CLARK FORKLIFT ET103 Introduction to SCR TECHNICAL TRAINING MANUAL

ET103

Introduction to SCR

TECHNICAL TRAINING Copyrighted Material Intended for CLARK dealers only Do not sell or distribute

Copyrighted Material Intended for CLARK dealers only Do not sell or distribute

Contents About this class..........................................................................................................

About safety................................................................................................................

Glossary of Scientific Terms......................................................................................

Section 1 What is an SCR?..................................................................................

EVl00 Schematic............................................................................................

Section 2 Power Circuit Components..............................................................

Battery...........................................................................................................

OSC Card .......................................................................................................

Silicon Controlled Rectifiers (SCRs).............................................................. #1 Rectifier (#1 REC) .................................................................................... #2 Rectifier (#2 REC) .................................................................................... #5 Rectifier (#5 REC) ....................................................................................

Diode Rectifiers.............................................................................................. #3 Rectifier (#3 REC)..................................................................................... #4 Rectifier (#4 REC).....................................................................................

Transf01mer....................................................................................................

Reactor............................................................................................................

1-C Capacitor.................................................................................................. lX Choke........................................................................................................

Drive Motor Armature...................................................................................

Drive Motor Fields........................................................................................

Fuses...............................................................................................................

Power Fuses...................................................................................................

Other Fuses....................................................................................................

3 4 5 7 8 9 9 9 10 10 10 10 10 11 11 11 11 12 12 12 12 12 13 13

Contactors.................................. .....................................................................

Directional Contactors...................................................................................

1-A Contactors.................................................................................................

Power Steering Motor Contactor...................................................................

Pump Motor Contactor....................................................................................

Wires...............................................................................................................

Large Wires....................................................................................................

Crossed Wires.................................................................................................

Sensor Wires....................................................................................................

Accelerator......................................................................................................

Thermal Protector...........................................................................................

Oscillator Circuit.............................................................................................

Sensor..............................................................................................................

Power Steering Motor....................................................................................

Pump Motor.....................................................................................................

Summary........................................................................................................

Section 3 The SCR Circuit..................................................................................

Turning on the #1 Rectifier...........................................................................

Starting the #1 Rectifier................................................................................

Capacitor Charge.............................................................................................

Shutting Down the #1 REC...........................................................................

13 13 13 14 14 14 14 14 15 15 15 15 15 15 16 16 17 17 17 18 20

Filter...............................................................................................................

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13

Introduction to SCR page l

Flyback Current.............................................................................................

Pulsing and Power.........................................................................................

Plugging..........................................................................................................

Summary.......................................................................................................

Section 4 SCR Troubleshooting........................................................................

Preliminary Cleaning.....................................................................................

Materials Needed............................................................................................

Procedures......................................................................................................

Summary........................................................................................................

Step 1 Getting the Facts...........................................................................................

Materials Needed...........................................................................................

Procedures......................................................................................................

Summary........................................................................................................

Step 2 Performing Basic Checks..............................................................................

Materials Needed...........................................................................................

Checking the Battery.....................................................................................

Visually Inspecting the Wires and Cables....................................................

Checking for Grounds....................................................................................

Checking for Shorts........................................................................................

Summary..........................................................................................................

Step 3 Operating the Truck......................................................................................

Procedures......................................................................................................

Summary..........................................................................................................

Step 4 Locating the Problem....................................................................................

Materials Needed...........................................................................................

Finding the Right Publications......................................................................

Finding the Problem Circuits in the Schematic Diagram...........................

Finding the Right Chart in the Troubleshooting Guide..............................

Finding Information in the Sequence of Operation Manual........................

Summary.........................................................................................................

Step 5 Solving the Problem......................................................................................

Materials Needed............................................................................................

Using a Flow Chart........................................................................................

How to Test the Truck's Components.............................................................

Testing a Component.....................................................................................

Finishing the Job.............................................................................................

Summary..........................................................................................................

Troubleshooting Review..............................................................................................

EVl00 Training Schematic........................................................................................

©Copyright Clark Material Handling Company 1990.

Revised 1998.

Introduction to SCR page 2

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21 21 22 23 24 24 24 25 25 26 26 26 26 27 27 28 29 29 30 30 31 31 31 32 32 32 33 34 35 35 35 35 36 36 37 38 38 39 40

About this class This course is designed to introduce mechanics to the electric truck's Power Circuit.

The letters S C R stand for Silicon Control Rectifier. These rectifiers control and regulate the electric flow in the Power Circuit. When the SCRs turn on and off, they create a pulsing that provides the power for the electric truck to move.

Although most electric trucks have four circuits, Power, Direction, Speed, and Accessory, this manual will concentrate on the Power Circuit. In this class you will learn: •

The elements that comprise the Power Circuit

•

How these elements combine to produce power

•

Basic troubleshooting techniques.

To complete this class, you will need to pass a quiz that will test your knowledge in these areas.

This class will use the EV 100 as its model because this truck represents the latest innovations in SCR Power Circuits. Even though this manual will present a general introduction to troubleshooting, other classes will discuss troubleshooting in greater detail.

You may find the following scientific principles useful when studying the Power Circuit: •An electric current is a flow of electrons.

