CHAPTER ONE

INTRODUCTION

1.1 Introduction

The solar campus traveller is meant as a challenge to get, on sunny summer

days the most pedal assistance possible out of solar panel used. The solar campus

traveller is sportive.it may not cost substantially more energy to drive the solar campus

traveller, When there is no sunlight the batteries are charged the bycle should be

running.

A solar traveller bicycle has the advantage of it can handel weight upto 60 to

70kg and can use the riders foot power to supplement the power generated by the solar

panel. In this way, a comparatively simple and in expensive vehicle can be driven

without the use of any fossil fuels.

The solar traveller is easily accessible, safe and practical with limited

maintenance requirements due to a fewer mechanical parts. It is ideal not only for the

experienced cyclists but also for those non athletes, the elderly and individuals with

health problems.

Solar campus traveller need large and heavy batteries to allow riding long

distances, because the battery is charged only once at home. The solar bike approach is

different.the photo voltaic panels have enough power and give the traveller an infinite

range.

In our college distance frome central block to A-block it take arount 5 min to

walk to reduse the time of wastage we thought to prepare a scooter in less coat which

runs on solar energy. So we preapre a solar scooter and name it as solar campus

traveler.

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An electric scooter is a small platform with two or more wheels that is

propelled by an electric motor. Besides the motor, propulsion can also happen by the

rider, pushing off to the ground.

The most common scooters today have two hard small wheels, are made

primarily of aluminum and fold for convenience. Some kick scooters have 3 or 4 wheels,

or are made of plastic, or are large, or do not fold. High performance trickster scooters

made for adults resemble the old "penny-farthing" with much larger wheel in

front. Electric kick scooters differ from electric scooters in that they also allow human

propulsion, and have no gears. Range is typically about 5 km, and maximum speed is

around 30 km/h.

1.1 Blockdiagram:

Coupling Belt

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Solar photo- voltaic module

Charge control

Rechargeable battery

High torque DC motor

Drive wheel arrangement

Brake arrangement

1.3 MODEL

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CHAPTER TWO

SOLAR PANEL

2.1 Science of Silicon PV Cells

Scientific base for solar PV electric power generation is solid-state physics of

semiconductors Silicon is a popular candidate material for solar PV cells because:

It is a semiconductor material. Technology is well developed to make silicon to be

positive (+ve) or negative (-ve) charge-carriers – essential elements for an electric cell or

battery Silicon is abundant in supply and relatively inexpensive in production

Micro- and nano-technologies have enhanced the opto-electricity conversion efficiency

of silicon solar PV cells a solar cell or photovoltaic cell is a device that converts solar

energy into electricity by the photovoltaic effect. Sometimes the term solar cell is

reserved for devices intended specifically to capture energy from sunlight, while the term

photovoltaic cell is used when the source is unspecified. Assemblies of cells are used to

make solar panel, solar modules, or photovoltaic arrays. Photovoltaic is the field of

technology and research related to the application of solar cells for solar energy.

Solar cell efficiencies vary from 6% for amorphous silicon-based solar cells to 40.7%

with multiple-junction research lab cells and 42.8% with multiple dies assembled into a

hybrid package.   Solar cell energy conversion efficiencies for commercially available

multi crystalline Si solar cells are around 14-19%.

Solar cells can also be applied to other electronics devices to make it self-power

sustainable in the sun. There are solar cell phone chargers, solar bike light and solar

camping lanterns that people can adopt for daily us

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Equivalent circuit of a solar cell

Fig 2.1 Equivalent circuit of a solar cell

Equivalent circuit switch of a solar cell

Fig 2.2 equivalent circuit switch of a solar cell

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2.2 Description of a solar cell

1. Photons in sunlight hit the solar panel and are absorbed by semi conducting

materials.

2. Electrons are knocked loose from their atoms, allowing them to flow through the

material to produce electricity. Due to the special composition of solar cells, only

allow the electrons to move in a single direction. The complementary positive

charges that are also created are called holes and flow in the direction opposite of

the electrons in a silicon solar panel.

3. An array of solar panels converts solar energy into a usable amount of DC

electricity.

4. Solar battery chargers are better for the environment in a few ways. For one, with

them, batteries can be recharged, therefore no longer contributing to growing

landfills. Also, batteries have potentially harmful metals inside them – we do not

want to be simply throwing them out into landfills! Also, if using batteries that

can be recharged with a solar battery charger, a person can stop wasting his or her

money on the purchase of new batteries.

5. The batteries of cell phones, PDAs, laptops, mp3 players, and more can be

charged by solar battery chargers. This means that you do not have to rely on

electricity to charge these devices. This is especially good because most

electricity is created by non-sustainable, polluting methods.

6. Solar battery chargers are also good because they allow the users to charge

devices, even when no power outlets are around. This makes them especially

useful when working out in the field, traveling, hiking, and/or during an

emergency.

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7. The solar cells positive terminal is connected through the diode to the positive

terminal of the 1.2V battery. If the voltage of the solar cell drops below 1.4 volts

then with the 0.2V the blocking diode takes there wont be enough potential to

charge the 1.2V battery. The purpose of the diode is to disallow current

dissipating out from the battery to the solar cell when this low voltage situation

occurs in the solar cell.

Fig 2.3 solar panel

A solar battery is one of the most important energy sources available to save energy

consumption, and serves as a spare source while normal power supply shuts down.

Systems using solar batteries have various scales from a few watts to a few thousands of

kilowatts, and also have various types. Conventionally, the solar battery has been

dominantly used in the form of a solar electricity generation plant where a large number

of solar batteries are arranged, or used for securing power supply at a remote location.

Recently, it becomes more and more popular to install a solar battery module panel on a

house roof or on an outer wall of a building. Generally, a solar battery is composed of a

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plurality of photoelectric power generating elements connected in series on a substrate to

obtain a photo voltage. In a solar panel battery, the solar cell is the smallest constituent

unit of a device having the function of photoelectric conversion. The solar cell is

considered a major candidate for obtaining energy from sun, since it can convert sunlight

directly to electricity with high conversion efficiency, can provide nearly permanent

power at low operating cost without having any influence on the climate.

2.2.1 Working process:

Solar power systems employ photovoltaic cells to convert the radiant energy of sunlight

directly into electrical energy. Photovoltaic solar cells are semiconductor devices which

convert sunlight into electricity. Solar cells which utilize crystalline semiconductors,

such as silicon, offer the advantages of high performance and reliability. Photovoltaic

cells are silicon-base crystal wafers which produce a voltage between opposite surfaces

when light strikes one of the surfaces, which surface has a current collecting grid

thereon. The photons of the light are absorbed by photovoltaic cells and yield their

energy to the valence electrons of the semiconductor and tear them from the bonds that

maintain them joined to the cores of the atoms, promoting them to a superior energetic

state called conduction band in which they can move easily through the semiconductor.

Typically, a plurality of solar cells are assembled and interconnected so as to form a

physically-integrated module, and then a number of such modules are assembled

together to form a solar panel. Several solar panels may be connected together to form a

larger array. The individual photovoltaic cells in a module may be connected in series or

parallel, typically by an internal wiring arrangement and similarly two or more modules

in a panel may be connected in series or parallel, depending upon the voltage output

desired. Solar cells are usually interconnected into series strips by electrically

interconnecting a collector pad on the grid to the opposite surface of the adjacent cell in

the strip.

Photovoltaic cells are manufactured in a variety of configurations, but generally

comprise a layered structure on a substrate. There are many different types of converging 8

solar cell modules in which sunlight is converged by means of a lens system so that the

total area of expensive solar cells can be reduced in order to reduce the cost of electric

power generating systems using these solar cells. In order to most efficiently use the

electrical power generated by a photovoltaic cell or photovoltaic array, it is desirable to

maximize the power generated by the photovoltaic cell or photovoltaic array, despite

varying weather conditions.

2.2.2 Theory:

A solar energy battery is different from the regular battery. The solar battery module is

constructed by having a multiplicity of solar battery elements carried on a supporting

base plate. When the sunlight impinges on the individual solar battery elements, the

energy of the light which makes no contribution to the photoelectric conversion is

accumulated in the form of heat to elevate the temperature of the solar battery elements

and lower the efficiency of photoelectric conversion.

A solar cell having a photoelectric conversion layer in which at least one PIN junction is

formed using an amorphous or microcrystalline silicon film is utilized. A solar battery

converts light into electrical energy, its P-N junction structure when exposed to incident

light generates large quantities of electron-hole pairs, and in the meantime electrons

carrying negative electricity and holes carrying positive electricity migrate to the N-type

semi-conductor and P-type semi-conductor respectively.

