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Title: Modern Refrigeration and


1
Modern Refrigeration and Air Conditioning
Althouse Turnquist Bracciano
PowerPoint Presentation by Associated Technical
Authors
PublisherThe Goodheart-Willcox Company,
Inc.Tinley Park, Illinois
2
Chapter 6
Electrical Magnetic Fundamentals
3
Modules
  • Electrical Fundamentals
  • Applied Electronics and Electricity

4
Learning Objectives
  • Define the terms electricity and electronics.
  • Distinguish between types of electricitystatic
    and current.
  • Explain the difference between direct and
    alternating current.
  • Define electrical and electronic terms.
  • Describe the difference between parallel circuits
    and series circuits.
  • Discuss the basic theory of electric motors and
    related devices.

5
Learning Objectives
  • Use various electrical formulas to solve
    problems.
  • Explain the use of computers in refrigeration
    controls.
  • Explain the components of an electrical circuit.
  • Identify and use the proper electrical symbols.
  • Follow approved safety procedures.

6
Generating Electricity
6.1
  • Electricity is most commonly generated by
    electromechanical equipment (generator).
  • Electricity may be generated chemically (dry cell
    batteries). An automobile battery does not
    generate electricity it stores it.
  • Other forms of energy are heat, friction,
    mechanical, light, chemistry, and magnetism.
  • Any method that produces a movement of free
    electrons creates an electrical potential.

7
Types of Electricity
6.2
  • The two common types of electricity are
  • Static electricity.
  • Current electricity.

8
Types of Electricity
6.2
  • Static Electricity
  • Electricity at rest.
  • Produced by friction.
  • Lightning is a discharge of static electricity.

9
Types of Electricity
6.2
  • Current Electricity
  • Electricity that is flowing through a circuit.
  • Produced by coiled wires moving in an
    electromagnetic field.
  • Supplied to homes and industry through a fuse or
    breaker panel.
  • Electricity supplied to most homes use 240V AC
    for electric stoves, water heaters, and air
    conditioners 120V AC is used for lighting and
    appliance circuits.

10
Types of Electricity
6.2
11
Electrostatic Electricity
6.2.1
  • There are two types of electrical charges one is
    a positive charge, the other is a negative
    charge.
  • Like charges repel. Two positive or two negative
    charges repel each other.
  • Unlike charges attract. One positive and one
    negative charge will attract each other.

12
Electrostatic Electricity continued
6.2.1
  • An example of electrostatic generation occurs
    when a person walks across a carpet. This charges
    the entire body with static electricity.
  • When the person touches an object such as a
    doorknob, this will dissipate the charge.
  • Capacitors that are used with some motors also
    store an electrical charge. The storage capacity,
    called capacitance, is measured in farads. The
    higher the farad rating, the greater the storage
    capacity.

13
Current Electricity
6.2.1 6.2.2
  • The movement of electrons along an electrical
    conductor.
  • There are two types of current electricity
    direct current (DC) and alternating current (AC).
  • Direct current is the continuous flow of
    electrons in one direction.
  • DC is used on cordless electric appliances, such
    as drills. Other uses for DC include electronics,
    elevator service, electric welding, and
    automobiles
  • Batteries are a main source of DC.

14
Current Electricity continued
6.2.1 6.2.2
  • Alternating current is the flow of electrons
    along a conductor, first in one direction, then
    in the other.
  • Alternating current in many countries is 60 Hz
    this means that it makes 60 complete cycles in
    one second.

15
Current Electricity
6.2.1 6.2.2
One complete cycle of AC.
16
Current Electricity continued
6.2.1 6.2.2
  • Many voltmeters, ammeters, and wattmeters measure
    an AC circuit by indicating the rms (root mean
    square) value.
  • Rms value is an average that is equal to the
    maximum value times the constant 0.707.
  • Example
  • Vrms Vmax X Constant
  • 120 V V 170 V X 0.707

17
Pulse Wave and Digital Control Signals
6.2.2
  • Computer or digital control applications use an
    alternating current known as pulse wave
    electronics.
  • Control is obtained by the spacing of the pulses
    and the width of the pulses.
  • Most control systems using computers have 5-volt
    pulses.
  • If used in motor control, the voltage is
    amplified.

18
Pulse Wave andDigital Control Signals
6.2.2
19
Circuit Fundamentals
6.3
  • Electrical circuits are much like water systems.
  • Like water pipes, wires must be large enough to
    carry current.
  • When pipes carry water, there is always a
    pressure drop there is always a voltage drop
    when electricity flows along a wire.

20
Circuit Fundamentals
6.3
When both valves are open, water flowsand
pressure drops through the system.
21
Circuit Fundamentals continued
6.3
  • Voltmeters are used to measure voltage drop
    throughout system once switches are closed and
    circuit is complete.
  • If a line is large enough to carry the current
    flow, voltage drop will be very small, as low as
    .001 V to .0001 V.
  • If the line is too small, voltage will be
    greater. An undersized wire will become warmer
    than usual.

22
Circuit Fundamentals
6.3
23
Circuits and Circuit Symbols
6.3.1
  • An electrical circuit is a complete path for
    electrons to follow.
  • A circuit consists of a power source, a circuit
    control, a load, and conductors.

24
Circuits and Circuit Symbols continued
6.3.1
  • The battery is the power source, the switch is
    the circuit control, the lamp is the load and the
    wire is the conductor.
  • When circuit is connected and switch is closed,
    there is a continuous path for electrons to flow.
  • Electrons leave the power source, flow through
    the switch and conductors, through the lamp, and
    return to the power source.

25
Circuits and Circuit Symbols continued
6.3.1
  • When the switch is opened, current ceases to flow
    since there is a break in the path.

26
Circuits and Circuit Symbols continued
6.3.1
  • A short circuit is a circuit in which electrons
    have taken a shortcut back to their power source.
  • In this example, the conductor placed across the
    load gives electrons a lower resistive path.
    Current will always take the path of least
    resistance.
  • In a short circuit, current flows around the load
    causing amperage to increase within the wire due
    to decreased resistance.

27
Circuits and Circuit Symbols continued
6.3.1
  • A circuit that has a grounded condition occurs
    when a conductor touches the metal structure of a
    device.
  • Example
  • A bare conductor that touches the metal frame
    of a lamp.

