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POWER GENERATION SYSTEM THROUGH

FOOT STEPS

By,

D. Anuroop Reddy

ID No: 08H51A0210

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Abstract

Power Generation through footsteps is a very useful system because nowadays the powerdemand creating much more problems in industries and home applications.

In this thesis we are constructing an Electrical system to generate power by simply walking

or running on the foot step and this system is basically Non Conventional energy system. Non-

conventional energy system is very essential at this time to our nation.

Here the force energy produced from foots of human Beings is converted in to electrical

energy. And the control mechanism carries the rack & pinion, D.C generator, battery and inverter

control. We have discussed the various applications and further extension also. The D.C generator

used in this project is Permanente Magnet D.C generator. The Generator is coupled to the Plywheel Shaft with the help of Spur Gear Mechanism.

The Output of the generator is 12 Volts. This 12 Volt is stored in a 7 Amp-Hour Battery. The

battery type is Lead-Acid battery. The battery is connected to the inverter which is used to convert

the D.C 12 Volt to the 230 Volt A.C. By increasing the capacity of battery and inverter circuit, the

power rating is increased.

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Contents

1. Introduction

1.1 Block Diagram

2. Inside View of Electrical Power Generating System

2.1 Foot Step Arrangement 2.2

Springs

2.2.1 Silicon etched probe can used as springs

2.3 Sprocket

2.4 Rack & Pinion

2.5 Chain Drive System

2.6 Gear Wheel

2.7 Flywheel

2.8 Permanent Magnet DC Generator

2.9 Lead acid battery

2.10 Inverter

2.10.1 Circuit of 12V DC to 120/230V AC Inverter with IC 555

2.11 Field Controller

2.12Types ofLoads

3. Advantages and Disadvantages 3.1

Advantages

3.2 Disadvantages

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1. Introduction

Walking is the most common activity in day to day life. When a person walks, he

loses energy to the road surface in the form of impact, vibration, sound etc, due to

the transfer of his weight on to the road surface, through foot falls on the ground

during every step and this type of energy is Non Conventional. This energy can be

tapped and converted in the usable form such as in electrical form by constructing

an Electrical Power Generating System.

1.1 Block Diagram

The constructed electrical power generating system mainly consists of:

Foot Step Arrangement

Rack , Pinion and Chain Sprocket Arrangement

DC Generator

Inverter

Loads like light, TV, PC, Radio etc.,

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2. Inside View of Electrical Power Generating System

2.1 Foot Step Arrangement

The material use for foot step arrangement should be of light weight so that springs can move

perfectly in upward and downward direction during its motion and the floor should be well balanced.

2.2 Springs

A spring is an elastic object used to store mechanical energy. Springs are usually made out

ofspring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from

annealed steel and hardened after fabrication. According to Hooke's law ofelasticity the extension of a

spring is in direct proportion with the load applied to it. So when a spring is compressed or stretched,

the force it exerts is proportional to its change in length.

Where

x is the displacementof the spring's end from itsequilibrium position (a distance, in SI units: meters);

F is the restoring force exerted by the spring on that end (in SI units: N or kg-m/s2); and

kis a constant called the rate or spring constant (in SI units: N/m or kg/s2).

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To determine this quantitative relationship between the amount of force and the amount of stretch,

objects of known mass could be attached to the spring. For each object which is added, the amount of

stretch could be measured. The force which is applied in each instance would be the weight of the object.

A regression analysis of the force-stretch data could be performed in order to determine the quantitative

relationship between the force and the amount of stretch. The data table below shows some representative

data for such an experiment.

The equation for this line is

Stretch = 0.00406Force + 3.43x10-5 (m)

So if we take the average weight of the person walking on the step is 50-80 kg then the force is inbetween 490N and 588N. Then the extension / stretch of spring is between 1.989m and 3.183m

Let us assume maximum and minimum weight applied on the springs is 30 and 110 kg. Then thestretch should be between 1.193 and 4.376.

