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The Design Process Abstraction & Synthesis Part II Solar Candle Continued…

The Design Process Abstraction & Synthesis Part II Solar Candle Continued…. by Prof. Bitar. Abstraction & Synthesis Homework #2. Research Prior Art Brainstorm. Possible Solutions. HW#2 Abstraction & Synthesis. Perform Value Analysis. Viable Options. Apply Constraints. Preferred

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The Design Process Abstraction & Synthesis Part II Solar Candle Continued…

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  1. The Design ProcessAbstraction & SynthesisPart IISolar Candle Continued… by Prof. Bitar

  2. Abstraction & SynthesisHomework #2 Research Prior Art Brainstorm Possible Solutions HW#2 Abstraction & Synthesis Perform Value Analysis Viable Options Apply Constraints Preferred Solution

  3. Product Reminder

  4. The Customer Requirements • Explicit • Cat Safe • Look Nice • Different Colors • Automatic • Implicit • Low Cost • Reliable / Durable • Low Maintenance

  5. Product Specifications yet to be quantified… • Safety / Durability • Heavy Base • Unbreakable LED • Secure to Window Sill, Sash or Window Pane • No Cords • Low Voltage • Aesthetics • Traditional Look • Interchangeable Color LEDs • Flickering Option • Low Operating Cost • Long Battery Life (Efficient) • Rechargeable • Solar Rechargeable • Photo Sensor or Timer

  6. Current Block Diagram Photo Sensor White LED 3.2V @ 20mA (worst case) Solar Cell Charge Controller Rechargeable Battery Efficient Drive Circuit Mode Selection Flickering Control

  7. A fundamental question to answer… How much energy is required to operate our solar candle (LED)?

  8. How much energy? • Consider worst case output requirement… 3.2V x 20mA = 64 mW • How much time will the LED be on? 64 mW x 6 hrs = 384 mW•hrs • Answer: 384 mW•hrs (units of ENERGY!) • Assuming 70% efficiency, 384 / 0.70 ≈ 550 mW•hrs needed NOTE: On average, this minimum amount of energy needs to be supplied by the solar panel and stored in the battery during the day, if our candle is to be sustainable.

  9. Focusing on the Battery Photo Sensor White LED 3.2V @ 20mA (worst case) Solar Cell Charge Controller Rechargeable Battery Efficient Drive Circuit Mode Selection Flickering Control

  10. Things to consider… Types: What rechargeable technologies will work in this application? (NiMH, NiCd, Lithium Ion, Sealed Lead Acid, Super Capacitors…) Voltage: What is the minimum battery voltage? Capacity: How long does the battery need to hold a charge? (Six Hours Minimum) Shape: Needs to fit in candle stem or base. Cost: I don’t want to spend a lot on batteries!

  11. Possible choice: NiCd / NiMH

  12. Battery SpecificationDischarge Curve

  13. Battery Feasibility Check… THREE 1.2V (nominal) NiCD or NiMH batteries wired in series (3.6V nominal). Cost: $2.37 each (single qty) / $1.30 (1000 qty) Shape: AA cells would fit in candle stem or base. Voltage Check: 1.2V x 3 = 3.6V Charge Capacity: 700 mA•hrs (units of charge) Energy Capacity: 700 mA•hrs x 1.2V = 840 mW•hrs (per battery) = 2,520 mW•hrs (for 3 batteries) NOTE: Since only 550 mW•hrs are required, one battery has enough energy capacity to do the job, BUT the voltage will need to be BOOSTED!

  14. Question: Do we know the specs for a possible drive circuit? YES! Photo Sensor Solar Cell Charge Controller Rechargeable Battery 1.2V NiCd Efficient Drive Circuit LED 3.2V 20mA Mode Selection Flickering Control

  15. Focusing on the Solar Cell Photo Sensor Solar Cell Charge Controller Rechargeable Battery 1.2V NiCd Efficient Drive Circuit LED 3.2V 20mA Mode Selection Flickering Control

  16. How about the solar cell from Home Depot? After taking the Home Depot Landscape Light apart, I made the following measurements (in direct sun): ISC = 50mA , VOC = 4.3V

  17. Solar Panel V-I Characteristic

  18. Question: How long would it take this solar cell to recharge a completely discharged battery? • Battery Capacity = 700mA•hrs • Solar Cell (in full sun) = 50mA Therefore, 700mA•hrs / 50mA = 10 hrs Q: Is this realistic?

  19. What voltage are we operating at? Is this efficient? Does it matter?

  20. The Process Continues…

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