ELECTRICAL - CDTA Employee Portalportal1.cdta.org/maintenance/elearning/basic electrical.pdf ·...

CDTA Technical Training Center

ELECTRICAL

ATOMIC STRUCTURE

Protons – positive charge

Electron – negative charge

Neutron - neutral

Electricity is the movement of electrons from atom to atom

ELECTRON FLOW

CONDUCTOR - Materials which have extra electrons that will move freely Gold, silver, copper, lead

INSULATOR - Materials that do not allow for free electron movement Glass, plastic, rubber

SEMI-CONDUCTOR - Material which has some properties of a conductor and some properties of an insulator An example would be a diode

BASIC PROPERTIES OF ELECTRICITY

LIKE CHARGES REPEL

OPPOSITE CHARGES ATTRACT

ELECTRICAL THEORY

ELECTRON THEORY – Electrons flow negative to positive

CONVENTIONAL THEORY – Electrons flow positive to negative

Electron Theory

Conventional Theory

Current Flow Theories

ELECTRICAL MEASUREMENTS

VOLTAGE – Force that causes electron flow

EMF, push, pressure, potential difference

Symbol – E

Unit of measurement – V

Checking – voltmeter ; use leads in parallel with source.

AMPERAGE – Rate of current flow through a conductor.

Intensity, flow, current

Symbol – I

Unit of measurement – A

Checking – ammeter ; use leads in series with circuit (or inductive pick-up)

Note; wire gauge is determined by amperage draw.

RESISTANCE – The opposition to current flow through a conductor. Symbol – R Unit of measurement –

ohms Checking – ohmmeter;

connected in a series loop of an isolated circuit or component. Note – circuit must

contain no voltage when checking resistance

RESISTANCE – The opposition to current flow through a conductor

Infinity – open circuit; no current flow

Low resistance – short; high current flow

High resistance – corrosion; low current flow

LAWS OF ELECTRICITY

VOLTS = AMPS x OHMS (Ohms Law)

ELECTRONS TAKE THE PATH OF LEAST RESISTANCE

ELECTRON FLOW THROUGH A CONDUCTOR WILL CREATE A MAGNETIC FIELD

WATTS = AMPS x VOLTS

Types of Current

Direct current – (DC) electron flow in one direction only

Alternating current – (AC) electron flow changes direction many times per second

CURRENT FLOW

TYPES OF CIRCUITS

Series circuit

Parallel circuit

Series – parallel circuit

CURRENT FLOW

SERIES CIRCUIT

All controls and current consuming devices are connected in a single line.

One path from source through loads to ground.

12 Volt

OHMS LAW

If two values are known in a circuit, the remaining value can be found using ohms law

CURRENT FLOW

SERIES CIRCUIT LAWS

Connecting loads in series

Voltage drops across loads

Amperage remains constant

Resistances are added

Series Circuit

12 Volt

1 OHM 3 OHM

CURRENT FLOW

PARALLEL CIRCUITS

Devices are connected in a parallel line providing several current paths to ground.

12 Volt

CURRENT FLOW

PARALLEL CIRCUIT LAWS

Loads connected in parallel

Voltage remains constant

Amperages are added

Resistance is divided

Parallel Circuit

12 Volt

CURRENT FLOW

SERIES–PARALLEL CIRCUITS

Combination of each type of current path

Rules of each circuit apply

12 Volt

Rheostat

(Variable resistor)

OHM’S LAW VISUALIZEDAmperage and Resistance

Resistance

Voltage

Constant

Current Flow

OHM’S LAW VISUALIZEDAmperage and Resistance

ResistanceVoltage

Constant

Current Flow

OHM’S LAW VISUALIZEDAmperage and Voltage

Resistance

Constant

Voltage

Current Flow

OHM’S LAW VISUALIZEDAmperage and Voltage

Resistance

Constant

Voltage

Current Flow

CIRCUIT MALFUNCTIONS

OPEN CIRCUIT

SHORT CIRCUIT

GROUNDED CIRCUIT

OPEN CIRCUIT

SHORT CIRCUIT

GROUNDED CIRCUIT

12 Volt

OPEN CIRCUIT

SHORT CIRCUIT

OPEN CIRCUIT

SHORT CIRCUIT

GROUNDED CIRCUIT

12 Volt

Shorted or grounded components can damage circuits due to additional current flow.

To protect circuits, fuses or circuit breakers are used

CIRCUIT PROTECTION

FUSE – A thin metal strip designed to break (open) at a specific current draw.

Once a fuse is blown (opens) it must be replaced

Fuses come in various amperage ratings –USE CORRECT FUSE

FUSE TYPES

FUSE RATING

CIRCUIT PROTECTION

CIRCUIT BREAKER – Uses a heat sensitive bi-metallic strip designed to break contact in an overload condition.

Circuit breakers can be manual reset or auto reset.

When replacing a circuit breaker use correct rating.

WIRE GAUGE RATING

A.W.G. – American Wire Gauge

The higher the number the smaller the diameter of the wire.

Large diameter = less resistance

Smaller diameter = more resistance

10 Gauge 18 Gauge

ELECTRICAL COMPONENTS

BATTERIES

Purpose

Energy for cranking

Supply current when demand exceeds output of charging system

Stabilize voltage/dampen voltage spikes

BATTERIES

SAFETY

While charging, batteries produce hydrogen gas that WILL EXPLODE if exposed to open flame or spark

Acid will burn – Protect eyes, skin, and clothing

BATTERIES Construction

Hard plastic case

Plates; made of lead alloy Positive plate –

lead peroxide

Negative plate –sponge lead

Separator plate -PVC

BATTERIES

Cell Construction

Negative and positive plates alternate; there is one more negative plate to occupy the exposed end of each group.

