Download Electrical Circuits - MR.Chew

Electrical Circuits
What you need to Know!
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Safety
2- Types of Current
3-Types of Electrical Circuits
2- Theories of Electron Flow
OHMS Law
Voltage
Amperage
Resistance
Voltage Drop
Personal
Safety practices
Remove jewelry, watches and rings
Tie hair back and avoid loose clothing
Be aware of other workers unsafe habits
SOURCES OF ELECTRICITY
Electricity can be created by several means: Friction, Heat, Light,
Pressure, Chemical Action, or Magnetic Action.
Only a few of these sources of energy are used in the automobile. The
battery produces electricity through chemical action, and the alternator
produces electricity through magnetic action.
Friction creates static electricity.
Heat can act upon a device called a thermo couple to create DC.
Light applied to photoelectric materials will produce DC electricity.
Pressure applied to a piezoelectric material will produce DC electricity.
Chemical Action of certain chemicals will create electricity.
What do we need to make an
electrical circuit “Work”
Break into groups and write a list of
the basic requirements to control and
use electricity
Think of what has to happen to turn on
a light.
BASIC CIRCUIT
CONSTRUCTION
1. Power Source
(Battery, Alternator,
Generator, etc.)
2. Protection Device
(Fuse, Fusible Link, or
Circuit Breaker)
3. Load Device (Lamp,
Motor, Winding, Resistor,
etc.
4. Control (Switch, Relay,
or Transistor)
5. Conductors (A Return
Path, Wiring to Ground
DIRECT CURRENT (DC)
• Electricity with
electrons flowing in
only one direction is
called Direct Current
or DC.
• DC electrical
systems are used in
cars.
ALTERNATING
CURRENT (AC)
• Electricity with
electrons flowing
back and forth,
negative - positivenegative, is called
Alternating Current,
or AC.
• The electrical
appliances in your
home use AC power.
ELECTRON THEORY
• The Electron Theory
states that current
flows from
NEGATIVE to
POSITIVE. Electrons
move from atom to
atom as they move
through the conductor
towards positive
Conventional theory
• also known as HOLE
THEORY, states that
current flows from
POSITIVE to
NEGATIVE. Protons or
the lack of electrons (the
holes) move towards the
negative. (Current flow
direction in Hole Theory
is the opposite of that in
Electron Theory.)
AUTOMOTIVE
ELECTRICAL CIRCUITS
In an automotive electrical circuit,
one end of the wire from each
load returning to the battery is
connected to the vehicle body or
frame. Therefore, the vehicle
body or frame itself functions as
a conductor, allowing current to
flow though the body or frame
and back to the battery. The
body or frame is then referred to
as the body ground (or earth) of
the circuit (meaning that part of
the circuit that returns the
current to the battery).
Ohms Law E=IxR
1 volt can push 1 amp through 1  of resistance
12 volts can push 12 amps through 1  of resistance
12 volts can push 1 amp through 12  of resistance
Ohms Law E=IxR
As Voltage increases the current will…
…increase
As Resistance increases the current will…
…decrease
As Resistance decreases the current will…
…increase
OHM'S LAW SYMBOL SHORTCUT
OHM'S LAW FORMULA
When voltage is applied to an electrical circuit, current flows in the
circuit. The following special relationship exists among the voltage,
current and resistance within the circuit: the size of the current that flows
in a circuit varies in proportion to the voltage which is applied to the
circuit, and in inverse proportion to the resistance through which it must
pass. This relationship is called Ohm's law, and can be expressed as
follows:
E=IR
Voltage = Current x Resistance
E Voltage applied to the circuit, in volts (V)
I Current flowing in the circuit, in amperes (A)
R Resistance in the circuit, in ohms
In practical terms "V = I x R" which means
"Voltage = Current x Resistance".
1 volt will push one amp through 1 ohm of resistance
.
Voltage
Electromotive Force
(EMF)
the electrical pressure that forces
electrons to move from atom to atom
Voltage is present when there
is a difference in electrical
pressure
VOLTAGE
Voltage is the electrical force that moves electrons through a conductor.
Voltage is electrical pressure also known as EMF (Electro Motive Force)
that pushes electrons.
The greater the difference in electrical potential push (difference between
positive and negative), the greater the voltage force potential.