So the average spring constant is 29.00232/m and the range of spring constant should be between15.082 and 25.137

Note: The spring constant k, is a function of the spring's dimension and material property. It is

expressed as:

The spring displacement then becomes:

Mass

(kg)

Force on Spring

(N)

Amount of

Stretch (m)

0.000 0.000 0.0000

0.050 0.490 0.0021

0.100 0.980 0.0040

0.150 1.470 0.0063

0.200 1.960 0.0081

0.250 2.450 0.0099

0.300 2.940 0.0123

0.400 3.920 0.0160

0.500 4.900 0.0199

WhereG: modulus of rigidity (shear modulus)d: diameter of spring wiresD: diameter of spring coiln: number of active coils (see below)

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Cantilever

Resonant Frequency,

kHz

Spring Constant, N/m

min typical max Min typical max

15 Series 265 325 400 20 40 7516 Series 150 170 190 25 40 60

2.2.1 Silicon etched probe can used as springs

Silicon etched probe tip of the NSC/CSC series has a conical shape.

Typical probe tip radius=10 nm

SEM image of uncoated silicon SPM SEM micrograph of Silicon

SPM probe tip etched probe tip end

Schematic drawing of the probe chip.Cantilever and probe

Full tip cone angle*=40

Tip aspect ratio more than 3:1 (4:1 typical)

Total tip height 20-25 m

Probe material n-type silicon (phosphorus doped)

Probe bulk resistivity**0.01-0.05 Ohm*cm

*The full cone angle may be less than 40 at the last 200 nm of the tip end.

**The surface of Silicon has a native oxide layer that makes the probe non-conducting. Thethickness of the native oxide film is 1-4 nm.

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2.3 Sprocket

Each of several projections on the rim of a wheel that engage with the links of a chain or

with holes in film, tape or paper is called as Sprocket. Example:

2.4 Rack & Pinion

Rack and pinion gears are used to convert rotation into linear motion or linear motion into rotation.The rack is the flat toothed part and the pinion is the gear. The diameter of the gear determines the speed

that the rack moves as the pinion turns.

Ft = Transmitted force, Fn = Normal force, Fr = Resultant force

= pressure angle, Fn = Ft tan , Fr = Ft/Cos

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Power (W)& Torque (Nm) : Assuming rotational losses as zero

N =Speed in rpm, g= 9.8 m/s, K= Spring Constant, x= displacement of the spring

2.5Chain Drive System

The chain drive system uses a continuous roller chain with support track and idler

sprockets. The roller shafts are fitted with sprockets, which engage the drive chain.

Chain drive is usually used in very oily applications, dirty conditions, and in extremetemperature conditions.

A chain is made up of a series of links with the links held together with steel pins. This

arranges makes a chain a strong, long lasting way of transmitting rotary motion from

one gear wheel to another.

Chain drive has one main advantage over a traditional gear train. Only two gear wheels

and a chain are needed to transmit rotary motion over a distance. With a traditional

gear train, many gears must be arranged meshing with each other in order to transmit

motion. When working out gear / velocity ratio and the rpm of chain driven gears it must be

remembered that the chain is ignored. This means the you simply find out the teeth per

gear wheel and the rpm and use the same method of calculating as you would with anormal, meshing gear system (see gear work sheets)

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Note:

The following formulae can be used in the design and selection of chain belt drive

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2.6 Gear Wheel

A gear is a rotating machine part having cut teeth, or cogs, which mesh with another

toothed part in order to transmit torque. Two or more gears working in tandem are called

a transmission and can produce a mechanical advantage through a gear ratio and thus may be

considered a simple machine. Geared devices can change the speed, torque, and direction ofapower source. The most common situation is for a gear to mesh with another gear; however a

gear can also mesh a non-rotating toothed part, called a rack, thereby

producing translation instead of rotation.

The gears in a transmission are analogous to the wheels in a pulley. An advantage of gears

is that the teeth of a gear prevent slipping.

When two gears of unequal number of teeth are combined a mechanical advantage is

produced, with both the rotational speeds and the torques of the two gears differing in a simple

relationship.

As the velocities v of the points of contact of the two pitch circles are the same, therefore

Where input gearGA has radius rA and angular velocity, and meshes with output gearGB of radius rBand angular velocity.

r 1/n

2.7 Flywheel

A flywheel is a mechanical battery (a mechanical means of storing energy - simply a mass

rotating about an axis).

