INDEX

TOPICS

Certificates

Acknowledgement........

CHAPTER 1: INTRODUCTION

1.1 Introduction of the project

1.2 Project overview...

1.3 Thesis

CHAPTER 2: HARDWARE DESCRIPTION

2.1 Introduction with block diagram

2.2 Regulated power supply...

2.4 LED Indicator...........

2.5 Solar plate..

2.6 Motor..

2.7 Comparator..

2.8 Relay...

CHAPTER 3: PROJECT DESCRIPTION

CHAPTER 4: ADVANTAGES, DISADVANTAGES AND APPLICATIONS

CHAPTER 5: RESULTS, CONCLUSION, FUTURE PROSPECTS

REFERENCES

CHAPTER 1: INTRODUCTION

1.1 Introduction: The project aims at designing a system which makes the grass cutter based motor running through solar energy.

Power plays a great role wherever man lives and works. The living standard and prosperity of a nation vary directly with the increase in the use of power. The electricity requirement of the world is increasing at an alarming rate due to industrial growth, increased and extensive use of electrical gadgets. According to world energy report, we get around 80% of our energy from conventional fossil fuels like oil (36%), natural gas (21%) and coal (23%). It is well known that the time is not so far when all these sources will be completely exhausted. So, alternative sources should be used to avoid energy crisis in the nearby future. The best alternative source is solar energy.

A solar panel is a large flat rectangle, typically somewhere between the size of a radiator and the size of a door, made up of many individual solar energy collectors called solar cells covered with a protective sheet of glass. The cells, each of which is about the size of an adult's palm, are usually octagonal and colored bluish black. Just like the cells in a battery, the cells in a solar panel are designed to generate electricity; but where a battery's cells make electricity from chemicals, a solar panel's cells generate power by capturing sunlight instead. They are sometimes called photovoltaic cells because they use sunlight ("photo" comes from the Greek word for light) to make electricity (the word "voltaic" is a reference to electricity pioneer Alessandro Volta).

The system depending on the charging circuit the motor can be controlled using relay switch. The solar power stores the energy to a battery and then runs the motor through the relay switch. The system also includes comparator circuit for checking the temperature of the motor and when it goes beyond the limit the motor gets switched off automatically using relay switch.Features:

1. Utilization of free available source of energy from sun2. Storage of energy into rechargeable battery.

3. Stored energy is used for running grass cutter motor.4. Temperature sensor based comparator

5. Charging circuit

6. Relay switch for ON/OFF control7. Low Power consumption8. Long life.

1.2 Project Overview:

An embedded system is a combination of software and hardware to perform a dedicated task. Some of the main devices used in embedded products are Microprocessors and Microcontrollers.

The project Solar based grass cutter using solar panel which is used to recharge the battery for running the grass cutter motor, freely available source of energy solar energy. 1.3 Thesis:

The thesis explains the implementation of Solar based grass cutter using Solar panel, relay, charging circuit, comparator, temperature sensor and also motor. The organization of the thesis is explained here with:

Chapter 1 Presents introduction to the overall thesis and the overview of the project. In the project overview a brief introduction of Solar panel, relay, charging circuit, comparator, temperature sensor and also motor, grass cutter and its applications are discussed. Chapter 2 Presents the hardware description. It deals with the block diagram of the project and explains the purpose of each block. In the same chapter the explanation of Solar panel, relay, charging circuit, comparator, temperature sensor and also motor are considered.

Chapter 3 Presents the software description. It explains the implementation of the project using PIC C Compiler software.

Chapter 4 Presents the project description along with Solar panel, relay, charging circuit, comparator, temperature sensor and also motor, interfacing circuit.

Chapter 5 Presents the advantages, disadvantages and applications of the project.Chapter 6 Presents the results, conclusion and future scope of the project.CHAPTER 2: HARDWARE DESCRIPTION3.1 Introduction:

In this chapter the block diagram of the project and design aspect of independent modules are considered. Block diagram is shown in fig: 3.1:

FIG 3.1: Block diagram of Solar based grass cutterThe main blocks of this project are:1. Regulator2. Solar cell/plate

3. Charging circuit4. DC motor

5. Relay 6. Comparator

7. Temperature sensor

3.3 REGULATED POWER SUPPLY:

3.3.1 Introduction:

Power supplyis a supply ofelectrical power. A device or system that supplieselectrical or other types ofenergyto an output loador group of loads is called a power supply unitorPSU. The term is most commonly applied to electrical energy supplies, less often to mechanical ones, and rarely to others. A power supply may include a power distribution system as well as primary or secondary sources of energy such as Conversion of one form of electrical power to another desired form and voltage, typically involving convertingACline voltage to a well-regulated lower-voltageDCfor electronic devices. Low voltage, low power DC power supply units are commonly integrated with the devices they supply, such ascomputersand household electronics.

Batteries. Chemicalfuel cellsand other forms ofenergy storagesystems.

Solar power.

Generators oralternators.

3.3.2 Block Diagram:

Fig 3.3.2 Regulated Power Supply

The basic circuit diagram of a regulated power supply (DC O/P) with led connected as load is shown in fig: 3.3.3.

Fig 3.3.3 Circuit diagram of Regulated Power Supply with Led connection The components mainly used in above figure are

230V AC MAINS

TRANSFORMER

BRIDGE RECTIFIER(DIODES)

CAPACITOR

VOLTAGE REGULATOR(IC 7805)

RESISTOR

LED(LIGHT EMITTING DIODE)

The detailed explanation of each and every component mentioned above is as follows:

Transformation: The process of transforming energy from one device to another is called transformation. For transforming energy we use transformers.

Transformers:

Atransformeris a device that transferselectrical energyfrom onecircuitto another throughinductively coupledconductors without changing its frequency. A varyingcurrentin the first or primarywinding creates a varyingmagnetic fluxin the transformer's core, and thus a varyingmagnetic fieldthrough thesecondarywinding. This varying magnetic fieldinducesa varyingelectromotive force (EMF)or "voltage" in the secondary winding. This effect is calledmutual induction.

If aloadis connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. This field is made up from lines of force and has the same shape as a bar magnet.

If the current is increased, the lines of force move outwards from the coil. If the current is reduced, the lines of force move inwards.

If another coil is placed adjacent to the first coil then, as the field moves out or in, the moving lines of force will "cut" the turns of the second coil. As it does this, a voltage is induced in the second coil. With the 50 Hz AC mains supply, this will happen 50 times a second. This is called MUTUAL INDUCTION and forms the basis of the transformer.

The input coil is called the PRIMARY WINDING; the output coil is the SECONDARY WINDING. Fig: 3.3.4 shows step-down transformer.

Fig 3.3.4: Step-Down Transformer

The voltage induced in the secondary is determined by the TURNS RATIO.

For example, if the secondary has half the primary turns; the secondary will have half the primary voltage.

