“How Things Work” Gen Ed Engineering Name:______

Mission College / Hope College

Lab #11

Solar Photovoltaic Battery Recharger

In this lab you will construct photovoltaic battery recharger. Photovoltaic cells are used to generate current that is used to recharge two AA batteries. The photovoltaic cells, also called solar cells, produce an electric current when illuminated with light. They are energy conversion devices that convert light energy into energy in the form of electric current.

The batteries used are Nickel-Metal-Hydride (NiMH) rechargeable batteries. These are common rechargeable batteries such as those made by Energizer or Duracell. A diode is also used. Diodes allow current to flow in only one direction. The diode prevents the current from flowing backwards and draining the batteries in low light conditions.

Materials List:

2 – Photovoltaic Cells with wire leads (PowerFilm® MP3-37, rated 3V @ 37 mA )

2 – AA Rechargeable Batteries (NiMH)

2 – AA Battery Holders

1 – Diode (1N5817 - low forward on voltage 0.45 V)

1 – Foamcore Base (5 inch x 5 inch)

1 - Insulated 22 gauge wire (12 inch)

Tools and Supplies:


Light Source (Halogen or Fluorescent)*

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“How Things Work” Gen Ed Engineering Name:______

Mission College / Hope College

Hot Glue Gun

Scissors

Wire cutters/strippers

Pliers

DMM to measure Voltage and Current

Scotch Tape

Electrical Tape

Large Nail

Alligator Clip leads (4 per person)

Resistors (10-30 ohms, 2 per person)

Tape Measure GLX Xplorer

DataStudio and PC

PasPort Current & Voltage Sensor

Lamp with 60 watt Halogen flood bulb *

Decade Load Box

Light Meter

Diffraction Grating

Note: 60W Halogen bulb will get hot. – 95% of full spectrum

* Can also use High Intensity Fluorescent Bulb

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“How Things Work” Gen Ed Engineering Name:______

Mission College / Hope College

______

In assembling the recharger, the photovoltaic cells will be connected in parallel. The batteries and the diode will be connected in series. The combined currents from photovoltaic cell will flow through the two batteries and the diode. The diagram below is a schematic of the circuit.

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Photovoltaic Battery Recharger

Part A: Draining the Batteries

The batteries must be completely drained or discharged. This is necessary to be able to prove that the photovoltaic charger is able to recharge the batteries. The batteries will be drained, or discharged, by connecting them to a resistor. Current will then flow through the resistor from the battery until the battery is discharged.

(Note: In general the batteries do NOT have to be fully drained before being recharged.)

1. Put each battery in a holder and connect each end of the battery holder to a 27 ohm resistor as shown. The resistor can be connected in either direction. The resistor allows the batteries to discharge rapidly but not so quickly that they are damaged by overheating.

2. Discharging may take 30 minutes or longer. Allow the battery to discharge while working on other parts of the laboratory.

3. Test in flashlight (should NOT work). If necessary continue discharging.

4. Measure the Voltage of each discharged battery. The voltage should be less than 1.2 V for the discharged batteries. Record the measured voltages.

Battery 1 Voltage:______

Battery 2 Voltage:______

Part B: Assembly of photovoltaic charger

1. Attach photovoltaic panels (PVs) to foamcore base

Locate the two photovoltaic panels. HANDLE WITH CARE. Do not tug on the red and black wires. The attachment between the red and black wires and the PV is easily broken.

Position the panels on the foamcore base. Wires should point to the middle. The red (positive) should be at the top of each.

Tape photovoltaic panels on front of the foamcore. Do not put tape over the gray active part of the PV. Tape will absorb light and reduce the amount of electric current produced by the PV. Tape only on the metal edge.

2. Send the PV wires from front to back of the foamcore

Punch a hole with nail through the foamcore at the top and bottom in the space between the PVs. Put the wires through to back through the holes.


3. Attach battery holders to the back of the foamcore

Glue battery holders to the back side of the foam core. Positive toward the top. Attach near edges toward the bottom as shown. Use sufficient amount of glue so the battery holders are attached firmly. Mark positive and negative on the foamcore

4. Install the diode on the right-side battery holder positive terminal.

Install diode on right side positive. White band goes toward positive battery terminal. Very important. Loop wire around itself. The diode must be secure and not able to detach.

The diode only allows current to flow in one direction. It prevents the batteries from discharging by preventing current from flowing out of the PVs and into the battery in low light conditions. The diode ensures that current only flows out of the solar cells and into the two batteries, and not in the reverse direction.


5. Prepare Red and Black Wires

Remove the plastic insulation from each red and black wire for the PVs. Remove about 1 inch (25 mm). Use wire strippers as shown.

6. Attach PV wires red to red and black to black.

Attach red to red and black to black (positive to positive and negative to negative) Twist ends of the wire as shown. This connects the two PV in parallel.


7. Connect PV red wires (positive) to the diode

Attach the two red wires to the diode. Twist the wires around the diode. Bend or fold over the diode and red wires so red wire will not slip off. It is very important that the red wires cannot slip off the diode wire. Secure with electrical tape.

8. Connect PV black wires (negative) to the negative terminal of the battery holder.

Wrap the ends of the black (negative) PV wire around negative terminal on the left side of the foamcore. Twist the wire around itself so it cannot be pulled off the battery holder.

Should look like picture.


9. Attach white wires to the battery holders.

Locate the white wire. Cut the wire in half to create two pieces. Remove the white plastic insulation from both ends of each wire, about 1 inch (25 mm) as shown.

Attach one white wire to each of the battery holders. One to the positive, one to the negative. Wrap wire around itself so it cannot be pulled off the battery holders.

DO NOT CONNECT THE WHITE WIRES TO EACH OTHER. LEAVE ONE END OF EACH WHITE WIRE UNCONNECTED.