28
Circuits and Circuit Symbols continued
6.3.1
  • Electrical wiring diagrams use symbols for their
    electrical components.

29
Circuits and Circuit Symbols
6.3.1
30
Electromotive Force (EMF)
6.3.2
  • Electromotive force, or EMF, is used to indicate
    electrical pressure or voltage that causes
    current to flow.
  • The volt is a unit of electrical pressure,
    similar to pressure used to make gases and
    liquids flow through pipes.
  • One volt is the force required to push one amp
    through one ohm of resistance.
  • Abbreviation for volt (EMF) is E.

31
Voltmeter
6.3.2
  • Voltmeters measure the electromotive force of a
    power source.
  • There are DC voltmeters that measure DC voltage
    and AC voltmeters that measure AC voltage.
  • One kilovolt (kV) is 1,000 volts.
  • One millivolt (mv) is 1/1000 (.001) of a volt.
  • One microvolt (mV) is 1/1,000,000 (.000001) of a
    volt.
  • Six types of voltmeters are used five of which
    are electromechanical and one is digital.

32
Voltmeter continued
6.3.2
  • Permanent-magnet, moving-coil type.

33
Voltmeter continued
6.3.2
  • Electrodynamic type using a dynamotor movement.

34
Voltmeter continued
6.3.2
  • Moving vane (iron) type.

35
Voltmeter continued
6.3.2
  • Moving magnet (polarized iron or iron vane) type.

36
Voltmeter continued
6.3.2
  • Moving plate (electrostatic) type.

37
Voltmeter continued
6.3.2
  • Digital type (uses electronic circuitry instead
    of electromagnetic effects).

38
Voltmeter continued
6.3.2
  • Advantages of digital meters include
  • No moving mechanical parts.
  • Easy readability.
  • Smaller size.

39
Voltmeter continued
6.3.2
  • Digital meters use solid-state semiconductors and
    can withstand shock and vibration.
  • Digital meters have a numeric (number) display
    instead of a pointer. Some designs offer
    auto-ranging, which automatically selects the
    voltage range and the proper scale.
  • Voltmeters are always connected in parallel with
    the circuit.

40
Voltmeter continued
6.3.2
41
Coulomb
6.3.3
  • A coulomb is a count of the number of electrons
    passing a given point on a conductor in one
    second.
  • The number of electrons in a coulomb is 6.24 X
    1018 or 6,240,000,000,000,000,000.
  • One coulomb per second equals one amp. This is
    the measurement of rate, or how fast the current
    is flowing.

42
Ampere
6.3.4
  • Measures rate of current flow.
  • The ampere has a one-to-one relationship with the
    coulomb. Ten amperes flowing past a point in one
    second is the same as 10 coulombs.
  • Current is measured with an ammeter.

43
Ammeter
6.3.4
  • Instrument that measures the rate of current flow
    in amperes.
  • There are two types of ammeters
  • the DC ammeter
  • the AC ammeter.
  • In refrigeration and air conditioning, the AC
    ammeter is most commonly used.

44
Ammeter continued
6.3.4
  • Operation of an ammeter depends on magnetic field
    that surrounds a conductor when current is
    flowing through it.
  • An ammeter must always be connected in series
    with the load being tested.
  • When using a clamp-on type ammeter, clamp it
    around one wire of the circuit being tested.

45
Ammeter
6.3.4
46
Ammeter continued
6.3.4
  • Current that flows through the wire creates a
    magnetic field around the wire. This field
    induces a current flow in the jaws of the ammeter
    and gives a meter reading.
  • Another type of ammeter is the inline type. When
    this meter is used, it must be placed in the
    circuit in series with the load being tested.

47
Ammeter continued
6.3.4
Inline ammeters (A, B, and C) and a clamp-on
ammeter (D) are connected in this electrical
circuit.
48
Ammeter continued
6.3.4
  • Caution An inline ammeter should always be
    connected in series with the circuit. If
    accidentally connected in parallel, it will burn
    up.

49
Watts
6.3.5
  • When amperes flow (coulombs per second) at a
    certain pressure (EMF), this is known as power.
  • Power is the time rate of doing work.
  • Electrical power is measured in watts (W), and in
    kilowatts (kW).
  • When calculating horsepower, there are 746 W in 1
    HP.
  • In DC circuits, wattage can be calculated by
    using the formula
  • E X I W

50
Wattmeter
6.3.5
  • Instrument used to measure the wattage consumed
    by an electrical device.
  • Connected in series with the circuit being
    tested.
  • Indicates the true wattage in the circuit.
  • Automatically adjusts for the power factor.

51
Wattmeter
6.3.5
52
Power Factor
6.3.6
  • Represents that fraction of the total possible
    power that can be generated in a circuit.
  • To calculate the wattage in an AC circuit that
    has the voltage and current out-of-phase with
    each other, use the formula
  • E X I X PF watts
  • When circuits have voltage and current in phase,
    the power factor is 100 therefore, the
    calculation (E X I W) will work.

53
Power Factor continued
6.3.6
  • If a wattmeter is connected to a circuit with the
    voltage and the current in phase, and the voltage
    is 120V with 10A, the meter will read 1200W.
  • E X I W
  • 120 X 10 1200

54
Power Factor continued
6.3.6
  • If a wattmeter is connected to a circuit with the
    current lagging behind the voltage by one-eighth
    cycle, the meter will read 1000W.
  • To calculate the wattage, multiply the voltage
    reading by the ammeter reading and then multiply
    that answer by .83 (PF).
  • 120 x 10 x .83 996 (1000 nominal)

55
ResistanceResistors
6.3.7
  • Conductors of electricity are made from metals
    such as silver, copper, and aluminum.
  • Some materials such as iron, steel, and carbon
    will conduct electricity,but have a higher
    resistance than silver, copper, or aluminum.
  • Extremely poor conductors are called resistors or
    resistances.
  • Materials known as resistors have few or no free
    electrons in their atoms.