Overview

Flywheels store energy mechanically in the form of kinetic energy. Kinetic energy is

energy of motion. The kinetic energy of an object is the energy it possesses because of its motion.As energy is transferred into a flywheel, as it spins, it builds up kinetic energy that can be released

when necessary. The flywheel has been used since ancient times, the most common traditional

example being the potter's wheel. In the Industrial Revolution, James Watt contributed to the

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development of the flywheel in the steam engine, and his contemporary James Pickard used a

flywheel combined with a crank to transform reciprocating into rotary motion.

A flywheel is a heavy rotating disk used as a storage device for kinetic energy. They come as an

alternative energy storage device. Flywheels resist changes in their rotational speed, which helps

steady the rotation of the shaft when an uneven torque is exerted on it by its power source such as a

piston-based, (reciprocating) engine, or when the load placed on it is intermittent (such as a piston-based pump). Flywheels can also be used by small motors to store up energy over a long period of

time and then release it over a shorter period of time, temporarily magnifying its power output for

that brief period. Recently, flywheels have become the subject of extensive research as power

storage devices; see flywheel energy storage.

How They Function

Like a wound up rubber band, a flywheel stores energy. When the energy is neeeded, the flywheel

slows down its rotation and releases the stored energy. A momentum wheel is a type of flywheeluseful in satellite pointing operations, in which the flywheels are used to point the satellite's

instruments in the correct directions without the use of thrusters.

The kinetic energy stored in a rotating flywheel is

Where is the moment of inertia of the mass about the center of rotation and (omega) is the

angular velocity in radian units. A flywheel is more effective when its inertia is larger, as when its

mass is located farther from the center of rotation either due to a more massive rim or due to a

larger diameter. Note the similarity of the above formula to the kinetic energyformula , where linear velocity is comparable to the rotational velocity, and the

mass is comparable to the rotational inertia.

Flywheels can take an electrical input to accelerate the rotor up to speed by using the built-in

motor, and return the electrical energy by using this same motor as a generator. Flywheels are one

of the oldest and most common mechanical devises in existence. They may still prove to serve us

as an important component on tomorrow's vehicles and future energy needs. Flywheels are one of

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the most promising technologies for replacing conventional lead acid batteries as energy storage

systems for a variety of applications, including automobiles, economical rural electrification

systems, and stand-alone, remote power units commonly used in the telecommunications industry.

Recent advances in the mechanical properties of composites have rekindled interest in using the

inertia of a spinning wheel to store energy.

In addition to energy density, flywheel energy storage systems (FES) also offer several important

advantages over chemical energy storage. The rate at which energy can be exchanged into or out of

the battery is limited only by the motor--generator design. Therefore, it is possible to withdraw

large amounts of energy in a far shorter time than with traditional chemical batteries. Indeed,

research into exploiting this property of FES systems to get short, intense bursts of energy is

ongoing with the most notable projects being a magnetic tank gun and a fusion ignition system. Of

course it is also possible to quickly charge FES batteries making them desirable for application in

electric cars where the charge time could be dropped from a matter of hours to a matter of minutes.

Advantages

Flywheels store energy very efficiently (high turn-around efficiency) and have the potential for

very high specific power compared with batteries. Flywheels have very high output potential and

relatively long life. Flywheels are relatively unaffected by ambient temperature extremes.

Disadvantages

Current flywheels have low specific energy. There are safety concerns associated with flywheels

due to their high speed rotor and the possibility of it breaking loose and releasing all of it's energy

in an uncontrolled manner. There are losses in converting electrical energy to mechanical and back

to electrical. Flywheels are a less mature technology than chemical batteries, and the current cost is

too high to make them competitive in the market.

2.8 Permanent Magnet DC Generator A basic DC generator has four basic parts:

Magnetic field

Single conductor, or loop

Commutator and

Brushes

The magnetic field may be supplied by either a permanent magnet.

A single conductor, shaped in the form of a loop, is positioned between the magnetic poles. Aslong as the loop is stationary, the magnetic field has no effect (no relative motion). If we rotate the

loop, the loop cuts through the magnetic field, and an EMF (voltage) is induced into the loop.

