Powering LEDs costs mere pennies

Posted by Matthew Tue, 07 Feb 2006 22:07:00 GMT

Lately the hoopla concerning LED lighting has been overwhelming. Everyone claims this costs mere pennies to power. I decided to put a new twist on a classic science experiment to prove that LEDs do cost pennies to power. Literally.

Creating a battery from pennies

In order to turn pennies into batteries, another electrode and an electrolyte are needed. In this case, dimes (zinc) are used as the positive electrodes and salt water is used an electrolyte. Copper wire, galvanized nails, and lemon juice are also popular and cheaper solutions. Such a battery produces a differential of about 0.5 volts.

Finding ample power for an LED

Unfortunately, this battery is not enough to light an LED. In order to string eight of these cells in series, an ice cube tray is used. Metal paperclips hang the pennies and dimes into the electrolyte banks. Because the paperclips are conductive, the eight cells are automatically connected in series forming a more powerful battery. This provides a differential of about two volts.

As you may notice, 0.5 volts * 8 != 2 volts. Not all of the banks produced a reliable voltage. In fact, one bank seemed to be working against me.

Lighting a LED with pennies

Generally, LEDs require a resistor to prevent excessive current flow from blowing them out. This project does not require a resistor because the battery simply cannot provide that amount of current.

Connecting the short end of the LED to the penny and the long end to the dime lights up the LED! Everything works as planned. The penny batteries provide about 110 micro-amps of current in series. At two volts, this is only about 220 micro-watts of power!

It does in fact ‘cost’ pennies to power an LED.

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Comments

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Joel said about 3 hours later:

Nicely written up little experiment - a useful resource for school students.

Groovy site!
Pauly said about 12 hours later:

Liking this a lot, proper practical science.
Yo said about 13 hours later:

This makes alot of cents!
Mark said about 14 hours later:

Sweet idea- you are on DIGG now, btw. ;)
Michael said about 15 hours later:

Wonderful science experiment. But isn’t each “cube” a cell and the entire tray a battery?
LewisB said about 15 hours later:

Cool. How long was it able to supply power enough to keep it lit?
steve said about 15 hours later:

could this setup be duplicated enough times to replace a table lamp?… replace all home lighting with this zero cost solution
Jared said about 15 hours later:

Cool site
Carl said about 16 hours later:

“zero cost solution?”

I wonder who is giving you the free pennies, dimes, ice cube trays, paper clips, LED, water and salt.

Having said that, it certainly is LOW cost and a good Saturday morning project with the kids.
Ronald said about 16 hours later:

Pretty cool stuff.
Geeks Are Sexy said about 16 hours later:

Oh man, that is a very interesting experiment!! Would be a nice project for highschool students. Similar to the “Light up a small bulb with a lemon” experiment.

Kiltak
[Geeks Are Sexy] Tech. News
carroll lee said about 16 hours later:

Pennies are 97% zinc and the cell working againtst you might have had some of the zinc exposed
Matthew said about 16 hours later:

Thanks for your comments.

I guess the ajax comments do need some work. My web hosts lag lately isn’t helping, I’m sure. A notification is a great idea. Also disabling the submit button and using a larger, brighter ‘busy’ spinner.

The LED remained lit for about 48 hours. It didn’t show any signs of slowing, but was starting to get really messy. I should have used a cheap ice cube tray even though it came clean.

Technically, you could string a bunch of these in a series-parallel combination to power a real LED lamp. Even though LEDs are becoming more power efficient, you would need quite a few ice cube trays.

Regarding the cost, galvanized nails (or anything zinc for that matter) could be used as the second electrode. Also copper wire makes a better first electrode. I just had more pennies and dimes laying around than nails.

Thanks Carrol. I didn’t realize the cores of pennies were zinc!
ehem said about 17 hours later:

0.5*8=2????

