Solar Night Light Operations Manual

SOLAR NIGHT LIGHT OPERATIONS MANUAL MyShelter Foundation and the University of Santo Tomas Electronics Engineering Department in Cooperation with Technical Education and Skills Development Authority

September 2013 Prepared by: Rikki Q. Macolor, BSECE

1 Prepared by: Rikki Q. Macolor, BSECE, University of Santo Tomas September 2013

Design Overview

Objectives

To provide locally fabricated solar lighting devices to rural communities to light up their homes, create livelihood activity with local fabrication and repair, and sustain the lighting activity as a rural business enterprise.

Project Concept

The Liter of Light initiative have successfully deployed thousands of bottles of light in homes and building to take advantage of natural day-lighting using a simple technology of placing a bottle through the roof. The success of the initiative is due to the simplicity and low cost of the technology that the beneficiary can participate in making the bottle of light. The project aims to push the Liter of Light initiative further by retrofitting the bottle of light with solar powered LED with a very simple design using locally available materials that can be locally fabricated and repaired.

Technical Design

The solar lamp uses solar energy to power the lamp that will illuminate the bottle at night.


Composition and Theory of Operation

LED Lamp

Specifications:

Power 1W

Operating Voltage 3.2V to 3.6V

Max Current 350mA

Lumen 90LM to 100LM

Color Temperature 3500K to 5500K

Working Temperature 0°C to 40°C

Storage Temperature -20°C to 60°C

Dimensions

The lamp used for the Solar Night Light is a single high power 1W LED with an operating voltage of 3.2V to 3.6V and a maximum current rating of 350mA. The prototype used a 10 Ohms resistor as the current limiter to reduce the current draw to 100mA when drawing power from the 3.7V lithium battery. It was observed that the LED heat sink temperature remains stable at 30 degrees Celsius at this current.


Battery

Specifications:

Nominal Voltage 3.7V

Charging Voltage 4.20V±0.05V

Max Current (Charging) 1760mA

Cycle Life > 300 cycles ( ≥ 80% Capacity)

Working Temperature -20°C to 60°C

Storage Temperature -5°C to 35°C

Dimensions

The battery selected for this device is the 3.7V 2200mA rechargeable lithium battery commonly used as the cells for laptop and camera battery packs. This battery technology has longer service life and higher power density. The high cell voltage makes is possible to power the LED using a single cell. This makes the light simple, easy and cost effective to build. At 100mA current, this battery will have storage of 20 hours for the LED lamp at full charge. At 12 hours of operation, the daily depth of discharge is 60%. No overcharging controller is used since the solar module to be used is too small to overcharge the battery under daily use. Lithium battery can tolerate deep discharge so no over-discharge controller is used. These overcharge and over-discharge controllers are eliminated to simplify the design for the lamp.


Solar Module

Specifications:

Max Output DC Voltage 5V, 1W

Max Output Current 180mA

Cycle Life > 300 cycles ( ≥ 80% Capacity)

Weight ~31g / 0.07lb / 154ct

Dimensions

The deliver a daily energy requirement for 12 hours of LED light consuming 100mA will require 1.2AH. At a voltage of 3.7V with 80% charging efficiency an average of 3.28 effective sun hours per day (Philippine setting), the required solar module size is 1.7Wp. The locally available solar module used is 1W module with 10 poly crystalline cells that is ideal for charging the 3.7V lithium battery.


Night Switch Control

The lamp will be used at night and the bottle will let sunshine into the house during daytime with the LED off. An automatic night switch is used instead of a manual switch to avoid the problem associated with a manual mechanical switch that often fails after several on-off cycles. An automatic switch also reduces the intervention of the user in the operation of the lamp hence increases reliability. The night switch uses a MOSFET to pull the cathode of the LED to ground and drive the current through the limiting resistor. The gate of the MOSFET has a pull-up resistor connected to the positive battery terminal to normally turn on the MOSFET. A bipolar transistor is used to sense the output of the solar module on the anode of the blocking diode that will drive its base though a resistor during daytime that will pull-down the gate of the MOSFET to ground and turn off the LED. At night when there is no drive current from the solar module to the base of the bipolar transistor, the MOSFET gate goes high and pulls the cathode of the LED to ground though the drain terminal and turns on the LED. When the battery charge is low, there is not enough drive on the gate of the MOSFET so the lamp will dim. This prevents that battery from being fully discharged.