This process produces electricity. In such converging solar cell modules, converging

solar cell elements each having solar cells and their electrodes for outputting electric

currents are used. When a spot formed by converged sunlight irradiates the light

receiving surface of the converging solar cell, free electrons and electron holes as

carriers are generated inside a silicon substrate.

The photoelectric conversion efficiency of a solar battery depends mainly on the internal

resistance of the solar battery. In particular, it depends on the series resistance of the

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upper and lower electrodes, and the series resistance of the elongation of the upper and

lower electrodes which are brought into contact with each other in order to connect

adjacent generating regions.

A typical solar battery comprises a glass substrate as a front side transparent protective

member at a light-receiving side, a back side protective member, ethylene-vinyl acetate

copolymer (EVA) films as sealing films arranged between the glass substrate and the

back side protective member, and solar cells or silicon photovoltaic elements sealed by

the EVA films. A solar battery module is generally composed of a solar battery panel

comprising a light-transmission panel and a solar battery element.

The solar battery element being provided on the surface which is opposed to the light-

receiving surface of the light-transmission plate, and a frame for fixing the solar battery

panel thereon. Solar panels have a large number of solar cells which are used to convert

power from sunlight.

Power generated by the solar cells is coupled via electric lines to a rectifier for feeding

into the alternating current (AC) network or to a battery. A connecting box is generally

provided for coupling to the solar panel.

Solar panels are comprised primarily of a strong back, insulation, receiver tubes, headers

and tube guide/supports. Tubes are connected at the top and bottom of the panel by the

headers. Solar panels are typically mounted on a mounting structure, which is supported

on a mounting surface, such as a rooftop.

The sun's thermal energy is intercepted by a collector system that is comprised of

thousands of sun tracking mirrors called heliostats. This energy is redirected and

concentrated on a heat exchanger, called a solar receiver. The receiver includes a

plurality of solar receiver panels positioned around an outside wall of the receiver.

A solar battery module panel has a plurality of photovoltaic elements resin-sealed

between a surface cover glass and a back cover film. In the case where several modules

are to be interconnected, and also in the case where two or more solar panels are to be 10

interconnected, external terminals are required for connections to cables that couple the

modules or panels together.

Solar batteries have been used in various electronic equipments as power supply

substitutes for dry batteries. Such batteries are highly reliable, have a long life, and now

are economically produced. Initially, large-surfaced solar cell arrangements are used in

photo-voltaic systems, for example, which can provide sufficient energy for consumers

with a higher demand. Solar panels are particularly well suited to situations where

electrical power from the grid is unavailable, such as in remote area power systems. Low

power consumption electronic equipment such as electronic desktop calculators,

watches, and portable electronic equipment (e.g., digital cameras, cellular phones and

commercial radar detectors) can be fully driven by the electromotive force of solar

batteries.

2.2.3 Applications

Solar cells can also be applied to other electronics devices to make it self-power

sustainable in the sun. There are solar cell phone chargers, solar bike light and solar

camping lanterns that people can adopt for daily use.

Solar power plants can face high installation costs, although this has been decreasing due

to the learning curve. Developing countries have started to build solar power plants,

replacing other sources of energy generation.

In 2008, solar power supplied 0.02% of the world's total energy supply. Use has been

doubling every two, or fewer, years. If it continued at that rate, solar power would

become the dominant energy source within a few decades.

Since solar radiation is intermittent, solar power generation is combined either with

storage or other energy sources to provide continuous power, although for small

distributed producer/consumers, net metering makes this transparent to the consumer.

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2.3 Working of Photovoltaic Cell

It all starts with sunlight. Sunlight is composed of photons. Photons have different

energies, we notice this when looking at a rainbow and see different colors; each colors

represents a photons with a different energy. When one of these photons sticks an atom

in a photo voltaic (PV) cell, the photon frees one electron from the atom.

The freed electron begins to wander around the PV cell, ultimately finding its way to the

opposite side of the PV cell where it comes into contact with a metal wire. Einstein won

the Noble Prize for describing the photovoltaic effect. The electron continues its journey

through the wire. The wire connects things that need electricity like a computer, light

bulb, batteries or refrigerators. Chances are the electricity you’re using now got its start

from a freed electron created by a photon from the sun.

2.3.1 Silicon solar cell

Pure silicon is not a very good conductor of electricity, though it conducts some

electricity; hence called a semi-conductor. To increase its conductivity impurities are

added; this is called doping. We’ll see in the next few paragraphs why adding impurities

like either phosphorous or boron atoms to silicon are desirable as well as what happens

when these two different types of doped-silicon are sandwiched together.

Digging back into our chemistry knowledge we know atoms have protons and neutrons

at the center or nucleus of the atom, and electrons whirling around the nucleus. Electrons

move in a predictable fashion, in fact we know there movement is confined to well

defined zones around the nucleus. It’s easiest to picture in our mind that these electron-

zones most resemble a cross section of an onion, where each onion layers represents a

different zone where we find electrons. Looking at phosphorous on the atomic level we

see that phosphorous has three onion layers. Again, we’re only interested in the last

onion layer; these layers in chemistry are often referred to as shells. So in phosphorous,

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the last onion layer or shell we see that phosphorous has 5 electrons in its last shell.

Boron has 2 shells, and again we’re only interested with the last shell in which boron has

3 electrons in its last shell. Silicon happens to have 3 onion layers and in its last shell, it

has 4 electrons which is a number right between phosphorous and boron. Below is a

picture of what the last shell of each atom would look like; silicon with 4 electrons or 4

dots (each dot is an electron), 5 for phosphorous, and 3 for boron. A more technical term

for these last electrons in an atom is a valance electron.

What we’re going to do next is make two different types of silicon. To one type we’ll

add phosphorous. To the other we’ll boron. Our goal is to sandwich together these two

different types of silicon, one doped with phosphorous, the other silicon doped with born

to make a PV cell. Before doing this, we better review a little more chemistry,

specifically bonding. To make a bond between atoms, you need 2 electrons. There are a

maximum number of bonds an atom wants to make, and for the vast majority of

molecules it’s 4 bonds. Silicon is always looking to form four bounds so when silicon

forms its four bonds to a phosphorous atom it would look like the picture below.

Remember, 2 electrons per bond, now referring to the valance electron picture above for

silicon and phosphorous we end up with a picture below. Notice in the picture below,

phosphorous ends up with one extra electron, that extra electron can’t bond to anything

else.

This extra electron creates a negative charge in the silicon-phosphorous doped

semiconductor. Whenever silicon is mixed with phosphorous this negative charge is

produced and this type of silicon is referred to as an n-type conductor, the “n” referring

to negative charge. N-type conductors have an excess of electrons. A similar analogy

applies to boron. When boron binds to silicon, boron only has 3 electrons and silicon has

4 electrons. So what ends up happening is silicon is stuck without being able to make

four bonds. In this case, the silicon, is trying to make another bond, and it can’t. Silicon

comes up short one electron. It would look like this:

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Since the silicon atom is short one electron a positive charge forms on the silicon atom.

Whenever silicon is mixed with boron positive charge is produced. This type of silicon-

boron semiconductor is called a p-type conductor, the “p” referring to the positive

charge. P-type conductors lack electrons. From this point forward, it is best to think of

the boron doped silicon, where the missing electron is really just a hole and this hole is

looking for another electron to fill it up. Therefore, the p-type material has an excessive

number of positive holes to fill (that’s the end of our chemistry review).

P-Types, n-Types

To create a PV cell, two different types of semiconductors are sandwiched together. The

"n" and "p" types of semiconductors correspond to "negative" abundance of electrons

and "positive" abundance of holes (really just an absence of electrons).

Although both materials are electrically neutral, sandwiching these together creates a p/n

junction at their interface, thereby creating a one-way electric field or diode which we’ll

discuss later.

2.4 The p-n junction

The region in the solar cell where the n-type and p-type layers meet is called the p-n

junction. When p-type and n-type materials are placed in contact with each other, a

junction is automatically formed. An interesting interaction occurs at the p-n junction of

a solar cell when the n-type layer comes into contact with the p-type layer. Electrons will

only flow in one direction (forward biased) but not in the other (reverse biased).

Remembering back to the n-type, phosphorous doped silicon with its extra electron, and

the p-type, boron doped silicon with its missing electron. When the p-type and n-type

semiconductors are sandwiched together, the points at which they touch, a sudden, mad-

rush of an extra free electron in the n-type layer, fall into a hole on the p-type side.