56
ResistanceResistors continued
6.3.7
  • The harder it is for free electrons to move, the
    greater the heat generated in the conductor.
  • Impedance is the total electrical resistance in
    an AC circuit.
  • The resistance of an electrical conductor
    increases as its length and its temperature
    increase. The resistance also increases as a
    conductors diameter decreases.
  • Resistors are electrical components designed to
    provide a specific level of resistance in a
    circuit.

57
Ohms
6.3.8
  • Electrical resistance is measured in ohms.
  • An ohm is the amount of resistance that allows 1
    volt to push 1 amp through an electrical circuit.
  • The symbol for ohm is the Greek letter omega (W).
  • The resistance in a conductor depends on
  • Material used.
  • Diameter of conductor.
  • Length of conductor.
  • Temperature of conductor.

58
Ohmmeter
6.3.8
  • An ohmmeter is used to measure an electrical
    circuit for resistance, opens, shorts, and
    grounds.
  • Power must always be disconnected from the
    circuit being tested.

59
Ohmmeter
6.3.8
Correct method for using an ohmmeter.
60
Ohms Law
6.3.9
  • Ohm's law is the relationship between the volt,
    the ampere, and the ohm.
  • Formula for Ohms law
  • E Electromotive force in volts.I Intensity
    of current in amperes.R Resistance in ohms.
  • E I X R
  • or
  • E IR and therefore,
  • I E/R or R E/I

61
Ohms Law
6.3.9
62
Ohms Law continued
6.3.9
  • If resistance stays constant, the current will
    only increase if there is an increase in voltage.
  • If the voltage stays constant and the resistance
    becomes low, the current will increase.
  • Formula
  • E IR R
  • Example
  • A 240W lamp draws 2A at 120V. What is its
    resistance?
  • Solution R
  • R
  • R 60 ohm

E
I
E
I
120V
2A
63
Ohms Law continued
6.3.9
  • If resistance stays constant, the current will
    only increase if there is an increase of voltage.
  • If the voltage stays constant and the resistance
    becomes low, the current will increase.
  • Formula
  • E IR R

E
I
  • Example
  • A 240W lamp draws 2A at 120V. What is its
    resistance?
  • Solution R
  • R
  • R 60 ohm

E
I
120V
2A
64
Questions
repel
attract
  • Like charges ________ and unlike charges ________.
  • Name two types of electrical currents.

Direct (DC) and alternating (AC).
  • Name the components of a simple circuit.

Power source, control (switch), load, and
conductors (wire).
  • What happens to the current in a short circuit?

The current increases.
65
Questions continued
  • What is another name for electromotive force
    (EMF)?

Voltage.
  • What is the single-letter abbreviation for
    electromotive force (voltage)?

E
  • What instrument measures the EMF of an electrical
    circuit?

A voltmeter.
  • A voltmeter must always be placed in _________
    with the circuit being tested.

parallel
66
Questions continued
  • How many electrons are in one coulomb?

6.24 X 1018
  • One coulomb per second equals one

Ampere.
  • Which electrical meter measures current?

Ammeter.
  • A clamp-on type ammeter must be clamped around
    ________ wire(s) to obtain a proper reading.

one
  • Name a type of ammeter other than the clamp-on
    type.

An inline ammeter.
67
Questions continued
  • What is the definition for power?

The time rate of doing work.
  • Electrical power is measured in

Watts.
  • The symbol for the watt is

W or P.
  • State the formula for determining wattage.

E X I W
  • Name three common conductors used in electrical
    circuits.

Silver, copper, and aluminum.
68
Questions continued
Ohms.
  • Electrical resistance is measured in
  • The symbol for ohm is

The Greek letter omega (W).
  • Ohmmeters are used to measure an electrical
    circuit for

Measurable resistance, open circuits, short
circuits, and grounded circuits.
69
Questions continued
  • Name two important rules when using an ohmmeter
    in an electrical circuit.

1) Power must always be disconnected from the
circuit being tested. 2) The component being
tested must be isolated from the circuit.
  • State Ohms law.

E I X R
70
Series Circuit
6.3.10
  • A circuit that has only one path for current to
    flow.
  • All resistances are added together to determine
    total resistance.
  • Total voltage equals the sum of the voltages
    across each of the resistances.
  • Current is the same throughout a series circuit.
  • An open switch, load, or conductor anywhere in
    the circuit will stop current flow through the
    circuit.

71
Series Circuit
6.3.10
A series circuit.
72
Parallel Circuit
6.3.11
  • A circuit that has two or more paths for current
    to flow.
  • Sum of the current flowing through each
    individual path equals the total input current.
  • Voltage is the same across each load in parallel.
  • Total resistance in a parallel circuit will
    always be lower than the lowest resistance in its
    circuit.

73
Parallel Circuit
6.3.11
A parallel circuit.
74
Series-Parallel Circuit
6.3.12
  • Series-parallel circuits are a combination of a
    series circuit and a parallel circuit connected
    together.
  • Most commonly in the HVAC/R field, electrical
    controls are connected in series with loads that
    are wired in parallel with each other.

Series-parallel circuit.
75
Voltage Drop (IR)
6.3.13
  • The sum of the voltage drop in an electrical
    circuit always equals the applied voltage.
  • The voltage drop across any part of a circuit is
    equal to I X R.

76
Voltage Drop (IR) continued
6.3.13
Voltage drop in a typical refrigeration circuit.
77
Voltage Drop (IR) continued
6.3.13
  • To determine the voltage drop, use the formula E
    IR.
  • Equivalent resistance of circuit wiring is 0.5W.
  • 5 X .5 2.5
  • Equivalent resistance of thermostat is 0.5W.
  • 5 X .5 2.5
  • Equivalent resistance of start relay is 1.0W.
  • 5 X 1 5.0
  • Equivalent resistance of compressor motor is
    22.0W.
  • 5 X 22 110.0
  • The total voltage drop is
  • 2.5 2.5 5.0 110.0 120V

78
Power Loss (I2R)
6.3.14
  • Power loss in a circuit due to resistance is
    equal to the square of the current multiplied by
    the resistance.
  • I2R loss I2 X R Power Loss

79
Power Loss (I2R) continued
6.3.14
  • Power applied to 120V.
  • Total current in the circuit is 5A, the total
    resistance is 24W.
  • 52 25
  • 25 X 24 600W power loss
  • Power applied is equal to E X I.
  • 120V X 5A 600 W
  • Power loss results in the generation of heat.
  • One watt 3.4144 Btu/hr. 860 calories/hr. (1
    Btu 252 calories 0.252kg-calories.

