hollow flashlight
TRANSCRIPT
HOLLOW FLASHLIGHT
FOR THE AWARD OF THE DEGREE OFFOR THE AWARD OF THE DEGREE OF
BACHELOR OF TECHNOLOGYBACHELOR OF TECHNOLOGY
in
ELECTRONICS & COMMUNICATION ENGINEERING
By
VAIBHAW MISHRA(1130434053)
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CERTIFICATE
It is certified that the work contained in this report entitled “ HOLLOW FLASHLIGHT”
by VAIBHAW MISHRA (Roll No. 1130434053), for the award of Bachelor of
Technology from Babu Banarasi Das University has been carried out under my supervision.
Miss Richa Verma Mrs. Poonam Pathak
Lect. Electronics& Communication Head, Electronics &communication
School of Engineering School of Engineering
BBD University BBD University
Lucknow (U.P) Lucknow (U.P)
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ABSTRACT
The Abstract deals with the proper usage of unused energy generated by humans in the form
of heat by making it in glowing a Flashlight. Thereby the Flashlight runs solely on the heat
of human palm without using any batteries.
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ACKNOWLEDGEMENT
Whenever a module of work is completed successfully, a source of inspiration and guidance
is always there for the student. I, hereby take the opportunity to thank those entire people who
helped me in many different ways.
First and foremost, I am grateful to my seminar report guide Miss Richa Verma,Lect. B.B.D.
University and my classs coordinator Miss Pallavi Gupta Lect. B.B.D. University, for
showing faith in my capability and providing able guidance and his generosity and advice
extended to me throughout my report.
Last, but not least I would like to thank my entire faculty and my friends for helping me in all measure
of life and for their kind cooperation and moral support.
VAIBHAW MISHRA
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TABLE OF CONTENTS
Page No.
Certificate...............................................................................................................ii
Abstract ..................................................................................................................iii
Acknowledgment....................................................................................................iv
List of Contents………………………………………………………………….. v
List of Figure .........................................................................................................vi
1: Introduction …………………………………………………………………..1
2: Report …………………………………………………………………...……..2
3: Basic Principle ………………………………………………….......................5
I ) Seebeck Effect…………………………………………………………..6
II ) Peltier Effect……………………………………………………………7
III ) Thomson effect…………………………………………………………9
4: Design of body heat powered light…………………………………………..10
5: Peltier Tiles……………………………………………………………………11
6: Oscillator Circuit……………………………………………………………..13
7: Stepup Transformer………………………………………………………….16
8:Heat Sink………………………………………………………………………18
9: Advantages ………………………………………………………………….19
10: Conclusion…………………………………………………………………...20
11: References …………………………………………………………………..21
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LIST OF FIGURES
Figure No. Figure Name Page No.
F.1 Body heat comparison 1
F. 2 Seebeck Effect 6
F. 3 Peltier Effect 8
F. 4 Effect of Peltier coefficient on current 8
F.5 Peltier Tiles 12
F.6 Cross section of Peltier tile 12
F.7 LTC 3108 Pin diagram 13
F.8 Output voltage sequencing 15
F.9 Peltiers connected to linear IC 16
F.10 Graph of Vout vs Vin 17
F.11 Air flow through Al tube 18
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1: INTRODUCTION
The average human consumes approximately 2000 Calories per day. This means that the
average person expends ~8.37 x 106 joules of energy per day, since most of us are in some
sort of equilibrium with our surroundings. Assuming most of this energy leaves us in the
form of heat, on average we radiate ~350,000 J of energy per hour. Since Watt is just Joules
per second, this is roughly equal to energy given off by a 100 Watt light bulb!
F.1 Body heat comparison.
This assumption, that most of our expended energy leaves us in the form of heat, is actually a
decent one. Speaking as a relatively normal college student (in all relevant respects), the
amount of energy I expend doing non-thermal work on my surroundings every day seems
pretty trivial. Aside from playing tennis , probably the most energetic thing I do is walk up 5
flights of stairs to my dorm room. This increase in gravitational potential energy, however, is
only ~12,000 J, or on the order of 0.1% of my total energy expenditutre.
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2: REPORT
Hypothesis
If I can capture enough heat from a human hand and convert it efficiently to electricity, then
I can power a flashlight without any batteries or kinetic energy.
Objective
To make a flashlight that runs on the heat of the human hand.