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What does this produce? Before now, our two separate pieces of silicon were electrically

neutral; the interesting part begins when you put them together. What is created is an

electric field. The electric field forms when the mad-rush of free electrons on the N side

to the holes on the P side. Do all the free electrons fill all the free holes? No, just the

atoms right at the junction, they mix forming something of an electrical barrier, making

it harder and harder for electrons on the N side to cross over to the P side. Eventually,

equilibrium of positive and negative produces an electric field on each side of the

junction.

In the picture below, you can see how all of the extra electrons, at the junction, on the

phosphorous side, pink, jumped over to the boron side colored blue. When the extra

electron on the phosphorous mad-rushes or jumps into the boron hole, the phosphorous

leaves behind a positive hole. To you and I it looks like a hole is also moving, however

this is best described as to what happens when looking at a bubble moving in a liquid.

Although it's the liquid that is actually moving, it's easier to describe the motion of the

bubble as it moves in the opposite direction or as we say rising. So applying our bubble

analogy to positive holes moving, it looks like positive holes are moving and in reality,

it’s the electrons jumping, leaving behind a hole, so as more and more electrons jump

into holes, holes appear to be moving.

2.4.1 Combining of p-Types, n-Types

At the junction all of the phosphorous electrons jump to the boron side, creating a

negative charge on the boron side, leaving behind holes or positive charge on the

opposite side. This separation of charge creates an electric field. This electric field is the

exact location where energy or work is extracted from the PV cell. The reason is the

electric field acts as a diode, allowing (and even pushing) electrons to flow from the P

side (colored Blue below) to the N side (colored Pink below), but not the other way

around. It's like a hill -- electrons can easily go down the hill (to the N side), but can't

climb it (to the P side).

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2.5 Effect of the electric field in a PV cell

Through this flow of electrons and holes, the two halves of the semiconductors act as a

battery, creating an electric field at the surface where they meet (known as the

"junction"). It's this field that causes the electrons to jump across the junction, and then

pushes the electrons further out toward the outer surface of the semiconductor. Once the

electrons have reached the surface of the semiconductor, they are available for the

electrical circuit.

Remembering though, that as the electron jumped across the junction, what it leaves

behind is a hole. So as the electron is weaving its way up to the surface of the n-type

material, the hole it created on the p-type side begins moving in the opposite direction,

toward the positive surface, where, ultimately the electron and hole will meet up again to

finish the circuit.

Light, in the form of photons, hits our solar cell. When a photon of sunlight strikes an

atom in either layer, it knocks loose an electron. If the photon has enough energy, the

photon will strike a valence electron, releasing the electron and creating a positive hole.

Normally one photon will free exactly one electron, unless the photon has twice the

energy in which case it will release two electrons and create two positive holes.

Freed electrons in the P-layer easily cross, even pulled through the electrical field into

the n-layer, and holes move, even pulled to the p-layer. As a result, an excess of free

electrons build up in the N-layer. The movement of electrons to the N side and holes to

the P side causes a disruption of electrical neutrality in the junction sometimes referred

to as the depletion zone. In the depletion zone (p-n junction) acts as a diode.

The electrical imbalance at the junction or depleted zone is about 0.6 to 0.7 volts. So due

to the p-n junction, a built in electric field is always present across the solar cell. Another

way to think of it is to say that that is the strength of a photon you’ll need to knock an

electron free, to make it jump the p-n junction gap. You could also say that’s how much

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electricity you’ll get from your PV cell. Knowing the voltage allows you to calculate the

energy of all the photons, from the sun, striking your PV cell with 0.6 to 0.7 volts to

knock an electron lose; that will give you the theoretical efficiency of a PV cell. So

we've got an electric field acting as a diode in which electrons can only move in one

direction.

2.5.1Operation of a PV cell

P = V × I

The number of electrons moving are called current, symbol “I.” A cell's electric field

causes a voltage, symbol “V.” With both current and voltage, we have power, which is

the product of the two. Since voltage, in our above example is fixed at 0.6 to 0.7 volts,

the only current is variable; so the brighter the day the more photons you’ll have,

creating more current, making more power. A Photon causes the Photoelectric Effect in

more detail

2.6 Band Gap

Today's most common PV devices use a single junction, or depleted region, to create an

electric field. In our previous example of phosphorous and boron, the measure of energy

across the junction or depleted region was between 0.6 to 0.7 volts. Therefore, only

photons whose energy is equal to or greater than 0.6 to 0.7 volts can free an electron to

make our electric circuit. The 0.6 to 0.7 volts is referred to as the band gap. If the

photon's energy is at least as large as the material's energy band gap, the energy from the

photon creates an electron-hole pair.

Close to the junction, in the presence of an electric field, the junction acts more like a

magnet, attracting and repelling negatively charged electron and the positively charged

hole. Further away from the junction what typically happens is electrons and holes stay

together, in a process called recombination, because the electron or holes doesn’t have

enough energy to make it all the way to junction.

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2.7 Absorption and Conduction

In a PV cell, photons are absorbed in the p layer. It's very important to "tune" this layer

to the properties of the incoming photons to absorb as many as possible and thereby free

as many electrons as possible. Another challenge is to keep the electrons from meeting

up with holes and "recombining" with them before they can escape the cell. To do this,

we design the material so that the electrons are freed as close to the junction as possible,

so that the electric field can help send them through the "conduction" layer (the n layer)

and out into the electric circuit. By maximizing all these characteristics, we improve the

conversion efficiency of the PV cell.

To make an efficient solar cell, we try to maximize absorption, minimize reflection and

recombination, and thereby maximize conduction. Junctions in semiconductors create

electrical fields. A junction can be formed at the border between p-and n-doped regions,

or between different semiconducting materials.

You can also try to capture more photons with different amounts of energy. You can

probably envision doping silicon with elements other than phosphorous or boron.

Changing the type of atom combinations will give a different band gap voltage other

than our 0.6 to 0.7 volts for phosphorous or boron. It is possible to make stacks all of

these different cells together to create a multi-junction cell. The advantage being that by

changing the atom combination, you can change the voltage in the band gap, thereby

effectively creating a PV cell that can capture all the photons with different energies.

The conversion efficiency of a PV cell is the proportion of sunlight energy that the cell

converts to electrical energy. This is very important when discussing PV devices,

because improving this efficiency is vital to making PV energy competitive with more

traditional sources of energy (e.g., fossil fuels). Naturally, if one efficient solar panel can

provide as much energy as two less-efficient panels, then the cost of that energy (not to

mention the space required) will be reduced.

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For comparison, the earliest PV devices converted about 1%-2% of sunlight energy into

electric energy. Today's PV devices convert 7%-17% of light energy into electric energy.

Of course, the other side of the equation is the money it costs to manufacture the PV

devices. This has been improved over the years as well. In fact, today's PV systems

produce electricity at a fraction of the cost of early PV systems.

2.8 Energy Loses

Why does our solar cell absorb only about 15 percents of the sunlight's energy? Visible

light is only part of the electromagnetic spectrum. Electromagnetic radiation is not

monochromatic -- it is made up of a range of different wavelengths, and therefore energy

levels. Light can be separated into different wavelengths, and we can see them in the

form of a rainbow. Since the light that hits our cell has photons of a wide range of

energies, it turns out that some of them won't have enough energy to form an electron-

hole pair. They'll simply pass through the cell as if it were transparent. Still other

photons have too much energy.

Only a certain amount of energy, measured in electron volts (eV) and defined by our cell

material (about 1.1 eV for pure crystalline silicon), is required to knock an electron

loose. We call this the band gap energy of a material. If a photon has more energy than

the required amount, then the extra energy is lost (unless a photon has twice the required

energy, and can create more than one electron-hole pair, but this effect is not significant).

These two effects alone account for the loss of around 70 percent of the radiation energy

incident on our cell.

Why can't we choose a material with a really low band gap, so we can use more of the

photons? Unfortunately, our band gap also determines the strength (voltage) of our

electric field, and if it's too low, then what we make up in extra current (by absorbing

more photons), we lose by having a small voltage. Remember that power is voltage times

current. The optimal band gap, balancing these two effects, is around 1.4 eV for a cell

made from a single material.

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We have other losses as well, many just the physical design of a solar panel. Here is an

example. Once our electron is free we want the electron to go to a wire which is more

conductive than metal. So where do we place the metal. It’s not possible to completely

cover the top and bottom of the PV cell with metal otherwise our photons will never hit

the PV cell. Placing the wires to far apart will cause our electrons to travel extremely

long distances. The more time an electron spends by itself the great the chance it will

recombine with its whole and other problem being, silicon is a semiconductor -- it's not

nearly as good as a metal for transporting current. Putting PV cell production at the same

level of production as automobiles will decrease the cost of a PV cell. A MIT professor

said the cost of materials in a PV cell is less than the cost of paint on some of the newer

automobiles being produced today. Another MIT professor said 65% of the cost of a PV

cell is installing it on someone’s house. A more efficient way of putting solar panels on a

house would reduce the cost.