80
Instrument Connectingand Handling
6.3.15
  • Basic electrical instruments are used to measure
    volts, amperes, or ohms.
  • Voltmeter has a high internal resistance.
  • Ammeter is designed to bypass (shunt around) most
    of the current outside the instrument.
  • Ohmmeter allows only a few electrons in the
    circuit.
  • Because instruments are delicate, they should not
    be dropped.
  • Voltmeters are connected in parallel with the
    circuit.

81
Instrument Connectingand Handling continued
6.3.15
  • Ammeters are placed in series with the circuit
    being tested.
  • Ohmmeters are connected in parallel with the
    component being tested with no voltage applied to
    the circuit.
  • CAUTION A 120V voltmeter must not be used to
    measure a 240V circuit this will ruin the meter.

82
Shunt
6.3.16
  • Secondary circuit that is usually placed in
    parallel with an ammeter to prevent all
    electrical current from flowing through the
    instrument.
  • Shunts are usually built into the ammeter.

83
Shunt
6.3.16
84
Shunt continued
6.3.16
  • Several shunts are used in ammeters that have
    many different ranges.

85
Electrical Materials
6.4
  • ConductorsSilver, copper, and aluminum.
  • SemiconductorsMetal oxides or compounds.
  • Nonconductors or insulatorsGlass, wood, paper,
    and mica.

86
Conductors
6.4.1
  • Have free electrons.
  • Any EMF moves electrons through the material.
  • Electron movement is from negative to positive.
  • Best conductors are gold and silver.
  • Conductivity is expressed in ohms per circular
    mil foot at a standard temperature.
  • 1 mil cross-sectional area has a diameter of
    0.001".
  • Standard temperature used for measuring
    conductivity is 69F (20C).

87
Conductors
6.4.1
88
Semiconductors
6.4.2
  • Semiconductors are located between a conductor
    and an insulator.
  • Ordinarily, semiconductors are insulators, but,
    under certain conditions, the material is made to
    conduct electricity.
  • Semiconductors make up electronic devices such as
    transistors, diodes, and photocells.
  • Silicon controlled rectifiers (SCRs) are
    semi-conductive switches.
  • Semiconductors can be controlled by various
    signals such as electrical, light, pressure, and
    temperature.

89
Nonconductors (Insulators)
6.4.3
  • Nonconductors or insulators resist electron flow.
  • They have no free electrons.
  • Common nonconductors (insulators) are quartz,
    ceramic, mica, glass, rubber, wood, paper, and
    plastics.
  • Resistance ranges of nonconductors are between
    109 and 1018 ohms.

90
Insulation Testers
6.4.4
  • A meter used to detect leaks or failures along
    nonconductors or insulators.
  • Can be used in two ways
  • Applied to a live circuit.
  • Where power is disconnected.

91
Magnetism
6.5
  • The operation of a compass depends on the earths
    magnetic field.

92
Magnetism continued
6.5
  • All magnets have north and south poles.

93
Magnetism continued
6.5
  • Unlike poles attract and like poles repel.
  • Lines of force (flux) connect the north and south
    poles.
  • Lines of force will flow through any substance.
  • Soft iron is used around instruments as a shield
    to bend the flux around the shield and prevent
    flux to pass through the instrument.

94
Permanent Magnetism
6.5.1
  • Usually made of hardened steel.
  • Once magnetized, they remain magnetized.
  • Alloys of iron, aluminum, nickel, and cobalt make
    strong permanent magnets.
  • Used in some electrical controls to produce snap
    action.
  • Used in some motors where either the stator or
    rotor are permanent magnets (DC, servo motors).

95
Induced Magnetism
6.5.2
  • Magnetism that produces magnetism in metals
    nearby is known as induced magnetism.
  • Any material capable of being magnetized becomes
    a magnet if placed in a magnetic field.

96
Electromagnetism
6.5.3
  • When current passes through a conductor, a
    magnetic field is set up around the conductor.

97
Electromagnetism continued
6.5.3
  • When the conductor is wound around a soft iron
    core, the iron becomes a magnet. This is known as
    electromagnetism.

98
Electromagnetism continued
6.5.3
  • When current flow stops in an electromagnet, the
    magnet is de-magnetized.
  • The magnetic field that is set up around current
    carrying conductor is shown.

99
Electromagnetism continued
6.5.3
  • The left hand rule The thumb shows direction of
    current, the fingers show the direction of
    magnetic flux.
  • The strength of an electromagnet increases with
    more turns of wire and with an increase of
    current.
  • Ampere-turns is a measurement of the strength of
    an electromagnet. The more turns or amps, the
    stronger the electromagnet.

100
Electromagnetism
6.5.3
The flow of magnetic flux in the rotor and stator
of a motor.
101
Polarity of Electromagnets
6.5.3
  • Polarity is determined by the direction of flow
    in an electromagnet.
  • The left hand rule also applies to the polarity
    of an electromagnet.

102
Electromagnetic Induction
6.5.3
  • Electromagnetic induction is the principle for
    induction motors.

103
Electromagnetic Induction continued
6.5.3
  • In order to create magnetic induction, one or a
    combination of the following must occur
  • The magnetic field must be changing.
  • The magnet must be moving.
  • The wires must be moving.

104
Magnetic Field Strength
6.5.4
  • Depends on the density of the flux lines.
  • The flux lines are less dense further away from
    the magnet.
  • If magnets are 1/2" apart and have a pull of 20
    lbs. when they are 1" apart, they will have a
    pull of 5 lbs. (If the distance is doubled, the
    strength decreases four times).
  • Measured in units of Gauss.

105
Solenoid
6.5.5
  • A coil wound around a nonmagnetic substance will
    become a magnet once current flows through it.

106
Solenoid continued
6.5.5
  • Magnetism increases if an iron core is placed in
    its center.

107
Solenoid continued
6.5.5
  • The soft iron core will always try and center
    itself in an electromagnet.

108
Solenoid continued
6.5.5
  • Solenoids are coils of wire with movable soft
    iron cores. When current is applied, the solenoid
    will open or close valves or switches.
  • Can be used in AC or DC circuits.