10. Install the batteries.

Be sure that the batteries are completely drained and discharged. Install batteries with positive toward top of holder. It is very important that the batteries are installed in the correct way. The charger is now ready to test.


11. TEST. Connect meter between white wires to measure CURRENT.

Attach meter to two white wires. Set to measure CURRENT. It is very important to establish that CURRENT is flowing through the batteries when the PVs are illuminated.

Set the meter on a LOW CURRENT scale of approximately 2 mA.

12. Turn PV charger over to face the light.

With the meter connected, turn the charger over so the PV panels are facing light. The meter should show some small amount of CURRENT even with just the normal room lights. Cover the photovoltaics with your hand (or a book) and the current should decrease. This establishes that the PVs are working. Record your results.

CURRENT with PV in room light: ______(mA)

CURRENT with PV covered:______(mA)

NOT WORKING?

--Check the wires is every thing connected?

--Is diode in the right way?

--Are the batteries in the proper orientation (positive up)?

--Are the positive and negative (red and black wires) in proper locations?

Part C: Testing charger and recharging batteries.

1. Testing using artificial light (indoor).

In this test the charging current produced by the PVs will be tested using an artificial light (light bulb).

A meter should be connected between the white wires and set to measure CURRENT.

Place the PV close to the light bulb about 1 inch (25 mm) away. Record CURRENT in milliamps (mA)

Repeat for distances of 5 cm, 10 cm, 25 cm, 50 cm, 100 cm. Record the results

Artificial Light Test Results. CURRENT in milliamps (mA)

1 inch (2.5 cm) ______

5 cm: ______

10 cm: ______

25 cm: ______

50 cm: ______

100 cm: ______

QUESTION: From the test results what distance from the light should the PV charger be located to recharge the batteries the fastest?

______
2. Testing using sunlight (outdoor test).

In this test the charging current produced by the PVs will be tested using sunlight.

A meter should be connected between the white wires and set to measure CURRENT as before.

Point the PV directly toward the sun. Record CURRENT in milliamps (mA)

Try holding the PV at a tilt or angle to the sun. Try several angles. Record the results

Sun Light Test Results. CURRENT in milliamps (mA)

Direct Sun ______(Perpendicular to sun’s rays)

Angle 1 ______

Angle 2 ______

Angle 3 ______

Angle 4 ______

QUESTION: From the test results what is the best angle or orientation toward the sun to recharge the batteries fastest?

______
3. Start Battery Recharge

Locate your PV charger either indoors close to the lamp or outside in the sunlight. Record the CURRENT.

Recharging CURRENT:______(mA)

DISCONNECT METER AND ATTACH WHITE WIRES TOGETHER

Disconnect the meter from the PV charger. The white wires must be connected together to have a complete circuit. Twist the ends of the white wires together and cover with electrical tape.

4. Recharge Batteries for 30 minutes.

Leave the PV charger in the sun or by the lamp for at least 30 minutes.

Conduct other laboratory activities while the batteries are being recharged.

5. Test Recharged Batteries.

After charging, battery voltage should measure 1.2 V or higher with the meter. If the voltage is less than 1.2 V continue charging.

Record Battery VOLTAGE after recharging.

Battery 1 Voltage:______

Battery 2 Voltage:______

6. Test the recharged batteries in the flashlight.

7. Customize and/or decorate your PV charger.

Explanation of charger operation.

The photovoltaic cells are connected in parallel. Each cell produces 37 mA at 3V in full sun. The 37 mA is an average value that varies with the amount of light present and the type of components connected to the cell so individual results will vary. The combined currents from the photovoltaic cells will flow through the two batteries and the diode. This current input recharges the batteries. Diodes allow current to flow in only one direction. The diode prevents the current from flowing backwards and draining the batteries in low light conditions. The combined voltages of the diode and the batteries must be less than or equal to the 3V produced by the photovoltaic cells. This insures that current will flow from the cells (higher voltage) to the batteries (lower voltage).

Batteries

The energy content of batteries is specified in units of mAh (milli-amp-hours). For example a battery rated at 1700 mAh can supply a current of 1700 mA for 1 hour of total operation or it can supply half as much current for twice as long – 850 mA for 2 hours of total operation. If a flashlight requires 60 mA of current, then a 1700 mAh battery will run the flashlight for 1700 mAh / 60 mA = 28.3 hours.

When a rechargeable battery is recharged, current is put into the battery, reversing the chemical reaction in the battery and restoring the ability of the battery to provide current. In recharging, the energy input is comparable to the energy removed. A 1700 mAh battery that is completely drained, will require at least 1700 mAh of energy to recharge. If the recharging current is 200mA then the time needed to recharge would be at least 1700 mAh / 200 mA = 8.5 hours.

Solar Photovoltaic Battery Recharger Questions

1.) Comparing cost of solar recharged batteries to non-rechargeable batteries.

The cost of the components for the photovoltaic battery recharger is $14.13. This includes the cost of the rechargeable batteries ($2.37 each). The NiMH rechargeable batteries can be recharged more than 100 times.

a)  Assuming that the batteries are completely discharged each time they are used, and they are recharged 100 times using the solar charger. What is the cost per use?

b)  A package of 8 non-rechargeable AA batteries of comparable capacity costs $3.99. What is the cost per battery?

c)  Are the solar recharged batteries less expensive than non-rechargeable batteries? Explain why or why not.

2.) Determination of recharging time.

One person’s solar photovoltaic charger is found to produce 54 mA of current to the AA batteries in sunny conditions. The batteries used have an energy capacity of 2000 mAh. The recharging process is 66% (2/3) efficient. That means that only 66% of the input current is converted into stored energy in the battery. How much time is needed in sunny conditions to fully recharge the battery?