When we have relative motion between a magnetic field and a conductor in that magnetic field,and the direction of rotation is such that the conductor cuts the lines of flux, an EMF is induced

into the conductor. The magnitude of the induced EMF depends on the field strength and the rate at

which the flux lines are cut, as given in equation. The stronger the field or the more flux lines cut

for a given period of time, the larger the induced EMF.

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E g=KN

Where

E g= generated voltageK = fixed constant

= magnetic flux strengthN= speed in RPM

The direction of the induced current flow can be determined using the "left-hand rule" for

generators. This rule states that if you point the index finger of your left hand in the direction of the

magnetic field (from North to South) and point the thumb in the direction of motion of theconductor, the middle finger will point in the direction of current flow. In the generator shown in

Figure, for example, the conductor closest to the N pole is traveling upward across the field;

therefore, the current flow is to the right, lower corner. Applying the left-hand rule to both sides ofthe loop will show that current flows in a counter-clockwise direction in the loop.

Left-Hand Rule for Generator

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Commutator Action:The commutator converts the AC voltage generated in therotating loop into a DC voltage. It also serves as a means of connecting thebrushes to the rotating loop. The purpose of the brushes is to connect thegenerated voltage to an external circuit. In order to do this, each brush mustmake contact with one of the ends of the loop. Since the loop or armature

rotates, a direct connection is impractical. Instead, the brushes are connectedto the ends of the loop through the commutator. In a simple one-loopgenerator, the commutator is made up of two semi cylindrical pieces of asmooth conducting material, usually copper, separated by an insulatingmaterial, as shown in Figure. Each half of the commutator segments ispermanently attached to one end of the rotating loop, and the commutatorrotates with the loop.

Commutator Segments and BrushesThe brushes, usually made of carbon, rest against the commutator and slidealong the commutator as it rotates. This is the means by which the brushesmake contact with each end of the loop. Each brush slides along one half ofthe commutator and then along the other half. The brushes are positioned onopposite sides of the commutator; they will pass from one commutator half tothe other at the instant the loop reaches the point of rotation, at which pointthe voltage that was induced reverses the polarity. Every time the ends of theloop reverse polarity, the brushes switch from one commutator segment to thenext. This means that one brush is always positive with respect to another.The voltage between the brushes fluctuates in amplitude (size or magnitude)

between zero and some maximum value, but is always of the same polarity. Inthis manner, commutation is accomplished in a DC generator.

One important point to note is that, as the brushes pass from onesegment to the other, there is one important point to note is that, as thebrushes pass from one segment to the other, there is an instant when thebrushes contact both segments at the same time. The induced voltage at thispoint is zero. If the induced voltage at this point is not zero, then extremely

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high currents would be produced due to the brushes shorting the ends of theloop together. The point at which the brushes contact both commutatorsegments, when the induced voltage is zero, is called the"Neutral plane"

Commutation in a DC Generator

Field Excitation: The magnetic fields in DC generators are most commonlyprovided by electromagnets. A currentmust flow through the electromagnetconductors to produce a magnetic field. In order for a DCgenerator to operateproperly, the magnetic field must always be in the same direction. Therefore,the current through the field winding must be direct current. This current isknownas the field excitation current and can be supplied to the field winding in oneof two ways. Itcan come from a separate DC source external to the generator(e.g., a separately excitedgenerator) or it can come directly from the outputof the generator, in which case it is called aSelf-excited generator.

In a self-excited generator, the field winding is connected directly to thegenerator output. The field may be connected in series with the output, inparallel with the output, or a combination of the two. Separate excitationrequires an external source, such as a battery or another DC source.

It isgenerally more expensive than a self-excited generator. Separatelyexcited generators are, therefore, used only where self-excitation is notsatisfactory. They would be used in cases wherethe generator must respondquickly to an external control source or where the generated voltagemust bevaried over a wide range during normal operations.

But in this case the separately excited DC generator is used because thecontroller design is simple.

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Terminal Voltage:

DC generator output voltage is dependent on three factors:(1) The number of conductor loops in series in the armature(2) Armature speed and

(3) Magnetic field strength.

In order to change the generator output, one of these three factorsmustbe varied. The number ofconductors in the armature cannot be changed in anormally operating generator, and it is usually impractical to change the speedat which the armature rotates. The strength of the magnetic field, however,can be changed quite easily by varyingthe current through the field winding.This is output voltage of a DC generator.

