Wireless Power Transfer Project

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A PROJECT REPORT ON
WIRELESS POWER TRANSFER
BACHELOR OF TECHNOLOGY
IN
ELECTRICAL ENGINEERING
SUBMITTED BY :-
SAGNIK CHOUDHURY
DEPARTMENT OF ELECTRICAL ENGINEERING
GURU NANAK INSTITUTE OF TECHNOLOGY

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Department of Electrical Engineering
Guru Nanak Institute of Technology
Kolkata – 700114
Certificate
I hereby recommend that the project report, entitled as WIRELESS
POWER TRANSFER, prepared by ANIRBAN BISWAS (Registration
No. 101430110301 of 2010-2014) under my guidance, be accepted in partial
fulfillment of the requirement for the Degree of Bachelor of Technology
(Electrical Engineering) from the Department of Electrical Engineering of
Guru Nanak Institute of Technology.
-------------------------------------------
SHYMAL KUMAR ROY
Asst. Professor
Department of Electrical Engineering
Countersigned by:
----------------------------------------
TIC of the Department of Electrical Engineering

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ACKNOWLEDGEMENT
The satisfaction and euphoria that accompany the successful completion of any
task would be incomplete without the mentioning of the people whose constant
guidance and encouragement made it possible. We take pleasure in presenting
before you, our project, which is result of studied blend of both research and
knowledge.
We express our earnest gratitude to our internal guide, Assistant Professor Sri
Shyamal Kumar Roy, Department of EE, our project guide, for his constant
support, encouragement and guidance. We are grateful for his cooperation and his
valuable suggestions.

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DECLARATION
We, the undersigned, declare that the project entitled ‘WIRELESS POWER
TRANSFER’, being submitted in fulfillment for the final year project of Electrical
Engineering of Guru Nanak Institute of Technology.

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CONTENTS
TOPICS PAGE NO.
1. ABSTRACT 7
2. BLOCK DIAGRAM OF PROJECT 8
3. HARDWARE REQUIREMENTS 9
3.1 HF TRANSFORMERS 10
3.2 VOLTAGE REGULATOR (LM7805) 13
3.3 FILTER 15
3.4 RECTIFIER 16
3.5 TRANSISTOR 19
3.6 LED 20
3.7 BRUSHLESS DC MOTOR 22
3.7 1N4007 24
3.8 RESISTOR 25
3.9 CAPACITOR 26
3.10 ELECTROMAGNETIC COIL 27
4. SCHEMATIC DIAGRAM 28
4.1 DESCRIPTION 29
5. HARDWARE TESTING 31
6. RESULTS 32
7. FUTURE PROSPECTS 33
8 . MEDICAL APPLICATIONS 34
9. CONCLUSION 35
10. BIBLIOGRAPHY 36

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LIST OF FIGURES PAGE NO.
BLOCK DIAGRAM OF THE PROJECT 8
A TYPICAL TRANSFORMER 12
BLOCK DIAGRAM OF VOLTAGE REGULATOR 14
RC FILTER RECTIFIER 18
TRANSISTOR 19
LED 20
BRUSHLESS DC MOTOR (FAN) 22
SCHEMATIC DIAGRAM 28

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1. ABSTRACT
The main objective of this project is to develop a device for wireless power
transfer. The concept of wireless power transfer was realized by Nikolas Tesla.
Wireless power transfer can make a remarkable change in the field of the electrical
engineering which eliminates the use conventional copper cables and current
carrying wires. Based on this concept, the project is developed to transfer power
within a small range. This project can be used for charging batteries those are
physically not possible to be connected electrically such as pace makers (An
electronic device that works in place of a defective heart valve) implanted in the
body that runs on a battery. The patient is required to be operated every year to
replace the battery. This project is designed to charge a rechargeable battery
wirelessly for the purpose. Since charging of the battery is not possible to be
demonstrated, we are providing a DC fan that runs through wireless power.
This project is built upon using an electronic circuit which converts AC 230V
50Hz to AC 12V, High frequency. The output is fed to a tuned coil forming as
primary of an air core transformer. The secondary coil develops a voltage of HF
12volt. Thus the transfer of power is done by the primary(transmitter) to the
secondary that is separated with a considerable distance(say 3cm). Therefore the
transfer could be seen as the primary transmits and the secondary receives the
power to run load.
Moreover this technique can be used in number of applications, like to charge a
mobile phone, iPod, laptop battery, propeller clock wirelessly. And also this kind
of charging provides a far lower risk of electrical shock as it would be galvanically
isolated. This concept is an Emerging Technology, and in future the distance of
power transfer can be enhanced as the research across the world is still going on.