MEASUREMENT
A VOLTMETER measures
the voltage potential
across or parallel to the
circuit.
The Voltmeter measures the
amount of electrical
pressure difference
between two points being
measured.
Voltage can exist between
two points without
electron flow
VOLTAGE UNITS
Voltage is measured in units called VOLTS.
Voltage measurements can use different value prefixes such as millivolt,
volt, Kilovolt, and Megavolt.
LESS THAN
VOLTAGE
BASE UNIT
LARGER THAN
BASIC UNIT
BASE UNIT
Symbol
mV
V
kV
Pronounced
millivolt
Volt
Kilovolt
Multiplier
0.001
1
1,000
Amperage
The more electrons moving from atom to
atom, the more current or Amperage
How many electrons (amps) move is
decided by the pressure (volts) and the
resistance to the flow of electrons
Amperage or Electrical Current
the Intensity of the electron movement
between atoms
one amp = 6,280,000,000,000,000,000
electrons per second
Carl Sagan would say that one amp equals
over six billion, billion electrons per second
Low Amps
High Amps
Amperage
Higher Voltages (pressure) will cause more
amps (electrons) to flow
Increasing the resistance to the electron
movement will lower Amp flow
MEASUREMENT
An AMMETER measures the quantity of current flow. Ammeters are
placed in series (inline) to count the electrons passing through it.
Example: A water meter counts the gallons of water flowing through it.
AFFECTS OF CURRENT FLOW
Two common effects of current flow are Heat Generation and
Electromagnetism.
HEAT: When current flows, heat will be generated. The
higher the current flow the greater the heat generated. An
example would be a light bulb. If enough current flows across
the filament, it will glow white hot and illuminate to produce
light.
ELECTROMAGNETISM: When current flows, a small
magnetic field is created. The higher the current flow, the
stronger the magnetic field. An example: Electromagnetism
principles are used in alternators, ignition systems, and other
electronic devices.
Define Resistance?
Resistance is the opposition to amp flow
may be caused by heat, excessive amp flow,
corrosion or any insulated material
Resistance is required to perform “work”
RESISTANCE
Resistance is the force that reduces or stops the flow of electrons. It
opposes voltage.
Higher resistance will decrease the flow of electrons and lower resistance
will allow more electrons to flow.
Ohms
• An OHMMETER
measures the resistance of
an electrical circuit or
component. No voltage
can be applied while the
ohmmeter is connected, or
damage to the meter will
occur.
• Example: Water flows
through a garden hose,
and someone steps on the
hose. The greater the
pressure placed on the
hose, the greater the hose
restriction and the less
water flows.
RESISTANCE FACTORS
Various factors can affect the resistance. These include:
LENGTH of the conductor. The longer the conductor, the higher
the resistance.
DIAMETER of the conductor. The narrower the conductor, the
higher the resistance.
TEMPERATURE of the material. Depending on the material, most
will increase resistance as temperature increases.
PHYSICAL CONDITION (DAMAGE) to the material. Any damage
will increase resistance.
TYPE of MATERIAL used. Various materials have a wide range of
resistances.
Materials with High Resistance
Wood
Rubber
Plastics
Glass
These materials have many electrons in their outer “valence”
electron orbit.
It takes tremendous pressure (Voltage) to move electrons
between these atoms
LOADS
The illustration below has a
horn in place of the lamp. Any
device such as a lamp, horn,
wiper motor, or rear window
defogger, that consumes
electricity is called a load. In an
electrical circuit, all loads are
regarded as resistance. Loads
use up voltage and control the
amount of current flowing in a
circuit. Loads with high
resistance cause less current to
flow while those with lower
resistance allow high current
rates to flow.
TYPES OF CIRCUITS
Individual electrical circuits normally combine one or more
resistance or load devices. The design of the automotive
electrical circuit will determine which type of circuit is used.
There are three basic types of circuits:
• Series Circuit
• Parallel Circuit
• Series-Parallel Circuit
Series Circuits
A series circuit is a voltage dividing circuit
SERIES CIRCUITS
A series circuit is the simplest
circuit. The conductors, control
and protection devices, loads,
and power source are connected
with only one path to ground for
current flow. The resistance of
each device can be different.
The same amount of current
will flow through each. The
voltage across each will be
different. If the path is broken,
no current flows and no part of
the circuit works. Christmas tree
lights are a good example; when
one light goes out the entire
string stops working.
