Instructables
This instructable shows how to create a simple aluminum air battery from a soda can and a piece of charcoal from the backyard BBQ. This instructable is being published early but I hope to combine this device with a joule thief and an LED to provide a rechargeable backyard lighting system that can be emptied and refilled.

I believe that well burned campfire charcoal could also be used. Backpackers could have an extremely lightweight, wholly renewable and non CO2 generating light source.

From Wikipedia:Aluminum Air Battery
Aluminium batteries or aluminum batteries are commonly known as aluminium-air batteries or Al-air batteries, since they produce electricity from the reaction of oxygen in the air with aluminium. They have one of the highest energy densities of all batteries, but they are not widely used because of previous problems with cost, shelf-life, start-up time and byproduct removal, which have restricted their use to mainly military applications. An electric vehicle with aluminium batteries could have potentially ten to fifteen times the range of lead-acid batteries with a far smaller total weightt.

Step 1: Bill of Materials

Picture of Bill of Materials
We'll need:

An aluminum can. I use a soda can.
A piece of sandpaper. I happen to have some sticky sandpaper for a sanding block. Very convenient. This is used to remove the surface treatments from the can. This actually may be optional. I will experiment and update the instructable appropriately.
A sponge. This will be cut to fit inside the battery. I used a cellulose sponge from a 6 pack my wife had under the sink. A natural sponge may be more conductive.
A charcoal briquet.
Several readers have suggested alternative, readily available carbon sources. The most scientific sites I've visited have recommended activated charcoal for the carbon electrode.
  • Britta disposable filters
    • Aquarium filter charcoal
1 gallon plastic garbage bag
Rolling pin or short piece of pipe for crushing charcoal
Duck Tape - That's right its called Duck Tape, not Duct Tape.

Some copper wire or copper mesh. The effectiveness of this device is directly linked to connectivity between the copper drain and the carbon cathode. Also it is not possible to solder a lead to the aluminum.

I am using copper mesh and foil from K&S Metals to obtain connectivity. In the first release I tried a simple copper mesh/carbon combination that generates power but I am working on second generation and will update the instructable when it's available.

Hammer
 
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You have been charged with a salt and battery!

msw1005 years ago
Warning to everyone do not install the free fish screensav'er advertised on this page it is spyware
Wareagle msw1004 years ago
 i thought it was common knowledge that ads almost always contain spyware/viruses.
also third party advert from some company lik mayfaire. com allows them. i told them abut it tho. ill check with them nect month
 I believe that the ads on the page change every time you refresh, and btw almost all of those are viruses. =)
Aritusa5 years ago
Actually aluminum can be soldered, check out this site for an easy solution www. solder-it. com they have an aluminum soldering paste that also works with soldering aluminum to dissimilar metals. There are also special brazing rods for aluminum.
egbertfitzwilly (author)  Aritusa5 years ago
How to solder some of the more difficult metals such as aluminum would make an excellent and extremely useful instructable. I don't think most of us have ready access to welding equipment unless I can make an easy arc welder from like a boatload of aluminum cans....
Aluminum has a extremely low melting point. You can melt it over a small fire. If you had a really hot soldering iron, you could probably work with that.
The AlL "brazing" rods available only need a common simple propane torch to use, for small projects that don't sink the heat away fast. Their down side can be cost. Unless you find a motivated carnival/fair demenstrator with a large stock of the stuff to move. For most tape or alligator tips would work well enough.
Alumalloy welding rods, let you weld AL with just a propane torch. Bend-&-crimp works too.
With only 0.5 volts, you would probably only be able to get a joule thief to run if it is made with a Germanium transistor. Otherwise, you might try putting two cells in series.
egbertfitzwilly (author)  Dick Cappels5 years ago
Agreed. With my "Easy Carbon Electrode" I got as high as .925 mV. I'm putting together my Joule Thief this week. Will advise.
And...
egbertfitzwilly (author)  Dick Cappels4 years ago
And....nothing ever happens on time or in budget....
Nice! I think Americans and Englishmen should agree on a general term that refers to an object that is spelled differently in both...... Like aluminium and aluminum and duct and duck tape. Honestly though, let's just refer to alumin(i)um to its ID in the periodic table. Back to topic of instructable, can I use homemade charcoal instead? People here don't sell charcoal briquettes (we prefer LPG). And what's the shelf-life of this battery?
Speedmite5 years ago
This looks like a fun battery. I make potatoes get 1.8 volts, which is more than pickles, onions, celery, grapefruit, a vinegar battery, lemons, and a few others. These were in pairs of halves, except the vinegar,which there was 2. But awesome, and simple. I think the activated charcoal would work better, but this does seem a little messy. I was also wondering if it smelled bad. Pickle and onion batteries stink very bad after only an hour.
egbertfitzwilly (author)  Speedmite5 years ago
Check out my Easy Carbon Electrode instructable. That's got a much, much cleaner design. No, there are no detectable odors as far as I can tell.
What is the conductive foam you find with computer motherboards made from and could it be used instead of the carbon?
egbertfitzwilly (author)  buteman4 years ago
I'm not familiar with a conductive foam, most electronics are packed in non-conductive materials. However I expect that any non-reactive, conductive material could work but keep in mind I'm not a scientist, I just play one on Instructables.

Actually many commerical aluminum oxide devices use metal electrodes. In my projects I use carbon to ensure that no confusion arises about the operation or results.

The al-oxide rig in Salt-Water-and-Aluminum-Foil-Night-Light/ might be a better test bed for that sort of experiment.

I would be very pleased to hear how this experiment comes out. Don't forget to put a porous non-conductive layer ( such as paper towels or something ) between the aluminum and the carbon (or foam) electrode.