Step 1
Step 1 involves much research, to calculate how much heat per cm2 we radiate in our inner
palm, where we normally hold a flashlight. Research shows that an average human
dissipates around 350,000 Joules per hour, or 97 watts. The average surface area of the
human skin is 1.7 m2 or 17,000 cm2, so the heat dissipation equals to (97/17000) * 1000
= 5.7 mW / cm2.
A useful area of the palm is about 10 cm2. This implies that 57 mW could be available.
The thermal efficiency of a Peltier tile is cited at about 10%. This means that we should be
able to generate 5.7mW in the palm of the hand. From testing a new batch of LED’s, it is
found that at least 0.5 mW is needed to obtain usable LED brightness. Now we could go on
to step 2 and the physical measurement and design of the flashlight.
Step 2: Characterizing the Peltier Tiles:
Two sets of cheap, different sized tiles were obtained. Tile 1 had an area of 1.36 cm2 and an
internal resistance of 5 ohms, and Tile 2 was 4 cm2 and had an internal resistance of 2.4 ohms.
The power generated by each Peltier stack is tested on a per cm2 basis.
To do this, we taped each tile onto a square aluminum tube. One side of the Peltiers was
cooled by an ice pack, and the other was heated with a 12-volt light bulb connected to a
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variable power supply. The temperature difference between the sides of the Peltier tile was
measured. Both Peltier tiles produced enough power to light an LED, but only at 50 and 73
mV.
We need 2500 mV to light the flashlight LED.
Step 3: Boosting the Voltage.
Direct Current cannot be multiplied, but if the DC is changed to AC, the voltage can be
stepped up with a transformer . The answer lay in constructing a simple oscillator circuit with
a step-up transformer.
To do this construct a feedback oscillator with a field effect transistor and wound
transformers with step-up ratios of 5:125.
The oscillator worked, but the LED did not light up until the Peltier voltage was 120 mV.
We need it to light up at about 50 mV (voltage produced at a 5°C temperature difference).
The circuit of LTC3108 contained FET’s that would oscillate at voltages as low as 20mV.
When used with a recommended transformer, the IC would provide well over 2.5 volts AC.
The IC also worked fine as a very low voltage transistor oscillator. The circuit now had only
4 components: The IC, the step-up transformer, a 47µF capacitor, and the LED. With the
LED across the transformer, I was able to obtain good LED brightness with only 50 mV DC
iut axGthe oscillator. The efficiency of the converter to be about 50% at 100 mV.
Step 4: Physical Flashlight Design.
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I decided to make the flashlight with dimensions of 25mm in diameter and 125mm long. Four
of the large Peltier tiles covered 16cm2, and four of the smaller tiles had a combined area of
5.4cm2 .
Tiles were mounted on a milled area of 25mm diameter aluminum tubing, and placed inside a
larger PVC pipe,nsul{Grom it by air. The hand griped the tiles through an opening in the
PVC pipe. Air flowing through and around the aluminum tube cooled the flashlight. The
circuit was mounted in the front, and the LED was centered in the middle of the tube. The
PVC pipe was wrapped with insulating foam.
Results:
The results prove hypothesis, that even with all the thermal and voltage conversion losses,
there was still enough power in the palm to provide usable light. The actual power at the LED
was difficult to measure accurately because it was an irregular square wave at 40 kHz. So I
made a comparative measurement with a light meter and an external white LED (connected
to a DC power supply). I measured the DC power into the external white LED, that gave the
same amount of light as the white LED in my circuit. Both LED’s were identical types, 5mm,
15 degree types from Digikey.
The theoretical power calculated, and the actual power obtained were within 20% of each
other.Measurements with a Spectra light meter showed that flashlights produced good light.
In outside walking tests at an ambient temperature of 10ºC, both flashlights maintained a
steady beam of light for over 20 minutes.
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3: BASIC PRINCIPLE : THERMOELECTRICITY
The first important discovery relating to thermoelectricity occurred in 1821 when German
scientist Thomas Seebeck found that an electric current would flow continuously in a closed
circuit made up of two dissimilar metals, provided that the junctions of the metals were
maintained at two different temperatures. Seebeck did not actually comprehend the scientific
basis for his discovery, however, and falsely assumed that flowing heat produced the same
effect as flowing electric current.
In 1834, a French watchmaker and part-time physicist, Jean Peltier, while investigating the
Seebeck Effect, found that there was an opposite phenomenon where by thermal energy
could be absorbed at one dissimilar metal junction and discharged at the other junction when
an electric current flowed within the closed circuit. Twenty years later, William Thomson
(eventually known as Lord Kelvin) issued a comprehensive explanation of the Seebeck and
Peltier Effects and described their relationship. At the time, however, these phenomena were
still considered to be mere laboratory curiosities and were without practical application.