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2. BLOCK DIAGRAM
3.
H
A
R
D
W
A
R
E
R
E
Q
UI
R
E
M
E
N
TS

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COMPONENT NAME QUANTITY
RESISTORS
330R 1
1K 1
CAPACITORS
1000uF/35V 1
DIODES
BA159 4
1N4007 2
RED LED 1
YELLOW LED 1
MISCELLENEOUS
7805 REGULATOR 1
PCB CONNECTOR 2-PIN 3
MALE BURGE 2-PIN 2
FEMALE BURGE 2-PIN 2
HIGH FREQUENCY POWER SUPPLY BOARD 1
PRIMARY COIL- DIAMETER 9 cm 9X2 TURNS 26 GUAGE 1
SECONDARY COIL- DIAMETER 9 cm 36 TURNS 26 GUAGE 1
12V DC FAN 1
POWER CORD 1
PLAIN PCB 1
SOLDERING LEAD (50gm) 1

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3.1 HIGH FREQUENCY TRANSFORMER
A transformer is an electrical device that transfers energy from one circuit to
another purely by magnetic coupling. Relative motion of the parts of the transformer is
not required for transfer of energy. Transformers are often used to convert between high
and low voltages, to change impedance, and to provide electrical isolation between
circuits.
High frequency transformers transfer electric power. The physical size is dependent on
the power to be transferred as well as the operating frequency. The higher the frequency
the smaller the physical size is. Frequencies are usually between 20 and 100kHz. Ferrite
is mainly used as the core material.
Transformers are essential in high voltage power transmission providing an
economical means of transmitting power over large distances. Transformers come in a
range of sizes from a thumbnail-sized coupling transformer hidden inside a stage
microphone to gigawatt units used to interconnect large portions of national power grids,
all operating with the same basic principles and with many similarities in their parts.
Design of HF transformers
The transformer is one of the simplest of electrical devices. Its basic design,
materials, and principles have changed little over the last one hundred years, yet
transformer designs and materials continue to be improved.
The first step to calculate a high frequency transformer is usually to choose an
appropriate core with the help of the data book which provides certain tables for this
purpose. In the second step, the primary number of turns is calculated because this
determines the magnetic flux-density within the core. Then the wire-diameter is
calculated, which is dependent on the current in the primary and secondary coils.

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It is assumed that there is a square-wave voltage V1 at the primary side of the transformer.
This causes an input current I1, which consists of the back transformed secondary current I2 and
the magnetizing current IM. A core without an air-gap is used in order to keep the magnetizing
current as small as possible.
The square-wave voltage at the input of the transformer causes a triangular shaped
magnetising current IM which is almost independent of the secondary current (see also the
equivalent circuit). The magnetising current is approximately proportional to the magnetic flux Φ
i.e. to the magnetic flux density B. The input voltage V1 determines the magnetic flux in the
transformer core corresponding to Faraday's Law V = N · d(Φ)/dt.
The high-frequency transformers are
calculated with the help of the effective core
volume Ve and the minimum core-cross-section
Amin. For a required power output Pout = Vout ·
Iout and a chosen switching frequency a suitable
core volume Ve must be determined. Then an
optimal ΔB is selected depending on the chosen
switching frequency and also regarding the
temperature rise of the transformer.

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High Frequency Operation
The universal transformer emf equation indicates that at higher frequency, the core flux
density will be lower for a given voltage. This implies that a core can have a smaller cross-
sectional area and thus be physically more compact without reaching saturation. It is for this
reason that the aircraft manufacturers and the military use 400 hertz supplies. They are less
concerned with efficiency, which is lower at higher frequencies (mostly due to increased
hysteresis losses), but are more concerned with saving weight. Similarly, flyback transformers
which supply high voltage to cathode ray tubes operate at the frequency of the horizontal
oscillator, many times higher than 50 or 60 hertz, which allows for a more compact component.
Transformers for use at power or audio frequencies have cores made of many thin laminations of
silicon steel. By concentrating the magnetic flux, more of it is usefully linked by both primary
and secondary windings. Since the steel core is conductive, it, too, has currents induced in it by
the changing magnetic flux. Each layer is insulated from the adjacent layer to reduce the energy
lost to eddy current heating of the core. Certain types of transformer may have gaps inserted in
the magnetic path to prevent magnetic saturation. These gaps may be used to limit the current on
a short-circuit, such as for neon sign transformers.