Solar PV is used primarily for grid-connected electricity to operate residential

appliances, commercial equipment, lighting and air conditioning for all types of

buildings. Through stand-alone systems and the use of batteries, it is also well suited for

remote regions where there is no electricity source. Solar PV panels can be ground

mounted, installed on building rooftops or designed into building materials at the point

of manufacturing. The future will see everyday objects such as clothing, the rooftops of

cars and even roads themselves turned into power-generating solar collectors.

The efficiency of solar PV increases in colder temperatures and is particularly well-

suited for Canada's climate. A number of technologies are available which offer different

solar conversion efficiencies and pricing. Solar PV modules can be grouped together as

an array of series and parallel connected modules to provide any level of power

requirements, from mere watts (W) to kilowatt (kW) and megawatt (MW) size. On the

technology side, it is easy to interconnect your PV system to your local utility company

-- there are no technical barriers. There may be regulations, however, that you will need

to work through with your utility, in order for them to allow you to generate your own

electricity.

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CHAPTER THREE

DIODES

3.1 Description of Diode:

In electronics, a diode is a two-terminal electronic component  with a symmetric 

conductance ; it has low (ideally zero) resistance to current in one direction and high

(ideally infinite) resistance in the other. A semiconductor diode, the most common type

today, is a crystalline piece of semiconductor  material with a p–n junction connected to

two electrical terminals. A vacuum tube diode has two electrodes, a plate (anode) and

a heated cathode.

Semiconductor diodes were the first semiconductor electronic devices. The discovery

of crystals' rectifying abilities was made by German physicist Ferdinand Braun in 1874.

The first semiconductor diodes, called cat’s, developed around 1906, were made of

mineral crystals such as galena. Today, most diodes are made of silicon, but other

semiconductors such as selenium or germanium are sometimes used.

3.1.1 Main functions

The most common function of a diode is to allow an electric current to pass in one

direction (called the diode's forward direction), while blocking current in the opposite

direction (the reverse direction). Thus, the diode can be viewed as an electronic version

of a check valve. This unidirectional behavior is called rectification, and is used to

convert alternating current to direct current, including extraction of modulation from

radio signals in radio receivers—these diodes are forms of rectifiers.

However, diodes can have more complicated behavior than this simple on–off action,

due to their nonlinear current-voltage characteristics. Semiconductor diodes begin

conducting electricity only if a certain threshold voltage or cut-in voltage is present in

21

the forward direction (a state in which the diode is said to be forward-biased). The

voltage drop across a forward-biased diode varies only a little with the current, and is a

function of temperature; this effect can be used as a temperature sensor or voltage

reference.

3.2 Semiconductor diodes

Semiconductor diodes' current–voltage characteristic can be tailored by varying

the semiconductor materials and doping, introducing impurities into the materials. These

techniques are used to create special-purpose diodes that perform many different

functions. For example, diodes are used to regulate voltage (Zener diodes), to protect

circuits from high voltage surges (avalanche diodes), to electronically tune radio and TV

receivers (varactor diodes), to generate radio-frequency oscillations (tunnel diodes, Gunn

diodes,IMPATT diodes), and to produce light (light-emitting diodes). Tunnel, Gunn and

IMPATT diodes exhibit negative resistance, which is useful in microwave and switching

circuits.

3.2.1Electronic symbol

The symbol used for a semiconductor diode in a circuit diagram specifies the type of

diode. There are alternative symbols for some types of diodes, though the differences are

minor.

Diode

 

Light Emitting Diode(LED)

 

22

Photodiode

 

Schottky diode

Transient Voltage Suppression (TVS)

Tunnel diode

Varicap

Zener diode 

Typical diode packages in same alignment as diode symbol. Thin bar depicts

the cathode. A point-contact diode works the same as the junction diodes described

below, but their construction is simpler. A block of n-type semiconductor is built, and a

conducting sharp-point contact made with some group-3 metal is placed in contact with

the semiconductor. Some metal migrates into the semiconductor to make a small region

of p-type semiconductor near the contact.

23

3.3 Junction diode

p–n junction diode

Main article: p–n diode

A p–n junction diode is made of a crystal of semiconductor, usually silicon,

but germanium and gallium arsenide are also used. Impurities are added to it to create a

region on one side that contains negative charge carriers (electrons), called n-type

semiconductor, and a region on the other side that contains positive charge carriers

(holes), called p-type semiconductor.

When two materials i.e. n-type and p-type are attached together, a momentary flow of

electrons occur from n to p side resulting in a third region where no charge carriers are

present. This region is called the depletion region due to the absence of charge carriers

(electrons and holes in this case).

The diode's terminals are attached to the n-type and p-type regions. The boundary

between these two regions, called a p–n junction, is where the action of the diode takes

place. The crystal allows electrons to flow from the N-type side (called the cathode) to

the P-type side (called the anode), but not in the opposite direction.

Shockley diode

Main article: Scotty diode

Another type of junction diode, the Schottky diode, is formed from a metal–

semiconductor junction rather than a p–n junction, which reduces capacitance and

increases switching speed.

24

Current–voltage characteristic

Graph 3.1 I–V (current vs voltage)

A semiconductor diode's behavior in a circuit is given by its current–voltage

characteristic, or I–V graph (see graph below). The shape of the curve is determined by

the transport of charge carriers through the so-called depletion layer or depletion

region that exists at the p–n junction between differing semiconductors. When a p–n

junction is first created, conduction-band (mobile) electrons from the N-doped region

diffuse into the P-doped region where there is a large population of holes (vacant places

for electrons) with which the electrons "recombine".

When a mobile electron recombines with a hole, both hole and electron vanish, leaving

behind an immobile positively charged donor (dopant) on the N side and negatively

charged acceptor (dopant) on the P side. The region around the p–n junction becomes

depleted of charge carriers and thus behaves as an insulator. However, the width of the

depletion region (called the depletion width) cannot grow without limit. For each

electron that recombines, a positively charged dopant ion is left behind in the N-doped

region, and a negatively charged dopant ion is left behind in the P-doped region. As

recombination proceeds more ions are created, an increasing electric field develops

through the depletion zone that acts to slow and then finally stop recombination. At this

point, there is a "built-in" potential across the depletion zone.25

If an external voltage is placed across the diode with the same polarity as the built-in

potential, the depletion zone continues to act as an insulator, preventing any significant

electric current flow (unless electron are actively being created in the junction by, for

instance, light; see photodiode). This is the reverse bias phenomenon. However, if the

polarity of the external voltage opposes the built-in potential, recombination can once

again proceed, resulting in substantial electric current through the p–n junction (i.e.

substantial numbers of electrons and holes recombine at the junction). For silicon diodes,

the built-in potential is approximately 0.7 V (0.3 V for Germanium and 0.2 V for

Schottky). Thus, if an external current passes through the diode, the voltage across the

diode increases logarithmic with the current such that the P-doped region is positive with

respect to the N-doped region and the diode is said to be "turned on" as it has a forward

bias. The diode is commonly said to have a forward "threshold" voltage, which it

conducts above and is cutoff below. However, this is only an approximation as the

forward characteristic is according to the Shockley equation absolutely smooth (see

graph below).

3.3.1 Diodes I–V characteristic :

At very large reverse bias, beyond the peak inverse voltage or PIV, a process called

reverse breakdown occurs that causes a large increase in current (i.e., a large number of

electrons and holes are created at, and move away from the p–n junction) that usually

damages the device permanently. The avalanche diode is deliberately designed for use in

the avalanche region. In the Zener diode, the concept of PIV is not applicable. A Zener

diode contains a heavily doped p–n junction allowing electrons to tunnel from the

valence band of the p-type material to the conduction band of the n-type material, such

that the reverse voltage is "clamped" to a known value (called the Zener voltage), and

avalanche does not occur. Both devices, however, do have a limit to the maximum

current and power in the clamped reverse-voltage region. Also, following the end of

forward conduction in any diode, there is reverse current for a short time. The device

does not attain its full blocking capability until the reverse current ceases.26

At reverse biases more positive than the PIV, has only a very small reverse saturation

current. In the reverse bias region for a normal P–N rectifier diode, the current through

the device is very low (in the µA range). However, this is temperature dependent, and at

sufficiently high temperatures, a substantial amount of reverse current can be observed

(mA or more).

