1. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. BATTERY BASICS The Lemon Cell (Battery)

2. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. BATTERY BASICS INTRODUCTION 1800 – Alessandro Volta discovered the chemical battery by creating a portable electricity source known as a “Voltaic Pile”. A Voltaic Pile is a device using pieces of silver and zinc separated by moist cloth soaked in an electrolyte (in Volta’s case, sea water) solution. Humphry Davy later proved that the electricity from voltaic piles was caused by the chemical reaction, and not the different metals, as first assumed.

3. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. BATTERY BASICS Voltaic Pile In the lemon experiment, the lemon juice allows the metal plates to gain or lose electrons. Then, those electrons travel over to the other plate (via the electrolyte solution, lemon juice), forming a redox reaction. The electrolyte is electrically the same on both sides, but the reaction creates a different electrical potential on the two different plates, so connecting them shows a voltage difference.

4. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Battery Material List Figure 1: Alligator clips with wires attached. Figure 2: Copper and Zinc metal strips (Galvanized Sheet Steel will work fine for the Zinc strips)

5. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Cell (Battery) Material List Figure 3: A sharp knife and extra fine steel wool or Scott’s Brite Figure 4:Galvanometer

6. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Cell (Battery) Material List Figure 5: Multi-Meter Figure 6: LED’s (1.8 volt)

7. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Cell (Battery) Material List Figure 7: Thermometer with LCD Digital Display Figure 8: DC Motors and computer fans.

8. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Cell (Battery) Material List Figure 9: Lemons Figure 10: Egg Crate to hold lemons

9. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Cell (Battery) Assembly Procedures Step 1: Obtain a Copper and Zinc Strip and clean both sides with steel wool or Scott’s Brite Step 2: Obtain a Lemon, and roll it on the bench top to break internal fibers in the Lemon.

10. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Cell (Battery) Assembly Procedures Step 3: Using a sharp knife, make two slits on one end of the lemon, as shown. Be careful not to cut yourself! Step 4: Insert a copper strip into one of the slits and a zinc strip into the other, as shown. Use an egg crate to hold the lemons. SAFETY

11. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Cell (Battery) Experiment Procedures Step 1: Connect the alligator clips with wires to the metal strips, as shown. Step 2: Connect the wires to the galvanometer on the Go terminal. Note that the needle is pegged.

12. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Cell (Battery) Experiment Procedures Step 3: Connect the lemon to the G1 terminal of the galvanometer. The G1 terminal has a resistor inline. What happened? Why? Step 4: Now connect the lemon to the multi- meter with the range set at DCV 2. How much voltage is the lemon cell producing?

13. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Cell (Battery) Experiment Procedures Step 5: Put 3 lemon cells in series. Why in series? Note copper is connected to zinc. Why? Connect as shown. Now we have a lemon battery. Why? Step 6: Connect this Lemon battery to the multi-meter that is set to DCV 20. Why DCV 20 and not DCV2? How much voltage is the battery producing?

14. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Cell (Battery) 1.8 Volt LED Lemon Powered Figure 1: LED Off Figure 2: LED On. Using 5 Lemons. What is the voltage of the Lemons? What is the amperage of the 5 Lemons? What is the minimum number of Lemons that will Power the LED? What is the voltage of the minimum number? What is the amperage?

15. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Cell (Battery) Powers 3Volt Digital Electric Thermometer Figure 1: Thermometer unplugged. What is the voltage of the 4 lemons? What is the amperage? Figure 2: Thermometer on. What is the minimum number of lemons needed to power the thermometer? What is the voltage and amperage of this minimum number?

16. Vex 1.0 © 2005 Carnegie Mellon Robotics Academy Inc. The Lemon Cell (Battery) Can the Lemons power a computer fan? How many lemons will be needed to power a 12 VDC computer fan? Will this be possible?