4D battery has 19 plates per cell.

8D battery has 27 plates per cell.

Each cell is filled with electrolyte

BATTERIES

Construction

Electrolyte; a solution that consists of sulfuric acid in water

64% water + 36% acid = electrolyte

BATTERIES

Each cell will produce approximately 2.2 volts

Six cells connected in series will produce a 12 volt battery (13.2 volts)

BATTERY RATINGS Cold Cranking Amps (CCA) – cranking

current available at 0 degrees 8D battery = 900 CCA

4D battery = 550 CCA

Amp Hours (AH) – Amp hours is determined by placing a specific load on a battery and measuring the time required for it to discharge

BATTERY CHARGING

Restores the active chemicals of the plates and the electrolyte to their original condition, by feeding direct current to the cell.

BATTERY CHARGING

Connecting a charger

Red clamp to positive terminal

Black clamp to negative terminal

NOTE – when disconnecting batteries remove negative cable first; when connecting cables connect negative last.

Battery Tests

Specific gravity

Load test

Specific Gravity

The weight of a substance in relation to that of water

Affected by temperature

For every 10* F above 80* add .004 pts.

For every 10* F below 80* subtract .004 pts.

Measured at each cell with hydrometer

Indicates a cell’s STATE OF CHARGE

BATTERY TESTING

Hydrometer; An instrument that measures the specific gravity of electrolyte

1.280 is full charge at 80* F

.025 difference between cells indicates a defective battery.

Load Test

A carbon pile load is connected to a fully charged battery for 15 seconds and minimum voltage is recorded

The load is equal to 1/2 the CCA rating of the battery

Minimum voltage is affected by temperature

Checks WORK CAPABILITY of the battery

Load Test Minimum Voltages Temp. Min. Volts

70* 9.6

60* 9.5

50* 9.4

40* 9.3

30* 9.1

20* 8.9

10* 8.7

0* 8.5

BATTERY MAINTENANCE

Check battery state of charge (hydrometer)

Clean terminals and battery casing

Check work capability (load test)

Check cables for stiffness

Check battery hold downs

WATTS LAW

Watts law is used to determine power availability and usage

Watts = Amps x Volts

WATTS LAW

Power sources connected in SERIES

Positive to Negative

Voltages are added

Amperage remains the same

12 Volt 12 Volt

400 AMPS 400 AMPS

24 VOLTS / 400 AMPS

24v x 400a = 9600 Watts

= 9600 WATTS

WATTS LAW

Power sources connected in PARALLEL

Positive to positive; negative to negative

Voltage remains the same

Amperages are added

12 Volt 12 Volt

400 AMPS 400 AMPS

12 VOLTS / 800 AMPS

12v x 800a = 9600 Watts

= 9600 WATTS

WATTS LAW

12 Volt 12 Volt

400 AMPS 400 AMPS

24 VOLTS / 400 AMPS

24v x 400a = 9600 Watts

= 9600 WATTS

12 Volt 12 Volt

400 AMPS 400 AMPS

12 VOLTS / 800 AMPS

12v x 800a = 9600 Watts

= 9600 WATTS

RELAYS

Another name for a relay is a magnetic switch

Relays are 12 or 24 volts

Relays normally have 5 posts and are 85,86,87,87a and 30.

85 and 86 is power and ground, 87 and 87a is the switch, 30 is power

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

RELAY OPERATION

12 Volt

Relays are 12 or 24 volt

Determined by voltage placed on coil

12 Volt

24 Volt

12 Volt bulb

12 Volt

24 Volt

12 Volt bulb

CHARGING SYSTEM

ALTERNATOR; Theory & operation

REGULATOR; Theory & operation

CHARGING SYSTEM

CHECKING AND ADJUSTING ALTERNATOR OUTPUT

FULL FIELDING THE ALTERNATOR

ALTERNATOR OUTPUT TEST

Carbon Pile Load

12V Relay

ALTERNATOR

24 Volt12 Volt

REGULATOR

AMMETER

VOLTMETER

Ignition

50 “DN” ALTERNATOR

F2 Terminal

F1 Terminal

12 Volt relay terminal

VOLTAGE REGULATOR

Controls output of alternator by controlling the strength of the field coil

Constantly monitors system voltage & adjusts magnetic field accordingly

Stronger field – Higher output

Weaker field – Lower output

“NOT” CHARGING

24 Volt12 Volt

87a 8785

REGULATOR

Alternator indicator light

12V Relay

ALTERNATOR

Climate Control

CB 100 Circuit

Circuit

lt circ

Neoplan - Off

CHARGING

24 Volt12 Volt

87a 8785

REGULATOR

Alternator indicator light

12V Relay

ALTERNATOR

Climate Control

CB 100 Circuit

Circuit

John Miller

lt circ

Neoplan - Charging

FLOW CHART

ELECTRICAL SYMBOLS

CURRENT FLOW

SERIES CIRCUITS

Connecting sources (batteries) in series

Voltages are added

Amperage remains constant

CURRENT FLOW

PARALLEL CIRCUITS

Connecting sources in parallel

Voltage remains constant

Amperage is added

ELECTRICAL - CDTA Employee Portalportal1.cdta.org/maintenance/elearning/basic electrical.pdf ·...

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