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What You Haven’t Read about Lemon Batteries

Are you building a lemon battery?  Here is how you build the battery, but I am going to tell you a few tips I learned through the process that I didn’t easily find on the internet.

(I apologize for not having pristine step by step photos of this process, but I am thinking about teaching when I’m taking these photos, so they don’t usually look perfect and bloggish.  The potatoes are above also since we did potato batteries as well.)

1.  Get about 3-4 lemons.

2.  Roll the lemons on the table pressing a bit with the palm of your hand to get the lemon juicy.

3.  Insert one copper penny into each lemon.  The penny acts as the positive terminal. Push the pennies about halfway in.

*The penny should be made before 1982 (these were made with almost entirely copper).  If they were made in 1982 or after they are only coated with copper.  You may have to borrow a child’s piggy bank.  I offered to pay my neighbor 5 cents for every penny she could find made before 1982.  I decided to do this because when I got rolls of pennies from the bank, there were only about 2 or 3 made before 1982 in the whole roll.  I was quite disappointed.  I say don’t waste your time, and find someone with a piggy bank.

4.  Insert one zinc nail (or screw) into each lemon.  The nail acts as the negative terminal.  Push it in with about 2 cm left outside of the lemon.    Make sure the nail doesn’t touch the penny inside the lemon.

*The more contact the nail has with the lemon juice the better your lemon will work.

5. Buy some alligator clips to connect the penny in each lemon to the nail in the next lemon.  You will need at least 5 wires for each set of four lemons you attach.  Attach the wire on one penny and the the other end of wire on one nail successively.  The wires on the lemons on the end need to be left unattached.  These ends will attach to the lightbulb.  This is my favorite go to image of the lemon battery.  I leave this on the SMART board for the kids to see while putting together their batteries.

*You can order alligator clips from here and many other places.  If you are in a pinch, you can go to Wal-mart’s automotive section and find red and black alligator clip wires there.  (Lowes and Home Depot didn’t have the whole wire and clip put together).

6. Attach each end of the LED bulb to the lose alligator clips.  Reference image link above in step 5.  One end of an LED is positive and one end is negative, so students will have to switch sides of the bulb if their circuit isn’t working.

*To get LED bulbs cheaply, you can buy a $1 flashlight at War-Mart etc. and beat it with a hammer until you can break the bulbs out.  This is a bit frustrating and took me about 30 minutes.  You may also see if anyone you know including parents of your students have old LED Christmas lights they want to get rid of.  When I put out a request for Christmas light strands, I got about 5-6 strands!!!  Score!

*This is a great video if you are wanting students to understand how the electrons flow to make electricity work in batteries.  If you are just wanting students to see the part about the battery, watch 1:34-3:55. If you want them to see how the lemon battery is built, you can continue watching until the end of the video.

What I definitely learned from experience:

*Yes, you can use the lemons for multiple classes.  They will still work.  I used the same lemons 3 back to back classes one day and four back to back classes the next.   After a few days (I can’t remember exactly how many) the lemons will mold, and you won’t want to use them anyway.

*The nails will no longer work when they turn too black after a couple of classes.  This is most often the reason the lemon battery doesn’t work for students who have all the wiring, pennies, and nails connected the right way.  You will have to use new nails.  They are relatively cheap, so no problem.

*The LED can burn out if you leave it connected too long.  I tell the students to count to 20 seconds after they see it light up and  then disconnect it.  It will last longer than 20 seconds, but this is just what I tell them.

*You can use a 9-volt battery as a light bulb tester if you want to see if the LED works in case the kids insist that the light bulb is the problem.  Touch each wire end of the LED lightbulb to the positive and negative terminals of the 9-volt battery.  This will FOR SURE blow out the LED bulb if left for too long so just touch it barely to the 9-volt for half a second to see if it lights up.  See here.

  • Most often when the students’ lemon battery doesn’t work it is because:
    • they have an alligator clip connected to two pennies or two nails.  It is important that there is a penny, nail, penny, nail, penny, nail, penny, nail connection, or the electrons won’t flow from the negative to the positive.
    • they have the LED light bulb turned the wrong way
    • the zinc on their nails has corroded and the nails need to be replaced.  This doesn’t happen with the pennies because lemon juice actually cleans pennies.

A great question to pose after this is, do you think you could light up an LED with fewer lemons?

The answer…Yes, you can sometimes light up the bulb with 3 lemons, but it will be dimmer.  It is also possible to light it up with only one lemon if you can put enough pennies and nails into a single lemon.  Now, I was never successful at this but, there are You Tube videos in which this has been explained.

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