Step 1: Bill of Materials

The basic construction of this device is extremely simple. We're going to use some non-conductive trays and make a sandwich of aluminum foil, paper towels and a carbon brush electrode which begins its life as an aquarium filter.

You're going to need some non-conductive tray containers. I used some carryout containers from a local rib joint but almost any tray may be used. Since there only two dinners I used two bases and one lid. The common glass 9X11 glass cooking trays would be perfect.

3 paper towels to act as the porous layer.

A box of carbon aquarium filters. I used the Fluval brand of carbon pad replacement filters available at PetSmart for about $4. These come 4 to a box, I used the "4 Plus" size. These are used as the carbon electrodes in our assembly and function in this role quite nicely.

Some salt to use as an electrolyte. Ordinary table salt is fine, you'll need about 5g to start with. That's approximately 1/2 TBSP. In a liter of water that should produce approximately a 5% solution. Feel free to vary electrolyte strength.

A solar yard light. (see picture). These are available at most hardware stores for about $4. This is a self contained solar powered light with a rechargeable battery. it works by using a joule thief type circuit to maximize energy stored in the battery, the difference being that this circuit uses a capacitor rather than a traditional toroid so it doesn't provide the power amplification normally associated with a joule thief. NOTE: In the joule thief circuit the toroid provides both power amplification and capacitance.

4 electrical leads with clips, these are available from Radio Shack in a package of 12. These are used to make all connections.

A scissors, ruler and ball point pen along with a small screwdriver for dissassembling the solar light.

Now let's get started...