With a small forward bias, where only a small forward current is conducted, the current–

voltage curve is exponential in accordance with the ideal diode equation. There is a

definite forward voltage at which the diode starts to conduct significantly. This is called

the knee voltage or cut-in voltage and is equal to the barrier potential of the p-n junction.

This is a feature of the exponential curve, and is seen more prominently on a current

scale more compressed than in the diagram here.

At larger forward currents the current-voltage curve starts to be dominated by the ohmic

resistance of the bulk semiconductor. The curve is no longer exponential; it is asymptotic

to a straight line whose slope is the bulk resistance. This region is particularly important

for power diodes. The effect can be modeled as an ideal diode in series with a fixed

resistor.

In a small silicon diode at rated currents, the voltage drop is about 0.6 to 0.7 volts. The

value is different for other diode types—Schottky diodes can be rated as low as 0.2 V,

Germanium diodes 0.25 to 0.3 V, and red or blue light-emitting diodes (LEDs) can have

values of 1.4 V and 4.0 V respectively.

At higher currents the forward voltage drop of the diode increases. A drop of 1 V to 1.5

V is typical at full rated current for power diodes.

27

3.4 Shockley diode equation

The Shockley ideal diode equation or the diode law (named after transistor co-

inventor William Bradford Shockley) gives the I–V characteristic of an ideal diode in

either forward or reverse bias (or no bias). The following equation is called the Shockley

ideal diode equation when n, the ideality factor, is set equal to 1 :

where

I is the diode current,

IS is the reverse bias saturation current (or scale current),

VD is the voltage across the diode,

VT is the thermal voltage, and

N is the ideality factor, also known as the quality factor or sometimes emission

coefficient.

The ideality factor n typically varies from 1 to 2 (though can in some cases be higher),

depending on the fabrication process and semiconductor material and in many cases is

assumed to be approximately equal to 1 (thus the notation n is omitted). The ideality

factor does not form part of the Shockley ideal diode equation, and was added to account

for imperfect junctions as observed in real transistors. The factor is mainly accounting

for carrier recombination as the charge carriers cross the depletion region. By setting n =

1 above, the equation reduces to the Shockley ideal diode equation.

The thermal voltage VT is approximately 25.85 mV at 300 K, a temperature close to

"room temperature" commonly used in device simulation software. At any temperature it

is a known constant defined by:

28

where k is the Boltzmann constant, T is the absolute temperature of the p–n junction,

and q is the magnitude of charge of an electron (the elementary charge).The reverse

saturation current, IS, is not constant for a given device, but varies with temperature;

usually more significantly than VT, so that VD typically decreases as Increases.

The Shockley ideal diode equation or the diode law is derived with the assumption that

the only processes giving rise to the current in the diode are drift (due to electrical field),

diffusion, and thermal recombination–generation (R–G) (this equation is derived by

setting n = 1 above). It also assumes that the R–G current in the depletion region is

insignificant.

This means that the Shockley ideal diode equation doesn't account for the processes

involved in reverse breakdown and photon-assisted R–G. Additionally, it doesn't

describe the "leveling off" of the I–V curve at high forward bias due to internal

resistance. Introducing the ideality factor, n, accounts for recombination and generation

of carriers.

Under reverse bias voltages the exponential in the diode equation is negligible, and the

current is a constant (negative) reverse current value of −IS. The reverse breakdown

region is not modeled by the Shockley diode equation.

For even rather small forward bias voltages the exponential is very large, since the

thermal voltage is very small in comparison. The subtracted '1' in the diode equation is

then negligible and the forward diode current can be approximated by

The use of the diode equation in circuit problems is illustrated in the article on diode

modeling.

29

Reverse-recovery effect

Following the end of forward conduction in a p–n type diode, a reverse current can flow

for a short time. The device does not attain its blocking capability until the mobile charge

in the junction is depleted. The effect can be significant when switching large currents

very quickly. A certain amount of "reverse recovery time" tr (on the order of tens of

nanoseconds to a few microseconds) may be required to remove the reverse recovery

charge Qr from the diode. During this recovery time, the diode can actually conduct in

the reverse direction.

This might give rise to a large constant current in the reverse direction for a short period

of time and while the diode is reverse biased. The magnitude of such reverse current is

determined by the operating circuit (i.e., the series resistance) and the diode is called to

be in the storage-phase.  In certain real-world cases it can be important to consider the

losses incurred by this non-ideal diode effect. However, when the slew rate of the current

is not so severe (e.g. Line frequency) the effect can be safely ignored. For most

applications, the effect is also negligible for Schottky diodes.

Fig 3.3.1 several types of diodes. The scale is centimeters.

30

Fig 3.3.2 P type diode

There are several types of p–n junction diodes, which emphasize either a different

physical aspect of a diode often by geometric scaling, doping level, choosing the right

electrodes, are just an application of a diode in a special circuit, or are really different

devices like the Gunn and laser diode and the MOSFET:

Normal (p–n) diodes, which operate as described above, are usually made of

doped silicon or, more rarely, germanium. Before the development of silicon power

rectifier diodes, cuprous oxide and later selenium was used; its low efficiency gave it a

much higher forward voltage drop (typically 1.4 to 1.7 V per "cell", with multiple cells

stacked to increase the peak inverse voltage rating in high voltage rectifiers), and

required a large heat sink (often an extension of the diode's metal substrate), much larger

than a silicon diode of the same current ratings would require. The vast majority of all

diodes are the p–n diodes found in CMOS integrated circuits, which include two diodes

per pin and many other internal diodes.

31

CHAPTER FOUR

RECHARGEABLE BATTERY AND BATTRY CHARGER

4.1 Rechargeable battery

A rechargeable battery, storage battery, or accumulator is a type of electrical battery. It

comprises one or more electrochemical cells, and is a type of energy accumulator. It is

known as a secondary cell because its electrochemical reactions are electrically

reversible. Rechargeable batteries come in many different shapes and sizes, ranging

from button cells to megawatt systems connected to stabilize an electrical distribution

network. Several different combinations of chemicals are commonly used,

including: lead–acid, nickel cadmium (NiCd), nickel metal hydride (NiMH), lithium

ion(Li-ion), and lithium ion polymer (Li-ion polymer). Rechargeable batteries have

lower total cost of use and environmental impact than disposable batteries. Some

rechargeable battery types are available in the same sizes as disposable types.

Rechargeable batteries have higher initial cost but can be recharged very cheaply and

used many times.

Fig 4.1.1 Batteries in series

32

4.1.1 Usage and applications

Rechargeable batteries are used for automobile starters, portable consumer devices, light

vehicles (such as motorized wheelchairs, golf carts, electric bicycles, and

electric forklifts), tools, and uninterruptible power supplies. Emerging applications

in hybrid electric vehicles and electric vehicles are driving the technology to reduce cost

and weight and increase lifetime. Traditional rechargeable batteries have to be charged

before their first use; newer low self-discharge NiMH batteries hold their charge for

many months, and are typically charged at the factory to about 70% of their rated

capacity before shipping.

Grid energy storage applications use rechargeable batteries for load leveling, where they

store electric energy for use during peak load periods, and for renewable uses, such as

storing power generated from photovoltaic arrays during the day to be used at night. By

charging batteries during periods of low demand and returning energy to the grid during

periods of high electrical demand, load-leveling helps eliminate the need for expensive

peaking and helps amortize the cost of generators over more hours of operation. The

US National Electrical Manufacturers Association has estimated that U.S. demand for

rechargeable batteries is growing twice as fast as demand for non rechargeable.

4.1.2 Charging and discharging

During charging, the positive active material is oxidized, producing electrons, and the

negative material is reduced, consuming electrons. These electrons constitute

the current flow in the external circuit. The electrolyte may serve as a simple buffer for

internal ion flow between the electrodes, as in lithium-ion and nickel-cadmium cells, or

it may be an active participant in the electrochemical reaction, as in lead–acid cells.

charge time with solar; 10 hours

Charge time with charger; 6 hours

Discharge time; 2 hours continuous use around 10-15km

33

Fig 4.1.2 Diagram of secondary cell battery.

Fig 4.2 Battery Charger34

4.2 A solar-power consumer

The energy used to charge rechargeable batteries usually comes from a battery

charger using AC mains electricity, although some are equipped to use a vehicle's 12-

volt DC power outlet. Regardless, to store energy in a secondary cell, it has to be

connected to a DC voltage source. The negative terminal of the cell has to be connected

to the negative terminal of the voltage source and the positive terminal of the voltage

source with the positive terminal of the battery. Further, the voltage output of the source

must be higher than that of the battery, but not much higher: the greater the difference

between the power source and the battery's voltage capacity, the faster the charging

process, but also the greater the risk of overcharging and damaging the battery.

