Aluminum Can, Saltwater and Charcoal Battery




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.

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Step 1: 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.


Step 2: Preparing the Anode

Okay, first we're going to remove the surface treatment from the inside and outside of the can. It's not clear to me that the outside really needs to be stripped but hey it looks cooler that way. There's another instructable in which the author demonstrates a really cool way of cutting the bottom off of a soda can smoothly. The arrangement is shown but didn't work very well for me so I resorted to using household scissors.

Cut the soda can by whatever means about 1.5 inches high or about 1 inch above the lower rim. Using your sandpaper sand the inside lightly to remove any anti-oxidant coating.

Prepare enough warm salt water solution to fill the container. Use warm water and enough salt that it won't dissolve. Stir the solution to faciltate dissolving the salt and set aside.

In the Mark II I will be attaching a copper lead to get a good electrical connection with the can. Since aluminum cannot be soldered we're going to secure our drain mechanically with tape. We're going to use Duck Tape which was invented during WW II by Johnson and Johnson when the U.S. Navy needed a durable waterproof tape for use in the field. I understand this position is akin to posing a solution to "who writ Shakespare" but there you have it.

Step 3: Preparing the Cathode

The cathode is a carbon cathode with a copper lead to complete the circuit. The sponge is used to provide a bed to rest the carbon on. The copper mesh is secured to the grid and the carbon is heaped on top of it.

Take the sponge (dry is easier), invert the anode over it and draw a circle.the diameter of the can. Cut a circle from the sponge slightly smaller than the circle. The sponge will expand so you want to leave 1/8" or so all around.

Take the charcoal briquet and break it up into smaller and smaller pieces until you have a reasonably fine powder.

Put the briquet in a 1 gallon plastic garbage and break it with a hammer. Take care not to puncture the bag. I used a short length of PVC pipe as a rolling pin to grind down the charcoal. Remove any unburned particles of wood that you see.

The finer you make the powder the more power transfer will be available. Or at least that's my understanding. Its not clear at this point how much carbon is required in the cathode.

Step 4: Assembling the Battery..

Okay Macgyver we're off and running.

Place the sponge inside the aluminum can and pour in the salt water gradually allowing the sponge to expand. When the water just comes to the top of the sponge place the copper mesh on top of the sponge making sure it lays flat.

Now carefully pour the crushed carbon onto the copper grid.

Attach one lead from the voltmeter to the can, attach the other to the copper mesh. In this particular shot you can see the multimeter showing 3.6 mA, the intro shot shows the .5V reading.

If I've been reading everything correctly I believe this can be hooked up to a "Joule Thief" to power an LED.

Look for continuing updates to this project to reflect the Mark II design.

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133 Discussions


10 years ago on Step 2

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.

6 replies

Reply 10 years ago on Step 2

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.


Reply 1 year ago

Not that low. It is 660 degrees C. Lead is 327, Tin is 232 although Gold is 1,064 and Iron is 1538. Your soldering iron would need to be a very hot one.


Reply 10 years ago on Introduction

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.


Reply 10 years ago on Step 2

Alumalloy welding rods, let you weld AL with just a propane torch. Bend-&-crimp works too.


10 years ago on Introduction

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.

11 replies

Reply 10 years ago on Introduction

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" or The answer of why may be hidden somewhere in this search or I'm running behind with reading this weeks weekend builder so I'll let you have at it., if you wish :)


Reply 10 years ago on Introduction

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...


Reply 10 years ago on Introduction

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.


Reply 10 years ago on Introduction

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:

"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.


Reply 3 years ago

Not a fuel cell, an electrochemical cell. A battery is just a group of cells. For example, a 9-volt battery is just six 1.5 volt cells connected in series. Cut one open and check it out. Technically, a AA battery is a cell, not a battery. A car battery, a lantern battery, and a 9-volt battery are all true batteries.


Reply 10 years ago on Introduction

>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

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.


Reply 10 years ago on Introduction

You are thinking of crystal microphone elements, the carbon mic element don't generate power.


Reply 9 years ago on Introduction

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.