<p>Should the cell be fully submerged or just up to (but not touching) the electrode clips? I'm thinking of making a compact version of this and am trying to make it last as long as possible without maintenance (like changing out the electrolyte)</p>
<p>wow that is great </p>
<p>Can i recharge it? I did it with carbon pellets and vinegar, when i wanted to recharge it it gave off a bad smell (12v7ah battery, a lot of amps)</p>
<p>I and my wife live near a national park......We like to hike often....guns are not allowed in national parks...says nothing about stun guns.....Question How to increase amperage on stun gun to kill a wolf, cougar or black bear I ask because I was tracked by wolves and my wife was trail biking and stalked by a cougar don't want that situation ever again so I either carry illegally or at least if it gets into a fight the stun gun will kill the problem</p>
<p>the solution is to go hike elsewhere, not to kill animals.</p>
<p>Forget the stun gun, to get it powerful enough to kill would be very hard and you would have to place it where the current would pass through the heart. I would suggest a shark stick,(divers use them) that is a short tube with a 12 gauge shotgun shell that is activated by pressing the shaft forward against the shark, or in your case the wolf, cougar or bear. I don't think it would be consider a &quot;gun&quot; if not then a good sharp knife with a six inch or longer blade, preferably 8 inches or so, any longer and it might be too hard to use in close quarters. </p>
how can i increase the output
Output is a function of surface area of aluminum, amount of available oxygen and strength of the electrolyte. The easiest way is to just add more cells. Keep in mind that your max theoretical output is 1.2V per cell. To increase the voltage use more cells wired in parallel..<br><br>Using a dilute lye solution will increase the output amps but shorten the life, using more aluminum will also increase the output amps.
Thank you
ADD H2O2 OR KNO3 TO THE ELECTROLYTE!!!!!!this would keep the output stable
That will short out the circuit since you can't keep the H202 separated and everything will happen on the surface of the aluminum. For that you need a two cell aparatus similar to the one in my MFC project.
nice experiment a simple galvonic cell , I used to use a lemon to get the same effect,any acid or in this case a ionic solution,and to disimilar metals will create electricity, but this one can be done at any diner table with scraps,basicly
Its not a galvanic cell, there is only one metal ( Aluminum ) which reacts with a saline solution. There is an excellent explanation of the chemistry here:<br>http://en.wikipedia.org/wiki/Aluminum-air_battery
Absolutely. I have on many occasions made a cell out of piece of foil, a carryout salt packet and a pencil lead....<br />
Now you got me thinking about that old electronics kit from radio shack I had waayyy back when.... I think theres some graphite rods from some old dry cell batteries in that box,I could teach this trick while camping with my nephews
There's an instructable that shows how to make biochar in an altoids tin. You could make the biochar on the camping trip and use soda can strips.<br /> <br /> Run some water through wood ash to get a mild sodium hydroxide solution and I think you've pretty much MacGyver'ed yourself out....I believe with a little experimentation in advance you can drive an LED directly from such a device but you'll probably need multiple cells.<br /> <br /> And let's face it, showing them how to make light from a campfire and a soda can pretty much rocks....<br />
brilliant instructable :) im going to go and try that now. Im studying engineering and technology and think fuel cells are extremely interesting and could become the future, expecially hydroged based or methanol based fuel cells. <br><br>By the way, if you've got a camp fire you dont really need the light do you... :D<br>but i still think its a great idea and would do the very same thing on a camping trip :)
what is another option for a carbon electrode. i cannot find the fluval carbon pads anywhere. were your carbon pads filled with small carbon &quot;rocks&quot;?
As I understand it, you just need two different metals to cause the galvanic reaction. Copper can fill this requirement so you could try copper flashing. You might be able to find this at your local Hardware store.
Its not a galvanic cell, its an aluminum air battery which requires a non reactive electrode.
I am no expert, what makes it non-reactive?
It is electrically conductive and does not react with the salt or the aluminum. This insures that the voltage output is being produced by the aluminum oxidation process. While using copper will work it clouds the measurement of the result since there is both an aluminum-air as well as a galvanic reaction happening.
Its more of a carbon brush so its not filled with anything. However almost any solid carbon object should work, pencil lead is an alternative, there is also carbon paper which I used in another project. <br><br>If you ask at a store for 'carbon pads' they cannot help you, try a pet store and ask for aquarium filters.<br><br>There are also carbon electrodes available at your local ACE (or other) hardware store, tell them you're looking for a replacement brush for an electric motor.<br><br>
so what did you do with the salt to make this work and did you put layers of alumine foil down or one
I layer of aluminum foil, the salt is dissolved in water to obtain a 5% solution. The salt will react naturally with the aluminum and does not require additional processing.
One layer of foil, one layer of paper towel and the carbon electode. Measure out about 300 ml of a 10% salt solution in a measuring cup and pour into the cell. the salt is merely dissolved in the water, no particular prep is done. This link points to another instructable of mine that contains detailed instructions for making a 10% solution. I didn't use iodized salt, not sure if that would make a difference.<br /> <br /> <a href="https://www.instructables.com/id/Making-a-Saline-or-Hydroxide-Solution/" rel="nofollow">www.instructables.com/id/Making-a-Saline-or-Hydroxide-Solution/</a><br /> <br /> More layers of aluminum will probably increase your current. You might try with and without layers of paper towel between each layer of aluminum.<br />