Another example is if the primary has 5000 turns and the secondary has 500 turns, then the turns ratio is 10:1.

If the primary voltage is 240 volts then the secondary voltage will be x 10 smaller = 24 volts. Assuming a perfect transformer, the power provided by the primary must equal the power taken by a load on the secondary. If a 24-watt lamp is connected across a 24 volt secondary, then the primary must supply 24 watts.

To aid magnetic coupling between primary and secondary, the coils are wound on a metal CORE. Since the primary would induce power, called EDDY CURRENTS, into this core, the core is LAMINATED. This means that it is made up from metal sheets insulated from each other. Transformers to work at higher frequencies have an iron dust core or no core at all.

Note that the transformer only works on AC, which has a constantly changing current and moving field. DC has a steady current and therefore a steady field and there would be no induction.

Some transformers have an electrostatic screen between primary and secondary. This is to prevent some types of interference being fed from the equipment down into the mains supply, or in the other direction. Transformers are sometimes used for IMPEDANCE MATCHING.

We can use the transformers as step up or step down.

Step Up transformer:

In case of step up transformer, primary windings are every less compared to secondary winding. Because of having more turns secondary winding accepts more energy, and it releases more voltage at the output side.

Step down transformer:

Incase of step down transformer, Primary winding induces more flux than the secondary winding, and secondary winding is having less number of turns because of that it accepts less number of flux, and releases less amount of voltage.

Battery power supply:

Abatteryis a type of linear power supply that offers benefits that traditional line-operated power supplies lack: mobility, portability and reliability. A battery consists of multiple electrochemical cells connected to provide the voltage desired. Fig: 3.3.5 shows Hi-Watt 9V battery Fig 3.3.5: Hi-Watt 9V Battery

The most commonly useddry-cellbattery is thecarbon-zincdry cell battery.Dry-cell batteries are made by stacking a carbon plate, a layer of electrolyte paste, and a zinc plate alternately until the desired total voltage is achieved. The most common dry-cell batteries have one of the following voltages: 1.5, 3, 6, 9, 22.5, 45, and 90. During the discharge of a carbon-zinc battery, the zinc metal is converted to a zinc salt in the electrolyte, and magnesium dioxide is reduced at the carbon electrode. These actions establish a voltage of approximately 1.5 V.

Thelead-acidstorage battery may be used. This battery is rechargeable; it consists of lead and lead/dioxide electrodes which are immersed in sulfuric acid. When fully charged, this type of battery has a 2.06-2.14 V potential (A 12 voltcar batteryuses 6 cells in series). During discharge, the lead is converted to lead sulfate and the sulfuric acid is converted to water. When the battery is charging, the lead sulfate is converted back to lead and lead dioxide Anickel-cadmiumbattery has become more popular in recent years.This battery cell is completely sealed and rechargeable. The electrolyte is not involved in the electrode reaction, making the voltage constant over the span of the batteries long service life. During the charging process, nickel oxide is oxidized to its higher oxidation state and cadmium oxide is reduced. The nickel-cadmium batteries have many benefits. They can be stored both charged and uncharged. They have a long service life, high current availabilities, constant voltage, and the ability to be recharged. Fig: 3.3.6 shows pencil battery of 1.5V.

Fig 3.3.6: Pencil Battery of 1.5V

Rectification:

The process of converting an alternating current to a pulsating direct current is called as rectification. For rectification purpose we use rectifiers.Rectifiers:

A rectifier is an electrical device that converts alternating current (AC) to direct current (DC), a process known as rectification. Rectifiers have many uses including as components of power supplies and as detectors of radio signals. Rectifiers may be made of solid-state diodes, vacuum tube diodes, mercury arc valves, and other components.

A device that it can perform the opposite function (converting DC to AC) is known as an inverter.

When only one diode is used to rectify AC (by blocking the negative or positive portion of the waveform), the difference between the term diode and the term rectifier is merely one of usage, i.e., the term rectifier describes a diode that is being used to convert AC to DC. Almost all rectifiers comprise a number of diodes in a specific arrangement for more efficiently converting AC to DC than is possible with only one diode. Before the development of silicon semiconductor rectifiers, vacuum tube diodes and copper (I) oxide or selenium rectifier stacks were used.Bridge full wave rectifier:

The Bridge rectifier circuit is shown in fig:3.3.7, which converts an ac voltage to dc voltage using both half cycles of the input ac voltage. The Bridge rectifier circuit is shown in the figure. The circuit has four diodes connected to form a bridge. The ac input voltage is applied to the diagonally opposite ends of the bridge. The load resistance is connected between the other two ends of the bridge. For the positive half cycle of the input ac voltage, diodes D1 and D3 conduct, whereas diodes D2 and D4 remain in the OFF state. The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL.

For the negative half cycle of the input ac voltage, diodes D2 and D4 conduct whereas, D1 and D3 remain OFF. The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle. Thus a bi-directional wave is converted into a unidirectional wave.

Input

Output

Fig 3.3.7: Bridge rectifier: a full-wave rectifier using 4 diodesDB107:

Now -a -days Bridge rectifier is available in IC with a number of DB107. In our project we are using an IC in place of bridge rectifier. The picture of DB 107 is shown in fig: 3.3.8. Features:

Good for automation insertion

Surge overload rating - 30 amperes peak

Ideal for printed circuit board

Reliable low cost construction utilizing molded

Glass passivated device

Polarity symbols molded on body

Mounting position: Any Weight: 1.0 gram Fig 3.3.8: DB107

Filtration:

The process of converting a pulsating direct current to a pure direct current using filters is called as filtration.Filters:

Electronic filters are electronic circuits, which perform signal-processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones.

Introduction to Capacitors:

TheCapacitoror sometimes referred to as aCondenseris a passive device, and one which stores energy in the form of an electrostatic field which produces a potential (static voltage) across its plates. In its basic form a capacitor consists of two parallel conductive plates that are not connected but are electrically separated either by air or by an insulating material called theDielectric. When a voltage is applied to these plates, a current flows charging up the plates with electrons giving one plate a positive charge and the other plate an equal and opposite negative charge this flow of electrons to the plates is known as theCharging Currentand continues to flow until the voltage across the plates (and hence the capacitor) is equal to the applied voltageVcc. At this point the capacitor is said to be fully charged and this is illustrated below. The construction of capacitor and an electrolytic capacitor are shown in figures 3.10 and 3.11 respectively.

Fig 3.3.9:Construction Of a Capacitor Fig 3.3.10:Electrolytic CapaticorUnits of Capacitance:

Microfarad(F)1F = 1/1,000,000 = 0.000001 = 10-6F

Nanofarad(nF)1nF = 1/1,000,000,000 = 0.000000001 = 10-9F

Pico farad(pF)1pF = 1/1,000,000,000,000 = 0.000000000001 = 10-12F

Operation of Capacitor:

Think of water flowing through a pipe. If we imagine a capacitor as being a storage tank with an inlet and an outlet pipe, it is possible to show approximately how an electronic capacitor works.