In the 1930s, Russian scientists began studying some of the earlier thermoelectric work in an
effort to construct power generators for use at remote locations throughout their country. This
Russian interest in thermoelectricity eventually caught the attention of the rest of the world
and inspired the development of practical thermoelectric modules. Today's thermoelectric
coolers make use of modern semiconductor technology in which doped semiconductor
material takes the place of the dissimilar metals used in early thermoelectric experiments.
The Seebeck, Peltier and Thomson effects, together with several other phenomena, form the
basis of functional thermoelectric modules.
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I) Seebeck Effect
The conductors are two dissimilar metals denoted as material A and material B. The junction
temperature at A is used as a reference and is maintained at a relatively cool temperature
(TC).
The junction temperature at B is used as temperature higher than temperature TC. With heat
applied to junction B, a voltage (Eout) will appear across terminals T1 and T2 and hence an
electric current would flow continuously in this closed circuit. This voltage as shown in
Figure17.1, known as the Seebeck EMF, can be expressed as
Eout = α (TH – TC) (17.1)
Where:
• α = dE / dT = α A – α B
• α is the differential Seebeck coefficient or (thermo electric power coefficient) between the
two
materials, A and B, positive when the direction of electric current is same as the direction of
thermal
current, in volts per oK.
• Eout is the output voltage in volts.
• TH and TC are the hot and cold thermocouple temperatures, respectively, in oK.
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F.2 Seebeck Effect
II) Peltier Effect
Peltier found there was an opposite phenomenon to the Seebeck Effect, whereby thermal
energy could be absorbed at one dissimilar metal junction and discharged at the other
junction when an electric current flowed within the closed circuit.
In F. 3 the thermocouple circuit is modified to obtain a different configuration that illustrates
the Peltier Effect, a phenomenon opposite that of the Seebeck Effect. If a voltage (Ein) is
applied to terminals T1 and T2, an electrical current (I) will flow in the circuit. As a result of
the current flow, a slight cooling effect (QC) will occur at thermocouple junction A (where
heat is absorbed), and a heating effect (QH) will occur at junction B (where heat is expelled).
Note that this effect may be reversed whereby a change in the direction of electric current
flow will reverse the direction of heat flow. Joule heating, having a magnitude of I2 x R
(where R is the electrical resistance), also occurs in the conductors as a result of current flow.
This Joule heating effect acts in opposition to the Peltier Effect and causes
a net reduction of the available cooling. The Peltier effect can be expressed mathematically as
QC or QH = β x I (17.2)
= (α T) x I
Where:
• β is the differential Peltier coefficient between the two materials A and B in volts.
• I is the electric current flow in amperes.
• QC and QH are the rates of cooling and heating.
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F.3 Peltier effect
Peltier coefficient β has important effect on Thermoelectric cooling as following:
a) β <0 ; Negative Peltier coefficient
High energy electrons move from right to left. Thermal current and electric current flow in
opposite directions.
b) β >0 ; Positive Peltier coefficient
High energy holes move from left to right. Thermal current and electric current flow in same
direction.
F.4 Effect of Peltier coefficient on current flow
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III) Thomson Effect
William Thomson, who described the relationship between the two phenomena, later issued a
more comprehensive explanation of the Seebeck and Peltier effects. When an electric current
is passed through a conductor having a temperature gradient over its length, heat will be
either absorbed by or expelled from the conductor. Whether heat is absorbed or expelled
depends on the direction of both the electric current and temperature gradient. This
phenomenon is known as the Thomson Effect.
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4: DESIGN OF BODY HEAT POWERED LIGHT
The average surface area of the human skin3 is 1.7 m2 or 17,000 cm2, As human dissipates
around 350,000 Joules per hour, or 97 watts so the heat dissipation equals to 5.7mW/cm2. A
useful area of the palm is about 10 cm2. This implies that 57 mW could be available but only
0.5 mW is needed to generate a bright light at the LED. The design of body heat powered
light includes
Peltier Tiles
Oscillator Circuit
Step-up Transformer
Heat Sink 1)
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5: PELTIER TILES A Peltier cell also known as a thermoelectric cooler is made up of a large number of series-
connected P-N junctions, sandwiched between two parallel ceramic plates. Although Peltier
cells are often used as coolers by applying a DC voltage to their inputs, they will also
generate a DC output voltage, using the Seebeck effect, when the two plates are at different
temperatures. The polarity of the output voltage will depend on the polarity of the
temperature differential between the plates. The magnitude of the output voltage is
proportional to the magnitude of the temperature differential between the Plates. When used
this manner, a Peltier cell is referred to as a thermoelectric Generator. The output from the
Peltier Device is Direct Current. Direct Current cannot be multiplied, but if the DC is
changed to AC, the voltage can be stepped up with a transformer. The upper surface of the
the peltier is made up of dielectric substrate and internally consists of P-type and N-type. they
have a lot of P-N contacts connected in series. They are also heavily doped, meaning that
they have special additives that will increase the excess or lack of electrons.