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3.2 VOLTAGE REGULATOR 7805
A voltage regulator is an electrical regulator designed to automatically maintain a
constant voltage level. A voltage regulator may be a simple "feed-forward" design or may
include negative feedback control loops. It may use an electromechanical mechanism, or
electronic components. Depending on the design, it may be used to regulate one or more AC or
DC voltages.
Features
• Output Current up to 1A
• Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V
• Thermal Overload Protection
• Short Circuit Protection
• Output Transistor Safe Operating Area Protection
Description
The LM78XX/LM78XXA series of three-terminal positive regulators are available in the
TO-220/D-PAK package and with several fixed output voltages, making them useful in a Wide
range of applications. Each type employs internal current limiting, thermal shutdown and safe
operating area protection, making it essentially indestructible. If adequate heat sinking is
provided, they can deliver over 1A output Current. Although designed primarily as fixed voltage
regulators, these devices can be used with external components to obtain adjustable voltages and
currents.
Voltage regulators are found in devices such as computer power supplies where they
stabilize the DC voltages used by the processor and other elements. In automobile alternators and
central power station generator plants, voltage regulators control the output of the plant. In an
electric power distribution system, voltage regulators may be installed at a substation or along
distribution lines so that all customers receive steady voltage independent of how much power is
drawn from the line.

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Internal Block Diagram
Absolute Maximum Ratings

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3.3 FILTER
Electronic filters are electronic circuits which perform signal processing functions,
specifically to remove unwanted frequency components from the signal, to
enhance wanted ones, or both. Electronic filters can be:
 passive or active
 analog or digital
 high-pass, low-pass, band pass, band-reject (band reject; notch), or all-pass.
 discrete-time (sampled) or continuous-time
 linear or non-linear
 infinite impulse response (IIR type) or finite impulse response (FIR type)
The most common types of electronic filters are linear filters, regardless of other
aspects of their design. See the article on linear filters for details on their design
and analysis.
Capacitive filter is used in this project. It removes the ripples from the
output of rectifier and smoothens the D.C. Output received from this filter is
constant until the mains voltage and load is maintained constant. However, if either
of the two is varied, D.C. voltage received at this point changes. Therefore a
regulator is applied at the output stage.
The simple capacitor filter is the most basic type of power supply filter. The
use of this filter is very limited. It is sometimes used on extremely high-voltage,
low-current power supplies for cathode-ray and similar electron tubes that require
very little load current from the supply. This filter is also used in circuits where the
power-supply ripple frequency is not critical and can be relatively high.

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3.4 RECTIFIER
A rectifier is an electrical device that converts alternating current (AC), which
periodically reverses direction, to direct current (DC), current that flows in only one direction, 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.
The output from the transformer is fed to the rectifier. It converts A.C. into pulsating
D.C. The rectifier may be a half wave or a full wave rectifier. In this project, a bridge rectifier is
used because of its merits like good stability and full wave rectification.
Half-wave rectification
In half wave rectification, either the positive or negative half of the AC wave is passed,
while the other half is blocked. Because only one half of the input waveform reaches the output,
it is very inefficient if used for power transfer. Half-wave rectification can be achieved with a
single diode in a one-phase supply, or with three diodes in a three-phase supply.
The output DC voltage of a half wave rectifier can be calculated with the following two ideal
equations
Full-wave rectification
A full-wave rectifier converts the whole of the input waveform to one of constant polarity
(positive or negative) at its output. Full-wave rectification converts both polarities of the input
waveform to DC (direct current), and is more efficient. However, in a circuit with a non-center
tapped transformer, four diodes are required instead of the one needed for half-wave
rectification. Four diodes arranged this way are called a diode bridge or bridge rectifier.

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A full-wave rectifier using 4 diodes
For single-phase AC, if the transformer is center-tapped, then two diodes back-to-back (i.e.
anodes-to-anode or cathode-to-cathode) can form a full-wave rectifier. Twice as many windings
are required on the transformer secondary to obtain the same output voltage compared to the
bridge rectifier above.
Full-wave rectifier using a center tap transformer and 2 diodes
Rectifier output smoothing
While half-wave and full-wave rectification suffice to deliver a form of DC output,
neither produces constant-voltage DC. In order to produce steady DC from a rectified AC
supply, a smoothing circuit or filter is required. In its simplest form this can be just a reservoir
capacitor or smoothing capacitor, placed at the DC output of the rectifier. There will still remain
an amount of AC ripple voltage where the voltage is not completely smoothed.