First, let's consider the case of a "coupling capacitor" where the capacitor is used to connect a signal from one part of a circuit to another but without allowing any direct current to flow.

If the current flow is alternating between zero and a maximum, our "storage tank" capacitor will allow the current waves to pass through.

However, if there is a steady current, only the initial short burst will flow until the "floating ball valve" closes and stops further flow.

So a coupling capacitor allows "alternating current" to pass through because the ball valve doesn't get a chance to close as the waves go up and down. However, a steady current quickly fills the tank so that all flow stops.

A capacitor will pass alternating current but (apart from an initial surge) it will not pass d.c.Where a capacitor is used to decouple a circuit, the effect is to "smooth out ripples". Any ripples, waves or pulses of current are passed to ground while d.c. Flows smoothly.

Regulation:

The process of converting a varying voltage to a constant regulated voltage is called as regulation. For the process of regulation we use voltage regulators.

Voltage Regulator:

A voltage regulator (also called a regulator) with only three terminals appears to be a simple device, but it is in fact a very complex integrated circuit. It converts a varying input voltage into a constant regulated output voltage. Voltage Regulators are available in a variety of outputs like 5V, 6V, 9V, 12V and 15V. The LM78XX series of voltage regulators are designed for positive input. For applications requiring negative input, the LM79XX series is used. Using a pair of voltage-divider resistors can increase the output voltage of a regulator circuit.

It is not possible to obtain a voltage lower than the stated rating. You cannot use a 12V regulator to make a 5V power supply. Voltage regulators are very robust. These can withstand over-current draw due to short circuits and also over-heating. In both cases, the regulator will cut off before any damage occurs. The only way to destroy a regulator is to apply reverse voltage to its input. Reverse polarity destroys the regulator almost instantly. Fig: 3.3.11 shows voltage regulator.

Fig 3.3.11: Voltage Regulator

Resistors:A resistor is a two-terminal electronic component that produces a voltage across its terminals that is proportional to the electric current passing through it in accordance with Ohm's law:

V = IRResistors are elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel/chrome).

The primary characteristics of a resistor are the resistance, the tolerance, maximum working voltage and the power rating. Other characteristics include temperature coefficient, noise, and inductance. Less well-known is critical resistance, the value below which power dissipation limits the maximum permitted current flow, and above which the limit is applied voltage. Critical resistance is determined by the design, materials and dimensions of the resistor.

Resistors can be made to control the flow of current, to work as Voltage dividers, to dissipate power and it can shape electrical waves when used in combination of other components. Basic unit is ohms.Theory of operation: Ohm's law:

The behavior of an ideal resistor is dictated by the relationship specified in Ohm's law: V = IR

Ohm's law states that the voltage (V) across a resistor is proportional to the current (I) through it where the constant of proportionality is the resistance (R).

Power dissipation:

The power dissipated by a resistor (or the equivalent resistance of a resistor network) is calculated using the following:

Fig 3.3.12: Resistor Fig 3.3.13: Color Bands In Resistor

3.4. LED:

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly used for lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness. The internal structure and parts of a led are shown below.

Fig 3.4.1: Inside a LED Fig 3.4.2: Parts of a LEDWorking:

The structure of the LED light is completely different than that of the light bulb. Amazingly, the LED has a simple and strong structure. The light-emitting semiconductor material is what determines the LED's color. The LED is based on the semiconductor diode.

When a diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. An LED is usually small in area (less than 1mm2), and integrated optical components are used to shape its radiation pattern and assist in reflection. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. However, they are relatively expensive and require more precise current and heat management than traditional light sources. Current LED products for general lighting are more expensive to buy than fluorescent lamp sources of comparable output. They also enjoy use in applications as diverse as replacements for traditional light sources in automotive lighting (particularly indicators) and in traffic signals. The compact size of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are useful in advanced communications technology. The electrical symbol and polarities of led are shown in fig: 3.4.3.

Fig 3.4.3: Electrical Symbol & Polarities of LED LED lights have a variety of advantages over other light sources: High-levels of brightness and intensity

High-efficiency

Low-voltage and current requirements

Low radiated heat

High reliability (resistant to shock and vibration)

No UV Rays

Long source life

Can be easily controlled and programmed

Applications of LED fall into three major categories:

Visual signal application where the light goes more or less directly from the LED to the human eye, to convey a message or meaning.

Illumination where LED light is reflected from object to give visual response of these objects.

Generate light for measuring and interacting with processes that do not involve the human visual system.

3.5 Solar cell/Plate: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 multicrystalline 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 use

Equivalent circuit of a solar cell

The equivalent circuit of a solar cell

The schematic symbol of a solar cell

1. Photons in sunlight hit the solar panel and are absorbed by semi conducting materials, such as silicon.

2. Electrons (negatively charged) 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 (like bubbles) 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 direct current (DC) electricity.

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.

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.

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.

It does not matter if you use a 12 volt solar battery charger, a solar car battery charger, or any other type of charger the use of any solar battery charger is going to help alleviate waste. By supporting and using solar battery chargers and other sustainable technology, you can help make a difference in todays world.

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.

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 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.Working:

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 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. Various sun tracking systems have been used to enhance the power generating efficiency of the converging solar cell module.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 a 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 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 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.

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.

Photovoltaic Cells: Converting Photons to Electrons

The solar cells that you see on calculators and satellites are also called photovoltaic (PV) cells, which as the name implies (photo meaning "light" and voltaic meaning "electricity"), convert sunlight directly into electricity. A module is a group of cells connected electrically and packaged into a frame (more commonly known as a solar panel), which can then be grouped into larger solar arrays.

Photovoltaic cells are made of special materials called semiconductors such as silicon, which is currently used most commonly. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely.

PV cells also all have one or more electric field that acts to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off for external use, say, to power a calculator. This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce.

Solar Panel Setup:

The use of batteries requires the installation of another component called a charge controller. Batteries last a lot longer if they aren't overcharged or drained too much. That's what a charge controller does. Once the batteries are fully charged, the charge controller doesn't let current from the PV modules continue to flow into them. Similarly, once the batteries have been drained to a certain predetermined level, controlled by measuring battery voltage, many charge controllers will not allow more current to be drained from the batteries until they have been recharged. The use of a charge controller is essential for long battery life.

The other problem besides energy storage is that the electricity generated by your solar panels, and extracted from your batteries if you choose to use them, is not in the form that's supplied by your utility or used by the electrical appliances in your house. The electricity generated by a solar system is direct current, so you'll need an inverter to convert it into alternating current. Most large inverters will allow you to automatically control how your system works. Some PV modules, called AC modules, actually have an inverter already built into each module, eliminating the need for a large, central inverter, and simplifying wiring issues.