Ok, thanks,
My wife does a lot of craft work so we often visit art and craft shops. In one I saw some perforated plastic sheet. Next time I visit the mainland I will buy some and see how that works out as the insulator.
egbertfitzwilly (author)  buteman4 years ago
silkscreen material, plastic screen or thin cloth can also be used.
Well that's disappointing.
I checked the black open cell foam, the semi transparent electronic items often come in and just to complete the checks also the pink closed cell foam.
All very high resistance >40Mohm over about 1/2".
egbertfitzwilly (author)  buteman4 years ago
Don't overlook the possibilities of the foam as an insulating layer in place of the sponge. Line the can with foam and fill with the charcoal, cap with the copper grid and open cell foam. Remember that oxygen needs to get to the carbon so the top should be open, maybe some cheesecloth or a single layer of the open cell.

Add some saline and you have a much tidier cell that could easily be wired in series to produce 3-6V.
cool. At first I saw 2 leads, a black and red from the carbon electrode. Then I figured out that the black was a shadow. =)
The voltage is due to the reaction of the two half-cells.  One of the leads is usually copper, the other is usually zinc.  The vegetables contain the electrolyte to corrode the leads and generate the potential.

Sadly, it is not power from potatoes.  It is power from the metals reacting.  But its still fun.
macrumpton5 years ago
Very cool projectIf you used the full height of the can wouldn't you get more output? For that matter what about using a 5 gal paint bucket lined with aluminum foil, or aluminum flashing? Back when I was a kid the microphones from telephone handsets used carbon somehow. I am not sure whether it changed the resistance proportionally to the sound or whether it actually generated power.
egbertfitzwilly (author)  macrumpton5 years ago
Yes, the device can be scaled up quite nicely. The only gotcha is that scaling up increases the current but not the voltage. The maximum possible voltage is 1.2V per cell (multiple cell in series for increased voltage). The carbon in older microphones was part of converting sound to electricity but I have no idea what the actual mechanism was.
The carbon produced a piezoelectric effect. Sound pressure on the carbon produced a voltage with an amplitude in proportion to the intensity of the sound waves impinging on it.
static lorenrad5 years ago
You are thinking of crystal microphone elements, the carbon mic element don't generate power.
buteman static4 years ago
That's right. The carbon was in the form of small granules. It was wired in series with a fixed resistor. They were fed with a fixed voltage. As it picked up sound waves the carbon compressed and relaxed in response. This varied the resistance of the carbon and so a variable voltage was generated between the junction of the fixed resistor and the carbon and ground, which of course meant it was acting as a variable resistor.
Making one of those would be a cool instructable.
My guess the internal resistance has something to do with the observed voltage drop if the individual cells arranged into a battery as compared to there open circuit voltage. have measured the voltage of the cells with a load applied?
This is a primary battery. A larger physical size will only mean more total current will be available for use. As I recall the voltage that a battery can deliver has something to do with the location of the electrode materials on the periodic table of the elements. This supports my recollection, but doesn't give the "why" http://74.125.47.132/search?q=cache:Frhh9ymwCIYJ:www.collierpr.com/pdf/cr5_taec.pdf+periodic+table+of+elements+battery+voltage&cd=4&hl=en&ct=clnk&gl=us or http://preview.tinyurl.com/p7h83g The answer of why may be hidden somewhere in this search http://www.google.com/search?hl=en&q=periodic+table+of+elements+battery+voltage&sourceid=navclient-ff&rlz=1B3MOZA_enUS323US323&ie=UTF-8 or http://preview.tinyurl.com/odtfsv I'm running behind with reading this weeks weekend builder so I'll let you have at it., if you wish :)
Actually, you should check out the reactivity series. For a battery, the further apart the materials are in the reactivity series, the more current generated. If I am not wrong...
Yes is the reactivity series it seems, but from what I can tell it still determines the battery voltage. I'm not to say anything for certain the topic gets pretty deep,too deep considering the point I was trying to make. That a factor other than pysical size determines output. Output was undefined in the comment I responded to. I assumed voltage because power (E x I=P) is rarely used to refer to the output of a battery.
egbertfitzwilly (author)  static5 years ago
I believe its the electrode potentials rather than the basic reactivity series alone that determine voltages from a cell. This appears to be a standard table:

http://en.wikipedia.org/wiki/Electrochemical_series

Now if I can just figure out what the entries mean I'll be set....
egbertfitzwilly (author)  static5 years ago
Because the electrolyte and anodes can be replenished I believe this is properly called a fuel cell. If it were sealed it would be a battery.

It is my understanding, from sources I can't quote offhand, that Al-Air fuel cells (replenishable) are the leading candidate to replace conventional rechargeables in netbooks and cellphones. The most common battery type used in hearing aids is Zinc-Air so this makes sense.

Wikipedia has the math but it doesn't explain it:
http://en.wikipedia.org/wiki/Aluminium_battery

"About 1.2 volts potential difference is created by these reactions"

I'm too stupid to figure out +2.71, +.40 and -2.31 produce a potential difference of 1.2.
Moto13 static5 years ago
>This is a primary battery. A larger physical size will only mean more total current...something to do with the location...on the periodic table... Yup! As the electrons jump up/down from differing atom's electron shell sizes they release a proportional voltage and amperage...thas why to increase it you have to stack in series( + to - , for double voltage), or in parallel( -/- & +/+, for double the amperes).. most batteries are many "cells" in series, like a car battery that has 6 pairs of plates wired together to make 12 volts.. hope this clears it up least a bit :) Moto13
The carbon microphone element doesn't create electricity. The element is essentially a variable resistor, that varies the current in a circuit, so information can be transmitted using DC, varying DC to be more exact
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