Thermoelectric Principle of operation
The typical thermoelectric module is manufactured using two thin ceramic wafers with a
series of P and N doped bismuth-telluride semiconductor material sandwiched between them.
The ceramic material on both sides of the thermoelectric adds rigidity and the necessary
electrical insulation. The N type material has an excess of electrons, while the P type material
has a deficit of electrons. One P and one N make up a couple. The thermoelectric couples are
electrically in series and thermally in parallel. A thermoelectric module can contain one to
several hundred couples.
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F.5 Peltier Tiles
As the electrons move from the P type material to the N type material through an electrical
connector, the electrons jump to a higher energy state absorbing thermal energy (cold side).
Continuing through the lattice of material; the electrons flow from the N type material to the
P type material through an electrical connector dropping to a lower energy state and releasing
energy as heat to the heat sink (hot side).
F.6 Cross section of Peltier tiles
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6: OSCILLATOR CIRCUIT
Oscillators convert Direct current to Alternating Current. The output from the the Peltier is
such a low voltage that need to be busted for which Linear IC LTC3108 is used. The
LTC®3108 is a highly integrated AC/DC converter ideal for harvesting and managing
surplus energy from extremely low input voltage sources. The pin configuration of LTC 3108
us shown below
F.7 Pin diagram of LTC3108
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The LTC3108 utilizes a MOSFET switch to form a resonant step-up oscillator using an
external step-up transformer and a small coupling capacitor. This allows it to boost input
voltages as low as 20mV high enough to provide multiple regulated output voltages for
powering other circuits.
In application, a storage capacitor typically a few hundred microfarads is connected to VOUT
in. As soon as VAUX exceeds 2.5V, the VOUT capacitor will be allowed to charge up to its
regulated voltage. The current available to charge the capacitor will depend on the input
voltage and transformer turns ratio, but is limited to about 4.5mA. VOUT2 is an output that
can be turned on and off by the host, using the VOUT2_EN pin. When enabled, VOUT2 is
connected to VOUT through a 1.3Ω P-channel MOSFET switch. This output, controlled by a
host processor, can be used to power external circuits such as sensors and amplifiers that do
not have a low power sleep or shut down capability. VOUT2 can be used to power these
circuits only when they are needed.
A power good comparator monitors the VOUT voltage. The PGD pin is an open-drain output
with a weak pull-up(1MΩ) to the LDO voltage. Once VOUT has charged to within 7.5% of
its regulated voltage, the PGD output will go high. If VOUT drops more than 9% from its
regulated voltage, PGD will go low. The PGD output is designed to drive a microprocessor or
other chip I/O and is not intended to drive a higher current load such as an LED. Pulling PGD
up externally to a voltage greater than VLDO will cause a small current to be sourced into
VLDO. PGD can be pulled low in a wire-OR configuration with other circuitry.
The VOUT2 enable input has a typical threshold of 1V with 100mV of hysteresis, making it
logic-compatible. If VOUT2_EN (which has an internal pull-down resistor) is slow, VOUT2
will be off. Driving VOUT2_EN high will turn on the VOUT2 output. The VSTORE output
can be used to charge a large storage capacitor or rechargeable battery after VOUT has
reached regulation. Once VOUT has reached regulation, the VSTORE output will be allowed
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to charge up to the VAUX voltage. The storage element on VSTORE can be used to power
the system in the event that the input source is lost, or is unable to provide the current
demanded by the VOUT, VOUT2 and LDO outputs. If VAUX drops below VSTORE, the
LTC3108 will automatically draw current from the storage element.
The frequency of oscillation is determined by the inductance of the transformer secondary
winding and is typically in the range of 10kHz to 100kHz. For input voltages as low as
20mV, a primary-secondary turns ratio of about 1:100 is good.
The timing diagram showing the typical charging and voltage sequencing of the outputs is
shown below.
