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Electricity
What is electricity?

Is the movement of electrons from atom to
atom.

Some substances have atoms that allow
electrical flow, others do not.
 Conductors
 Insulators
The Players

Conductors
 Wires
and other metal objects have atoms that
allow the flow of electricity
 Copper, gold, aluminum, steel, etc

Insulators
 Resist the flow of electricity
 They do not contain free electrons
 Plastic, rubber, glass, ceramic
The Players

Atoms
 Basically consists
 Protons,
of small particles called:
neutrons and electrons
 Neg.
(-) charged electrons circle around a
center of neutrons and pos. (+) charged
protons

Free electrons
 Are
extra electrons in the orbit of an atom that
are not locked to a proton
Atoms and Electrons

The maximum number of electrons in the
atom’s valence (outer band) varies, but if it
is full, it will be a good insulator
 The
valence is filled, it is in a state of
equilibrium, and reluctant to give or take an
electron from a neighboring atom.
Atoms and Electrons

An atom with 2 or 3 valence electrons are
usually good conductors
 They
contribute to and receive electrons from
neighboring atoms.

Metals such as gold, silver and copper
have a single electron in their valence
band, and are excellent conductors.
Conductor atoms
Copper
Silver
Gold
Current, Voltage, & Resistance

Current is the flow of electrons through a
conductor
 Just as water flows through a garden hose,
electrons flow through a wire in a circuit
 When
current flows through a light bulb, the
electrons rub against the atoms causing
‘electrical friction’.
 The friction heats the filament, making it
glow.
Current, Voltage, & Resistance

2 Electron Flow theories:
 Conventional
Theory:
 States
that current flows from
Positive (+) to Negative (-)
 Electron
Theory:
 States
that current flows from
Negative (-) to Positive (+)
 This is more widely accepted than the
‘Conventional Theory’

Current is abbreviated I
Current,

Voltage, & Resistance
Voltage is the force, or ‘electron pressure’,
that causes electron flow
 Similar

to water pressure in a hose
An increase in voltage causes an increase
in current
 A decrease in voltage causes a decrease in
current
 Voltage is abbreviated V or E
Current, Voltage,
& Resistance

Is the opposition to current flow.
 Resistance is needed to control the flow of
current in a circuit.
 Circuit resistance can be increased or
decreased to control the flow of electricity
 High
resistance reduces current
 Low resistance increases current

Resistance is abbreviated R
…end of Part 1
**********************************
Part 2
Circuits and Terms
A Circuit

1.
To have a simple circuit you need 3
things:
A Power Source:

2.
A Load:

3.
Battery, alternator, or generator which supplies the
electricity for the circuit
An electrical device that uses electricity
Conductors:

Wires or metal parts that carry the current between
the power source and the load
A Simple Circuit
A Series Circuit

Has more than one load connected in one
electrical path
Closed circuit
Open circuit
A Parallel Circuit

Has more than one electrical path.
Closed circuit
Open circuit
Some Terms

Switch:
 Allows
an electrical circuit to be turned on or
off

Short Circuit:
 Is
a low-resistance connection that results in
excessive current flow

Fuse:
 Protects
a circuit against damage caused by a
short circuit
Types of Fuses
Fuses…
 When
a fuse blows, the link in the fuse will
melt and burn in half to stop the excess
current

Fusible Link:
 Small
section of wire designed o burn in half
when excess current is detected

Circuit Breaker:
 Performs
the same function as a fuse, but resets itself when current returns to normal
Relays

An electronically operated switch
 It allows a small dash switch to control
another circuit from a distant point
 It
also allows small wires to be used behind
the dash,while large wires might be needed to
operate the circuit
 Eg.The
starter circuit
The Starting
Circuit
… end of Part 2
**********************************
Using a Multi-Meter
or DMM
Testing for Voltage and Continuity
Testing voltage
Turn on the machine and set it to ‘V’
 (with dashed lines)
 Get a baseline reading

 In
most automotive applications voltage will
be…
 12V
 Test
or 24V
the battery to get your baseline
 Move to your test area and perform the tests!
Voltage

Remember that voltage can only flow if
there is a good path to ground.
 Make sure that the metal you are using for
ground (black lead) is connected to the
ground circuit of the vehicle
 Seat
belt bolt, metal dash support, engine
metal, etc.
Continuity test


THIS TEST is for fuses out of the vehicle**
Set the DMM to the speaker/sound icon
 Then press the corresponding grey button
 When you touch the leads together you
should hear a beep.
Test a fuse with continuity

Set the DMM to continuity
 Place one probe on each test point
 Listen for the beep
Test a fuse IN the vehicle

Set the DMM to volts
 Connect the black lead to ground
 Turn the ignition to ‘On’ (not running, but
dash lights on)
 Test each side of the fuse.
 You
should get 12V at each point
 If you don’t…
You have found a blown fuse!!
Check a fuse in the vehicle

Black lead to ground
 Ignition to ‘on’
 Probe each test point
 Look for around 12V
End of Part 3
**********************************