© goodheart-willcox co., inc. electrical fundamentals

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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 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

A Good Conductor Has Less Than 4 Electrons In The Valence

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Insulators 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

A Good Insulator Has More Than 4 Electrons In the valence

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Semiconductor

Substance capable of acting as both a conductor and an insulator

Semiconductors Have 4 Electrons In The Valence

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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 greatersmaller 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 increasesoIf voltage decreases, current decreases

Assuming that voltage stays the same:oIf resistance increases, current decreasesoIf 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 sourcebattery, alternator, or

generator Load

electrical device that uses electricity

Conductorswires 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 Lights o Radioo Motors (starter, door locks, windows, etc.)o Fuel Injectors

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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 CircuitRules 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 CircuitRules for a Parallel CircuitThe 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. Ohmsor you can move the decimal over to left six places:

1.000000with 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 AmperesOr 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 place in parallel with deviceNever place in series with deviceUnits: Volts (V) and Millivolts (mV)

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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 deviceNever – test while power is applied to circuitUnits – Ohms (Ω) 1.0

Kilo-ohms (KΩ) 1,000Megaohms (MΩ) 1,000,000

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Measuring ResistanceKeep 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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Electricaland

MagneticComponents

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Magnet BasicsA magnet is any object that attracts iron

and steel and certain other materialsThree basic types of magnets are:

NaturalMan-made or permanent magnetsElectromagnets

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 magnetismA 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 electricityThe 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.)

Control circuit current flow creates a magnetic field that

pulls the points closed

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SolenoidA solenoid, like a relay

produce motionHowever, 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 FaultsOpen 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 FaultsDirty Switch or Relay ContactsLoose 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 FaultsShort Circuit Normal current path is by-

passed 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