Chargers take from a few minutes to several hours to charge a battery. Slow "dumb"

chargers without voltage- or temperature-sensing capabilities will charge at a low rate,

typically taking 14 hours or more to reach a full charge. Rapid chargers can typically

charge cells in two to five hours, depending on the model, with the fastest taking as little

as fifteen minutes. Fast chargers must have multiple ways of detecting when a cell

reaches full charge (change in terminal voltage, temperature, etc.) to stop charging

before harmful overcharging or overheating occurs.

Battery charging and discharging rates are often discussed by referencing a "C" rate of

current. The C rate is that which would theoretically fully charge or discharge the battery

in one hour. For example, trickle charging might be performed at C/20 (or a "20 hour"

rate), while typical charging and discharging may occur at C/2 (two hours for full

capacity). The available capacity of electrochemical cells varies depending on the

discharge rate. Some energy is lost in the internal resistance of cell components (plates,

electrolyte, interconnections), and the rate of discharge is limited by the speed at which

chemicals in the cell can move about. For lead-acid cells, the relationship between time

and discharge rate is described by Peukert's law; a lead-acid cell that can no longer

sustain a usable terminal voltage at a high current may still have usable capacity, if

discharged at a much lower rate.

35

Flow batteries, used for specialised applications, are recharged by replacing the

electrolyte liquid. Battery manufacturers' technical notes often refer to VPC; this

is volts per cell, and refers to the individual secondary cells that make up the battery.

(This is typically in reference to 12-volt lead-acid batteries.) For example, to charge a 12

V battery (containing 6 cells of 2 V each) at 2.3 VPC requires a voltage of 13.8 V across

the battery's terminals.

Non-rechargeable alkaline and zinc–carbon cells output 1.5V when new, but this voltage

drops with use. Most NiMH AA and AAA cells are rated at 1.2 V, but have a flatter

discharge curve than alkaline and can usually be used in equipment designed to use

alkaline batteries.

4.2.1 Reverse charging

Subjecting a discharged cell to a current in the direction which tends to discharge it

further, rather than charge it, is called reverse charging; this damages cells. Reverse

charging can occur under a number of circumstances, the two most common being:

When a battery or cell is connected to a charging circuit the wrong way around.

When a battery made of several cells connected in series is deeply discharged.

When one cell completely discharges ahead of the rest, the remaining cells will force the

current through the discharged cell. Instead of supplying a forward voltage to the load,

the discharged cell becomes part of the load and presents a reverse voltage to the rest of

the circuit. This is known as "cell reversal", and can happen even to a weak cell that is

not fully discharged. If the battery drain current is high enough, the weak cell's internal

resistance can create a reverse voltage that is greater than the cell's remaining internal

forward voltage. This results in the reversal of the weak cell's polarity while the current

is flowing through the cells. 

36

The higher the required discharge rate of the battery, the better matched the cells should

be, both in kind of cell and state of charge, in order to reduce the chances of one cell

completely discharging before the others. Also, many battery-operated devices have a

low-voltage cutoff that prevents deep discharges from occurring that might cause cell

reversal.

In critical applications using Ni-Cad batteries, such as in aircraft, each cell is

individually discharged by connecting a load clip across the terminals of each cell,

thereby avoiding cell reversal, then charging the cells in series.

4.2.2 Depth of discharge

Depth of discharge (DOD) is normally stated as a percentage of the nominal ampere-

hour capacity; 0% DOD means no discharge. Seeing as the usable capacity of a battery

system depends on the rate of discharge and the allowable voltage at the end of

discharge, the depth of discharge must be qualified to show the way it is to be measured.

Due to variations during manufacture and aging, the DOD for complete discharge can

change over time or number of charge cycles. Generally a rechargeable battery system

will tolerate more charge/discharge cycles if the DOD is lower on each cycle.

BAT-03 6V / 1600mAh Ni-MH Rechargeable Battery

The Lynx motion 6.0vdc Ni-MH 1600mAh battery pack is made from five high capacity

AA cells and 18 gauge multi-conductor wires for the best power transfer possible. The

quick connect plug makes it easy to retrofit these battery packs into your cool robot

design. This pack weighs 5.03oz., about half the weight of an equivalent Ni-Cad pack,

perfect for your walking or fighting robot.

Note: These battery packs were rigorously tested with automated equipment that repeat

the charge and discharge cycles, logging the capacity in mAh's. These battery packs

routinely tested better than Sanyo packs, which cost three times as much.

37

4.3 Battery Specifications

Pack measures 2.10" x 2.88" x 0.63"

Full charge voltage: 7.25vdc

Nominal voltage: 6.0vdc

Nominal capacity: 1600mAh

Max discharge current: 16A

Rapid charge: 1600mA / 1.2 hours

Battery TypeNominal Voltage(V)

20hrate capacity(ah)

Size(mm)Weight(kg)

Length Width HeightTotal height

HYPLUSH 12-12

12 12 151 98 98 102 4.3

Table 4.1 Battery features

Table 4.2 Battery Parameter

Capacity 77°F(25°C)

20 hours rate (0.255A 5.25V) 4.5Ah

10 hours rate (0.43A 5.25V) 4.3aAh

5 hours rate (0.78A 5.25V) 3.9aAh

1 hour rate (2.8A 4.8V) 2.8aAh

Internal Resistance Full charged battery 77°F(25°C):30mΩ

Capacity affected by Temperature (20 hour rate)

104°F(40°C) 102%

77°F(25°C) 100%

32°F(10°C) 85%

5°F(-15°C) 65%

Self-Discharge 68°F(20°C)

Capacity after 3 month storage 90%

Capacity after 6 month storage 80%

Capacity after 12 month storage 60%

Max discharge current 77°F(25°C);61.5A(5S)

38

Charge (constant voltage)

Float:6.8 to 6.9V/77°F(25°F)

Cycle:7.25 to 7.45V/77°F(25°C)

Max Current: 1.13A

CHAPTER FIVE

D.C.MOTOR

5.1 Description of D.C. Motor

A dc motor uses electrical energy to produce mechanical energy, very typically

through the interaction of magnetic fields and current-carrying conductors. The reverse

process, producing electrical energy from mechanical energy, is accomplished by

an alternator, generator or dynamo. Many types of electric motors can be run as

generators, and vice versa. The input of a DC motor is current/voltage and its output is

torque (speed).

Fig 5.1 DC Motor

The DC motor has two basic parts: the rotating part that is called the armature and the

stationary part that includes coils of wire called the field coils. The stationary part is also

called the stator. Figure shows a picture of a typical DC motor, Figure shows a picture of

39

a DC armature, and Fig shows a picture of a typical stator. From the picture you can see

the armature is made of coils of wire wrapped around the core, and the core has an

extended shaft that rotates on bearings.

You should also notice that the ends of each coil of wire on the armature are terminated

at one end of the armature. The termination points are called the commentator, and this is

where the brushes make electrical contact to bring electrical current from the stationary

part to the rotating part of the machine.

5.1.1Operation:

The DC motor you will find in modem industrial applications operates

very similarly to the simple DC motor described earlier in this chapter. Figure shows an

electrical diagram of a simple DC motor. Notice that the DC voltage is applied directly

to the field winding and the brushes. The armature and the field are both shown as a coil

of wire. In later diagrams, a field resistor will be added in series with the field to control

the motor speed.

When voltage is applied to the motor, current begins to flow through the field

coil from the negative terminal to the positive terminal. This sets up a strong magnetic

field in the field winding. Current also begins to flow through the brushes into a

commentator segment and then through an armature coil.

The current continues to flow through the coil back to the brush that is attached to other

end of the coil and returns to the DC power source. The current flowing in the armature

coil sets up a strong magnetic field in the armature.

40

Fig 5.1.2 Simple electrical diagram of DC motor

Fig 5.1.3 Operation of a DC Motor

The magnetic field in the armature and field coil causes the armature to

begin to rotate. This occurs by the unlike magnetic poles attracting each other and the

like magnetic poles repelling each other. As the armature begins to rotate, the

commentator segments will also begin to move under the brushes. As an individual

commentator segment moves under the brush connected to positive voltage, it will

become positive, and when it moves under a brush connected to negative voltage it will

become negative. In this way, the commentator segments continually change polarity

from positive to negative.

41

Since the commentator segments are connected to the ends of the wires that make up the

field winding in the armature, it causes the magnetic field in the armature to change

polarity continually from North Pole to South Pole. The commentator segments and

brushes are aligned in such a way that the switch in polarity of the armature coincides

with the location of the armature's magnetic field and the field winding's magnetic field.