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RC-Filter Rectifier: This circuit was designed and simulated using Multisim 8 software
For a given tolerable ripple the required capacitor size is proportional to the load current
and inversely proportional to the supply frequency and the number of output peaks of the
rectifier per input cycle. The load current and the supply frequency are generally outside the
control of the designer of the rectifier system but the number of peaks per input cycle can be
affected by the choice of rectifier design.
A more usual alternative to a filter, and essential if the DC load is very demanding of a
smooth supply voltage, is to follow the reservoir capacitor with a voltage regulator. The reservoir
capacitor needs to be large enough to prevent the troughs of the ripple getting below the voltage
the DC is being regulated to. The regulator serves both to remove the last of the ripple and to
deal with variations in supply and load characteristics. It would be possible to use a smaller
reservoir capacitor (these can be large on high-current power supplies) and then apply some
filtering as well as the regulator, but this is not a common strategy. The extreme of this approach
is to dispense with the reservoir capacitor altogether and put the rectified waveform straight into
a choke-input filter. The advantage of this circuit is that the current waveform is smoother and
consequently the rectifier no longer has to deal with the current as a large current pulse, but
instead the current delivery is spread over the entire cycle. The downside is that the voltage
output is much lower – approximately the average of an AC half-cycle rather than the peak.

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3.5 TRANSISTOR
A transistor is a semiconductor device used to amplify and switch electronic signals. It
is made of a solid piece of semiconductor material, with at least three terminals for connection to
an external circuit. A voltage or current applied to one pair of the transistor's terminals changes
the current flowing through another pair of terminals. Because the controlled (output) power can
be much more than the controlling (input) power, the transistor provides amplification of a
signal. Today, some transistors are packaged
individually, but many more are found embedded in
integrated circuits.
The transistor's low cost, flexibility, and
reliability have made it a ubiquitous device.
Transistorized mechatronic circuits have replaced
electromechanical devices in controlling appliances and
machinery. It is often easier and cheaper to use a standard microcontroller and write a computer
program to carry out a control function than to design an equivalent mechanical control function.
The essential usefulness of a transistor comes from its ability to use a small signal applied
between one pair of its terminals to control a much larger signal at another pair of terminals. This
property is called gain. A transistor can control its output in proportion to the input signal; that is,
it can act as an amplifier. Alternatively, the transistor can be used to turn current on or off in a
circuit as an electrically controlled switch, where the amount of current is determined by other
circuit elements.
The two types of transistors have slight differences in how they are used in a circuit. A
bipolar transistor has terminals labeled base, collector, and
emitter. A small current at the base terminal (that is, flowing
from the base to the emitter) can control or switch a much
larger current between the collector and emitter terminals. For a
field-effect transistor, the terminals are labeled gate, source, and
drain, and a voltage at the gate can control a current between
source and drain.

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3.5 LED
LEDs are semiconductor devices. Like transistors, and other diodes, LEDs are made out of
silicon. What makes an LED give off light are the small amounts of chemical impurities that are
added to the silicon, such as gallium, arsenide, indium, and nitride. When current passes through
the LED, it emits photons as a byproduct
When the diode is forward biased (switched
on), electrons are able to recombine with holes and
energy is released in the form of light. This effect
is called electroluminescence and the color of the
light is determined by the energy gap of the
semiconductor. The LED is usually small in area
(< 1mm2
) with integrated optical components to shape its radiation pattern & assist in reflection.
LEDs present many advantages over traditional light sources including lower energy
consumption, longer lifetime, improved robustness, smaller size and faster switching. However,
they are relatively expensive and require more precise current and heat management than
traditional light sources.
Applications of LEDs are diverse. They are used as low-energy and also for replacements
for traditional light sources in well-established applications such as indicators and automotive
lighting. 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 communications technology. So here the
role of LED is to indicate the status of the components like relays and power circuit etc.

