Electrical Circuits

What you need to Know!• 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 - positive- negative, 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 FORMULAWhen 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 = I RVoltage = 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

VOLTAGEVoltage 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 UNITSVoltage is measured in units called VOLTS. Voltage measurements can use different value prefixes such as millivolt, volt, Kilovolt, and Megavolt.

 

VOLTAGE LESS THAN

BASE UNIT BASIC UNIT LARGER THAN

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

MEASUREMENTAn 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 FLOWTwo 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”

RESISTANCEResistance 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 ResistanceWood 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

LOADSThe 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 CIRCUITSA 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 CALCULATIONSIf, 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 CIRCUITSA 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 CIRCUITIn 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