Varying Generator Terminal Voltage

DC Generator Ratings:

A DC generator contains four ratings.

Voltage: Voltage rating of a machine is based on the insulation type and design of themachine.

Current: The current rating is based on the size of the conductor and the amount of heatthat can be dissipated in the generator.

Power: The power rating is based on the mechanical limitations of the device that is usedto turn the generator and on the thermal limits of conductors, bearings, and other

components of the generator. Speed: Speed rating, at the upper limit, is determined by the speed at which mechanical

damage is done to the machine. The lower speed rating is based on the limit for field

current (as speed increases, a higher field current is necessary to produce the same voltage).

Internal Losses:

There are four internal losses that contribute to lower efficiency of a DC generator.

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Copper losses

Eddy-current losses

Hysteresis losses

Mechanical losses

Each of these is described in the paragraphs that follow.Copper Losses

Copper loss is the power lost as heat in the windings; it is caused by the flow of current through the

coils of the DC armature or DC field. This loss varies directly with the square of the current in the

armature or field and the resistance of the armature or field coils.

Armature: Ia Ra

Field: IfRf

Eddy-Current Losses

As the armature rotates within the field, it cuts the lines of flux at the same time that thecopper coils of wire that are wound on the armature cut the lines of flux. Since the armature is

made of iron, an EMF is induced in the iron, which causes a current to flow. These circulatingcurrents within the iron core are called eddy-currents. To reduce eddy-currents, thearmature and field cores are constructed from laminated (layered) steelsheets. The laminated sheets are insulated from one another so that currentcannot flow from one sheet to the other.

Hysteresis Losses

Hysteresis losses occur when the armature rotates in a magnetic field. The magnetic domains

of the armature are held in alignment with the field in varying numbers, dependent upon field

strength. The magnetic domains rotate, with respect to the particles not held in alignment, by onecomplete turn during each rotation of the armature. This rotation of magnetic domains in the iron

causes friction and heat. The heat produced by this friction is called magnetic hysteresis loss. To

reduce hysteresis losses, most DC armatures are constructed of heat-treated silicon steel, which hasan inherently low hysteresis loss. After the heat-treated silicon steel is formed to the desired shape,

the laminations are heated to a dull red and then allowed to cool. This process, known as

annealing, reduces hysteresis losses to a very low value.

Mechanical Losses

Rotational or mechanical losses can be caused by bearing friction, brush friction on the

commutator, or air friction (called windage), which is caused by the air turbulence due to armature

rotation. Careful maintenance can be instrumental in keeping bearing friction to a minimum. Cleanbearings and proper lubrication are essential to the reduction of bearing friction. Brush friction is

reduced by assuring proper brush seating, using proper brushes, and maintaining proper brush

tension. A smooth and clean commutator also aids in the reduction of brush friction.

2.9Lead Acid Battery

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Lead-acid batteries store energy using a reversible chemical reaction between lead plates

and dilute sulphuric acid (electrolyte). There are three basic types of lead acid battery - starter

batteries: used to start engines in cars etc, deep-cycle batteries: used in renewable energyapplications and camping etc, and marine batteries: used both for starting and for deep cycle

applications.

Different Types of Lead Acid Battery:

Starter batteries have many thin lead plates which enable them to discharge a lot of

energy very quickly - i.e. to start a vehicle. However, if a starter battery is discharged

deeply (more than 20-25% depth of charge), its plates can be permanently damaged and thelifetime of the battery greatly reduced. Deep cycle batteries have fewer thicker lead plates, and

so cannot discharge energy so quickly, but can be cycled deeply and recharged many times

without damaging the battery. Deep cycle batteries are designed to provide a steady currentover a long period of time.

Batteries and Renewable Energy:In renewable energy systems multiple batteries are usually connected together to make

a battery bank. Click here to find out thecorrect way to connect batteries into abattery bank.

Ideally a deep cycle battery should not be discharged below 40% charge, and should be keptfully charged whenever possible in order to maximize its useful lifetime. When selecting a

battery (or battery bank) for a renewable system, this should be considered.