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LED Circuits
A LED circuit needs some resistance in it, so that it isn't a short circuit. Among the
specifications for LEDs, a maximum forward current rating is usually given. This is the most
current that can pass through the LED without damaging it, and also the current at which the
LED will produce the most light. A specific value of resistor is needed to obtain this exact
current. LEDs consume a certain voltage known as the "forward voltage drop", and are usually
given with the specs for that LED. This must be taken into account when calculating the correct
value of resistor to use. So to drive an LED using a voltage source and a resistor in series with
the LED, use the following equation to determine the needed resistance:
Ohm's = (Source Voltage - LED Voltage Drop) / Amps
For example, to drive an LED from your car's 12v system, use the following values:
Source Voltage = 13.4 volts (12v car systems aren't really 12v in most cases)
Voltage Drop = 3.6 volts (Typical for a blue or white LED)
Desired Current = 30 milliamps (again, a typical value)
So the resistor we need is:
(13.4 - 3.6) / (30 / 1000) = 327 ohms

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3.6 BRUSHLESS DC MOTOR
Brushless DC motors (BLDC motors, BL motors) also known as electronically commutated
motors (ECMs, EC motors) are synchronous electric motors powered by direct-current (DC)
electricity and having electronic commutation systems, rather than mechanical commutators and
brushes. The current-to-torque and frequency-to-speed relationships of BLDC motors are linear.
BLDC motors may be described as stepper motors, with fixed permanent magnets and
possibly more poles on the rotor than the stator, or reluctance
motors. The latter may be without permanent magnets, just
poles that are induced on the rotor then pulled into alignment
by timed stator windings. However, the term stepper motor
tends to be used for motors that are designed specifically to
be operated in a mode where they are frequently stopped with
the rotor in a defined angular position; this page describes
more general BLDC motor principles, though there is
overlap.
Brushless Versus Brushed Motor:
Limitations of brushed DC motors overcome by BLDC motors include lower efficiency
and susceptibility of the commutator assembly to mechanical wear and consequent need for
servicing, at the cost of potentially less rugged and more complex and expensive control
electronics. BLDC motors develop
maximum torque when stationary and have
linearly decreasing torque with increasing
speed as shown in the adjacent figure.
BLDC motors offer several
advantages over brushed DC motors, including more torque per weight and efficiency,
reliability, reduced noise, longer lifetime (no brush and commutator erosion), elimination of

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ionizing sparks from the commutator, more power, and overall reduction of electromagnetic
interference (EMI). With no windings on the rotor, they are not subjected to centrifugal forces,
and because the windings are supported by the housing, they can be cooled by conduction,
requiring no airflow inside the motor for cooling.. The maximum power that can be applied to a
BLDC motor is exceptionally high, limited almost exclusively by heat, which can weaken the
magnets.
A BLDC motor's main disadvantage is higher cost, which arises from two issues. First,
BLDC motors require complex electronic speed controllers to run. Brushed DC motors can be
regulated by a comparatively simple controller, such as a rheostat (variable resistor). However,
this reduces efficiency because power is wasted in the rheostat. Second, some practical uses have
not been well developed in the commercial sector. For example, in the Radio Control (RC)
hobby, even commercial brushless motors are often hand-wound while brushed motors use
armature coils which can be inexpensively machine-wound. (Nevertheless, see "Applications",
below.)
In general, manufacturers use brush-type DC motors when low system cost is a priority
but brushless motors to fulfill requirements such as maintenance-free operation, high speeds, and
operation in explosive environments where sparking could be hazardous.
Applications:
 Consumer electronics
 Transport
 Heating and ventilation
 Industrial engineering
 Model engineering

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3.6 1N4007
Diodes are used to convert AC into DC; these are used as half wave rectifier or full wave
rectifier. Three points must he kept in mind while using any type of diode.
1. Maximum forward current capacity
2. Maximum reverse voltage capacity
3. Maximum forward voltage capacity
Current Flow in the N-Type Material
The positive potential of the battery will attract the free electrons in the crystal. These
electrons will leave the crystal and flow into the positive terminal of the battery. As an result,
an electron from the negative terminal of the battery will enter the crystal, thus completing the
current path. So, the
majority current
carriers in the N-type
material (electrons)
are repelled by the
negative side of the
battery & move
through the crystal
toward the positive
side of the battery.
Current Flow in the P-Type Material
Conduction in the P material is by positive holes, instead of negative electrons. A hole moves
from the positive terminal of the P material to the negative terminal. Electrons from the
external circuit enter the negative terminal of the material and fill holes in the vicinity of this
terminal. At the positive terminal, electrons are removed from the covalent bonds, thus
creating new holes. This process continues as the steady stream of holes (hole current) moves
toward the negative terminal.

