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Human Power Harvesting

Human Power Harvesting. ECE 445 – Senior Design at UIUC. 04/28/2008. Team #29 Fred Raddatz Siddhant Rana. 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.

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Human Power Harvesting

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  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

  6. Charge Indicator LED Solar Panels Solar Circuit Source Adding Circuitry NiCd Batteries Piezoelectric Device Piezo Circuit Original Block Diagram

  7. Charge Indicator LED Solar Panels Solar Circuit Source Switching NiCd Batteries Piezoelectric Device Piezo Circuit Final Block Diagram

  8. Piezo Solar NiCad Cells Piezoelectric Transducer DPDT Switch

  9. Piezo Circuit Diagram

  10. 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

  11. Piezoelectric Source

  12. Piezoelectric Source At approximately 2Hz frequency of walking the internal resistance of the piezoelectric sensor is about 250KΩ 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

  13. Piezoelectric Source

  14. 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.

  15. 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)

  16. 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.

  17. 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.

  18. Piezo Circuit Diagram

  19. 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

  20. Basic Solar Circuit • 80% efficiency if: • Solar battery voltage exceeds full charge NiCd output by one diode drop, but… Solar Panel

  21. 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

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

  23. 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

  24. MAX639 Solar Ckt. Schematic Solar Panel MAX639

  25. 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

  26. 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

  27. NiCd Charge Details SOURCE: http://www.sentex.net

  28. 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

  29. Piezo Power Output • We wanted to test the circuit in 3 ways: • Charge a Capacitor • Charge a Resistor • Charge the battery pack

  30. Piezo Power Output – Using Capacitor • The capacitor easily charged to around 4.66V. We got the following images on the oscilloscope.

  31. Piezo Power Output – Using Resistor • Across a 2.5Ω resistor we get a maximum power of approximately 40mW

  32. 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.

  33. 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

  34. Solar Circuit Testing • MAX639 IC: operation verified • Solar Panel: Voc, Isc, Voperating, Ioperating • Overall Circuit: Vcharging, Icharging, η • Testing Performed Outdoors

  35. Performance Under Various Conditions SOURCE: PowerFilm Inc.

  36. Example Test #1 Power = I2 * R

  37. …(cont. Ex. Test 1) *Readings taken 45 minutes after

  38. 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

  39. Example Test #2

  40. …(cont. Ex. Test 2)

  41. …(cont. Ex. Test 2)

  42. 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

  43. Solar Circuit Efficiency

  44. Regulated Charging Voltage Demo

  45. Solar Circuit Successes • Proper charge current • Regulated charging voltage • Efficient • Low cost (~$30)

  46. 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

  47. 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

  48. 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

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

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