnetism can be used to produce electricity
The generator uses mechanical energy from the
engine to create a magnetic field, and uses it to
produce electromotive force (voltage)
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Electromagnetism
 Current flow through any
conductor (wire) creates a
magnetic field in the space
surrounding the conductor
 To concentrate the magnetic field,
the wire must be looped into a
coil
 A soft iron core inserted into the
coil, further strengthens the
magnetic field
 The magnetic strength of an
electromagnet is proportional to
the number of turns of wire in the
coil and the current flowing
through the wire
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Horns
 An automotive horn is an
electromagnetic device that
creates sound by creating
vibration
 Contains a coil, points, and
a flexible diaphragm
 Coil and point action makes
the plunger slide in and out
of the coil, moving the
diaphragm creating a “click”
 Because the vibrating is so
rapid, the click sounds like
a blare of the horn
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Relay
 A relay allows one circuit
(control circuit) to move an
electrical contact that
opens and closes another
circuit (load circuit)
ISO relays are the same
size, have the same
terminal pattern, and have
terminals with specific
numbers assigned to them
(#85, #86, etc.)
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Control circuit current flow
creates a magnetic field that
pulls the points closed
Solenoid
A solenoid, like a relay
produce motion
However, solenoids produce
more holding power and can
do more than close electrical
contacts
When current flows through
the coil, electromagnetism
pulls an iron core into the
coil; when current stops, the
core returns to its base
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Work Sheet #7
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Circuit Faults
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Types of Circuit Faults
There are three basic types of faults:
 High Resistance
 Low Resistance
 Component Failure
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Common Circuit Faults
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High Resistance Faults
Open Circuit
 Prevents systems from
working
 Caused by broken wire,
disconnected electrical
connection or switch
 To test, use a test light or
voltmeter
 Check for power at the
supply (fuse), moving
toward the component
(load) until open is found
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High Resistance Faults
Dirty Switch or Relay Contacts
Loose or corroded connections
 Reduces current flow in a circuit
 Motors may run slow, lights may be dim
 To test, measure the voltage drop across
suspected problem components such as a switch
 High resistance causes a high voltage drop
 Total supply side voltage drop should not exceed
0.5 volts
 Total ground side voltage drop should not exceed
0.3 volts
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Low Resistance Faults
Short Circuit
 Normal current path is bypassed at any point, causing it
to flow back to the power
source before it has traveled
the complete path
 “Shorts” cause trouble
because electricity always
takes the path of least
resistance.
 Shorts to ground or to other
circuits, cause electrical
circuits to operate when they
shouldn’t
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Defective Components
 Certain electrical parts, such as lamps,
batteries, motors, fuses, and switches,
wear out occasionally and need to be
replaced
 When some components fail, they
result in high amperage draw in the
circuit causing circuit protectors to also
fail.
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Intermittents
 Some problems only happen once in a while
 Because of this fact, intermittent shorts or
opens, are pretty difficult to isolate because
you could get good test results when you test
the circuit, even though the circuit problem
could reoccur
 Service and diagnostic manuals provide
some direction on how to handle intermittent
problems
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Always Remember…
 To Make a Complete Circuit you need four
things:




Voltage Source
A Complete Conductive Pathway
Load Device
Ground
 A problem in one of these four areas will
usually be due to one of the following:
 Improper high or low resistance in the supply
circuit
 Improper high or low resistance within the
conductive pathway
 Improper high or low resistance in the load device
 Improper high or low resistance in the ground
circuit
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