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3.7 RESISTORS
A resistor is a two-terminal electronic component designed to oppose an electric current
by producing a voltage drop between its terminals in proportion to the current, that is, in
accordance with Ohm's law: V = IR
Resistors are used as part of electrical networks and
electronic circuits. 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 resistors are their
resistance and the power they can dissipate. 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 depends upon the materials
constituting the resistor as well as its physical dimensions; it's determined by design.
Power dissipation
The power P dissipated by a resistor (or the equivalent resistance of a resistor network) is
calculated as:
The total amount of heat energy released over a period of time can be determined from the
integral of the power over that period of time:
Practical resistors are rated according to their maximum power dissipation. Resistors
required to dissipate substantial amounts of power, particularly used in power supplies, power
conversion circuits, and power amplifiers, are generally referred to as power resistors; this
designation is loosely applied to resistors with power ratings of 1 watt or greater. Power resistors
are physically larger and tend not to use the preferred values, color codes, and external packages
described below.
If the average power dissipated by a resistor is more than its power rating, damage to the
resistor may occur, permanently altering its resistance; this is distinct from the reversible change
in resistance due to its temperature coefficient when it warms.

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3.8 CAPACITORS
A capacitor or condenser is a passive electronic component consisting of a pair of
conductors separated by a dielectric, used for storing electric charge.
An ideal capacitor is characterized by a single constant value,
capacitance, which is measured in farads. This is the ratio of the electric charge
on each conductor to the potential difference between them. When a voltage
potential difference exists between the conductors, an electric field is present in
the dielectric. This field stores energy and produces a mechanical force between
the plates. The effect is greatest between wide, flat, parallel, narrowly separated
conductors.
The properties of capacitors in a circuit may determine the resonant frequency and
quality factor of a resonant circuit, power dissipation and operating frequency in a digital logic
circuit, energy capacity in a high-power system, and many other important aspects.
Capacitors are widely used in electronic circuits for blocking direct current while
allowing alternating current to pass, in filter networks, for smoothing the output of power
supplies, in the resonant circuits that tune radios to particular frequencies and for many other
purposes.The capacitance is therefore greatest in devices made from materials with a high
permittivity.
3.7
ELECTROMAGNETIC COIL
A coil is a series of loops. An electromagnetic coil (or simply a "coil") is formed when a
conductor (usually an insulated solid copper wire) is wound around a core or form to create an
inductor or electromagnet. One loop of wire is usually referred to as a turn, and a coil consists of
one or more turns.

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For use in an electronic circuit, electrical connection terminals called taps are often
connected to a coil. Coils are often coated with varnish and/or wrapped with insulating tape to
provide additional insulation and secure them in place. A completed coil assembly with taps etc.
is often called a winding. A transformer is an electromagnetic device that has a primary winding
and a secondary winding that transfers energy from one electrical circuit to another by magnetic
coupling without moving parts.
Analysis
The inductance of single-layer air-cored cylindrical
coils can be calculated to a reasonable degree of
accuracy with the simplified formula :
where Henry [µH] (microhenries) are units of
inductance, R is the coil radius (measured in inches to
the center of the conductor), N is the number of turns,
and L is the length of the coil in inches. Higher
accuracy estimates of coil inductance require
calculations of considerably greater complexity.
Note that if the coil has a ferrite core, or one made of another metallic material, its inductance
cannot be calculated with this formula.

