Human Power Harvesting

1
Human Power Harvesting

• ECE 445 Senior Design at UIUC

04/28/2008

• Team 29
• Fred Raddatz
• Siddhant Rana

2
Introduction

• Desirable to extend battery life of DAGR handheld
  GPS receiver
• Human power provides effective, convenient
  solution
• There are different ways to harvest power from
  humans

IMAGE SOURCE Rockwell Collins
DAGR (Defense Advanced GPS Receiver) is a
product of Rockwell Collins
3
Objective

• Harvest power from multiple sources
• Human movement - through piezoelectric material
  in boots
• Environment - by power generated from backpack
  mounted solar panels

4
Benefits

• Power is available on the go
• Extended battery life
• Maintenance free
• Reliable power

5
Features

• Zero emissions
• Silent production of energy
• Discrete integration with existing equipment
• Weather resistant

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Original Block Diagram
7
Final Block Diagram
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Piezo
Solar
NiCad Cells
Piezoelectric Transducer
DPDT Switch
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Piezo Circuit Diagram
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Piezoelectric Source

• The Piezoelectric power source used for this
  circuit was the thunder actuator TH-6R made by
  Face International Corp
• This sensor was chosen since it was relatively
• Cheaper (Around 110 plus shipping)
• It has been used in a lot of other research
  regarding piezoelectric power generation

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Piezoelectric Source
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Piezoelectric Source

• At approximately 2Hz frequency of walking the
  internal resistance of the piezoelectric sensor
  is about 250KO
• We calculated the maximum power that we could get
  out of sensor
• We got a max power of 5 mW for 35V peaks
• We could not test the device for the actual
  values received because of the limitations of the
  oscilloscope

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Piezoelectric Source
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Piezo Rectifier Circuit

• We used a simple bridge rectifier. We used a W02
  bridge rectifier that can handle a peak voltage
  of 200V and 2A current.
• For our purposes we were not expecting higher
  voltages or currents so we stuck with this.

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Piezo Power Converter Voltage Regulator

• The circuit consists of two parts
• The Power Converter Circuit
• The Low Power Voltage Regulator
• The Power Converter Circuit makes use of a BJT
  and an N-MOSFET
• The Low Power Voltage Regulator consists of a
  MAXIM Chip (666)

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Piezo Power Converter Circuit

• The Power from the Piezoelectric source is of the
  order of mW.
• We therefore store energy in a capacitor and then
  using a SCR with Supercritical feedback and a
  Voltage regulator we output 5V.

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Low Power Voltage Regulator

• The low power voltage regulator is a Max666 chip.
• Had dual modes of fixed 5V or adjustable 1.3V to
  16V output.
• Low Battery Detector.
• Current output 40mA.

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Piezo Circuit Diagram
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Overview of Solar Circuit Components

• MPT6-150 Solar Panel Characteristics
• Operating Voltage 6 V
• Operating Current 100 mA
• Total Size 114mm x 150mm (4.9 x 5.9 inches)

IMAGE SOURCE PowerFilm Inc.

• MAX639 Integrated Circuit
• High efficiency, step-down, DC-DC converter

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Basic Solar Circuit
Solar Panel

• 80 efficiency if
• Solar battery voltage exceeds full charge NiCd
  output by one diode drop, but

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Problems w/ Basic Solar Ckt.

• Charge voltage adjustment not always possible
• Voltage mismatch ? slow NiCd charging
• Solar cell current is constant with cell voltage
  - output peaks near cell's open ckt. voltage

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MAX639 Solar Charging Ckt. Design
SOURCE MAXIM-IC
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MAX639 Solar Charging Ckt. Design

• VFB (feedback voltage)
• Set by voltage divider
• LBO, LBI
• LBO low when input voltage at LBI is less than
  1.28 V (internal chip reference)
• Following MAX639 Datasheet

- where LBI is 1.28V, and VLB is the desired
low-battery voltage
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MAX639 Solar Ckt. Schematic
Solar Panel
MAX639
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Benefits of MAX639 circuit

