Too_Many_Tools said:
Reading the thread on the Voltaic pile in sci.chem.electrochem.battery,
I started considering what would one have to do to build a "Robinson
Crusoe" battery to power equipment in an emergency.
Assuming a battery of 12v and respectable current to power
communications equipment, how would you do it?
What materials would you use?
How would you charge it?
I look forward to your contributions.
Main thing is, where do you get the "active" component, the fuel - e.g.
anode material.
Cathode material can be carbon/oxigen, which is widely availabe on the
island assuming you can make fire and carbonize some branches.
The only known to humans (since more than 4 thousand years) method
of getting material suited as active anode is high-temperature reduction
of iron ores with carbon (same applies to Zn ores if you can find them).
This can be done in hand-made large ceramic
pots that are pre-heated with outside camp-fire (with a blower) with
subsequent placement of iron ore and carbon and closing the lead.
Rudimentary iron will be produced. It will be very corrosive because of
impurities, but that is exactly what we want. Purr iron on a flat stone
to make a semi-flat shape electrodes.
While iron electrodes are cooling, make wires out of Cu nuggets that are
found in nearby mountains by flattening them with a stone and cutting in
stripes.
Once done, connect iron plates to Cu wires as Anode,
and Cu wires to carbonized branches as cathode.
Further assembly provides easy access of oxigen to carbon:
1) wrap iron plate with a self-woven out of coconat fibers piece
of cloth
2) atach carbon cathodes to the outer side of the cloth, wrap
it again with loose coconut fibers.
3) immerce the contraption into salt-water by 1/3, so that both
cloth get wet, but oxigen access is still there.
Battery is ready. It is going to have Fe vs O2 potential (about 1V),
so place 12 of them in series to get 12V. Because we used large
surface area electrodes, it will give a noticeable current, while only
for a few days until iron is heavily passivated with corrosion.
After that, disassemble and clean the rust by strongly hitting the iron
electrodes with stone.
If current value is not enough for your radio, make ten of such
contraptions and place it in parallel. That is what Volta did for
his electricity demonstrations with his voltaic piles (in fact he
had about 200 placed in parallel!).
If you use the method of producing sulfuric acid by pyrolysis of FeSO4
ores, described in Misterious Island by Joule Verne:
http://www.nalanda.nitc.ac.in/resources/english/etext-project/julesverne/milnd10/index.htm
you can use sulfuric acid instead of salt water.
In this case you will be able to achieve realy high currents,
maybe even your satellite-phone would work! Buy me some beer once
you arrive home...
Regards,
Evgenij