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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 - PowerPoint PPT Presentation
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The Design ProcessThe Design Process
Abstraction & SynthesisAbstraction & SynthesisPart IIPart II
Solar Candle Continued…Solar Candle Continued…
byby
Prof. BitarProf. Bitar
Abstraction & SynthesisAbstraction & SynthesisHomework #2Homework #2
ViableOptions
PreferredSolution
Research Prior ArtBrainstorm
ApplyConstraints
HW#2
Abstraction&
Synthesis
Possible Solutions
PerformValue Analysis
Product ReminderProduct Reminder
The Customer RequirementsThe Customer RequirementsExplicitExplicit– Cat SafeCat Safe– Look NiceLook Nice– Different ColorsDifferent Colors– AutomaticAutomatic
ImplicitImplicit– Low CostLow Cost– Reliable / DurableReliable / Durable– Low MaintenanceLow Maintenance
Product SpecificationsProduct Specifications yet to be quantified… yet to be quantified…
Safety / DurabilitySafety / Durability– Heavy BaseHeavy Base– Unbreakable LEDUnbreakable LED– Secure to Window Sill, Sash or Window Secure to Window Sill, Sash or Window
PanePane– No CordsNo Cords– Low VoltageLow Voltage
AestheticsAesthetics– Traditional LookTraditional Look– Interchangeable Color LEDsInterchangeable Color LEDs– Flickering OptionFlickering Option
Low Operating CostLow Operating Cost– Long Battery Life (Efficient) Long Battery Life (Efficient) – RechargeableRechargeable– Solar RechargeableSolar Rechargeable– Photo Sensor or TimerPhoto Sensor or Timer
Current Block DiagramCurrent Block Diagram
Solar CellCharge
ControllerRechargeable
Battery
EfficientDriveCircuit
White LED3.2V @ 20mA(worst case)
FlickeringControl
ModeSelection
PhotoSensor
A fundamental question to answer…A fundamental question to answer…
How much energy is How much energy is required to operate our required to operate our
solar candle (LED)?solar candle (LED)?
How much energy?How much energy?Consider worst case output requirement…Consider worst case output requirement…
3.2V x 20mA = 64 mW3.2V x 20mA = 64 mW
How much time will the LED be on?How much time will the LED be on?64 mW x 6 hrs = 384 mW•hrs64 mW x 6 hrs = 384 mW•hrs
Answer: 384 mW•hrs (units of ENERGY!)Answer: 384 mW•hrs (units of ENERGY!)
Assuming 70% efficiency, Assuming 70% efficiency,
384 / 0.70 ≈ 384 / 0.70 ≈ 550 mW•hrs needed550 mW•hrs neededNOTE: On average, this minimum amount of energy needs to be NOTE: On average, this minimum amount of energy needs to be
supplied by the solar panel and stored in the battery during the supplied by the solar panel and stored in the battery during the day, if our candle is to be sustainable.day, if our candle is to be sustainable.
Focusing on the BatteryFocusing on the Battery
Solar CellCharge
ControllerRechargeable
Battery
EfficientDriveCircuit
White LED3.2V @ 20mA(worst case)
FlickeringControl
ModeSelection
PhotoSensor
Things to consider…Things to consider…Types: What rechargeable technologies will Types: What rechargeable technologies will work in this application? (NiMH, NiCd, Lithium work in this application? (NiMH, NiCd, Lithium Ion, Sealed Lead Acid, Super Capacitors…)Ion, Sealed Lead Acid, Super Capacitors…)
Voltage: What is the minimum battery voltage? Voltage: What is the minimum battery voltage?
Capacity: How long does the battery need to Capacity: How long does the battery need to hold a charge? (Six Hours Minimum)hold a charge? (Six Hours Minimum)
Shape: Needs to fit in candle stem or base.Shape: Needs to fit in candle stem or base.
Cost: I don’t want to spend a lot on batteries!Cost: I don’t want to spend a lot on batteries!
Possible choice: NiCd / NiMHPossible choice: NiCd / NiMH
Battery SpecificationBattery SpecificationDischarge CurveDischarge Curve
Battery Feasibility Check…Battery Feasibility Check…THREE 1.2V (nominal) NiCD or NiMH batteries wired in THREE 1.2V (nominal) NiCD or NiMH batteries wired in series (3.6V nominal).series (3.6V nominal).
Cost: $2.37 each (single qty) / $1.30 (1000 qty)Cost: $2.37 each (single qty) / $1.30 (1000 qty)
Shape: AA cells would fit in candle stem or base.Shape: AA cells would fit in candle stem or base.
Voltage Check: Voltage Check: 1.2V x 3 = 3.6V 1.2V x 3 = 3.6V
Charge Capacity:Charge Capacity: 700 mA•hrs (units of charge) 700 mA•hrs (units of charge)
Energy Capacity:Energy Capacity: 700 mA•hrs x 1.2V 700 mA•hrs x 1.2V
= 840 mW•hrs (per battery)= 840 mW•hrs (per battery)
= 2,520 mW•hrs (for 3 batteries)= 2,520 mW•hrs (for 3 batteries)
NOTE: Since only 550 mW•hrs are required, one battery NOTE: Since only 550 mW•hrs are required, one battery has enough energy capacity to do the job, BUT the voltage has enough energy capacity to do the job, BUT the voltage will need to be BOOSTED!will need to be BOOSTED!
Question: Do we know the specs for a Question: Do we know the specs for a possible drive circuit? YES!possible drive circuit? YES!
Solar CellCharge
Controller
RechargeableBattery
1.2V NiCd
EfficientDriveCircuit
LED3.2V
20mA
FlickeringControl
ModeSelection
PhotoSensor
Solar CellCharge
Controller
RechargeableBattery
1.2V NiCd
EfficientDriveCircuit
LED3.2V
20mA
FlickeringControl
ModeSelection
PhotoSensor
Focusing on the Solar CellFocusing on the Solar Cell
How about the solar cell from Home Depot?How about the solar cell from Home Depot?
After taking the Home Depot Landscape Light apart, I After taking the Home Depot Landscape Light apart, I made the following measurements (in direct sun): made the following measurements (in direct sun): IISCSC
= 50mA , V = 50mA , VOCOC = 4.3V = 4.3V
Solar Panel V-I CharacteristicSolar Panel V-I Characteristic
T
Solar Cell Voltage (V)0.00 1.00 2.00 3.00 4.00 5.00
So
lar
Ce
ll C
urr
en
t (A
)
0
10m
20m
30m
40m
50m
Question: How long would it take this Question: How long would it take this solar cell to recharge a completely solar cell to recharge a completely
discharged battery?discharged battery?
Battery Capacity = 700mA•hrsBattery Capacity = 700mA•hrs
Solar Cell (in full sun) = 50mASolar Cell (in full sun) = 50mA
Therefore, 700mA•hrs / 50mA = 10 hrsTherefore, 700mA•hrs / 50mA = 10 hrs
Q: Is this realistic?Q: Is this realistic?
What voltage are we operating at?What voltage are we operating at?T
Solar Cell Voltage (V)0.00 1.00 2.00 3.00 4.00 5.00
So
lar
Ce
ll C
urr
en
t (A
)
0
10m
20m
30m
40m
50m
Is this efficient? Does it matter?Is this efficient? Does it matter?
The Process Continues…The Process Continues…