Superpositioned: Powering LEDs costs mere pennies

Powering LEDs costs mere pennies

Matthew — Tue, 07 Feb 2006 14:07:00 -0800

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.

Project Photo Gallery

"Powering LEDs costs mere pennies" by snappleman

Tue, 19 Dec 2006 20:06:56 -0800

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.

"Powering LEDs costs mere pennies" by Alex

Mon, 30 Oct 2006 18:28:50 -0800

Just tried this on a boring monday night and it worked great. Thanks.

"Powering LEDs costs mere pennies" by Zippie at NMSU

Fri, 13 Oct 2006 10:01:11 -0700

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.

"Powering LEDs costs mere pennies" by Brandon

Sat, 05 Aug 2006 19:57:13 -0700

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.

"Powering LEDs costs mere pennies" by Murali

Thu, 08 Jun 2006 12:26:09 -0700

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.

"Powering LEDs costs mere pennies" by sparky carbonarco

Sun, 16 Apr 2006 13:16:34 -0700

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.

"Powering LEDs costs mere pennies" by mattP

Sun, 12 Mar 2006 10:14:41 -0800

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.

"Powering LEDs costs mere pennies" by Matthew

Sat, 18 Feb 2006 19:34:31 -0800

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.

"Powering LEDs costs mere pennies" by Nessie

Fri, 17 Feb 2006 13:01:24 -0800

Why bother with the liquid? Why not just stack the coins?

"Powering LEDs costs mere pennies" by TEd

Wed, 15 Feb 2006 15:58:44 -0800

for some reason it did not work

"Powering LEDs costs mere pennies" by carroll lee

Sat, 11 Feb 2006 18:33:14 -0800

"Powering LEDs costs mere pennies" by BibitBibitBibit

Fri, 10 Feb 2006 01:54:14 -0800

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

"Powering LEDs costs mere pennies" by Ivan Minic

Wed, 08 Feb 2006 16:19:40 -0800

Cool thing :)

"Powering LEDs costs mere pennies" by Matthew

Wed, 08 Feb 2006 13:24:01 -0800

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!

"Powering LEDs costs mere pennies" by dummy

Wed, 08 Feb 2006 13:03:45 -0800

How many trays stacked in a series would it take to be able to zap someone?

"Powering LEDs costs mere pennies" by seventoes

Wed, 08 Feb 2006 10:12:18 -0800

I wonder how many it would take to power a computer?… alot.

"Powering LEDs costs mere pennies" by Todd

Wed, 08 Feb 2006 09:22:26 -0800

Very Cool

"Powering LEDs costs mere pennies" by Alan

Wed, 08 Feb 2006 09:12:37 -0800

Great idea!

"Powering LEDs costs mere pennies" by Kevin

Wed, 08 Feb 2006 07:36:35 -0800

it actually says:

0.5*8 != 2

!= means not equal to

"Powering LEDs costs mere pennies" by ehem

Wed, 08 Feb 2006 06:57:41 -0800

0.5*8=2????

I would say 0.5*8= 4

"Powering LEDs costs mere pennies" by Matthew

Wed, 08 Feb 2006 06:14:02 -0800

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!

"Powering LEDs costs mere pennies" by carroll lee

Wed, 08 Feb 2006 06:05:29 -0800

Pennies are 97% zinc and the cell working againtst you might have had some of the zinc exposed

"Powering LEDs costs mere pennies" by Geeks Are Sexy

Wed, 08 Feb 2006 05:54:12 -0800

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

"Powering LEDs costs mere pennies" by Ronald

Wed, 08 Feb 2006 05:44:24 -0800

Pretty cool stuff.

"Powering LEDs costs mere pennies" by Carl

Wed, 08 Feb 2006 05:40:18 -0800

“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.