Electrical Fundamentals

What is Electricity? A good technical definition of electricity is: The flow of electrons through a conductor.

ATOM Made up of three parts: Protons–positively charged particles Neutrons–particles with no charge Electrons–negatively charged particles

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

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.

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

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

Semiconductor Semiconductors Have 4 Electrons In The Valence 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

Characteristics of Electricity

Electrical Principles

Electrical Terms Three terms are used in the study of electricity: current voltage resistance

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

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

Resistance Opposition to current flow Measured in ohms () R is the abbreviation for resistance High resistance reduces current Low resistance increases current

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.

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.

Ohm’s Law

One volt can push one amp of current through one ohm of resistance Ohm’s Law One volt can push one amp of current through one ohm of resistance

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

Ohm’s Law Here are four very important electrical facts to learn form ohm’s law Assuming that resistance stays the same: If voltage increases, current increases If voltage decreases, current decreases Assuming that voltage stays the same: If resistance increases, current decreases If resistance decreases, current increases Notice that current is determined by voltage and resistance. Current cannot change on its own

Work Sheet #1

The Complete Electrical Circuit

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

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

Load Device A load device is anything that is powered by, or consumes electricity. Such as the following: 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

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.

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

Series & Parallel Circuits

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

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

Calculating Resistance in a Two Branch Parallel Circuit If there are only two branches, use the following formula Rt= R1 x R2 R1 + R2

Work Sheet #2

Work Sheet #3

Introduction To Digital Multimeters

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

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

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

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

Milli (m) 0.015 Amperes 15 Milliamperes 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

Connecting Black Lead The black lead is called the “common” lead. You plug the black lead into the input terminal that says COM

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

Work Sheet #4

Voltmeter A voltmeter is used to measure voltage potential… Always place in parallel with device Never place in series with device Units: Volts (V) and Millivolts (mV)

Voltmeters Always Remember A voltmeter always measures the differences in electrical potential (or electrical “pressure”) between two points

Voltage Drop

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

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

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

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)

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)

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

Work Sheet #5

Work Sheet #6

Electrical and Magnetic Components

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

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)

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

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

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

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

Work Sheet #7

Circuit Faults

Types of Circuit Faults There are three basic types of faults: High Resistance Low Resistance Component Failure

Common Circuit Faults

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

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

Low Resistance Faults Short 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

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.

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

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