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4.1 DESCRIPTION
Operation Explanation:
Electronic transformer works on half bridge and double line frequency. The AC power is
given as an input to the bridge rectifier where it is converted into DC through resistor. Capacitor
gets charged in one half cycle Q1 (collector to emitter) starts conducting. F1 provides biasing for
this Q1 transistor. Current flows from P1 to P2 of primary coil. Then current passes through
capacitor C4 and reaches ground. In another half cycle Q2 (collector to emitter) starts conducting
and F2 provides bias for this transistor. Then current flows through C3 and then P2 to P1 reaches
Q2 and then negative. So in one half cycle flow of current is from P1 to P2, in another half cycle
flow of current is from P2 to P1. Biasing for F1, F2 is done automatically i.e. we can’t say that
when which coil gets bias. So current flowing in the primary coil in both half cycles generates
AC in secondary coil. As the transistors are fast switching devices frequency of AC becomes 25
KHz. This is fed to copper windings L1 which are connected to secondary of transformer. L1
transfers the 25 KHz AC to L2 by means of EMF (Principle of transformer).
Voltage induced L2 coil is fed to 4 diodes forming a Bridge Rectifier that delivers dc
which is then filtered by an electrolytic capacitor of about 1000microf. The filtered dc being
unregulated IC LM7805 is used to get 5v constant at its pin no 3 irrespective of input dc varying
from 9v to 14v.
The regulated 5volts dc is further filtered by a small electrolytic capacitor of 10 microf
for any noise so generated by the circuit which can be used for battery charging. One LED is
connected of this 5v point in series with a resistor of 330ohms to the ground i.e. negative voltage
to indicate 5v power supply availability. The 5v dc is used for other applications as on when
required. The output of bridge rectifier i.e. +12V is taken to drive the 12V DC Fan.
Circuit Description:
The line voltage is rectified by the full-bridge rectifier, generating a semi-sinusoidal
voltage at double the line frequency. When the cycle has started, the current in the feedback
transformer increases until the core saturates. At this point the feedback drive of the active
transistors is therefore removed, and, once its storage time has passed, it turns off. In this
application the oscillation frequency would be around 25 kHz.The dependence upon the storage
time is minimized by the RC network at the base of the transistor, which increases the rate of
charge extraction from the base at turn-off.

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Voltage rating:
The required voltage rating of the devices is defined by the half-bridge topology. Supplying the
circuit with 220V RMS AC mains, calculating peak value, and adding a safety margin, gives a
maximum supply voltage Vcc of:
Vcc(max)= 220V x √2 + 10% = 310V + 10%. ≈ 350V.
To this figure must also be added the overvoltage generated by the input filter at turn-off. In
practice, devices are used with a rating of:
Vce(max) = 450 - 500V
Current rating:
The nature of the half-bridge topology is such that in normal operation, half the supply voltage is
dropped across each device, so from the above figures VCE in the steady state is 310V /2, 155V.
Hence the collector current in the steady state can be calculated using.
Pout = Ic(RMS) . Vce(RMS)
Vce(RMS)= 1/2 . Vmains
Ic(RMS)=2. Pout / Vmains
Ic(RMS) =Ic(peak)/ √2
Ic(peak)= 2 √2 . Pout / Vmains = 2 √2 . 50W / 220V = 0.64A
As stated above, when the circuit is first turned on, the low initial resistance the load causes a
large current to flow through the transistors. This current can be up to ten times the current in the
steady state, and the devices must be selected to withstand this. In this example, the device used
is bipolar transistor, rated at 450V and around 2A ie Q1 and Q2. Storage & fall times are decided
by the R 330k and C3,C4 & fall time, tf, of the transistors influences the losses of the circuit,
while the storage time, ts , is important as it affects the switching frequency of the converter.
The transistors used must be manufactured, tested and selected to have storage times within
certain limits. Transistors with too large a storage time may cause the circuit to oscillate below
the operating limits of the output transformer, causing saturation of the core towards the end of
each cycle. This will cause a spike in the collector current of the transistors every cycle, which
will eventually cause them to overheat and be destroyed.

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5. HARDWARE TESTING
Continuity Test:
In electronics, a continuity test is the checking of an electric circuit to see if current flows
i.e is in fact a complete circuit. A continuity test is performed by placing a small voltage (wired
in series with an LED or noise-producing component such as a piezoelectric speaker) across the
chosen path. If electron flow is inhibited by broken conductors, damaged components, or
excessive resistance, the circuit is "open".
This test is the performed just after the hardware soldering and configuration has been
completed. This test aims at finding any electrical open paths in the circuit after the soldering.
Many a times, the electrical continuity in the circuit is lost due to improper soldering, wrong and
rough handling of the PCB, improper usage of the soldering iron, component failures and
presence of bugs in the circuit diagram. We use a multimeter to perform this test. We keep the
multimeter in buzzer mode and connect the ground terminal of the multimeter to the ground. We
connect both the terminals across the path that needs to be checked. If there is continuation then
you will hear the beep sound.
Power ON Test:
This test is performed to check whether the voltage at different terminals is according to
the requirement or not. We take a multi meter and put it in voltage mode. This test is performed
without ICs because if there is any excessive voltage, this may lead to damaging the ICs. Firstly,
if we are using a transformer we check the output of the transformer; whether we get the required
12V AC voltage. If we use a battery then we check if the battery is fully charged or not
according to the specified voltage of the battery by using multimeter.
Then we apply this voltage to the power supply circuit. If a circuit consists of voltage
regulator then we check for the input to the voltage regulator i.e. are we getting an input of 12V
and a required output depending on the regulator used in the circuit.f we are using 7805 we get
output of 5V and if using 7809 we get 9V at output pin and so on.
This output from the voltage regulator is given to the power supply pin of specific ICs.
Hence we check for the voltage level at those pins whether we are getting required voltage.
Similarly, we check for the other terminals for the required voltage. In this way we can assure
that the voltage at all the terminals is as per the requirement.