Throw in the mounting hardware, wiring, junction boxes, grounding equipment, over current protection, DC and AC disconnects and other accessories, and you have yourself a system. You must follow electrical codes (there's a section in the National Electrical Code just for PV), and it's highly recommended that a licensed electrician who has experience with PV systems do the installation. Once installed, a PV system requires very little maintenance (especially if no batteries are used), and will provide electricity cleanly and quietly for 20 years or more.

Categories of Solar Panel:

POLYCRYSTALLINE MODULES

Polycrystalline (or multicrystalline) modules are composed of a number of different crystals, fused together to make a single cell (hence the term 'multi'). They have long been the most popular type of solar module, due to the lower cost in manufacturing the cells. Recently, the cost of monocrystalline has come down, making them more popular in the residential market.

As you can see in the image (left), the construction of these different crystals gives the solar panel a visible crystal grain, or a 'metal flake effect'. They are slightly cheaper to produce than Mono panels, but are also less efficient (anywhere from 0.5% to 2% less efficient depending on the manufacturer). This is because the crystal grain boundaries can trap electrons, which results in lower efficiency.

The BP Solar modules that EnviroGroup installs are approximately 13.5% efficient (meaning that if 100 Watts of potential solar energy strikes the panel, it will produce approximately 13.5 Watts of solar electricity).

These panels are very popular in Australia, and offer a good balance of value vs performance.

MONOCRYSTALLINE MODULES

Monocrystalline, as the name suggests, is constructed using one single crystal, cut from ingots.This gives the solar panel a uniform appearance across the entire module.These large single crystals are exceedingly rare, and the process of 'recrystallising' the cell is more expensive to produce.

This technology is now the most widely available in Australia, with the cost of producing monocrystalline cells coming down every year.They are still more expensive than polycrystalline, but can be up to 2% more efficient. EnviroGroup uses SunOwe (14.5%) and Suntech (16.5%) monocrystalline solar modules for our installations.

Suntech have recently made some exciting developments in monocrystalline efficiency, with the patent pending Pluto technology.Unique texturing technology, with lower reflectivity, ensures more sunlight can be absorbed throughout the day even without direct solar radiation, and thinner metal lines on the top surface reduces shading loss. Importantly, the process was developed at the University of New South Wales, and has achieved lab efficiency of 25%, and verified efficiency of approx 19%. These panels will be more expensive, but will offer far more solar electricity for less area of solar panel.

AMORPHOUS MODULES

Amorphous (or 'thin film') solar modules have recently become very popular in the Australian market. They offer better performance in higher temperatures, and have some benefits in shady locations. However, the benefits have been greatly exaggerated by some suppliers, and it is important to weigh that up against the negatives of thin film technology.

The manufacture of these panels is highly automated - silicon is sprayed onto the substrate as a gas (called 'vapour deposition'), which means that the silicon wafer is approx 1 micron thick (compared to approx 200 microns for mono and poly). This means that the panel uses less energy to produce therefore will pay itself back from an energy point of view in a shorter time. However, it also means that the panels are far less efficient than mono or poly (approx 5-6% efficient).

The electrical connections are etched by a laser.Etching these as long horizontal cells across the panel makes these less susceptible from being blocked by shade, but it's important to recognise that there will still be a significant drop-off in performance when the panel is shaded.

Thin-film panels are significantly less efficient than crystalline panels, and a greater number is required for the same output. On average, a thin film solar array will need 2.5 times more roof area than mono or poly. This is critical if you intend to increase the size of your system later, as you may take up all of your north-facing roof for a relatively small system.

One of the biggest selling points of thin film is the performance in hotter temperatures. Unfortunately this has been misrepresented by some suppliers of thin film panels. As an example, if you live in Melbourne, and you are shown a graph that indicates the performance of thin film panels in Alice Springs, it's obvious that those panels won't provide the same advantage in a cooler climate.

Advantages of Solar Power Generation

The greatest advantage of solar power generation is perhaps its minimal environmental impact. It requires no water for cooling of the system, thus creating no large heat imbalance. Also, no by-products are produced that are detrimental to the environment. Another advantage of solar power generation is that bulky mechanical generators are not needed. The process of electricity generation is quick and the arrays are available in a variety of sizes according to the specific use.

Voltage Divider Network:

In electronics, a voltage divider (also known as a potential divider) is a simple linear circuit that produces an output voltage (Vout) that is a fraction of its input voltage (Vin). Voltage division refers to the partitioning of a voltage among the components of the divider.The formula governing a voltage divider is similar to that for a current divider, but the ratio describing voltage division places the selected impedance in the numerator, unlike current division where it is the unselected components that enter the numerator.

A simple example of a voltage divider consists of two resistors in series or a potentiometer. It is commonly used to create a reference voltage, and may also be used as a signal attenuator at low frequencies.

Fig. 4.5 Simple resistive voltage divider

A resistive divider is a special case where both impedances, Z1 and Z2, are purely resistive .

Substituting Z1 = R1 and Z2 = R2 into the previous expression gives:

As in the general case, R1 and R2 may be any combination of series/parallel resistors.

4.2.1 MOS voltage divider:We can use the enhanced MOSFET as a nonlinear resistor while its gate and drain are connected.

4.2.2 Examples:Resistive dividerAs a simple example, if R1 = R2 then

As a more specific and/or practical example, if Vout=6V and Vin=9V (both commonly used voltages), then:

And by solving using algebra, R2 must be twice the value of R1.

To solve for R1:

To solve for R2:

Any ratio between 0 and 1 is possible. That is, using resistors alone it is not possible to either reverse the voltage or increase Vout above Vin3.7 TEMPERATURE SENSOR:

LM 35: (TEMPERATURE /FIRE SENSOR)

The LM35 sensor series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature.

To detect the heat produced during fire occurrence we use temperature sensor.

The Temperature Sensor LM35 sensor series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature.

LM35 Sensor Specification:The LM35 series are precision integrated-circuit LM35 temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 sensor thus has an advantage over linear temperature sensors calibrated in Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling. The LM35 sensor does not require any external calibration or trimming to provide typical accuracies of C at room temperature and C over a full -55 to +150C temperature range. Low cost is assured by trimming and calibration at the wafer level. The LM35's low output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy. It can be used with single power supplies, or with plus and minus supplies. As it draws only 60 A from its supply, it has very low self-heating, less than 0.1C in still air. The LM35 is rated to operate over a -55 to +150C temperature range, while the LM35C sensor is rated for a -40 to +110C range (-10 with improved accuracy). The LM35 series is available packaged in hermetic TO-46 transistor packages, while the LM35C, LM35CA, and LM35D are also available in the plastic TO-92 transistor package. The LM35D sensor is also available in an 8-lead surface mount small outline package and a plastic TO-220 package.

LM35 Sensor Pin outs and Packaging:

LM35 Sensor Sources:There are several manufacturers of this popular part and each has LM35 sensor specs, datasheets and other free LM35 downloads. This amplifier is available from the following manufacturers.