SERIES CIRCUITS
• A Series Circuit has only one
path to ground, so electrons
must go through each
component to get back to
ground. All loads are placed in
series.
• Therefore:
• 1. An open in the circuit will
disable the entire circuit.
• 2. The voltage divides (shared)
between the loads.
• 3. The current flow is the same
throughout the circuit.
• 4. The resistance of each load
can be different
SERIES CIRCUIT CALCULATIONS
If, for example, two or more lamps (resistances R1 and R2, etc.) are
connected in a circuit as follows, there is only one route that the current
can take. This type of connection is called a series connection. The value
of current I is always the same at any point in a series circuit
What is the total resistance?
6 ohms
How many amps flow through R1?
2 amps
What is the Volt drop across R1?
4 volt
How many volts at the connection between R1 & R2
8 volt
Amp flow is determined by the TOTAL resistance
All amps flow through every resistor (when in series)
As amps flow through a resistor Voltage (pressure) is
used up……(voltage drop)
The sum of the individual voltage drops equal the
source voltage
In the following circuit, assume that resistance R is 2 and voltage V that
is applied to it is 12 V. Then, current I flowing in the circuit can be
determined as follows:
This law can also be used to determine the voltage V that
is needed to permit current I to pass through resistance
R: V = I x R (Voltage= Current x Resistance).
In the following circuit, assume that a voltage V of 12 V is
applied to the circuit and current I of 4 A flows in it.
Then, the resistance value R of the resistance or load can
be determined as follows:
Resistance R0 (a combination of resistances R1 and R2, which are
connected in series in the circuit as illustrated) and current I flowing in
this circuit can be determined as follows:
Parallel Circuit
A parallel circuit is an amperage dividing
circuit
PARALLEL CIRCUIT
•
A parallel circuit has more than
one path for current flow. The
same voltage is applied across
each branch. If the load
resistance in each branch is the
same, the current in each branch
will be the same. If the load
resistance in each branch is
different, the current in each
branch will be different. If one
branch is broken, current will
continue flowing to the other
branches.
PARALLEL CIRCUITS
•
•
•
•
A Parallel Circuit has multiple
paths or branches to ground.
Therefore:
1. In the event of an open in the
circuit in one of the branches,
current will continue to flow
through the remaining.
2. Each branch receives source
voltage.
3. Current flow through each
branch can be different.
4. The resistance of each branch
can be different.
PARALLEL CIRCUIT
In parallel connection, two or more resistances (R1, R2, etc.) are connected in a circuit
as follows, with one end of each resistance connected to the high (positive) side of the
circuit, and one end connected to the low (negative) side. Full battery voltage is
applied to all resistances within a circuit having a parallel connection.
Equal voltage will drop across each resistor in a
parallel circuit
Amperage flow will vary for each resistor
The sum of the amp flow through each resistor will
equal the total amp flow out of the battery
SERIES PARALLEL
CIRCUIT
A series-parallel circuit has some
components in series and others in
parallel. The power source and control
or protection devices are usually in
series; the loads are usually in parallel.
The same current flows in the series
portion, different currents in the
parallel portion. The same voltage is
applied to parallel devices, different
voltages to series devices. If the series
portion is broken, current stops
flowing in the entire circuit. If a
parallel branch is broken, current
continues flowing in the series portion
and the remaining branches.
VOLTAGE DROP
A voltage drop is the amount of
voltage or electrical pressure
that is used or given up as
electrons pass through a
resistance (load). All voltage
will be used up in the circuit.
The sum of the voltage drops
will equal source voltage. A
voltage drop measurement is
done by measuring the voltage
before entering the load and the
voltage as it leaves the load.
The difference between these
two voltage readings is the
voltage drop.
Voltmeter Testing
Available Voltage
Voltage Drop
checks for resistance
must be performed on an operating circuit
VOLTAGE DROP TOTAL
• When more than one load
exists in a circuit, the
voltage divides and will be
shared among the loads.
The sum of the voltage
drops equal source
voltage. The higher the
resistance the higher the
voltage drop. Depending
on the resistance, each
load will have a different
voltage drop.
Component Does Not Work
Verify the problem
Look for the obvious
Check for available voltage
Check for quality ground