109
Permeability - Reluctance
6.5.6
  • Soft iron materials are better conductors of
    magnetic flux than other substances.
  • If a substance can be magnetized easily, it is
    known to have a high magnetic permeability.
  • Air has a permeability value of 1.
  • Reluctance is the resistance of magnetic flux
    lines.

110
Permeability - Reluctance
6.5.6
111
Capacitance - Capacitors
6.5.7
  • Capacitance is a system of conductors and
    insulators that permits the storage of electrons.
  • The letter C indicates its ability.
  • The unit of capacitance is the farad.
  • The symbol for the farad is F.
  • The farad is a charge of one coulomb on the
    capacitor with a potential difference of one volt
    between plates.
  • Most capacitors are rated in microfarads (µF) or
    one-millionth of a farad (.000001).

112
Capacitance - Capacitors
6.5.7
113
Capacitance - Capacitors continued
6.5.7
  • Classified by their insulating material
    (dielectric)air, mica, paper, oil-filled,
    ceramic, and electrolytic.

114
Capacitance - Capacitors continued
6.5.7
  • The capacity value of capacitors in series may be
    expressed by the formula

Cn net capacitance (effective value) C1
capacity of capacitor No. 1 C2 capacity of
capacitor No. 2
  • The capacity of capacitors in parallel may be
    expressed by the formula

Cn C1 C2
115
Capacitance - Capacitors continued
6.5.7
  • Before handling capacitors, discharge with a
    20,000 ohm, 2 watt resistor.
  • Safety Never handle a charged capacitor this
    could cause electrocution or severe burns.

116
Reactance
6.5.8
  • The opposition to flow in an AC circuit.
  • Two types, capacitive and inductive.
  • Capacitive reactance is the opposition to current
    flow as a result of capacitance.
  • Inductive reactance is caused by the generation
    of counter EMF, usually produced in a coil or
    electromagnet.

117
Electrical Generator
6.5.9
  • As a conductor moves through a magnetic field, an
    electrical potential will generate in the
    conductor.

118
Electrical Generator continued
6.5.9
  • As the loop is parallel with the flux lines, no
    EMF is produced, as in the figure.

119
Electrical Generator continued
6.5.9
  • As the loop cuts across the magnetic flux lines,
    an EMF will be produced in both sides of the
    loop.
  • An electrical generator uses a revolving
    conductor (armature). These wires cut in one
    direction of magnetic flux lines at one moment
    and in the other direction in the next. This is
    how an electrical current is produced.
  • Lenzs law states The magnetic effect
    surrounding the conductor in which a current is
    induced opposes the movement by which the current
    is induced.

120
The Elementary Electric Motor
6.5.9
  • Electrical energy is converted to mechanical
    energy in an electrical motor.
  • Electrical energy is converted to magnetism
    first, then magnetism is converted to motion.
  • Like poles repel and unlike poles attract the
    motor operates based on this principle of
    attraction and repulsion.

121
The Elementary Electric Motor
6.5.9
122
The Elementary Electric Motor continued
6.5.9
  • One magnet is placed on a shaft (the rotor) and
    the other magnet is mounted in a fixed position
    (the stator).
  • The magnetism of the stator can be reversed by
    the use of electromagnets.

123
The Elementary Electric Motor
6.5.9
124
The Elementary Electric Motor continued
6.5.9
  • The direction of movement of the rotor depends on
    polarity.

125
The Elementary Electric Motor continued
6.5.9
  • The direction of movement of a current carrying
    conductor may be determined by the left hand rule.

126
The Elementary Electric Motor continued
6.5.9
  • A two pole motor is 3600 RPMs, it turns 60
    revolutions per second.

127
The Elementary Electric Motor continued
6.5.9
  • A four pole motor is 1800 RPMs, it turns 30
    revolutions per second.

128
The Elementary Electric Motor continued
6.5.9
  • The figures 1800 and 3600 are known as the
    synchronous speed. This is the actual speed of
    the rotating magnetic field. The actual rotor
    turns at 1750 and 3450 RPMs.
  • Speed reduction is due to a slight magnetic
    slippage, the rotor cannot keep up with the
    magnetic field of the stator.

129
The Elementary Electric Motor
6.5.9
An open capacitor-start motor.
130
Commutators
6.5.9
  • An EMF will be produced in a conductor as it is
    moved across a magnetic field.
  • Figure shows the action of a generator as it is
    producing alternating current.

131
Commutators continued
6.5.9
  • To produce direct current, a commutator and
    brushes are used in the generator.

132
Commutators continued
6.5.9
  • As the armature revolves, the commutator contacts
    are made so that one brush always carries current
    into the commutator in a negative and positive
    direction.
  • DC generators will always have commutators and
    brushes.

133
Counter EMF
6.5.9
  • Counter EMF is always developed in the rotor bars
    or windings of an operating electric motor.
  • Opposes applied EMF which drives the motor.
  • Counter EMF drops when load increases and speed
    decreases. Applied EMF increases, which will keep
    the motor speed constant.
  • If a motor is slowed considerably, the counter
    EMF reduces causing an increase in supply current
    which causes the motor to overheat.

134
Counter EMF continued
6.5.9
  • If a motor is locked and cannot turn, there will
    be no counter EMF, which will cause a great
    increase of current, which in turn will burn out
    the windings.
  • Counter EMF are also found in coils and
    electromagnets.

135
Inductance
6.5.10
  • When a switch is closed and current is passed
    through the coil of an electromagnet, the entire
    coil is saturated with magnetic lines of flux.
  • The instant current flows through the coil,
    magnetism is not yet built up there is a delay
    of a few hundredths of a second.
  • At this time, current continuous to increase
    until it reaches full value.
  • When the switch is opened and current stops, it
    takes time before the magnetic field collapses.

136
Inductance continued
6.5.10
  • The EMF that is built up in the coil is known as
    counter EMF. This counter EMF counter acts change
    in current flow.
  • The principle of inducing a current flow in a
    coil due to the change in current flow is known
    as inductance.

