CLARK FORKLIFT ETlOO Principles of Electricity TECHNICAL TRAINING MANUAL

ETlOO Principles of Electricity

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 thls Class .............................................................................

About Safety....................................................................................

Section1. What Is Electricity? ......................... .........................................

Objectives ........................................................................................

Fundamentals..................................................................................

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

Section2. Voltage, Current, Power, and Energy ......................................

Objectives ..........................................................................................

Voltage or Potential Difference..........................................................

Current.................. ............................................................................

Power and Energy.............................................................................

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

Section3. Resistance and Capacitance ......................................................

Objectives.............................................................................................

Resistance..........................................................................................

Capacitance.........................................................................................

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

Section4. Magnetism and Inductance ..................................... ..... ..............

Objectives ...........................................................................................

Magnetism ............. ......................... ... ......................................... .... ...

Inductance..........................................................................................

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

Section5. Series and Parallel Circuits ........................................................

Objectives ..................................... .... .... ................... ..........................

Circuits..............................................................................................

Resistance and Ohm's Law..............................................................

Rules that GovernSeries Circuits........ .........................................

Rules that Govern Parallel Circuits...............................................

Combined Circuits............................................................................

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

Section6. Using Meters ................................................ ......... ......................

Objectives ..........................................................................................

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

Types of Meters...................................................................................

Measwing Voltage.............................................................................

Measwing Cw·rent..............................................................................

Measuring Resistance........................................................................

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

Using the Clark Handyman Meter.....................................................

2 2 3 3 3 7 8 8 8 9 10 10 11 11 11 12 15 16 16 16 18 21 22 22 22 24 25 26 27 28 29 29 29 29 30 31 32 32 33

@Copyright Clark Material Handling Company 1990.

Revised 1998.

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Principles of Electricity page l

About this Class As an electric truck service technician, you need to know how the components of an electric truck work together to power and, control the truck. This knowledge enables you to prevent, as well as troubleshoot and eliminate, electrical problems that affect truck performance. In order to do that, you first you need to learn certain basic prin­ ciples about the nature of electricity. This class is designed to help you learn those principles. This class is divided into six sections: "What is Electricity" "Voltage, Current, Power, and Energy" "Resistance and Capacitance" "Magnetism and Inductance" "Series and Parallel Circuits" "Using Meters"

The beginning of each section has a list of learning objectives. The text provides you with the information you will need to reach those objectives. Additionally, your instructor will provide you with a class lecture on the same material, lead you through some hands-on exercises that supplement the text, and answerquestions you may have.

You will be tested at the end of the day to determine whether you have met the learning objectives.

About Safety 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.

Principles of Electricity page 2

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Section 1 . What Is Electricity?

Because we use it so much, we all have a notion of what electricity is. But, in order to learn about and work on electrical devices, it is necessary to know a set of fundamental scientific concepts that describe electricity. This section introduces these concepts.

Objectives After you complete this section, you should be able to match the following list of words to their definitions. electrons conductor component static electricity

energy current battery resistance

charge insulator terminal field force

Fundamentals Everything in the universe is composed of matter and energy. Energy is the ability to do work. Matter is the physical material we see all around us.

Energy exists in many different forms. These Include electrical energy, mechanical energy, chemical energy, light, and heat energy. Any type of energy can be converted to any other type. For example, in an electric truck, the battery converts chemical energy to electrical energy. The motor converts the electrical energy to mechanical energy to move the truck and run the hydraulic system. As the truck operates, some of its electrical and mechanical energy is wastefully converted to heat.

Electrical energy, which is the subject of this class, comes from a force found within atoms. Atoms are the incredibly small particles of which all matter is made.

Every atom consists of a central particle called a nucleus and an orbiting cloud of particles called electrons. The nucleus is made up of two subparticles called protons and neutrons. The electrons stay in orbit mainly because they are attracted to the protons. No one knows exactly what this attractive force is, but we call it the electric force and harness it to do work. ..-�----..

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Principles of Electricity page 3

Even though electrons and protons attract each other, they repel their own kind­ electrons push away other electrons, protons push away other protons. This indicates that protons are electrically opposite from electrons (otherwise protons and electrons would repel each other too). To distinguish the two opposites, we use a concept called charge. We say that protons have a positive charge and electrons have the opposite negative charge.

An important rule of electricity is: Like charges repel and unlike charges attract.

Atoms are normally electrically neutral, that is, they have an equal number of electrons and protons-an equal amount of positive and negative charge. Since all materials are made up of atoms, the materials are normally neutral too. It is possible, however, to separate electrons from atoms. When this happens, the material that gives up the electrons becomes positively charged-it has more protons than electrons. The neutral material that picks up these free electrons becomes negatively charged.

The illustration below shows charged materials attracting and repelling each other.

This ability of charged particles to exert a force on something they do not touch is called the electric field force. Another field force, magnetism, will be studied later in this class. Magnets can move other magnets or iron materials without touching them.