National Semiconductor

On Semiconductor

Texas Instruments

Fairchild Semiconductor

STMicroelectronics

Jameco Electronics

Analog Devices

Temperature Recorder using LM35:

Here is how you can make an LM35 a temperature recorder by using the 12F675 PIC microcontroller as the controller and data store. It generates serial output so that you can view the results on a PC and it also calculates the temperature reading in Fahrenheit sending both to the serial port at half second intervals.

LM35 Sensor Applications:Most commonly-used electrical temperature sensors are difficult to apply. For example, thermocouples have low output levels and require cold junction compensation. Thermistors are nonlinear. In addition, the outputs of these sensors are not linearly proportional to any temperature scale. Early monolithic sensors, such as the LM3911, LM134 and LM135, overcame many of these difficulties, but their outputs are related to the Kelvin temperature scale rather than the more popular Celsius and Fahrenheit scales. Fortunately, in 1983 two ICs, the LM34 Precision Fahrenheit Temperature Sensor and the LM35 Precision Celsius Temperature Sensor, were introduced. This application note will discuss the LM34, but with the proper scaling factors can easily be adapted to the LM35.

The LM35/LM34 has an output of 10 mV/F with a typical nonlinearity of only 0.35F over a 50 to +300F temperature range, and is accurate to within 0.4F typically at room temperature (77F). The LM34s low output impedance and linear output characteristic make interfacing with readout or control circuitry easy. An inherent strength of the LM34 sensor over other currently available temperature sensors is that it is not as susceptible to large errors in its output from low level leakage currents. For instance, many monolithic temperature sensors have an output of only 1 A/K. This leads to a 1K error for only 1 -Ampere of leakage current. On the other hand, the LM34 sensor may be operated as a current mode device providing 20 A/ F of output current. The same 1 A of leakage current will cause an error in the LM34s output of only 0.05F (or 0.03K after scaling).

Low cost and high accuracy are maintained by performing trimming and calibration procedures at the wafer level. The device may be operated with either single or dual supplies. With less than 70 A of current drain, the LM34 sensor has very little self-heating (less than 0.2F in still air), and comes in a TO-46 metal can package, a SO-8 small outline package and a TO-92 plastic package.

The LM35/LM34 is a versatile device, which may be used for a wide variety of applications, including oven controllers and remote temperature sensing. The device is easy to use (there are only three terminals) and will be within 0.02F of a surface to which it is either glued or cemented. The TO-46 package allows the user to solder the sensor to a metal surface, but in doing so, the GND pin will be at the same potential as that metal. For applications where a steady reading is desired despite small changes in temperature, the user can solder the TO-46 package to a thermal mass. Conversely, the thermal time constant may be decreased to speed up response time by soldering the sensor to a small heat fin.

3.8 Comparator LM324:

General Description:

The LM324 series consists of four independent, high gains; internally frequency compensated operational amplifiers which were designed specifically to operate from a single power supply over a wide range of voltages. Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage.

Application areas include transducer amplifiers, DC gain blocks and all the conventional op amp circuits which now can be more easily implemented in single power supply systems. For example, the LM124 series can be directly operated off of the standard +5V power supply voltage which is used in digital systems and will easily provide the required interface electronics without requiring the additional 15V power supplies.

Fig3.4.1 .soil moisture sensor LM324

Unique Characteristics

In the linear mode the input common-mode voltage range includes ground and the output voltage can also swing to ground, even though operated from only a single power supply voltage. The unity gain cross frequency is temperature compensated. The input bias current is also temperature compensated.

PIN Diagram of LM324:

Theory: The LM124LM124/LM224/LM324/LM2902 Low Power Quad Operational Amplifiers series are op amps which operate with only a single power supply voltage, have true-differential inputs, and remain in the linear mode with an input common-mode voltage of 0 VDC. These amplifiers operate over a wide range of power supply voltage with little change in performance Characteristics. At 25C amplifier operation is possible down to a minimum supply voltage of 2.3 VDC. The pinouts of the package have been designed to simplify PC board layouts. Inverting inputs are adjacent to outputs for all of the amplifiers and the outputs have also been placed at the corners of the package (pins 1, 7, 8, and 14). Precautions should be taken to insure that the power supply for the integrated circuit never becomes reversed in polarity or that the unit is not inadvertently installed backwards in a test socket as an unlimited current surge through the resulting forward diode within the IC could cause fusing of the internal conductors and result in a destroyed unit. Large differential input voltages can be easily accommodated and, as input differential voltage protection diodes are not needed, no large input currents result from large differential input voltages. The differential input voltage may be larger than V+ without damaging the device. Protection should be provided to prevent the input voltages from going negative more than 0.3 VDC (at 25C). An input clamp diode with a resistor to the IC input terminal can be used.

To reduce the power supply drain, the amplifiers have a class an output stage for small signal levels which converts to class B in a large signal mode. This allows the amplifiers to both source and sinks large output currents. Therefore both NPN and PNP external current boost transistors can be used to extend the power capability of the basic amplifiers. The output voltage needs to raise approximately 1 diode drop above ground to bias the on-chip vertical PNP transistor for output current sinking applications. For ac applications, where the load is capacitive coupled to the output of the amplifier, a resistor should be used, from the output of the amplifier to ground to increase the class a bias current and prevent crossover distortion. Where the load is directly coupled, as in dc applications, there is no crossover distortion. Capacitive loads which are applied directly to the output of the amplifier reduce the loop stability margin. Values of

50 pF can be accommodated using the worst-case non inverting unity gain connection. Large closed loop gains or resistive isolation should be used if larger load capacitance must be driven by the amplifier.

LM124/LM224/LM324/LM2902 The bias network of the LM124 establishes a drain current which is independent of the magnitude of the power supply voltage over the range of from 3 VDC to 30 VDC. Output short circuits either to ground or to the positive power supply should be of short time duration. Units can be destroyed, not as a result of the short circuit current causing metal fusing, but rather due to the large increase in IC chip dissipation which will cause eventual failure due to excessive junction temperatures. Putting direct short-circuits on more than one amplifier at a time will increase the total IC power dissipation to destructive levels, if not properly protected with external dissipation limiting resistors in series with the output leads of the amplifiers. The larger value of output source current which is available at 25C provides a larger output current capability at elevated temperatures (see typical performance characteristics) than a standard IC op amp.

