HW projects - Disposable battery capacity tests - DIY stuff

So...you would like to roll your own, huh?

This page contains some DIY MacGyver battery stuff for those who do not have anything better to do.

Potato / lemon battery:

Everyone knows or should know how to make a battery like this. This is a classic science demonstration and is usually taught at schools. This kind of battery can just barely power a small LED or a digital clock, but nothing more. The cell is made by inserting two electrodes of different metals (usually copper and zinc) to a potato, lemon or some other acidic fruit. The potato battery in the picture consists of four series connected potato cells and has an open circuit voltage of 3,8 volts. A higher voltage than one cell can provide is needed to light up the blue 5mm LED.

More info from: http://en.wikipedia.org/wiki/Potato_battery

Aluminium-air battery:

This kind of battery is quite effective and can be used to power a flashlight bulb, string of LEDs, a small DC motor and similar loads for quite long periods of time depending on the cell size.

1. parts needed

picture 1.) needed materials: - aluminium foil - activated carbon - salt - water - paper towels - few wires Optional materials: - flat piece of metal for larger center electrode - piece of cloth

2. ready to wrap	3. wrapped carbon	4. ready cell	5. two ready cells

picture 2.) Materials from bottom to top: aluminium foil, piece of cloth (optional), paper towel, activated carbon, copper electrode (inserted to carbon, optional) and a short wire connected to the copper electrode. The stripped bare wire end can be inserted directly to the carbon but in this case it was connected to a larger copper strip to increase the contact area with the carbon. The carbon with the inserted electrode/wire is wrapped to the paper towel and then to the optional piece of cloth. The cloth is there only to make the carbon bag more durable.

picture 3.) Saturated salt water electrolyte solution is poured on the carbon and electrode bag until it is thoroughly wet. The carbon powder and bare electrode/wire is supposed to stay inside the bag and should not come into direct contact with the foil wrapping.

picture 4.) The foil is carefully wrapped around the bag leaving the other end of the center electrode wire outside the wrapping. The battery is now ready, foil wrapping is the anode (-) and the wire to the carbon is cathode (+).

picture 5.) Two ready made cells in plastic bags to prevent electrolyte evaporation and to insulate the anodes for series connection. With two series connected cells the open circuit voltage is over 1.5 volts. It might be necessary to compress the cells by hand or by using a weight of some sort on top of the cells to make them work more efficiently.

Note:....and no, they are not drugs packed for smuggling =). Still, it would be wise not trying to get in to an airplane with this kind of stuff in your baggage.

Below is the two cell aluminium-air battery discharge graph to the same load that was used in AA cell testing.

Original instructions and info from here:
http://www.exo.net/~pauld/activities/AlAirBattery/alairbattery.html
http://www.exploratorium.edu/ti/conf/nsta2008/julie/Al-air.pdf
http://en.wikipedia.org/wiki/Aluminium_battery

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