BJT Pull-Down Network

MOSFET Switch Network


Master Switch

A separate manual 3P miniature slide switch is added to disconnect the battery from the circuit. This will prevent the lamp from turning on in its dark container during storage and transport. This is also a safety requirement when shipping the equipment. The switch should only be turned on during testing and installation.

Master Switch


Bill of Materials

Item Description Quantity Unit

1 Printed Circuit Board (1"x3") 1 pc

2 PVC Pipe Blue 1"x5" 1 pc

3 PVC Coupling 1" 1 pc

4 5V 1W Solar module 1 pc

5 Stranded wire #22 1 m

6 General Purpose Transistor 9014 1 pc

7 Lithium Battery 3.7V 2200mAH with terminals 1 pc

8 2W 10 ohm Resistor 1 pc

9 3P Slide Switch 1 pc

10 IRF510 1 pc

11 LED 1W 1 pc

12 Resistor 1k ohm 1/4W 2 pcs

13 Resistor 10k ohm 1/4W 1 pc

14 Schottky Barrier Diode 1 pc

15 Small Glass Fuse 1 pc

16 0.5” Transparent Plastic Hose 0.3 m

17 Soldering Lead 1 m

18 Glue gun stick 4 pcs

19 Coke/Pepsi 1.5 liter bottle 1 pc

Required Tools

Hack saw for cutting the PVC Pipe

Long nose plier

Side Cutter

Blade cutter

Soldering Iron

Glue gun

Alligator clips

Voltmeter (for troubleshooting and testing)


Schematic

PCB Layout and Parts Placement


Construction Procedures 1. Cut 5” in length of the 1” diameter PVC pipe using the hack saw. One side is cut at an angle, about

30 degrees, while the other end is flat. The slanted side will hold the solar module. This slanted side

reduces the accumulation of dirt and water on the solar panel. Set aside the PVC for later use.

2. Prepare the raw printed circuit board with the foil (copper) side on top. Cut the pattern on the foil

using an ordinary paper cutter and attach the components as shown:

You may use tools such as voltmeters with continuity testers to ensure that the etching and

boundaries are properly done. As an alternative, you may position the PCB in front of ample light to

see if the etching is done correctly. If there is still some parts of copper bridging to the other sides,

you might have to redo or re-etch that part.


Refer to the schematic and PCB layout diagram for the proper parts positioning. Do remember that

discrete active components such as the bipolar junction transistor (S9014) and the metal-oxide

semiconductor field-effect transistor (IRF510) are also heat sensitive. This means that prolonged

heating may cause the parts to be damaged.

3. Attach the battery on the positive and negative terminals as shown below:

Additionally, you may use other methods such as attaching aluminum strips to the ends of the

batteries to make the connections easier.

4. Set aside the circuit board and assemble the lamp unit. Use the alligator clip to mount the fuse

vertically and melt some lead on to one of the terminals.


5. Use the alligator clip to hold the LED face down and solder a drop lead on the back metal part.

6. Position the fuse with the lead side close to the back of the LED. Heat both to melt the lead and quickly but safely attach the fuse to the LED. Hold the fuse in place for about 8 seconds to ensure that the fuse has completely attached itself to the back of the LED. WARNING: Do not heat the LED for more than 3 seconds as this will damage the LED and possible render it useless.

7. Cut the pair of the stranded wires 14 inches from the LED lamp and mark the negative to avoid confusion. Alternatively, you may use a set of different colored wires to easily distinguish one from the other. Set aside the lamp for later use.


8. Cut about 12 inches of ½” transparent hose, dip for a minute in boiling water to straighten it.

9. Insert the stranded wire from the LED lamp into the plastic hose. Heat up the end of the hose to fit

the fuse and the wires at the end of the hose. Set aside for later use.

10. Prepare the solar module and lay it on the table with the solar cell facing down to expose the

connectors at the back. Cut about 3” length of stranded wires. Strip the ends of the stranded wire and solder on the positive and the negative terminals of the solar module. Similarly, make some distinguishing marks on the wires to differentiate the negative from the positive terminals

11. Tie a knot on the wire to ensure secure the wires.


12. Heat up the glue gun and drop glue on the soldered terminal connection of the solar module to hold the wire in place.