F.8 : Output Voltage Sequencing with VOUT Programmed for 3.3V
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7: STEPUP TRANSFORMER
The step-up transformer turns ratio will determine how low the input voltage can be for the
converter to start. On a step-up transformer there are more turns on the secondary coil than
the primary coil. The induced voltage across the secondary coil is greater than the applied
voltage across the primary coil or in other words the voltage has been “stepped-up”. Using a
1:100 ratio can yield start-up voltages as low as20mV. Other factors that affect performance
are the DC resistance of the transformer windings and the inductance of the windings. Higher
DC resistance will result in lower efficiency. The secondary winding inductance will
determine the resonant frequency of the oscillator, according to the following formula.
Frequency = Hz Where L is the inductance of the transformer secondary winding and C is the
load capacitance on the secondary winding. This is comprised of the input capacitance at
pinC2, typically 30pF, in parallel with the transformer secondary winding’s shunt capacitance
one side o. Here Two Peltiers are used which are connected to Linear IC peltier is heated by
the human palm and the other is cooled.
F.9 : Peltiers connected to Linear IC
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The above figure shows the two peltiers connection to the Linear IC using the step-up
transformer of the turns ratio 1:100. The output of the circuit is taken and is tabulated. For the
send time the 1:100 turns transformer is replaced by 1:20 turns, the output is found out and
tabulated. The Efficiency of the two transformers is compared is is plotted graphically.
F.10 : Vout vs Vin of 1:100 & 1:20 tansformers
The Vout obtained for the 1;100 ratio transformer is 4.5v and the capacitor used here is C1=1nF while in case of 1:20 ratio, the capacitor used is C1=10nF and efficency is calculated
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8: HEAT SINK
Heat sinks are used where the heat dissipation ability of the basic device is insufficient to
moderate its temperature. Here Heat sink is used to cool the peltier tiles. Generally aluminum
is used as heat sink due to the cheaper in cost and greater in the performance.
F.11 : Air flowing through Aluminum tube
Peltier Tiles were mounted on the aluminum tube and placed inside a PVC pipe with a cut
for the peltiers.The Hollow space inside the tube allows to pass the air currents freely. So the
Flashlight can be divided as the two medium the outer area and the inner area of the tube. The
area also referred as Hot side due to the contact of peltier with the with the Human Hand. The
inner area also referred as cold side due to the passage of air currents.
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9:ADVANTAGES
Only needs a five degree temperature difference to work and produce up to 5.4 mW at 5 foot
candles of brightness.
Harvesting energy, like with this flashlight, can provide a lot of potential for powering small
devices without necessarily having to have batteries
We use an enormous amount of batteries," said Albin Gasiewski of the Center for
Environmental Technology. "Most of them are not rechargeable and end up in landfills."
Hollow Flashlight could make a difference.
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10: CONCLUSION
Even with all the thermal and voltage conversion losses, there was still enough power in the
palm to provide usable light. The results proved that some of the unused energy that have
been wasted in the form of heat is utilized in glowing a Flashlight using thermo-electric
conversion by Peltier Tiles.
In conclusion, we succeeded in powering a flashlight using only the heat of the hand.
These flashlights do not use any batteries, toxic chemicals, or kinetic energy. They do not
create any noise or vibrations and will always work. The flashlight’s only limitation is its
need for at least a 5°C temperature difference to provide usable light.
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11: BIBILIOGRAPHY AND REFRENCES
1) Physics and Astronomy Online: http://www.physlink.com/education/askexperts/ae420.cfm
2) Makosinski, Ann. Fire or Ice - Electricity for an Emergency, VIRSF, 2010.
3) The Physics Factbook: http://hypertextbook.com/facts/2001/IgorFridman.shtml
4) Makosinski, Ann. The Piezoelectric Flashlight - A Novel Way to Generate Green
Electricity, VIRSF, 2012.
5) Laird Thermoelectric: http://www.lairdtech.com/Products/Thermal-Management-
Solutions/Thermoelectric-Modules/
6) David Salerno, Ultralow Voltage Energy Harvester Uses Thermoelectric Generator for
Battery Free Wireless Sensors; Journal of Analog Innovation, October 2010.
7) Futurlec: http://www.futurlec.com/Transistors/J310pr.shtml
8) Encyclopedia Britannica – Thermoelectric Power
Generator: http://www.britannica.com/EBchecked/topic/591615/thermoelectric-power-
generator
9) Stanford University, Physics 240 Coursework – Thermoelectric
Generators: http://large.stanford.edu/courses/2010/ph240/weisse1/
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