More aluminium? Do you mean adding more SEPERATE layers of foil, or more sheets of foil at the same electrode? For more surface area?
More sheets of foil at the same electrode, its all about surface area in contact with the electrolyte. If you use layers of paper towel between them make sure the towels are saturated. You will that as the towels dry out your current will increase, or at least that's what I experienced when I used a sponge. There will be an optimal amount of fluid for the towels.<br><br>It might interersting to soak the towels in a saturated solution and allow them to dry partially then assembling the cell. This should eliminate the surface oxidation that occurs while the towel is drying and may give a better overall performance curve.
One correction: It isn't 'air' but rather a saltwater reaction.<br /> Also zinc may work better then aluminum.<br />
I look forward to reading your update on wikipedia.<br />
agian sir if you dont mind me asking im srry im new i dont know mutch but is that yellow wire a positve or negative please do tell my teacher is useing this site and this is my project i have chosen and the teacher is really anoying
The yellow wire is used to cross connect the batteries in series so it isn't positive or negative. It connects the positive terminal of one cell ( the aluminum foil ) to the negative terminal of the next cell ( the carbon filter ).<br />
we used to do this back in school with aluminum foil paper towels and pennies. pretty simple homemade battery. but what we'de do is make a stack penny foil paper penny etc. then put that in a empty film container. use a paperclip as the terminals. it was like a real battery.<br />
That is a galvanic cell ( http://en.wikipedia.org/wiki/Galvanic_cell ) which is close relative and is actually a real battery....<br />
Wonderful project, although I do not really understand it. does it recharge itself, or is it simply a fuel cell?<br /> anyway, 4.5 for the rating.
Thank you for your kind words and I apologize if the overall operation is unclear. The fuel cell provides a constant output (which varies over time as the available aluminum is oxidized). This charge is routed through the battery. When the optical diode light levels fall enough current is routed to the light. I believe this current is composed of the fuel cell output plus the available battery voltage. When the sun comes up, or the lights go on, the optical diode blocks the current flow to the light and the battery is recharged by the fuel cell voltage during the day.<br /> <br /> The number of things I don't like about this circuit would only just about fill the Grand Canyon. The next project will probably a battery pack charger with a more sophisticated circuit and a toroid for power amplification.<br />
&nbsp;so it acts like a not very effecient battery right? It charges the other one inside the light, then after a while it dies.
Actually it acts like a moderately efficient aluminum oxide fuel cell with a sodium chloride electrolyte generating very close to the optimal voltage. Like any fuel cell (or engine) it must be periodically refueled or it will stop working. If it is maintained it will work until the battery dies from overcharging. <br /> <br /> If the electrolyte is refreshed it should run for a week to 10 days per sheet.<br />
&nbsp;If you somehow used thicker aluminum sheets, would it last longer. Or is it the carbon that is used up. And how would this be different than a battery? Is it that batteries dont need fillups on electrolyte? &nbsp;
With thicker aluminum you would need to periodically use a more aggressive electrolyte, such as lye, to clean off the accumulated surface oxidation.<br /> <br /> Yes, you are correct, the difference between a fuel cell and a battery is that a fuel cell can be refueled ( as opposed to being single use or recharged ). It's not that a battery doesn't need a fillup, its that it cannot be filled up even if one wants too.<br />
no sir this is a battery. your definition of a fuel cell is a little off.<br /> &quot;Fuel cells are different from conventional electrochemical cell batteries in that they consume reactant from an external source, which must be replenished&quot;<br /> http://en.wikipedia.org/wiki/Fuel_cell<br /> in this cell it remains a closed system replacing the anode isn't the same as having an external supply of fuel.<br />
Like this, great idea. Could I just ask did you mean 0.5% solution which 5gm in 1L is or 5%&nbsp; i.e 5gm in 100mls?<br />
Actually I used 5g in 1L, intended to use a 5% solution but ending up with a much milder electrolyte. I have not experimented with the salinity/energy ratio but I suspect the more salt the higher the current.<br />
Nice article.&nbsp; I think that if you put 5gm salt in 1L water in step five you have a .5% solution? 5gm in 100ml would be 5%?
You're right, I mistyped that it should be 50 grams not 5.<br />
If you're not a science teacher you should be. What I like best about this ible is that it demonstrates a couple of simple concepts but can be revisited to add knowledge (ie, the toroid for amplification). Excellent!<br />
Thank you for these kinds words but I'm afraid I'm much closer to W.C. Fields than Mr. Wizard. However I did hope that this project would be useful (and used) in classrooms. I think its suitable for a broad range of grades.<br />
Lovely project. Any alternatives to the carbon brush filter? Not sure whether I can get one in India!<br />
Check out this project which is a variation of the cell.<br /> https://www.instructables.com/id/Aluminum-Can-Saltwater-and-Charcoal-Battery/<br /> <br /> You also formcharcoal into shapes with only a moderate pressue.<br /> <br /> Activated charcoal and carbon rods from an exhausted batt4ery.<br />
Very cool preject.<br /> <br /> I&nbsp;feel that i simply must comment on the brand of salt...is the brand called&nbsp;&nbsp;&nbsp; &quot;plain salt&quot;? I absolutely love the names that&nbsp;the off brands give their products, their so funny some times!

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