•Like charges repel.

•Opposite charges attract.

•An electric current moves near the speed of light ( 186,000 miles per second).

In this manual we will discuss the traditional flow of current from positive to negative even though electron theorists insist the current flows from negative to positive. Since an electric current moves rapidly, events happen very quickly in the Power Circuit.

Thus, whether the current flows from positive to negative or from negative to positive is irrelevant for the purposes of this class.

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Introduction to SCR page 3

About safety The following messages will be used to emphasize important information: Note This message is used when special information, instructions or identification is required relating to procedures, equipment, tools, pressures, capacities and other special data.

Important This message is used when special precautions should be taken to ensure a correct action or to avoid damage to or malfunction of the truck or a component.

CAUTION This message is used as a reminder of safety practices which can result in personal injury if proper precautions are not taken.

WARNING This message is used when a hazard exists which can result in injury or death if proper precautions are not taken.

DANGER

This message is used when an extreme hazard exists which will result in death or serious injury if proper precautions are not taken.

When checking electrical components on an electric truck, always raise the drive wheels off the floor and put blocks under the truck, disconnect the battery, and discharge the capacitor. These actions prevent injury to yourself and damage to the truck.

Always familiarize yourself with the safety information in the Operator's and Service Manuals before you operate or repair the truck.

Introduction to SCR page 4

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Glossary of Scientific Terms These definitions should refresh your memory and help you better understand the principles of electricity.

Alternating Current

An electric cun·ent that reverses its polarity. AC usually reverses polarity 120 times a second.

Ampere

The rate of flow of electrical charge when one coulomb of charge passes a point in an electrical circuit in one second.

Battery Negative

The part of a battery that has negative charge.

Battery Positive

The part of a battery that has a positive charge.

Capacitor

A device that initially allows current to flow through with no voltage change. It eventually reduces flow (amps) to increase charge (volts) until the flow is zero. A capacitor is said to be charged when the voltage difference between its positive and negative plates is equal to the voltage difference between the two poles in a battery.

Circuit

The complete path of an electric current.

Conductor

A material (such as copper) that conducts electricity very well.

Coulombs

The standard quantity of electrical charge. A coulomb is 6.24 x 1018 (or six million, million, million) electrons.

Direct Current

An electric cwTent flowing in one direction only.

Electron

The negatively charged particle of an atom.

Electric Current

A flow of electrons.

Induced Voltage

Opposite polarity from the source.

Inductance

The tendency of a material to resist current change.

Inductor

A material that allows current to flow through it but slows the rate at which the current changes.

Insulator

A material (such as wood) that does not conduct electricity very well.

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Introduction to SCR page 5

Kilowatt Kilowatt Hour

One thousand watts.

The rate of kilowatts times hours used.

Magnetic Field

The area around a magnet or an electric current containing the magnet's or current's lines of force.

Negative Charge

The electron or"-" aspect of electricity. It indicates an excessive amount of electrons.

Neutron

The non-charged particle in an atom's nucleus.

Ohm

The amount of resistance causing a voltage drop of one volt when a current of one ampere (or amp) passes through a resistor.

Oscilloscope

A device that visually diagrams an electrical wave.

Polarity

The property of having two opposite poles. In electricity, these poles are the positive pole and the negative pole.

Positive Charge

The proton or"+" aspect of electricity. It represents a shortage of electrons and a capacity to store electrons.

Proton

The positively charged particle in an atom. The proton and neutron comprise the nucleus of an atom.

Resistance

The tendency of a material to hinder the flow of electrons.

Resistor

A material that hinders the flow of electrons.

Reverse Polarity

The changing of an object's original polarity

Watt

Electrical power. Watts are determined by multiplying Amperes x Volts. 746 Watts= 1 horsepower.

Volt

One volt is the potential difference between two points in a circuit when one unit of energy is involved in moving one coulomb of charge between two points.

Voltage

The electric potential to move or change.

Introduction to SCR page 6

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Section 1. What is an SCR? The letters S C R stand for Silicon Control Rectifier. The SCR is a switching component in the electric truck's Power Circuit that controls the flow of electricity from the battery through the Power Circuit. The turning on and off of these SCR switches creates a pulsing effect that determines the truck's speed. The Power Circuit has three SCRs. When you understand how these SCRs work in conjunction with each other and with the components of the Power Circuit, you will understand how the Power Circuit works.

Electric trucks have fow· areas of electrical circuity: • Power • Direction • Speed • Accessory.

As we mentioned earlier, this class will focus on the Power Circuit.

Since Clark has produced many electric trucks that vary from each other, and since the EV 100 control represents the latest in solid state SCR electric controls, we will teach you the functions of the SCRs and Power Circuit using the EV 100 as our model.

For your convenience, we've placed a schematic diagram of the EV 100 electrical system on page 8 and on page 40. This schematic drawing is a two-dimentional representation of the EV 100 electrical systems. Although the parts and their schematic symbols are depicted on this diagram, remember that this system has been flattened out to ease the tracing of electrical flow. Thus, although the electrical flow from part to part is represented coITectly, distances between these part and the locations of these parts will not be to scale.

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Introduction to SCR page 7

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Introduction to SCR page 8

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