Try This: Design a Battery

Getting Started

1. (Optional) Test your LED using a battery pack.
   Touch the end of one wire from the battery pack to one of the leads to the LED and touch the end of the other wire to the other lead. If the LED does not light up, turn it around so that the leads touch the opposite wires.  LEDs work in only one direction, so note which wire (positive or negative) goes to each lead.  If the LED still does not light up after switching the wires, check to make sure your battery pack is set-up correctly. If the LED still doesn't light up, you may need to find a different light.
2. Prepare on your electrolyte.
   If you are using a liquid like lemon juice or salt water, find a non-metal container to hold it.  You will probably want to set-up more than one container.  If using object like a lemon or potato, make sure that it is on a dry surface.  If using more than one object, try to sure that individual objects are separated.
3. Prepare your 2 metals.
   If you're using wire, check that there is no plastic coating that can obstruct the metal’s contact with the electrolyte. You can gently sand the ends of your wire pieces to better expose the metal.  If you're using a nail or other strip of metal, you may need to attach a piece of wire to the end that is not inserted into the electrolyte that can be attached to your LED.  Make sure than all your connections are secure and dry.
4. Set up a battery cell.
   Connect one metal to one side of the electrolyte and the other metal to the opposite side. Make sure that enough metal is protruding from the electrolyte to be able to connect to the LED or other cells.
5. Test your cell.
   Connect one wire of your LED to each electrode. Remember that LEDs work in only one direction so make sure your anode and cathode are connected to the proper leads.  Is it enough to light up your LED?  (Optional) Test the conductivity of your battery cell with a voltage meter. Touch one cable of the voltmeter to one of your metals and the other cable to the other metal. What voltage is created by your cell?
6. Create and connect additional cells.
   Construct a second cell using the same process as in Step 4. Connect the cathode of one cell to the anode of the next, leaving the anode of the first cell and the cathode of the second cell free. Connect the metals on
7. Test your series of cells.
   Is your two-cell battery powerful enough to light up the LED? Connect one wire of your LED to each electrode. Is it enough to light up your LED?  (Optional) Test the conductivity of your battery cell with a voltage meter. Touch one cable of the voltmeter to the free anode and the other cable to the free cathode. What voltage is created by your two-cell series?
8. Expand your series.
   One or two cells may not be enough to light up the LED, so make some more cells and add them into the loop. How many cells do you think it will take to power the LED? Remember, two of the same type of metal from two different cells should not be touching. For the battery to work, you need to connect opposite metals to one another to connect each cell.

If you’ve made a bunch of cells and are still having trouble getting your LED to light up – check out our tips for troubleshooting your battery, below. If troubleshooting works, you may have more cells than you need. Try taking away some of the cells until you minimize the number of cells needed to power the light. Does the number of cells affect the light intensity of the LED?

Troubleshooting Your Battery

If your LED isn’t lighting up – here are few things you can try:

1. Make sure none of the electrolytes are touching. This creates what’s called a “short circuit” whereby the electrons can travel through the electrolyte and bypass the LED light.
2. Make sure your electrodes and LED are making good contact wherever they are contacting each other or the electrolyte.  Any point in your circuit where you aren’t making a good connection can create an “open circuit” so electricity can’t flow. (See also #4)
3. The electrons that power the LED can only flow through it in one direction, so your LED might just be backwards. Try connecting the LED leads to the opposite wires.
4. Metal wires are often coated in very thin and clear plastic that can obstruct the metal’s contact with the electrolyte. Using a light sand paper, you can gently sand the ends of your wire pieces to better expose the metal. You might also use sandpaper on a penny to expose the zinc.
5. If the first four troubleshooting steps don’t work, you likely just need to keep adding more cells to your battery.  Use a voltmeter to check the voltage if you aren’t sure if your battery is working.  Each new cell should add an incremental voltage.

Supplies and materials

Possible anode materials:

• Galvanized nails, bolts, or screws
• New pennies, sanded (since 1982 pennies have been made of copper-plated zinc)
• Aluminum wire
• Aluminum strips (you can also cut a strip from an empty soda can and sand both sides – be very careful of sharp edges, and ask an adult for help if needed!)

Possible cathode materials:

• Copper wire
• Copper strips
• Pennies, cleaned (wash them thoroughly and dry)
• Sterling silver

Suggested Electrolyte Materials:

• Commercial play dough (or try this conductive dough recipe that you can make with ingredients from around the house)
• Lemons or other fruit
• Potato or other root vegetables
• Vinegar
• Carbonated soda or pop
• Salt water
• Cotton or paper soaked in one of the liquids above

Try this next!

If you enjoyed this activity – take it a step further with more design challenges!

• What was the voltage needed to light up the LED? Can you design a battery that maximizes voltage? Use a voltmeter to measure the voltage by connecting the meter probes to the electrodes connected to the LED light. If you add or remove cells from your circuit, does this affect the voltage?
• Instead of an LED light, how many cells would you need to power a hobby motor? What voltage is required to power the motor?
• What are some other devices you can power with your homemade battery? Do you need to add more cells to power these devices?