The switching action is timed so that the armature will not lock up magnetically with the

field. Instead the magnetic fields tend to build on each other and provide additional

torque to keep the motor shaft rotating.

When the voltage is de-energized to the motor, the magnetic fields in the armature and

the field winding will quickly diminish and the armature shaft's speed will begin to drop

to zero. If voltage is applied to the motor again, the magnetic fields will strengthen and

the armature will begin to rotate again.

5.1.2 Motor Features

2500RPM 24V DC motors with Metal Gearbox and Metal Gears 

18000 RPM base motor

6mm Dia shaft with M3 thread hole

Gearbox diameter 37 mm.

Motor Diameter 53.8 mm

Length 134.5 mm without shaft

Shaft length 30mm

180gm weight

30kgcm torque

No-load current = 800 mA, Load current = up to 7.5 A(Max)

Recommended to be used with DC Motor Driver 20A or Dual DC Motor Driver

20A  

5.2 High torque DC motor

42

The Direct Drive DC torque motor is a servo actuator which can be directly attached

to the load it drives. It has a permanent magnet (PM) field and a wound armature which

act together to convert electrical power to torque. This torque can then be utilized in

positioning or speed control systems. In general, torque motors are deigned for three

different types of operation: • High stall torque (“stand-still” operation) for positioning

systems High torque at low speeds for speed control systems, and Optimum torque at

high speed for positioning, rate, or tensioning systems.

Direct drive torque motors are particularly suited for servo system applications where

it is desirable to minimize size, weight, power and response time, and to maximize rate

and position accuracies. Frameless motors range from 28.7mm (1.13in) OD weighing 1.4

ounces (.0875 lbs) to a 4067 N-m (3000 lb-ft) unit with a 1067mm (42in) OD and a

660.4mm (26in) open bore ID. Housed motors range from a one inch cube design with

0.049 N-m (7 oz-in) peak torque to any of the frameless motors housed to customer

specifications with integral DC tachometers, resolvers, encoders and shaft

configurations.

5.3 Advantages of Direct Drive DC Torque Motors

5.3.1 High Torque-to-Inertia Ratio at the Load

A direct drive motor provides the highest practical torque to- inertia ratio where it counts

—at the oad. In a geared system, reflected output torque is proportional to the gear

reduction while reflected output inertia is proportional to the square of the gear

reduction. Thus, the torque-to-inertia ratio in a geared system is less than that of a direct

drive system by a factor equal to the gear-train ratio. The higher torque-to-inertia ratio of

direct drive motors makes them ideally suited for high acceleration applications with

rapid starts and stops.

43

5.3.2 High Torque-to-Power Ratio

Most torque motors are designed with a large number of poles and a high volume of

copper to achieve a high torque to- power ratio. Thus, input power requirements are

usually low.

Typical torque motor design features — such as high-level magnetic saturation of the

armature core and the use of a large number of poles — keep armature inductance at a

very low value. Consequently, the electrical time constant (the ratio of armature

inductance to armature resistance) is very low, providing excellent command response at

all operating speeds.

High Linearity

In a DC torque motor, torque increases directly with input current at all speeds and

angular positions. The theoretical speed-torque characteristic is a set of parallel straight

lines (Figure 1). This torque linearity is maintained even at low excitation, assuring no

dead-band created by torque non-linearity for all input currents up to the peak rating of

the motor.

Reliability and Long Life

Basic simplicity and an absolute minimum of moving parts make a torque motor

inherently reliable. Extensive design and production experience have placed

Kollmorgen’s motors in critical applications where high performance motion control is

required for the last three decades. These include applications in all conditions and

environments, ranging from thousands of feet underwater to years of unattended

44

operation in outer space. Brushes are capable of operating in a hard vacuum with “high

altitude” additives.

High Resolution

The direct drive use of torque motors allows them to position a shaft more precisely than

a geared system. With typical gearing, the backlash contributes to a “dead zone” which

falls in the region of the system null point and reduces positional accuracy. In a direct

drive system, however, the positional accuracy is limited only by the error detecting

transducer system.

Compact, Adaptable Design

Frameless torque motors are built to be “designed-in” as an integral part of a system,

thus saving the weight and space associated with conventional motor frames or housings.

This frameless design allows the motors to be mounted anywhere along the driven shaft.

The “pancake” configuration minimizes the volume required for mounting and offers a

convenient packaging arrangement for combinations of torque motors and tachometer

generators. Kollmorgen also supplies housed motors, complete with housing, shaft and

bearings for use in similar applications.

System Performance Characteristics

The same features which give torque motors an advantage over other types of servo

actuators also allow the designer to obtain the following system performance

characteristics.

High Servo Stiffness

The direct-drive torque motor is coupled directly to the load, thus eliminating gears and

backlash errors. The resulting high coupling stiffness and associated high mechanical

resonance frequency yield high servo stiffness.45

High Resolution

The direct-drive use of torque motors allows them to position a shaft more precisely than

a geared system. With typical gearing, the backlash contributes to a “dead zone” which

falls in the region of the system null point and reduces positional accuracy. In a direct-

drive system, however, the positional accuracy is, in practice, limited only by the error

detecting transducer system.

Low Speeds with High Accuracy

Because of the high coupling stiffness and high resolution of direct-drive torque motors,

it is possible to achieve high accuracy at low speeds. An example is a table for testing

rate and integrating gyros. This table has a speed range of 0.017 to 100 rpm with

absolute instantaneous accuracy over this speed range of 0.1 percent.

Smooth, Quiet Operation

Torque motors exhibit smooth, quiet operation when they are run at low speeds. They

typically have a large number of slots per pole to reduce cogging and allow for smooth

operation.

Frameless or Housed

Both the torque motor section and the servo motor section of this catalog are divided into

subsections of frameless motors and housed motors. Housed motors have a traditional

configuration including frame, bearings, and shaft. In use, the housed motor shaft is

coupled to the system element being driven. Housed motors are ideal for use in harsh

environments or other applications requiring totally closed units. The frameless motor

concept was developed to meet the need for motors with a large hole through the center. 46

This need is still one of the main reasons that the large diameter, narrow width frameless

configuration is often selected over the traditional housed configuration. The large rotor

bore can be used as a route for lead wires, as a mounting area for other hard ware such as

tachometer generators or resolvers, or as an optical path.

Frameless motors are built to be “designed in” as an integral part of the system hardware.

They are generally supplied as three separate components: stator assembly and brush

ring or brush segment assembly. The frameless motor can be integrated into the customer

hardware rather than coupling a motor shaft to the element being driven. This allows

significant savings in space and weight over housed motors by eliminating the motor

housings, bearings and shaft.

5.4 Torque Motor or Servo Motor?

A torque motor is typically described as having a “pancake” configuration, i.e., a large

diameter and a narrow width. This configuration generally has a large number of poles to

increase the torque available in a given volume. This large number of poles, however,

also causes more commutation arcing as speed increases than for a motor with few poles.

Torque motors are most commonly used in positioning and slow speed rate applications

where commutation is not a limitation.

A servo motor is characterized by a long, small diameter configuration. Lengthening a

motor while maintaining a small diameter allows a significant increase in torque while

minimizing the increase in rotor inertia. The end result is an improved mechanical time

constant and, therefore, improved motor response. Servo motors are most commonly

used in running applications where good high-speed commutation is demanded and

operation at or near stall is not required.

47

Fig 5.2 Magnet Material

Magnet Material

The motors are manufactured with one of two magnet materials:

Alnico or rare earth (Samarium Cobalt and Neodymium-Iron-Boron). Model numbers

preceded by “T’, “NT”, or “OT” has Alnico magnets and models preceded by “QT” have

rare earth magnets. These magnet materials have different characteristics which

determine their suitability for various applications.

5.4.1 Performance

A major advantage of rare earth magnet motors is stability of magnetic characteristics in

overcurrent conditions. In Alnico magnet motors, exceeding the rated current Ip to

develop more torque may demagnetize the permanent magnet field and cause a

permanent reduction in torque per unit current. The degree of demagnetization is

determined by the magnitude of the overload current in rare earth magnet units, currents

48

in excess of Ip can be applied for short duration to develop higher torque without

demagnetization of the PM Field. The limits now become primarily the thermal capacity

of the motor and the current density rating of the brushes Rare earth magnet motors that

are designed to have comparable resistance to similar Alnico designs will generally have

a lower inductance value than the Alnico design

5.4.2 Installation

Alnico magnet motors require a keeper ring or keeper segments to provide a return flux

path for the field when the rotor is not in place. Removing or shifting the keeper before

inserting the armature into the field will cause significant degradation of performance. In

rare earth magnet motors the magnet material has much higher intrinsic coercive force.