13. Run the wires through the PVC pipe and mount the pipe on the back of the solar module on the slanted end of the pipe. Drop glue on the edge of the pipe where it meets with the solar module surface. Hold the pipe in place until the glue can hold it in position.

14. Apply glue around the LED and fuse lamp assembly to protect the connection from corrosion. It is recommended to use transparent glue to minimize losses in the brightness of the lamp. Alternatively, you can insert the LED and fuse completely in the tube and seal the end with epoxy glue, glue gun or even just standard plastic sealers.


15. Solder the positive terminal of the solar module to the anode of the diode and the negative wire to the negative foil of the board (refer to the schematics for wire placement). Slowly insert the board into the pipe leaving the switch and lamp terminals exposed.

16. Prepare a bottle cap where the lamp will be mounted. Bore a hole on the cap to let the wire pass through. Make a knot of the wire on top of the cap to hold the wire in place. Place the lamp in the empty bottle and close the cap the position the lamp in the bottle with the wires exposed on top of the cap.

17. Insert a 1” x 1” PVC coupling without thread on top of the cap and let the wire through the coupling. Apply glue on the wires and the coupling to hold them in place.


18. Solder the negative terminal of the lamp to the PCB where the 10Ω resistor is connected. It will also be good to make a knot and fasten the wire on one of the holes of the miniature switch with a self-locking nylon tie wrap. This will prevent the soldered connection from being accidentally pulled off and disconnected.

19. Slowly insert the PCB into the PVC pipe exposing only the miniature switch. Snug fit the PVC pipe into the coupling on top of the bottle to assemble the whole lamp.


Testing 1. Cover the solar module or bring the lamp into a dark room.

2. Carefully remove the PVC pipe from the coupling and turn on the master switch. Turning on the

switch is sliding the knob in the direction away from the 10 ohm resistor. The light should turn on. 3. Carefully snug fit the PVC back to the coupling on top of the bottle. The lamp should stay on. 4. Uncover the solar module or bring it outdoor with bright light. The lamp should automatically turn

off. 5. The lamp should turn on when the solar module is covered, and turns off when the solar module is

exposed to the light. 6. If the lamp turns on and off properly it is ready to be retrofitted into a light bottle with.


Troubleshooting

1. The light does not turn ON when the solar module is covered or the lamp is in the dark.

• Check if the switch is ON. Check if the switch has poor connection or soldered points. • Check the voltage on the terminals of the LED, it should register at least 3 volts. Check the connection if there is a very low voltage. Fix possible open or shorted connections and solder points. • If there is 3V or more at the LED terminal, it is possible that the LED lamp is busted. Replace the LED. • Check if the battery voltage is still above 3V. Allow the battery to charge of the voltage is low.

2. The light turns on but does not turn off when the solar module is exposed to light

• Check the PCB of possible short circuits of open connections. • Check if the voltage between the solar module connection points increases if the solar module is exposed to strong light and decreases if the solar module is covered from light. If not, the solar module may be defective. Replace the solar module. • The voltage between the negative and Collector of the transistor should be zero when the solar module is exposed to light and goes low when the solar module is covered. If not, transistor may be defective. Replace the transistor. • The voltage between the positive and the Drain of the MOSFET should be high when the solar module is covered and the voltage goes low when the solar module is exposed to strong light. If not, MOSFET may be defective. Replace the MOSFET.


Alternative Parts

Part Tested Working Equivalent

SR360 1N5819 (low-powered, may heat up if current is >> 100mA)

IRF510 1RF510, IRF511, IRF512, IRF513, IRF520, IRF521

FCS9014/C9014/S9014 2N2222, 3904

10Ω 2W Resistor 3.3Ω 2W (Safe and brightest, heat tolerable) 12 Ω 2W (Longer runtime, low lumens)


Acknowledgements

Organizations Illac Angel Diaz and MyShelter Foundation University of Santo Tomas and Electronics Engineering Department University of Santo Tomas Network of Electronics Engineering Students

Technical Consultants

Rikki Q. Macolor, BSECE, University of Santo Tomas

Engr. Silver Navarro, Jr.


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Solar Night Light Operations Manual

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