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Design Process Analysis & Evaluation Part II Example Design: Solar Candle by Prof. Bitar.
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Transcript of Design Process Analysis & Evaluation Part II Example Design: Solar Candle by Prof. Bitar.
Design ProcessDesign Process
Analysis & EvaluationAnalysis & EvaluationPart II Part II
Example Design: Solar CandleExample Design: Solar Candlebyby
Prof. BitarProf. Bitar
Existing Window Candle Block Existing Window Candle Block Diagram Diagram
Solar CellCharge
Controller
RechargeableBattery
1.2V NiCd
DC-DCBoost
Converter
LED3.2V
20mA
FlickeringControl
ModeSelection
PhotoSensor
Modified System Block DiagramModified System Block Diagram
Solar PanelCharge
Controller
RechargeableBattery
1.2V NiCd700 mAhrs
ZetexLED
Driver85% Eff.
LED20mA
3.2V(min)
SwitchingControl
ModeSelection
PhotoSensor
Timer
Changing Focus to ChargingChanging Focus to Charging
How much energy is removed from the How much energy is removed from the battery during a typical evening? battery during a typical evening? • LED requires 20mA x 3.2V x 6hrs = 384 mW hrs LED requires 20mA x 3.2V x 6hrs = 384 mW hrs
(power x time = energy)(power x time = energy)• Converter is only 85% efficient, so energy taken Converter is only 85% efficient, so energy taken
from battery is 384 mW hrs / 0.85 ≈ from battery is 384 mW hrs / 0.85 ≈ 452 mW hrs452 mW hrs
How much charge?How much charge?• Dividing by the battery voltage gives the charge Dividing by the battery voltage gives the charge
removed: 452 mW hrs / 1.2V removed: 452 mW hrs / 1.2V ≈ ≈ 377 mA hrs 377 mA hrs
On to the Solar Panel RequirementsOn to the Solar Panel RequirementsAfter taking the Home Depot Landscape Light After taking the Home Depot Landscape Light apart, I made the following measurements (in apart, I made the following measurements (in
direct sun): 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
Solar Panel ConsiderationsSolar Panel Considerations
How much charge is restored if the panel is How much charge is restored if the panel is connected directly to the battery? What connected directly to the battery? What assumptions should we make?assumptions should we make?
How aboutHow about• 10 Hours of Daylight 10 Hours of Daylight • 50% Incident Light 50% Incident Light
This gives 50mA x 10hrs x 50% = 250mA hrsThis gives 50mA x 10hrs x 50% = 250mA hrs
Is this enough? Is this enough? We need 377 mA hrs. No. We need 377 mA hrs. No.
Charge Options?Charge Options?
Use two solar panels in parallel to boost Use two solar panels in parallel to boost the current (but we’re throwing away the current (but we’re throwing away voltage?)voltage?)
Use the existing panel with some sort of Use the existing panel with some sort of Buck Converter (will need to look at Buck Converter (will need to look at efficiency).efficiency).
Find a solar cell better suited for this Find a solar cell better suited for this application…application…
Found something at Found something at Futurlec.com !Futurlec.com !
Open Circuit Voltage (Voc): 2.2VOpen Circuit Voltage (Voc): 2.2V
Short Circuit Current (Isc): 100mAShort Circuit Current (Isc): 100mA
Dimensions:Dimensions:
61mm x 61mm61mm x 61mm
Price:Price:
$1.50 (100+ Qty)$1.50 (100+ Qty)
Modified CharacteristicModified CharacteristicT
Solar Panel Voltage (V)0.00 1.00 2.00 3.00
So
lar
Pa
ne
l Cu
rre
nt (
A)
0
20m
40m
60m
80m
100m
IISCSC = 100 mA , V = 100 mA , VOCOC = 2.2 V = 2.2 V
(V(VOCOC greater than V greater than VBATBAT))
A Possible SolutionA Possible Solution
Now we have: 100mA x 10 hrs x 50% = Now we have: 100mA x 10 hrs x 50% = 500 mA hrs.500 mA hrs.
Is this enough? We need 377mA hrs. Yes! Is this enough? We need 377mA hrs. Yes!
Solar Panel Update to System Solar Panel Update to System Block DiagramBlock Diagram
Solar PanelISC = 100mAVOC = 2.2V
IAVE = 50mAΔt = 10hrs
Q = 500mAHrs
ChargeController
RechargeableBattery
1.2V NiCd
ZetexLED
Driver
LED20mA
3.2V(min)
SwitchingControl
ModeSelection
PhotoSensor
Timer
And now the Charge And now the Charge Controller…Controller…
Solar PanelISC = 100mAVOC = 2.15VIAVE = 50mAΔt = 10hrs
Q = 500mAHrs
ChargeController
RechargeableBattery
1.2V NiCd
ZetexLED
Driver
LED20mA
3.2V(min)
SwitchingControl
ModeSelection
PhotoSensor
Timer
Which Charge Method to Choose?Which Charge Method to Choose?
Semi-Constant Current ChargeSemi-Constant Current Charge• Most Typical Charge SystemMost Typical Charge System• Simple and EconomicalSimple and Economical• Typical Charge Time = 15 HrsTypical Charge Time = 15 Hrs• Typical Charge Current = 0.1 It Typical Charge Current = 0.1 It
(0.1*700 mA Hrs = 70mA)(0.1*700 mA Hrs = 70mA)
Time Controlled ChargeTime Controlled Charge• More reliable than Semi-Constant CurrentMore reliable than Semi-Constant Current• Slightly more complicated. Requires timer.Slightly more complicated. Requires timer.• Typical Charge Time = 6-8 HrsTypical Charge Time = 6-8 Hrs• Typical Charge Current = 0.2 It (140mA)Typical Charge Current = 0.2 It (140mA)
Semi-Constant Current Charge Semi-Constant Current Charge Seems ViableSeems Viable
With our low average current of 50mA, With our low average current of 50mA, and charge time of 10 hrs, the Semi-and charge time of 10 hrs, the Semi-Constant Current Charge method seems Constant Current Charge method seems viable.viable.
Also, if we are concerned about over Also, if we are concerned about over charge, we can extend the on-time beyond charge, we can extend the on-time beyond 6 hrs.6 hrs.
This method is more economical and may This method is more economical and may not require a timer for this application. not require a timer for this application.