137
Inductors
6.5.10
  • When magnetism is induced in the rotor of an
    electric motor, its north and south poles are
    opposite of the stator poles.
  • The changing of polarity of field poles in the
    stator causes the rotor to have opposite field
    poles.
  • Since the stator and rotor field poles have the
    opposite polarity, the motor operates on the
    principle of attraction and repulsion.
  • A split phase motor has two windings, a run and a
    start winding.
  • The start winding is smaller in diameter than the
    run winding, but has a greater number of turns.

138
Inductors continued
6.5.10
  • The magnetic inductance of the start winding is
    greater than that of the run winding.
  • The start winding is always behind the run
    winding when building and collapsing a magnetic
    field this is known as self-inductance.
  • Mutual inductance is the flow of current in a
    conductor produced by the magnetic field of
    another conductor.
  • Induction motors use mutual induction.
  • Lenzs law states that the polarity of an induced
    voltage is such that it opposes the motion of
    the flux inducing it.

139
Questions
  • Which type of circuit has only one path for
    current to flow?

A series circuit.
Stays the same.
  • In a series circuit, current always
  • Which type of circuit has two or more paths for
    current to flow?

A parallel circuit.
  • What is known about voltage in a parallel circuit?

Voltage is the same across each load in parallel.
140
Questions
  • All magnets have north and south ____________.

poles.
attract
  • Unlike poles ___________ and like poles
    __________.

repel
  • When current passes through a conductor, a
    ____________ is set up around the conductor.

magnetic field
increases
  • The strength of an electromagnet ____________
    with more turns of wire and with an _________ of
    current.

increase
141
Questions
  • Solenoids are coils of wire with movable soft
    iron cores when current is applied the solenoid
    will open or close __________ and ______________.

valves
switches
  • What is reluctance?

It is the resistance of magnetic flux lines.
microfarads
  • Capacitors are rated in ______________.

142
Questions
  • What is known as the opposition to flow in an AC
    circuit?

Reactance.
  • The two main components of an electric motor are
    the _________ and ___________.

rotor
stator
  • Which motor has the highest speed, a two-pole or
    a four-pole motor?

A two-pole motor.
143
Questions
  • The EMF that is built up in the coil is known as
    _____________.

counter EMF
  • Motors operate based on the principle of
    ____________ and ___________.

repulsion
attraction
144
Electronics
6.6
  • Electrons flow through gasses, vacuums, and
    semiconductors.
  • Vacuum tubes cause electron flow from a heated
    element to another element when there is a
    potential difference between elements.

145
Electronics
6.6
A diagram of a vacuum tube rectifier, commonly
used in older radios.
146
Semiconductor Applications
6.6.1
  • Solid-state electronic devices make up most
    electrical control and computer control systems.
  • Two general types of semiconductors
  • Intrinsic.
  • Extrinsic.
  • Intrinsic semiconductors are made of pure
    substances, like silicon and germanium, or
    combined substances, like lead sulfide useful as
    thermometers/temperature sensors.

147
Semiconductor Applications continued
6.6.1
  • Extrinsic semiconductors are combinations of
    intrinsic semiconductors.
  • Extrinsic semiconductors use small impurities,
    are sensitive to electrical forces, and are the
    basic materials used in electronics.
  • Thermal electrical refrigerators use extrinsic
    semiconductors to produce cooling.

148
Diodes and Diacs
6.6.2
  • A solid-state diode is composed of two materials
    that allow electrons to flow in one direction.

149
Diodes and Diacs continued
6.6.2
  • The diode acts as a check valve.
  • Vacuum tubes can serve as diodes.

150
Diodes and Diacs continued
6.6.2
  • A diac is similar to a diode, but it allows
    electrons to flow in both directions.
  • A diac will not conduct current until a preset
    voltage is exceeded.
  • It operates as two diodes in parallel.

151
Diodes and Diacs continued
6.6.2
  • A diac is used in AC circuits where both halves
    of the sine wave are required.

152
Rectifiers
6.6.3
  • Rectifiers act as electronic valves that allow
    current to flow in one direction.
  • Rectifiers change AC into DC.
  • A simple rectifier uses only one-half of a sine
    wave.
  • Four diodes are needed for a simple rectifier.

153
Rectifiers
6.6.3
154
Silicon ControlledRectifiers, Triacs
6.6.3
  • Among silicon semiconductors are diodes and
    silicon controlled rectifiers (SCRs).
  • SCRs have three connections.

155
Rectifiers
6.6.3
156
Silicon ControlledRectifiers, Triacs continued
6.6.3
  • It conducts current from A to C when voltage at A
    is greater than C and a present voltage has been
    applied at B.
  • SCRs are used in electric motor controls.
  • SCRs are used to convert AC voltage to DC
    voltage.
  • SCRs can also take the place of standard relays.
  • A triac is similar to an SCR however, it can
    conduct current in both directions.

157
Silicon ControlledRectifiers, Triacs continued
6.6.3
158
Silicon ControlledRectifiers, Triacs continued
6.6.3
  • Current is conducted from A to C and C to A when
    a present voltage is applied at B.

159
Inverter
6.6.4
  • An inverter is a device used to change DC to AC.
  • Basic elements of a solid-state inverter are
  • A crystal that oscillates at the frequency of the
    AC power required.
  • A switching circuit using SCRs to switch DC power
    on and off.
  • A simple inverter will produce a square wave
    instead of the sine wave most common to AC power
    supplies. This will reduce the life of most
    motors.
  • Inverters are most commonly found on
    solarelectric energy systems.

160
Inverter
6.6.4
161
Transistors
6.6.5
  • A transistor is a three-layer sandwich of two
    different components that consist of silicon
    semiconductor material.

162
Transistors
6.6.5
How the material is connected.
163
Transistors continued
6.6.5
  • The material is labeled for its properties. P is
    positive (deficiency of electrons) and N is
    negative (surplus of electrons).
  • Three conductors are connected to the transistor
    in the middle and at both ends. They are called
    the collector, emitter, and base.
  • A small electron flow from the base to the
    emitter will control a large electron flow from
    the emitter to the collector (sometimes as much
    as 1000 times greater than the small flow).
  • Transistors act as a relay.