32
6. RESULTS
The fan has successfully been run. Both the LEDS have glowed. Electrical power has
successfully been transmitted without any wired connection.

33
7. Future Prospects
The electronic revolution of the past century has been a tangled affair. Remember when phones
were always wired into the wall? When the internet required one more cord from the back of
your computer? Wireless is the future, which is all well and good for information transfer. But
what about energy itself?
We live in a wireless world. Cell phones, Wi-Fi, Bluetooth, 2G, 3G, 4G — the always on,
always connected world of digital devices is driven by the magic of wireless. But all our devices,
from smart phones to laptops, still rely on cords and plugs for charging. Everyone’s had their cell
phone become useless for the day when the battery dies and there’s nowhere to charge it. Battery
life consistently shows up as a key factor in product ads, feature lists and reviews. As advanced
and powerful as phones, tablets and laptops are, when that bar hits 0%, they’re as good as
worthless without an outlet (the same outlet everyone else in the cafe or the airport wants to use).
Imagine if all we had to do to charge our phone was set it down in the right place. That’s the
reality wireless power aims to achieve.
Power Is the Final Cord to be Cut
Power is the final cord that needs to be cut for complete wireless freedom. Not only does the
technology exist, it’s already showing up in consumer technology.
Called magnetic induction, the technology allows power to be transferred without wires. You
simply have to set your device — phone, laptop, tablet, or anything else with an embedded
receiver — on a charging station, as the technology works best over short distances (the greater
the distance the less efficient the transfer is, but there are companies experimenting with
transmitting power over further distances, and the limits could change as the technology
advances).
However, distance isn’t much of an issue because power transmitters can be embedded in places
phones and other devices are normally set down, like the tables at a cafe, desks at work, the
bedside table at a hotel room, or even the furniture in your own home.
Charging stations and cases that work with current phones like the iPhone (the Duracell
Powermat, for example) are already available, and eventually the receivers will be built-in to
phones and other devices. The recently released Nexus 4 can be charged wirelessly, as well as
the Nokia Lumia 920, and there’s been speculation for years about wireless charging being built
into an upcoming iPhone. Wireless power is already becoming commonplace in Japan. Stateside,
Intel has demonstrated a laptop with a wireless charger built-in and the 2013 Dodge Dart is the

34
first car to offer a wireless charging mat inside, and there are now other cars offering the same
capability.
8. Medical Applications :-
Sometimes we get into a situation where we might need to charge a battery, but electrical wired
connection is fairly impossible there to achieve. Inside a human body, it is unquestionable to put
up a wire. Since invention, we use a battery in the pacemakers that needs to be replaced every
year as it has been fairly impossible to charge the battery with wired connections. As it requires
smooth, noiseless operation, further research is going on to improve the reliability of this
process. In near future with the help of Wireless Power Transfer, we will be able to charge the
battery of a pacemaker without any surgical operation.

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9. CONCLUSION
The godfather of wireless energy transfer was Nikola Tesla, a brilliant and fascinating figure in
the history of electrical engineering. In the late 1800′s, Tesla showed that electromagnetic energy
could be transferred wirelessly. He also postulated that someday, all of our electronics would be
able to harvest energy that is naturally present in space.
But wireless energy transfer is far from perfect. The coils still need to be shrunk down so they
can be easily integrated into everyday electronics (unless you want giant metal rings all over
your house). The distance limitation is a major hurdle, with the fields limited to a few meters at
this point. The energy transfer isn’t the most efficient process; MIT researchers transferred about
45% of the energy input, while Intel’s recent project showed an 80% transfer. That kind of
energy loss poses a significant roadblock to the commercial viability of these technologies, as
energy is not free.

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10. BIBLIOGRAPHY
 www.beyondlogic.org
 www.wikipedia.org
 www.howstuffworks.com
 www.thenextweb.com
 www.alldatasheets.com

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