This feature makes the field assembly immune to the effects of an open magnetic circuit

and therefore a keeper is not required. Eliminating the keeper can simplify installation

considerably.

The mounting surfaces for frameless Alnico magnet motors must be made of non-

magnetic material such as aluminum, brass or non-magnetic stainless steel. The

minimum thickness of non-magnetic material required to separate the field structure

from magnetic material is one quarter inch. Rare earth motors may be mounted in

magnetic or non-magnetic housings. Rare earth magnet material is more brittle than

Alnico, and care must be exercised to avoid chipping or cracking.

Because rare earth motors are designed with the magnets on the inner diameter of the

stator assembly facing the armature, extra care must be taken when inserting the

armature into the field assembly. Most rare earth units have larger radial air gaps than

similar size Alnico units. The larger air gap of rare earth units makes rotor-to-stator

concentricity less critical.

5.5 Motor Specifications

49

24V DC MOTOR SPECIFICATIONS FOR ELECTRIC TOYS ZY6310

1. CE Certified

2. Typical Designed Model

3. Used for Electronic Tools

Product Size: 53.8 mm in Diameter, 134.5mm in Length

Voltage:24V

Torque:0.31-0.46N.m 

RatedOutput:80W-120W 

Speed: 2200-2500rpm

5.5.1 Applications

Direct drive mechanisms are present in several products

Fans: Imprecise, depending on the fan, between 1000 and 12000 rpm.

Sewing machines: 3000 rpm to 5000 rpm depending on machine type.

Turn tables: CNC machines with fast and precise turning tables

CHAPTER SIX

COUPLING BELT, BRAKE AND WHEEL

Coupling belt:

50

Fig 6.1.1 Coupling belt

Table 6.1 BELT SPECIFICATION

Number Of Teeth 140

*Length Of Belt 420mm or ~16-1/2"

Peak To Peak Distance Between Two Adjacent Belt Teeth

3mm or ~1/8"

Width Of Belt 12mm or ~7/16"

6.1 V-Belt Drives

Recognized as “Large Sheave” experts…through 108-inch maximum capacity

Integrated foundry and machining for superior response time on stock and

made-to-order

Value-added services, including kitting and drive selection software program

51

6.1.1 Synchronous Drives

Combine the best of both chain and belted drives

Low noise compared to chain

Perfect for many high-speed, low-torque applications

6.1.2 Mechanical Variable Speed Drives

A proven lubrication system that eliminates fretting, corrosion, freezing, and

sticking.

Constant pitch diameter and constant speed are maintained under varying torque

loads

Belt arrangement

Fig 6.1.2 Belt arrangement

Band Brake

52

Fig 6.2.1 Band Brake

6.2 Brake specification

Black Band Brake with 60mm Rotor Universal fit band brake assembly with heavy-duty brake rotor for electric scooters and electric bikes.Band brake housing measures 3-1/8" across. Fits 1-3/8" (35mm) OD threaded wheel hubs. Rotor dimensions 2-3/8" (60mm)

Brake arrangement

53

Fig 6.2.2 Brake arrangement

54

Rear wheel with brake rotor

Fig 6.3.1 Rear wheel with Brake Rotor

6.3 Wheel Specification

5-1/2" Rear Wheel with Solid Urethane Tire, Brake Rotor, and Belt Cog 

Rear plastic electric scooter wheel with solid urethane airless flat-free tire. Includes

wheel bearings, bearing spacer, and 60mm band brake rotor.

55

CHAPTER SEVEN

ANALYSIS

7.1 Speed of scooter without load

V (linear velocity) =?

Rpm (angular velocity) =2500

Radius of wheel = 0.00007

7.2 Speed of scooter with load

As load is applied the motor draws more current, which increases torque. However as current flows through the windings their resistance causes the effective voltage to

drop, so motor speed decreases. Below rpm the power output will also

decrease.

When motor speed decreases to

V (linear velocity) =?

Rpm (angular velocity) = 1500

Radius of wheel = 0.00007

56

When motor speed decreases to

V (linear velocity) =?

Rpm (angular velocity) =1250

Radius of wheel = 0.00007

When motor speed decreases to

V (linear velocity) =?

Rpm (angular velocity) = 1000

57

Radius of wheel = 0.00007

GRAPH:

58

CHAPTER EIGHT

BODY PARTS AND DIMENSSIONS59

8.1 Front wheel

Fig 8.1.1 Front wheel

8.2 Handle rod

Fig 8.2.1 Handle

8.3 Base & battery box

60

Fig 8.3.1 Base & Battery box

8.4 Base panel or Standing plate

Fig 8.4.1 Base panel

8.5 IC circuit with charge controller

61

Fig 8.5.1 IC circuit

Advantages

Increased efficiency: The power is not wasted in friction (from the belt, chain, etc., and

specially, gearboxes .

Reduced noise: Being a simpler device, a direct-drive mechanism has fewer parts which

could vibrate, and the overall noise emission of the system is usually lower.

Longer lifetime: Having fewer moving parts also means having fewer parts prone to

failure. Failures in other systems are usually produced by aging of the component (such

as a stretched belt), or stress.

High torque at low rpm. Faster and precise positioning. High torque and low inertia

allows faster positioning times on permanent magnet synchronous servo drives.

Feedback sensor directly on rotary part allows precise angular position sensing. Drive

stiffness. Mechanical backlash, hysteresis and elasticity is removed avoiding use of

gearbox or ball screw mechanisms.

Disadvantages

62

The main disadvantage of the system is that it needs a special motor. Usually motors are

built to achieve maximum torque at high rotational speeds, usually 1500 or 3000rpm.

While this is useful for many applications (such as an electric fan), other mechanisms

need a relatively high torque at very low speeds, such as a phonograph turntable, which

needs a constant (and very precise) 331⁄3 rpm or 45 rpm.

The slow motor also needs to be physically larger than its faster counterpart. For

example, in a belt-coupled turntable, the motor diameter is about 1 inch (2.5 cm). On a

direct-drive turntable, the motor is about 4" (10 cm).

Also, direct-drive mechanisms need a more precise control mechanism. High speed

motors with speed reduction have relatively high inertia, which helps smooth the output

motion. Most motors exhibit positional torque ripple known as cogging torque. In high

speed motors, this effect is usually negligible, as the frequency at which it occurs is too

high to significantly affect system performance; direct drive units will suffer more from

this phenomenon, unless additional inertia is added (i.e. by a flywheel) or the system

uses feedback to actively counter the effect.

Conclusion:

The solar traveller is easily accessible, safe and practical with limited maintenance

requirements because of few mechanical parts.

It is ideal not only for the experienced cyclists but also for those non athletes, the elderly

and individuals with health problems.

This is the best source to replace the fuel which is exhausting day by day and becoming

more costly.

References:

63

NCA-CASI. "NCA-Council on Accreditation and School Improvement".

Retrieved 2009-06-23.

Jump up  Student Participation in Activities

 Jump up to: a  b "Biographies of the Justices of the Minnesota Supreme Court".

Minnesota State Library. Retrieved January 24, 2014.

Jump up  Marquette Player Page

John Horan '51, NBA Basketball Player

Michael Wright '56, former CEO and Chair of the Board of Directors

of Supervalu

Peter Matlon '63, former Economic Director, Rockefeller Foundation

Mike Ciresi  '64, lawyer from the Twin Cities with great success in mass tort

litigation. He has been a candidate for several offices in Minnesota

Patrick Lippert '76, Founding Executive Director of Rock The Vote

James O'Shaughnessy '78, CEO O'Shaughnessy Asset Management (OSAM)

Patck “Pat” Eilers ’85 - NFL Football Player (won a national championship at

Notre Dame; played for Minnesota Vikings, Washington Redskins and Chicago

Bears)

Tom Malchow  '95, Captain of U.S. Swim Team at the 2004 Summer Olympic,

gold medal winner (2000)

Maht Schnobrich  '97, 2008 Summer Olympics crew bronze medalist

Dan Fitzgerald  '03, Forward for the Marquette University basketball team

Michael Wright '56, former CEO and Chair of the Board of Directors

of Supervalu

Peter '63, former Economic Director, Rockefeller Foundation

Ciresi  '64, lawyer from the Twin Cities with great success in mass tort

litigation. He has been a candidate for several offices in Minnesota

Patrick Lippert '76, Founding Executive Director of Rock The Vote

Shaughnessy '78, CEO O'Shaughnessy Asset Management (OSAM)

64