164
Transistors continued
6.6.5
Two types of transistors.
165
Transistors continued
6.6.5
A transistor connected as an amplifier.
166
Transistors continued
6.6.5
A circuit board that utilizes transistors.
167
Sensors
6.6.6
  • A sensor is made from a solid-state semiconductor
    material.
  • Sensors control electron flow as their
    temperatures and pressures change.
  • A typical automotive air conditioning system uses
    three sensors.
  • One for outside (ambient) temperature.
  • One for in-the-car temperature.
  • One for the air discharge duct temperatures.

168
Thermistors
6.6.7
  • A thermistor is a solid-state semiconductor that
    changes its resistance on a change of
    temperature.
  • Resistance changes approximately 3 for every 1ºF
    change (6 for 1ºC).
  • Thermistors are made of lithium chloride or doped
    barium titanate.
  • The thermistor is used in three ways
  • A temperature-operated electric circuit control.
  • To measure temperatures.
  • To stop electric power flow to a motor if the
    windings temperature increases to the danger
    point.

169
Thermistors continued
6.6.5
A typical thermistor circuit.
170
Thermistors continued
6.6.7
  • A special thermistor that changes from a low to a
    high resistance with a temperature change of only
    two degrees can be used as a switch.
  • This thermistor can be used to control a
    crankcase heater or sequence heating elements in
    a heating system.
  • In the cooling system, it can be used on ice
    makers or for motor protection.

171
Amplifiers
6.6.8
  • An amplifier is an electronic device that
    receives a small signal and increases it to a
    larger signal.
  • Often used in control systems. They increase the
    signal from a sensor to a high enough level to
    control another device.
  • Differential amplifiers are used to determine the
    difference between a changing input voltage and a
    constant base voltage.

172
Amplifiers
6.6.8
173
Transducers
6.6.9
  • A transducer is sensitive to changes in intensity
    of some form of energy.
  • A transducer controls one form of energy by a
    signal from another form of energy.
  • Transducers may be operated by pressure,
    temperature, fluid flow, vibration, electrical
    potential, and other means.
  • Transducers can be used to change current flow in
    an electrical circuit by the change of a pressure
    variation in a pneumatic circuit.

174
Transducers continued
6.6.9
The application of a transducer.
175
Thermocouple and Thermoelectric
6.6.10
  • Thermocouples may be used to measure temperatures
    or to operate controls.
  • Thermocouples are made of two dissimilar metals
    that are connected at a junction point. When that
    point is heated, a voltage difference occurs.
  • Thermocouples may be made of metals such as
    copper and iron.
  • Voltage of a thermocouple varies with its
    temperature.

176
Thermocouple and Thermoelectric
6.6.10
  • As thermocouples are connected in series, voltage
    will increase.
  • Thermocouples are used as temperature sensors in
    an electronic circuit, a pilot safety circuit in
    a gas fired furnace, or a thermoelectric
    refrigerator.
  • If current is passed through a thermocouple, its
    junction will either become hot or cold.

177
Thermocouple and Thermoelectric
6.6.10
178
Photoelectricity
6.6.11
  • There are three types of photoelectric devices
  • Photoconductor.
  • Photovoltaic.
  • Photoemissive.

179
Photoelectricity continued
6.6.11
  • Photoconductors are semiconductors that increase
    their conductivity when illuminated.
  • Used in electronic eye devices and with infrared
    cameras.
  • Photovoltaic devices produce electrical energy
    when illuminated.
  • Used in solar cells and light meters in
    photography.
  • Photoemissive devices give off light when
    electrical energy is applied.
  • Used in light-emitting diodes (LEDs),
    fluorescent lights, and lasers.

180
Integrated Circuits
6.6.12
  • Integrated circuit chips incorporate multiple
    transistors and other semiconductor devices.

181
Integrated Circuits continued
6.6.12
  • An integrated circuit chip is usually constructed
    as follows.

1. The proper base material is selected, a form
of semiconductor layers like those of
transistors. 2. A circuit is designed and laid
out on the chip material. 3. The circuit is
burned into the material by lasers or acid. 4.
Input and output locations are identified and
attached to metal connectors on the chip. 5. The
chip is tested and packaged.
182
Integrated Circuits continued
6.6.12
  • A microprocessor is a single component containing
    many circuits using the integrated circuit
    technique.
  • A microprocessor is used in programmable
    thermostats and electronic controls.

183
Printed Circuit Boards
6.6.13
  • A support for electronic circuits.
  • A given circuit board is usually related to a
    specific function.
  • A series of circuit boards can be used as
    building blocks.
  • Used to simplify the servicing of electronic
    systems.
  • A circuit board that has failed can sometimes be
    repaired, but in the HVAC/R field they are most
    commonly discarded.

184
Printed Circuit Boards
6.6.13
185
Computers
6.6.14
  • Have assumed an important role in the HVAC/R
    industry.
  • Computer-supported HVAC/R systems can provide
    diagnostic analysis.

186
Computers continued
6.6.14
  • Provide specific outputs based on inputs.
  • Modern computers have microprocessors that
    provide thinking and response.
  • Microprocessors are combined with input devices,
    such as keyboard and mouse.
  • Microprocessors also have output devices such as
    monitors and LEDs.
  • Computers have on-off characteristics when
    programming, 1s are on and 0s are off.
  • Some of the computer languages that are used for
    programming are Basic, FORTRAN, COBOL, and C.

187
Electrical Power
6.7
  • Measured in watts (W), kilowatts (kW), and
    megawatts (MW).
  • One watt is the energy produced in one amp pushed
    by one volt.
  • MathematicallyPower (W) current (amps) X
    electrical potential (volts).
  • P I X
    V
  • Example
  • The power of an electric motor that draws 20A
    from a 120V power source is P 20 X 120 2400W
    2.4 kW
  • Power loss is I2R or I X V where V I X R.

188
Electrical Power continued
6.7
A simple DC motor circuit.
189
Electrical Power continued
6.7
  • When the switch is at C
  • The fan is on high speed.
  • The power used is the square of the current (IC)
    X motor resistance (RM) or PC IC2RM
  • The current, IC V/RM
  • Then, PC VIC V2/RM

190
Electrical Power continued
6.7
  • When the switch is at B
  • The fan is on low speed.
  • The power used is then
  • PB I2B (R1 RM)
  • The current is IB V/(R1 RM)
  • Then PB VIB
  • PB V2/(R1 RM)
  • When the switch is on low speed, the circuit
    power is lower.

