Chapter 3

1. Chapter 3 Electricity Fundamentals

2. OBJECTIVES After studying Chapter 3, the reader will be able to: • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “A” (General Electrical/Electronic System Diagnosis). • Define electricity. • Explain the units of electrical measurement. • Discuss the relationship among volts, amperes, and ohms. • Explain how magnetism is used in automotive applications.

3. Ammeter Ampere Atom Bound electrons Conductors Conventional theory Coulomb Electrical potential Electricity Electrochemistry Electromotive force (EMF) Electron theory Free electrons Insulators Ion Neutral charge Ohmmeter Ohms Peltier effect Photoelectricity Piezoelectricity Positive temperature coefficient (PTC) Potentiometer Resistance Rheostat Semiconductor Static electricity Thermocouple Thermoelectricity Valence ring Volt Voltmeter Watt KEY TERMS

4. INTRODUCTION • The electrical system is one of the most important systems in a vehicle today. • Every year more and more components and systems use electricity. • Those technicians who really know and understand automotive electrical and electronic systems will be in great demand. • Electricity may be difficult for some people to learn for the following reasons. • It cannot be seen. • Only the results of electricity can be seen. • It has to be detected and measured. • The test results have to be interpreted.

5. ELECTRICITYBACKGROUND • Our universe is composed of matter, which is anything that has mass and occupies space. • The smallest particle that an element can be broken into and still retain the properties of that element is known as an atom.

6. ELECTRICITYBACKGROUND • In an atom (left), electrons orbit protons in the nucleus just as planets orbit the sun in our solar system (right).

7. ELECTRICITYDEFINITION • Electricity is the movement of electrons from one atom to another. • The dense center of each atom is called the nucleus. • The nucleus contains: • Protons , which have a positive charge • Neutrons , which are electrically neutral (have no charge)

8. ELECTRICITYPOSITIVE AND NEGATIVE CHARGES • The parts of the atom have different charges. • The orbiting electrons are negatively charged. • The protons (located in the nucleus) are positively charged. • Neutrons (located in the nucleus) have no charge at all.

9. ELECTRICITYPOSITIVE AND NEGATIVE CHARGES • In a normal, or balanced, atom, the number of negative particles equals the number of positive particles. • The number of neutrons varies according to the type of atom.

10. ELECTRICITYMAGNETS AND ELECTRICAL CHARGES • The positive and negative charges within an atom are like the north and south poles of a magnet. • Charges that are alike will repel each other, similar to the poles of a magnet.

11. ELECTRICITYIONS • When an atom is not balanced, it becomes a charged particle called an ion. • Ions try to regain their balance of equal protons and electrons by exchanging electrons with neighboring atoms.

12. ELECTRICITYELECTRON SHELLS • Electrons orbit around the nucleus in definite paths. • These paths form shells, like concentric rings, around the nucleus. • The hydrogen atom is the simplest atom, with only one proton, one neutron, and one electron. More complex elements contain higher numbers of protons, neutrons, and electrons.

13. ELECTRICITYFREE AND BOUND ELECTRONS • The outermost electron shell or ring, called the valence ring, is the most important to our study of electricity. • When the valence ring has five or more electrons in it, it is fairly full. • The electrons are held tightly, and it is hard for a drifting electron to push its way into the valence ring. • These tightly held electrons are called bound electrons. • As the number of electrons increases, they occupy increasing energy levels that are further from the center of the atom.

14. ELECTRICITYFREE AND BOUND ELECTRONS • Electrons in the outer orbit, or shell, can often be drawn away from the atom and become free electrons.

15. ELECTRICITYCONDUCTORS • Conductors are materials with fewer than four electrons in their atom’s outer orbit.

16. ELECTRICITYCONDUCTORS • Copper is an excellent conductor of electricity because it has just one electron in its outer orbit, making it easy to be knocked out of its orbit and flow to other nearby atoms. This causes electron flow, which is the definition of electricity.

17. Is Water a Conductor? • Pure water is an insulator; however, if anything is in the water, such as salt or dirt, then the water becomes conductive. Because it is difficult to keep it from becoming contaminated, water is usually thought of as being capable of conducting electricity, especially high-voltage household 110 or 220 volt outlets.

18. ELECTRICITYINSULATORS • Insulators are materials with more than four electrons in their atom’s outer orbit.

19. ELECTRICITYSEMICONDUCTORS • Materials with exactly four electrons in their outer orbit are neither conductors nor insulators and are called semiconductor materials.

20. HOW ELECTRONS MOVE THROUGH A CONDUCTOR • CURRENT FLOW • Current electricity is the movement of electrons through a conductor. • CONVENTIONAL THEORY VERSUS ELECTRON THEORY • Conventional theory • Electron theory

21. HOW ELECTRONS MOVE THROUGH A CONDUCTOR • Conventional theory states that current flows through a circuit from positive (+) to negative (-). • Automotive electricity uses the conventional theory in all electrical diagrams and schematics.

22. UNITS OF ELECTRICITYAMPERES • The ampere is the unit used throughout the world to measure current flow. • When 6.28 billion billion electrons (the name for this large number of electrons is a coulomb) move past a certain point in 1 second, this represents 1 ampere of current.

23. UNITS OF ELECTRICITYAMPERES • Amperes are measured by an ammeter (not ampmeter). • An ammeter is installed in the path of the electrons similar to a water meter used to measure the flow of water in gallons per minute. The ammeter displays current flow in amperes.