The circuits presented in the section on typical applications emphasize operation on only a single power supply voltage. If complementary power supplies are available, all of the standard op amp circuits can be used. In general, introducing a pseudo-ground (a bias voltage reference of V+/2) will allow operation above and below this value in single power supply systems. Many application circuits are shown which take advantage of the wide input common-mode voltage range which includes ground. In most cases, input biasing is not required and input voltages which range to ground can easily be accommodated.Features:

1. Internally frequency compensated for unity gain

2. Large DC voltage gain 100 dB

3. Wide bandwidth (unity gain) 1 MHz (temperature compensated)

4. Wide power supply range: Single supply 3V to 32V or dual supplies 1.5V to 16V

5. Very low supply current drain (700 A)essentially independent of supply voltage

6. Low input biasing current 45 nA (temperature compensated)

7. Low input offset voltage 2 mV and offset current: 5 nA

8. Input common-mode voltage range includes ground

9. Differential input voltage range equal to the power supply voltage

10. Large output voltage swing 0V to V+ 1.5VAdvantages:

1. Eliminates need for dual supplies2. Four internally compensated op amps in a single package

3. Allows directly sensing near GND and VOUT also goes to GND

4. Compatible with all forms of logic

5. Power drain suitable for battery operation

3.9 D.C. Motor: ADC motoruseselectrical energyto producemechanical energy, very typically through the interaction ofmagnetic fieldsandcurrent-carrying conductors. The reverse process, producing electrical energy from mechanical energy, is accomplished by analternator,generatorordynamo. 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 3.19: DC Motor

The DC motor has two basic parts: the rotating part that is called thearmatureand the stationary part that includes coils of wire called thefield coils.The stationary part is also called thestator. Figure shows a picture of a typical DC motor, Figure shows a picture of 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 thecommutator,and this is where the brushes make electrical contact to bring electrical current from the stationary part to the rotating part of the machine.

Operation: The DC motor you will find in modem industrial applications operates very similarly to the simple DC motor described earlier in this chapter. Figure 12-9 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 commutator 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.

Fig 3.20: Simple electrical diagram of DC motor

Fig 3.21: 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 commutator segments will also begin to move under the brushes. As an individual commutator 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 commutator segments continually change polarity from positive to negative. Since the commutator 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 commutator 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.Types of DC motors:

1. DC Shunt Motor,

2. DC Series Motor,

3. DC Long Shunt Motor (Compound)

4. DC Short Shunt Motor (Compound)

The rotational energy that you get from any motor is usually the battle between two magnetic fields chasing each other. The DC motor has magnetic poles and an armature, to which DC electricity is fed, The Magnetic Poles are electromagnets, and when they are energized, they produce a strong magnetic field around them, and the armature which is given power with a commutator, constantly repels the poles, and therefore rotates.

1. The DC Shunt Motor:In a 2 pole DC Motor, the armature will have two separate sets of windings, connected to a commutator at the end of the shaft that are in constant touch with carbon brushes. The brushes are static, and the commutator rotate and as the portions of the commutator touching the respective positive or negative polarity brush will energize the respective part of the armature with the respective polarity. It is usually arranged in such a way that the armature and the poles are always repelling.

The general idea of a DC Motor is, the stronger the Field Current, the stronger the magnetic field, and faster the rotation of the armature. When the armature revolves between the poles, the magnetic field of the poles induce power in the armature conductors, and some electricity is generated in the armature, which is called back emf, and it acts as a resistance for the armature. Generally an armature has resistance of less than 1 Ohm, and powering it with heavy voltages of Direct Current could result in immediate short circuits. This back emf helps us there.

When an armature is loaded on a DC Shunt Motor, the speed naturally reduces, and therefore the back emf reduces, which allows more armatures current to flow. This results in more armature field, and therefore it results in torque.

Fig: Diagram of DC shunt motor

When a DC Shunt Motor is overloaded, if the armature becomes too slow, the reduction of the back emf could cause the motor to burn due to heavy current flow thru the armature.

The poles and armature are excited separately, and parallel, therefore it is called a Shunt Motor.

2. The DC Series Motor:

Fig: Diagram of DC series motor

A DC Series Motor has its field coil in series with the armature. Therefore any amount of power drawn by the armature will be passed thru the field. As a result you cannot start a Series DC Motor without any load attached to it. It will either run uncontrollably in full speed, or it will stop.

Fig: Diagram of DC series motor graph representation

When the load is increased then its efficiency increases with respect to the load applied. So these are on Electric Trains and elevators.Specifications DC supply: 4 to 12V

RPM: 300 at 12V

Total length: 46mm

Motor diameter: 36mm

Motor length: 25mm

Brush type: Precious metal

Gear head diameter: 37mm

Gear head length: 21mm

Output shaft: Centred

Shaft diameter: 6mm

Shaft length: 22mm

Gear assembly: Spur

Motor weight: 105gms

We generally use 300RPM Centre Shaft Economy Series DC Motor which is high quality low cost DC geared motor. It has steel gears and pinions to ensure longer life and better wear and tear properties. The gears are fixed on hardened steel spindles polished to a mirror finish. The output shaft rotates in a plastic bushing. The whole assembly is covered with a plastic ring. Gearbox is sealed and lubricated with lithium grease and require no maintenance. The motor is screwed to the gear box from inside.

Although motor gives 300 RPM at 12V but motor runs smoothly from 4V to 12V and gives wide range of RPM, and torque. Tables below gives fairly good idea of the motors performance in terms of RPM and no load current as a function of voltage and stall torque, stall current as a function of voltage.3. DC Compound Motor:A compound of Series and Shunt excitation for the fields is done in a Compound DC Motor. This gives the best of both series and shunt motors. Better torque as in a series motor, while the possibility to start the motor with no load.

Fig: Diagram of DC compound motor

Above is the diagram of a long shunt motor, while in a short shunt, the shunt coil will be connected after the serial coil.

A Compound motor can be run as a shunt motor without connecting the serial coil at all but not vice versa.

DC Motor Driver:

The L293 and L293D are quadruple high-current half-H drivers. The L293 is designed to provide bidirectional drive currents of up to 1 A at voltages from 4.5 V to 36 V. The L293D is designed to provide bidirectional drive currents of up to 600-mA at voltages from 4.5 V to 36 V. Both devices are designed to drive inductive loads such as relays, solenoids, dc and bipolar stepping motors, as well as other high-current/high-voltage loads in positive-supply applications.

All inputs are TTL compatible. Each output is a complete totem-pole drive circuit, with a Darlington transistor sink and a pseudo-Darlington source. Drivers are enabled in pairs, with drivers 1 and 2 enabled by 1,2EN and drivers 3 and 4 enabled by 3,4EN.When an enable input is high, the associated drivers are enabled and their outputs are active and in phase with their inputs.

When the enable input is low, those drivers are disabled and their outputs are off and in the high-impedance state. With the proper data inputs, each pair of drivers forms a full-H (or bridge) reversible drive suitable for solenoid or motor applications. On the L293, external high-speed output clamp diodes should be used for inductive transient suppression. A VCC1 terminal, separate from VCC2, is provided for the logic inputs to minimize device power dissipation. The L293and L293D are characterized for operation from 0C to 70C.