191
Electrical EfficiencyPower Factor
6.7.1
  • If voltage and current vary within a cycle, the
    power has to be calculated differently.
  • The average voltage X the current product must be
    used to calculate power.

192
Electrical EfficiencyPower Factor continued
6.7.1
  • The average voltage is obtained by multiplying
    the voltage maximum (Vmax) by a constant 0.707
    value. (Vmax) X 0.707 voltage average or Vrms
  • The rms current is also Irms Imax X 0.707
  • Voltage and current may vary where maximum
    voltage and current occur at the same time.

193
Electrical EfficiencyPower Factor
6.7.1
194
Electrical EfficiencyPower Factor continued
6.7.1
  • The power will be P Vrms X Irm
  • If voltage and current do not occur at the same
    time (out of phase), the power is multiplied by
    the power factor, PF.
  • P Vrms X Irms X PF
  • An out-of-phase circuit usually contains
    capacitors and inductors.
  • The efficiency of an inductive load will improve
    if a capacitor is connected in its circuit.

195
Electrical EfficiencyPower Factor continued
6.7.1
  • An increase of power factor reduces current flow
    in the windings of an inductor.
  • Its power consumption will be less.
  • Utility companies usually limit the power factor
    to 0.85 in industrial and commercial loads.

196
Grounding
6.7.2
  • Since most soils are fairly good conductors,
    early telephone distribution systems used the
    earth to complete a return circuit.
  • Figure shows the symbol for an electrical ground.

197
Grounding continued
6.7.2
  • If an appliance is installed where there is no
    three-prong receptacle, consult an electrician.
  • Two-prong adapters may be temporarily required.
  • Electrical components, such as compressors,
    condenser fan motors, and electrical controls,
    must be grounded.
  • Safety The standard accepted color code for
    ground wires is green or green with yellow
    stripe. These ground leads are not to be used
    as current-carrying conductors.

198
Grounding continued
6.7.2
  • Safety Grounding components may require
    servicing that makes necessary removing the
    ground wire. It is extremely important that the
    service technician replace any and all grounds
    prior to completing the service call. Under no
    conditions should a ground wire be left off. It
    is potential hazard to the service technician and
    the customer.

199
Grounding continued
6.7.2
Illustrates a three-prong grounding plug and
receptacle.
200
Grounding continued
6.7.2
A properly grounded wall receptacle.
201
Grounding continued
6.7.2
  • A GFCI opens the electrical circuit if the
    connected equipment is defective, misused, or
    under a grounded condition.

202
Single-Phase vs. Three-Phase
6.7.3
A single-phase sine wave.
203
Single-Phase vs. Three-Phase continued
6.7.3
Voltage and current characteristics.
204
Single-Phase vs. Three-Phase continued
6.7.3
  • Three-phase motors are generally more efficient
    than single-phase motors.
  • Three-phase motor sizes begin at 1/2 hp
    single-phase motors are commonly not used above 1
    hp.

205
Power Circuits
6.7.4
  • Electric motors are designed with the power
    supply of the utility company in mind.
  • The motor must match the power supplies EMF
    (volts), cycle (Hertz), and phase.
  • Wires must be sized to handle maximum current to
    the motor.
  • Common voltages may be

110V 115V 120V 208V 220V 230V 240V 277V 48
0V
206
Power Circuits continued
6.7.4
  • The number of cycles per second (Hertz) may be
  • 25 50 60
  • The phase may be
  • Single-phase.
  • Two-phase.
  • Three-phase.
  • Four-phase.

207
Power Circuits continued
6.7.4
  • Some popular power electrical sources are
  • 115V, 60 cycle, single-phase.
  • 120V, 60 cycle, single-phase.
  • 208V, 60 cycle, single-phase.
  • 230V, 60 cycle, single-phase.
  • 240V, 60 cycle, single-phase.
  • 230V, 60 cycle, three-phase.
  • 240V, 60 cycle, three-phase.
  • 480V, 60 cycle, three-phase.
  • Always check power source and electrical
    utilities before installing sizable horsepower
    equipment.

208
Transformer Principles
6.7.5
  • Transformers used by utility company change high
    voltage down to usable voltages such as 240V or
    480V.
  • At generating stations, power supplies are
    usually stepped up to 120,000V.

209
Transformer Principles continued
6.7.5
The basics of a power distribution system.
210
Transformer Principles continued
6.7.5
  • Step-down transformers are located along the
    transmission line.
  • Step-down transformers change 120,000V to
    40,000V.
  • 40,000V is carried to communities, then stepped
    down to 13,200V or 4800V.
  • Electricity is then carried to businesses or
    homes and finally stepped down to 480V, 240V, or
    120V.

211
Transformer and Motor Circuits (Characteristics)
6.7.5
  • The power enters a transformer through the
    primary windings.
  • The power leaves a transformer from the secondary
    windings.
  • The output of a transformer is determined by a
    ratio of the primary and secondary windings.
  • If a primary winding has 100 turns and a
    secondary winding has 10 turns, the turn ratio is
    101.
  • If the primary voltage is 200V, the secondary
    voltage will be 20V.

212
Transformer andMotor Circuits (Characteristics)
6.7.5
213
Transformer andMotor Circuits
(Characteristics) continued
6.7.5
A wiring diagram for an open delta transformer.
214
Transformer and Motor Circuits
(Characteristics) continued
6.7.5
  • 208V is popular where the buildings main load is
    lighting.
  • A serious condition may occur if the voltage drop
    to a motor compressor is greater than 5 the
    windings may burn out.

215
Transformer and Motor Circuits
(Characteristics) continued
6.7.5
A table of changes in a motors characteristics
as the input voltage changes.
216
Transformer and Motor Circuits
(Characteristics) continued
6.7.5
  • A 240V motor works with the same efficiency as
    a120V motor.
  • A 240V and a 120V motor will operate with the
    same kilowatt hours.
  • A 240V motor will operate with smaller
    conductors, since its current will be lower.
  • Motors that are labeled 208-230 will operate
    witheither voltage.

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