A good example of the electric field force is the static electricity we sometimes experience when combing our hair. When the comb goes through the hair, it removes electrons from the hair and deposits them on comb. The comb, then, becomes negatively charged and the hair becomes positively charged. If you hold the comb a short distance from the hair, you can see the hair fly out and try to touch the comb. This is because the electric field force is pulling the positively and negatively charged materials toward each other. Even when you take the comb away, the hair may still stand out in separate strands. This is because the individual strands are positively charged and are repelling each other. If the comb touches the hair, you might see spares jump from the comb to the hair. All these actions are evidence of charge doing work. This form of electricity is called "static" because the electrons are stationary initially.

Principles of Electricity page 4

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In electricity, as in all sciences, basic properties like charge are expressed in units. A unit is a standard quantity of something. For example, a pound is a unit of weight. In the case of charge, the standard unit is the coulomb.

A coulomb is the charge carried by 6.24 x 10 18 electrons.

That's more than 6 million million million electrons.

Charge is normally most useful when it is flowing through a conductor, such as a wire. A conductor is a means of moving (conducting) electrons to a desired location.

Metals, like copper-the most commonly used conductor-make good conductors, because they have loosely bound electrons that jump from atom to atom. These loosely bound electrons are called free electrons. The number of free electrons per volume of material determines how well a material conducts electricity. There are approximately 85,000 million, million, million free electrons in a cubic centimeter of copper.

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Free electrons jumping from atom to atom

Materials that don't conduct electricity very well are called Insulators. They have a much lower number of free electrons per volume of material. Wire typically has an outer covering of insulation that keeps electrons from leaking into other conductors that may touch the wire.

By using a source of electricity, such as a battery, to supply electrons to one end of a conductor and take them away at the other end, it is possible to get many trillions of free electrons to flow through the wire. This flow of electrons is called current.

A material's tendency to resist the flow of current is called resistance.

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Principles of Electricity page 5

The tendency to support the flow of current is called conductivity. Insulators, like rubber, have high resistance and low conductivity. Conductors, like copper, have high conductivity and low resistance.

The electric truck uses a battery as its source of electricity. A battery uses chemical energy to separate electrons from atoms so that there is an abundance(of electrons on one side of the battery and a lack of electrons on the other. The opposite sides of the battery are usually called positive and negative poles. Both poles of the battery have a terminal that allow a wire or other conductor to be connected. If a wire is connected between the terminals, the negative pole of the battery attracts free electrons from the wire, leaving a lack of electrons in the wire. At virtually the same instant, the positive pole supplies the wire with electrons to make up for the lacking electron. This happens at a rate of many trillions of electrons per second.

After a period of time, the number of electrons on the two sides of the battery balances out and cuITent ceases to flow through the wire-the battery has lost its charge and thus its ability to do work. Some batteries have to be thrown away when they lose their charge, others can be recharged, like the batteries in electric lift trucks.

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The wire and battery arrangement described above is called a circuit. The electrons flow in a "circle" from the positive pole of the battery through the wire and back to the negative pole of the battery. The circuit described above has no useful purpose, except perhaps to generate heat in the wire. This circuit discharges a battery very quickly because the path from one pole to another has no obstacles for slowing down the electrons. Such a rapid discharge could be very dangerous if you were using a powerful battery.

Normally, electrical circuits contain components that stop current, restrict cUITent, or convert electricity to some other useful form of energy. Typical circuit components that will be described in your electric truck classes include motors, lights, switches, resistors, capacitors, coils, and diodes.

Principles of Electricity page 6

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The current obtained from a battery is called direct current or DC current. DC current flows continuously from one pole of the battery to the opposite pole. The current from a wall socket at home is called alternating current or AC current. Because it is produced by an alternator that continuously reverses its positive and negative poles, household AC current actually reverses its direction 120 times per second. Since the electric truck uses DC current only, this class will not deal with AC cmTent.

Summary Positive and negative charges are attracted to each other. Electrons are negatively charged. Conductors, such as wires, allow charges to move through them. Insulators block the movement of charge. Batteries are negatively charged at one pole and positively charged at the other. When a conductor is connected to the poles, electrons move from the positive pole through the conductor into the negative pole. This movement of electrons is called DC current.

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Principles of Electricity page 7

Section 2. Voltage, CuITent, Power, and Energy.

The last section introduced energy and current by relating them to atomic structure and charge. This section introduces the concept of voltage and power and relates them to current and energy. This section also defines the units of measurement for these properties.

Objectives After completing this section, you should be able to write definitions for voltage, current, power, and energy. You should also be able to match water flow models to descriptions of current and voltage. You should also be able to match units of measurements to the electrical characteristics they are associated with.

Voltage or Potential Difference Voltage can be thought of as an "electric pressure" that forces free electrons to flow around a circuit. This idea can be demonstrated by comparing voltage to water pressw·e.

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The illustration above shows two water tanks side-by-side. The outlets from the tanks are capped off and a pressure gauge is connected to each pipe. A pressure is shown on each gauge. The dotted lines show how the two pipes can be connected to allow water to flow between the two tanks.

Because the tank on the left has more water than the tank on the right, the pressw·e in the left pipe is greater than in the right pipe. This pressure difference represents a potential to do work. If the two pipes were connected, the pressure difference would force water to flow. Work could be done with the flowing water.

Think of each tank as being like the pole of a battery. The different energy levels at each pole of the battery represent a potential to move a charge through the circuit.

This potential is called voltage and is also known as potential difference. The flowing charge can then be used to do work.

Principles of Electricity page 8

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