I would say 0.5*8= 4
Kevin said about 18 hours later:

it actually says:

0.5*8 != 2

!= means not equal to
Alan said about 19 hours later:

Great idea!
Todd said about 19 hours later:

Very Cool
seventoes said about 20 hours later:

I wonder how many it would take to power a computer?… alot.
dummy said about 23 hours later:

How many trays stacked in a series would it take to be able to zap someone?
Matthew said about 23 hours later:

It would take quite a a ton of pennies to zap yourself. They pennies provide resonable voltage, but not much current. This is actually a great idea for another post. Check back in a few days!
Ivan Minic said 1 day later:

Cool thing :)
BibitBibitBibit said 2 days later:

Mabey newer pennies or dime have a different electronegativity than older one s and that is why one of your cells is going against the flow
carroll lee said 4 days later:

More on Pennies stolen from wikipedia

1982–present 97.5% zinc, 2.5% copper 1962–1982 95% copper, 5% zinc 1944–1961 bronze (95% copper, 5% zinc and tin) 1943 zinc-plated steel 1864–1942 bronze 1857–1863 88% copper, 12% nickel (a.k.a. NS-12) 1837–1856 bronze 1793–1836 copper
TEd said 8 days later:

for some reason it did not work
Nessie said 9 days later:

Why bother with the liquid? Why not just stack the coins?
Matthew said 11 days later:

Ted: There mainly two reasons it wouldn’t work. First, there could be a break in the circuit somewhere and current can’t flow. Second, the pennies aren’t providing enough power to light your particular LED. My ultra-bright LED would not work. This particular LED is a 20mA red LED.

Nessie: You need the ions in the liquid to latch on and transport the copper ions around. You can wet paper towel and stack the pennies/dimes with that in between. However, if two levels of paper towels touch one another, then those two levels are essential short circuited together. I tried this, and it was extremely difficult to setup.
mattP said about 1 month later:

this is great… I wonder if you could use copper nails (for holding copper tubing to walls) and galvies and string them in series on a lemon tree and have enough “juice” to run a number of leds in christmas tree fasion. Im not sure on the chemistry but what is the best way to increase the voltage, the size/surface area of the electrodes? the electrolyte? or the difference in electronegativity. Obviously while keeping to cheap available materials.
sparky carbonarco said 2 months later:

This trick appeared in the late ‘50’s when I was a mere peanut. Back then, pennies were copper, and dimes were silver. The project called not for ice cube trays but to separate ten pairs of coins with circles of blotter paper, which also barely exists any more. You could probably get around this by making circles from really thick, premium paper towels, maybe those blue ones from the auto parts store. It went:–penny,dime,paper; penny,dime,paper, and so on, with a bare penny at one end and a bare dime at the other. Then the whole thing was soaked in salt water. The blotter paper held the salt water (electrolyte) and lit up a little bulb. I have not tried yet to translate the old method into todays coins, but I don’t see why it wouldn’t work in a similar fashion. I do remember that if I squeezed the coin stack, it worked better.
Murali said 4 months later:

May be I am dumb. But can someone tell me where the energy to light the LED comes from? The lemon juice? Obviously it can’t provide the current needed for ever because that would break Newton’s 3rd law.
Brandon said 5 months later:

I couldnt get it to work:(

i did the hole thing and then realized i was useing nickels so i got dimes and did it but nutin.
Zippie at NMSU said 8 months later:

Here are tips to get it to work:

Make a stack…penny,dime,paper; penny,dime,paper, and so on, like sparky says above. Make sure the bottom is a penny and the top is a dime. make sure you use a very strong (near saturated) salt solution to wet the paper. Try 30-35g per 100ml water. Use thick blotting paper…at least 1/16 of aand inch thick. 1/8 inch thick might be better. Do not let the papers from adjoining cells touch and don’t get it to wet or to dry. This may short the cells out or stop electrical flow. A single cell will give 0.5 to 0.7 volts and a stack of 10 cells will give about 2-4 volts depending on construction methods.
Alex said 8 months later:

Just tried this on a boring monday night and it worked great. Thanks.
snappleman said 10 months later:

this owrks so good i lvoe this project im gonna keep it for ever. because i did it i get to go to the scinece fair.
Orpheus said over 2 years later:

Great idea! You can use lemon juice, as it produces 1v per cell…