• Regulates voltage NiCd cells are being charged at
• Maintained at level necessary for maximum power
  transfer
• Efficiencies 85
• Up to four times the power of the single diode
  circuit

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Nickel-Cadmium Cell Properties

• NiCd Nominal Cell Voltage 1.2 Volts
• 1V/cell ? 99 of energy absent
• NiCd Charging Rate
• Should be 10 of rated (C/10 charge)
• NiCd cells for this project were rated at 1000mAh
• 0.10 1000mAh 100mA target charge rate
• Ioperating of solar panel is 100mA

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NiCd Charge Details
SOURCE http//www.sentex.net
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Additional Solar Panels

• Adding additional solar panels provide benefits
• If in series higher voltage
• Better low-light performance
• If in parallel more current
• Increases charging rate
• For this project, two panels were used in series

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Piezo Power Output

• We wanted to test the circuit in 3 ways
• Charge a Capacitor
• Charge a Resistor
• Charge the battery pack

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Piezo Power Output Using Capacitor

• The capacitor easily charged to around 4.66V. We
  got the following images on the oscilloscope.

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Piezo Power Output Using Resistor

• Across a 2.5O resistor we get a maximum power of
  approximately 40mW

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Power Output Using Battery

• When we tried charging the battery with source we
  realized that it would require constant pressing
  for a really long time.
• Besides since the pressing was simple tapping it
  would not be as powerful as walking around.

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Ways to Improve Piezoelectric Power Generation

• A lot of the power generation in piezoelectric
  substances comes down to design of the generator.
  There are some new materials out there being
  researched
• The more the number of sources the larger the
  power we get. Besides if these are connected in
  parallel then we get a lower overall internal
  resistance

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Solar Circuit Testing

• MAX639 IC operation verified
• Solar Panel Voc, Isc, Voperating, Ioperating
• Overall Circuit Vcharging, Icharging, ?
• Testing Performed Outdoors

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Performance Under Various Conditions
SOURCE PowerFilm Inc.
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Example Test 1
Power I2 R
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(cont. Ex. Test 1)
Readings taken 45 minutes after
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Example Test 1 Conclusions

• 1.12 Volts of total battery charge was gained
  with 10 minutes of charging fully discharged
  batteries
• Later data will show that initial charging is
  quick for discharged cells, and slows later
• Power ranged from 0.1 to 0.2 Watts

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Example Test 2
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(cont. Ex. Test 2)
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(cont. Ex. Test 2)
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Example Test 2 Conclusions

• Initial 15 minutes of charging, voltage increases
  rapidly to 1.37V/cell, then stabilizes
• 24 hours later, the charge was 0.1 Volt lower
  than after charging
• NiCd cells also lose 1 of their charge daily
  when not in use

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Solar Circuit Efficiency
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Regulated Charging Voltage Demo
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Solar Circuit Successes

• Proper charge current
• Regulated charging voltage
• Efficient
• Low cost (30)

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Solar Ckt. Challenges

• Collecting accurate data due to NiCd charge
  characteristics
• Voltage while charging is different than voltage
  after waiting time after charging
• Sunlight conditions constantly changing
• Clouds, rain, etc.
• Testing takes a lot of time
• Testing could not be completed indoors

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Solar Ckt. Recommendations

• Use higher quality solar panels
• Current circuit will charge 1-4 NiCd batteries
• Can modify to charge Lithium batteries
• Improve charge status indicator

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Recommended Improvements

• Add sources together so that manual switching is
  never necessary
• Additional sources may include
• - Infrared or terahertz transducers-
  Infrastructure power (AC power lines, landline
  telephone jacks, USB 2.0)- RF power- Magnetic
  fields- Heat transducers- Hand crank generators

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Acknowledgements

• Professor Gary Swenson
• Professor Chapman
• TA Tomasz Wojtaszek
• Rockwell Collins - Chuck Smiley