Fig 3.22: L293D IC Pin Diagram of L293D motor driver:

Fig 3.23: L293D pin diagram

Fig 3.24: Internal structure of L293D.Features of L293D:

600mA Output current capability per channel

1.2A Peak output current (non repetitive) per channel

Enable facility

Over temperature protection

Logical 0input voltage up to 1.5 v

High noise immunity

Internal clamp diodesApplications of DC Motors:1. Electric Train: A kind of DC motor called the DC Series Motor is used in Electric Trains. The DC Series Motors have the property to deliver more power when they are loaded more. So the more the people get on a train, the more powerful the train becomes.

2. Elevators: The best bidirectional motors are DC motors. They are used in elevators. Compound DC Motors are used for this application.

3. PC Fans, CD ROM Drives, and Hard Drives: All these things need motors, very miniature motors, with great precision. AC motors can never imagine any application in these places.4. Starter Motors in Automobiles: An automobile battery supplies DC, so a DC motor is best suited here. Also, you cannot start an engine with a small sized AC motor,

5. Electrical Machines Lab in Colleges.H Bridge

With switches:

AnH bridgeis anelectronic circuitthat enables a voltage to be applied across a load in either direction. These circuits are often used inroboticsand other applications to allow DC motors to run forwards and backwards.

When the switches S1 and S4 (according to the first figure) are closed (and S2 and S3 are open) a positive voltage will be applied across the motor. By opening S1 and S4 switches and closing S2 and S3 switches, this voltage is reversed, allowing reverse operation of the motor.

Using the nomenclature above, the switches S1 and S2 should never be closed at the same time, as this would cause a short circuit on the input voltage source. The same applies to the switches S3 and S4. This condition is known as shoot-through.

The H-bridge arrangement is generally used to reverse the polarity of the motor, but can also be used to 'brake' the motor, where the motor comes to a sudden stop, as the motor's terminals are shorted, or to let the motor 'free run' to a stop, as the motor is effectively disconnected from the circuit. The following table summarizes operation, with S1-S4 corresponding to the diagram above.

S1S2S3S4Result

1001Motor moves right

0110Motor moves left

0000Motor free runs

0101Motor brakes

1010Motor brakes

1100Shoot-through

0011Shoot-through

1111Shoot-through

With relays:

If you connect up these relay circuits, remember to put a diode across the coil of the relay. This will keep the spike voltage (back EMF), coming out of the coil of the relay, from getting into the MCU and damaging it. The anode, which is the arrow side of the diode, should connect to ground. The bar, which is the Cathode side of the diode, should connect to the coil where the MCU connects to the relay.

If you connect this circuit to a small hobby motor you can control the motor with a processor (MCU, etc.) Applying a logical one, (+12 Volts in our example) to point A causes the motor to turn forward. Applying a logical zero, (ground) causes the motor to stop turning (to coast and stop).

Hook the motor up in this fashion and the circuit turns the motor in reverse when you apply a logical one (+12Volts) to point B. Apply a logical zero, which is usually a ground, causes the motor to stop spinning.

If you hook up these circuits you can only get the motor to stop or turn in one direction, forward for the first circuit or reverse for the second circuit.You can also pulse the motor control line, (A or B) on and off. This powers the motor in short burst and gets varying degrees of torque, which usually translates into variable motor speed.But if you want to be able to control the motor in both forward and reverse with a processor, you will need more circuitry. You will need an H-Bridge. Notice the "H"-looking configuration in the next graphic. Relays configured in this fashion make an H-Bridge. The "high side drivers" are the relays that control the positive voltage to the motor. This is called sourcing current.

The "low side drivers" are the relays that control the negative voltage to sink current to the motor. "Sinking current" is the term for connecting the circuit to the negative side of the power supply, which is usually ground.

So, you turn on the upper left and lower right circuits, and power flows through the motor forward, i.e.: 1 to A, 0 to B, 0 to C, and 1 to D.

Then for reverse you turn on the upper right and lower left circuits and power flows through the motor in reverse, i.e.: 0 to A, 1 to B, 1 to C, and 0 to D.

You should be careful not to turn on both circuits on one side and the other, or you have a direct short which will destroy your circuit; Example: A and C or B and D both high (logical 1).

With transistors:

We can better control our motor by using transistors or Field Effect Transistors (FETs).Most of what we have discussed about the relays H-Bridge is true of these circuits. You don't need diodes that were across the relay coils now. You should use diodes across your transistors though. See the following diagram showing how they are connected.

These solid state circuits provide power and ground connections to the motor, as did the relay circuits. The high side drivers need to be current "sources" which is what PNP transistors and P-channel FETs are good at. The low side drivers need to be current "sinks" which is what NPN transistors and N-channel FETs are good at.

If you turn on the two upper circuits, the motor resists turning, so you effectively have a breaking mechanism. The same is true if you turn on both of the lower circuits. This is because the motor is a generator and when it turns it generates a voltage. If the terminals of the motor are connected (shorted), then the voltage generated counteracts the motors freedom to turn. It is as if you are applying a similar but opposite voltage to the one generated by the motor being turned. Vis--vis, it acts like a brake.

To be nice to your transistors, you should add diodes to catch the back voltage that is generated by the motor's coil when the power is switched on and off. This fly back voltage can be many times higher than the supply voltage! If you don't use diodes, you could burn out your transistors.

Transistors, being a semiconductor device, will have some resistance, which causes them to get hot when conducting much current. This is called not being able to sink or source very much power, i.e.: Not able to provide much current from ground or from plus voltage.

Mosfets are much more efficient, they can provide much more current and not get as hot. They usually have the flyback diodes built in so you don't need the diodes anymore. This helps guard against flyback voltage frying your MCU.

To use Mosfets in an H-Bridge, you need P-Channel Mosfets on top because they can "source" power, and N-Channel Mosfets on the bottom because then can "sink" power. N-Channel Mosfets are much cheaper than P-Channel Mosfets, but N-Channel Mosfets used to source power require about 7 volts more than the supply voltage, to turn on. As a result, some people manage to use N-Channel Mosfets, on top of the H-Bridge, by using cleaver circuits to overcome the breakdown voltage.

It is important that the four quadrants of the H-Bridge circuits be turned on and off properly. When there is a path between the positive and ground side of the H-Bridge, other than through the motor, a condition exists called "shoot through". This is basically a direct short of the power supply and can cause semiconductors to become ballistic, in circuits with large currents flowing. There are H-bridge chips available that are much easier, and safer, to use than designing your own H-Bridge circuit.

H-Bridge Devices

The L293 has 2 H-Bridges, can provide about 1amp to each and occasional peak loads to 2 amps. Motors typically controlled with this controller are near the size of a 35 mm film plastic canister.The L298 has 2 h-bridges on board, can handle 1amp and peak current draws to about 3amps. You often see motors between the size a of 35 mm film plastic canister and a coke can, driven by this type H-Bridge. The LMD18200 has one h-bridge on board, can handle about 2 or 3 amps and can handle a peak of about 6 amps. This H-Bridge chip can usually handle an average motor about the size of a coke. There are several more commercially designed H-Bridge chips as well.