24. UNITS OF ELECTRICITYVOLTS • The volt is the unit of measurement for electrical pressure. • Voltage is also called electrical potential, because if there is voltage present in a conductor, there is a potential (possibility) for current flow • Voltage also known as the electrical pressure that causes the electrons to flow through a conductor.

25. UNITS OF ELECTRICITYVOLTS • This digital multimeter set to read DC volts is being used to test the voltage of a vehicle battery. Most multimeters can also measure resistance (ohms) and current flow (amperes).

26. UNITS OF ELECTRICITYOHMS • Resistance to the flow of current through a conductor is measured in units called ohms. • The resistance to the flow of free electrons through a conductor results from the countless collisions the electrons cause within the atoms of the conductor.

27. UNITS OF ELECTRICITYWATTS • A watt is the electrical unit for power, the capacity to do work. • P (power) =I (amperes) xE (volts) • A display at the Henry Ford Museum in Dearborn, Michigan, that includes a hand-cranked generator and a series of light bulbs. This figure shows a young man attempting to light as many bulbs as possible. The crank gets harder to turn as more bulbs light because it requires more power to produce the necessary watts of electricity.

28. SOURCES OF ELECTRICITYFRICTION • When certain different materials are rubbed together, the friction causes electrons to be transformed from one to the other. • Because the charges are stationary, or static, this type of voltage is called static electricity.

29. SOURCES OF ELECTRICITYHEAT • When pieces of two metals are joined together at both ends and one junction is heated, current passes through the metals. • The current is very small, only millionths of an ampere, but this is enough to use in a temperature-measuring device called a thermocouple. • Electron flow is produced by heating the connection of two different metals.

30. SOURCES OF ELECTRICITYLIGHT • When certain metals are exposed to light, some of the light energy is transferred to the free electrons of the metal. • Electron flow is produced by light striking a light-sensitive material.

31. SOURCES OF ELECTRICITYPRESSURE • When subjected to pressure, certain crystals, such as quartz, develop a potential difference, or voltage, on the crystal faces. • Electron flow is produced by pressure on certain crystals. • Called piezoelectricity. • One example, used as a knock sensor for engine timing. FIGURE 3-23

32. SOURCES OF ELECTRICITYCHEMICAL • Two different materials (usually metals) placed in a conducting and reactive chemical solution create a difference in potential, or voltage, between them. • This principle is called electrochemistry and is the basis of the automotive battery.

33. SOURCES OF ELECTRICITYMAGNETISM • Electricity can be produced if a conductor • is moved through a magnetic field or a moving magnetic field is moved near a conductor. • This is the principle of how many automotive devices work, including: • Starter motor • Alternator • Ignition coils • Solenoids and relays

34. CONDUCTORS AND RESISTANCE • All conductors have some resistance to current flow. Several principles of conductors and their resistance include the following: • If the conductor length is doubled, its resistance doubles. • If the conductor diameter is increased, its resistance is reduced. • As the temperature increases, the resistance of the conductor also increases.. • Materials used in the conductor have an impact on its resistance.

35. CONDUCTORS AND RESISTANCE

36. Why Is Gold Used if Copper Has Lower Resistance? • Copper is used for most automotive electrical components and wiring because it has low resistance and is reasonably priced. Gold is used in airbag connections and sensors because it does not corrode. Gold can be buried for hundreds of years and when dug up it is just as shiny as ever.

37. RESISTORS • FIXED RESISTORS • VARIABLE RESISTORS • A potentiometer is a three-terminal variable resistor where a wiper contact provides a variable voltage output. • Another type of mechanically operated variable resistor is the rheostat. • A rheostat is a two -terminal unit in which all of the current flows through the movable arm.

38. RESISTORS

39. Fixed Resistor Color Chart

40. FIGURE 3-25 A typical carbon resistor. RESISTORS

41. RESISTORS • Two commonly used types • Potentiometers: • 3 wire • are most commonly used as throttle position (TP) sensors on computer-equipped engines. • Rheostat • 2 wire • Heater control, dimming etc.

42. SUMMARY • Electricity is the movement of electrons from one atom to another. • In order for current to flow in a circuit or wire, there must be an excess of electrons at one end and a deficiency of electrons at the other end. • Automotive electricity uses the conventional theory that electricity flows from positive to negative. • The ampere is the measure of the amount of current flow. • Voltage is the unit of electrical pressure. • The ohm is the unit of electrical resistance. • Sources of electricity include friction, heat, light, pressure, and chemical.

43. REVIEW QUESTIONS • What is electricity? • What are the ampere, volt, and ohm? • What are three examples of conductors and three examples of insulators? • What are the four sources of electricity?

44. CHAPTER QUIZ • An electrical conductor is an element with _____ electrons in its outer orbit. • Less than 2 • Less than 4 • Exactly 4 • More than 4

45. CHAPTER QUIZ 2. Like charges _____. • Attract • Repel • Neutralize each other • Add

46. CHAPTER QUIZ 3. Carbon and silicon are examples of _____. • Semiconductors • Insulators • Conductors • Photoelectric materials

47. CHAPTER QUIZ 4. Which unit of electricity does the work in a circuit? • Volt • Ampere • Ohm • Coulomb

48. CHAPTER QUIZ 5. As temperature increases _____. • The resistance of a conductor decreases • The resistance of a conductor increases • The resistance of a conductor remains the same • The voltage of the conductor decreases

49. CHAPTER QUIZ 6. The _____ is a unit of electrical pressure. • Coulomb • Volt • Ampere • Ohm

50. CHAPTER QUIZ 7. Technician A says that a two-wire variable resistor is called a rheostat. Technician B says that a three-wire variable resistor is called a potentiometer. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B