Inside a Lead Acid Battery:

A 12 volt lead acid battery is actually made up of six identical 2 volt cells. Each cell

contains lead plates of different compositions sitting in dilute sulphuric acid. Lead dioxide

plates (linked to the positive terminal of the battery) react with the acid to form lead sulphategiving up electrons (leaving the plate positive). The pure lead plates (linked to the negative

terminal of the battery) react with the sulphate ions to also form lead sulphate. The pure lead

plates therefore supply two positive charges and so are left negative. The passage of electronsfrom the lead oxide plates to the pure lead plates is the current of electricity generated by the

cell which can be used. When the battery is recharged, the lead sulphate in each cell is broken

down resulting in lead dioxide being redeposited on the positive electrode, and lead beingreplaced on the negative electrode.

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When batteries are frequently deeply discharged then sulphation build up occurs. Sulphur

molecules from the battery acid (electrolyte) start to coat the lead of the plates. Once the lead iscoverered in sulphur the battery is dead and cannot be recharged. Sulphation starts occuring

once the charge of a starting battery descends below 75%. Therefore lead acid batteries must belooked after well if they are to remain useable for a long time. Click here to read our articleonbattery desulphation - a method to bring dead batteries back to life.

2.9.1 Lead Acid Battery Charger Using Max773 IC

This battery chargercircuit uses a flyback converter topology, and implements a current-

limited power supply to charge lead-acid batteries. Here is the schematic diagram of

the charger circuit:

The flyback transformer provide isolation and voltage input range flexibility, event at supplyvoltage lower that the battery voltage. Monitoring the charging current is done by sensing the

output using MAX471 current sense amplifier. The result of the output current monitoring is then

used to give a feedback to a threshold detector, to detect if the value falls below the predetermined

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threshold. This detection is used to switch the charger into trickle mode, when a lower voltage is

applied for lower charging current.

2.10 Inverter

An inverter is a powerelectronic device that converts direct current (DC) to alternating current(AC); the converted AC can be at any required voltage and frequency with the use of

appropriate transformers, switching, and control circuits. Solid-state inverters have no moving

parts and are used in a wide range of applications, from small switching power supplies incomputers, to large electric utility high-voltage direct current applications that transport bulk

power. Inverters are usually used to supply AC power from DC sources such as solar panels or

batteries. It will be useful for emergency electric source

2.10.1 Circuit of 12V DC to 120/230V AC Inverter with IC 555

This is a DC-to-AC invertercircuit diagram which produces an AC output at line frequency and

voltage. The 555 is configured as a low-frequency oscillator, tunable over the frequency range of

50 to 60 Hz by Frequency potentiometer R4.

Parts List:

R1_________ 10KR2_________ 100K

R3_________ 100 ohm

R4_________ 50K pot meter, LinearC1,C2______ 0.1uF

C3_________ 0.01uF

C4_________ 2700uFQ1_________ TIP41A, NPN, or equivalent

Q2_________ TIP42A, PNP, or equivalent

L1_________ 1uH

T1_________ Filament transformer, your choice

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The 555 feeds its output (amplified by Q1 and Q2) to the input of transformer T1, a reverse-

connected filament transformer with the necessary step-up turns ratio. CapacitorC4 and coil L1filter the input to T1, assuring that it is effectively a sine wave. Adjust the value of T1 to your

voltage.

2.11 Field Controller

Here the 1-3 transformer is used to convert the single phase supply to three phasesupply and this is converted almost to a Square Wave varying from +V to V using a Phase

controlled 3-3 Cycloconverter. So the square wave obtained is used for exciting the field

windings to get the flux in one direction for positive half cycle and opposite direction to the beforeduring negative cycle. One thing which should be necessary is frequency of square wave is equal

to the twice of the input sinusoidal wave which is the output inverter.

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2.12 Types of Loads

All the household usage electrical devices, machines can be used as loads. For example

TV, Personal Computers, Lights, Radio.

3. Advantages and Disadvantages

3.1 ADVANTAGES

Power generation is simply walking on the step

Power also generated by running or exercising on the step

No need fuel input

Battery is used to store the generated power

3.2 DISADVANTAGES

Only applicable for the particular place.

Mechanical moving parts is high

Initial cost of this arrangement is high.

Care should be taken for batteries

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