Schematic diagram:

Features:

Delivers up to 5 A continuous 6 A peak current

Optimized for DC motor management applications

Operates at supply voltages up to 40 V

Very low RDS ON

; typ. 200 m @ 25 C per switch

Output full short circuit protected

Overtemperature protection with hysteresis

and diagnosis

Short circuit and open load diagnosis

With open drain error flag

Undervoltage lockout

CMOS/TTL compatible inputs with hysteresis

No crossover current

Internal freewheeling diodes

Wide temperature range; 40 C < Tj

< 150 C

3.10 Relay:

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism, but other operating principles are also used. Relays find applications where it is necessary to control a circuit by a low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays found extensive use in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly drive an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device triggered by light to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protection relays".

Types of relays:

1. Simple electromechanical relay:

A simple electromagnetic relay, such as the one taken from a car in the first picture, is an adaptation of an electromagnet. It consists of a coil of wire surrounding a soft iron core, an iron yoke, which provides a low reluctance path for magnetic flux, a movable iron armature, and a set, or sets, of contacts; two in the relay pictured. The armature is hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB.Basic design and operation:

When an electric current is passed through the coil, the resulting magnetic field attracts the armature and the consequent movement of the movable contact or contacts either makes or breaks a connection with a fixed contact. If the set of contacts was closed when the relay was De-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing.

If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to circuit components. Some automotive relays already include a diode inside the relay case. Alternatively a contact protection network, consisting of a capacitor and resistor in series, may absorb the surge. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle.

By analogy with the functions of the original electromagnetic device, a solid-state relay is made with a thyristor or other solid-state switching device. To achieve electrical isolation an opt coupler can be used which is a light-emitting diode (LED) coupled with a photo transistor. Small relay as used in electronics

2. Latching relay

Latching relay, dust cover removed, showing pawl and ratchet mechanism. The ratchet operates a cam, which raises and lowers the moving contact arm, seen edge-on just below it. The moving and fixed contacts are visible at the left side of the image.

A latching relay has two relaxed states (bi stable). These are also called "impulse", "keep", or "stay" relays. When the current is switched off, the relay remains in its last state. This is achieved with a solenoid operating a ratchet and cam mechanism, or by having two opposing coils with an over-center spring or permanent magnet to hold the armature and contacts in position while the coil is relaxed, or with a remnant core. In the ratchet and cam example, the first pulse to the coil turns the relay on and the second pulse turns it off. In the two coil example, a pulse to one coil turns the relay on and a pulse to the opposite coil turns the relay off. This type of relay has the advantage that it consumes power only for an instant, while it is being switched, and it retains its last setting across a power outage. A remnant core latching relay requires a current pulse of opposite polarity to make it change state.

3. Reed relayA reed relay has a set of contacts inside a vacuum or inert gas filled glass tube, which protects the contacts against atmospheric corrosion. The contacts are closed by a magnetic field generated when current passes through a coil around the glass tube. Reed relays are capable of faster switching speeds than larger types of relays, but have low switch current and voltage ratings.

4. Mercury-wetted relayA mercury-wetted reed relay is a form of reed relay in which the contacts are wetted with mercury. Such relays are used to switch low-voltage signals (one volt or less) because of their low contact resistance, or for high-speed counting and timing applications where the mercury eliminates contact bounce. Mercury wetted relays are position-sensitive and must be mounted vertically to work properly. Because of the toxicity and expense of liquid mercury, these relays are rarely specified for new equipment. See also mercury switch.

5. Polarized relayA polarized relay placed the armature between the poles of a permanent magnet to increase sensitivity. Polarized relays were used in middle 20th Century telephone exchanges to detect faint pulses and correct telegraphic distortion. The poles were on screws, so a technician could first adjust them for maximum sensitivity and then apply a bias spring to set the critical current that would operate the relay.

6. Machine tool relayA machine tool relay is a type standardized for industrial control of machine tools, transfer machines, and other sequential control. They are characterized by a large number of contacts (sometimes extendable in the field) which are easily converted from normally-open to normally-closed status, easily replaceable coils, and a form factor that allows compactly installing many relays in a control panel. Although such relays once were the backbone of automation in such industries as automobile assembly, the programmable logic controller (PLC) mostly displaced the machine tool relay from sequential control applications.

7. Contactor relayA contactor is a very heavy-duty relay used for switching electric motors and lighting loads. Continuous current ratings for common contactors range from 10 amps to several hundred amps. High-current contacts are made with alloys containing silver. The unavoidable arcing causes the contacts to oxidize; however, silver oxide is still a good conductor. Such devices are often used for motor starters. A motor starter is a contactor with overload protection devices attached. The overload sensing devices are a form of heat operated relay where a coil heats a bi-metal strip, or where a solder pot melts, releasing a spring to operate auxiliary contacts. These auxiliary contacts are in series with the coil. If the overload senses excess current in the load, the coil is de-energized. Contactor relays can be extremely loud to operate, making them unfit for use where noise is a chief concern.

8. Solid-state relay

Solid state relay, which has no moving parts

25 A or 40 A solid state contactors

A solid state relay (SSR) is a solid state electronic component that provides a similar function to an electromechanical relay but does not have any moving components, increasing long-term reliability. With early SSR's, the tradeoff came from the fact that every transistor has a small voltage drop across it. This voltage drop limited the amount of current a given SSR could handle. As transistors improved, higher current SSR's, able to handle 100 to 1,200 Amperes, have become commercially available. Compared to electromagnetic relays, they may be falsely triggered by transients.

9. Solid state contactor relayA solid state contactor is a very heavy-duty solid state relay, including the necessary heat sink, used for switching electric heaters, small electric motors and lighting loads; where frequent on/off cycles are required. There are no moving parts to wear out and there is no contact bounce due to vibration. They are activated by AC control signals or DC control signals from Programmable logic controller (PLCs), PCs, Transistor-transistor logic (TTL) sources, or other microprocessor and microcontroller controls.

10. Buchholz relayA Buchholz relay is a safety device sensing the accumulation of gas in large oil-filled transformers, which will alarm on slow accumulation of gas or shut down the transformer if gas is produced rapidly in the transformer oil.

11. Forced-guided contacts relayA forced-guided contacts relay has relay contacts that are mechanically linked together, so that when the relay coil is energized or de-energized, all of the linked contacts move together. If one set of contacts in the relay becomes immobilized, no other contact of the same relay will be able to move. The function of forced-guided contacts is to enable the safety circuit to check the status of the relay. Forced-guided contacts are also known as "positive-guided contacts", "captive contacts", "locked contacts", or "safety relays".

12. Overload protection relayElectric motors need over current protection to prevent damage from over-loading the motor, or to protect against short circuits in connecting cables or internal faults in the motor windings. One type of electric motor overload protection relay is operated by a heating element in series with the ele