cnidocyte - 22-8-2010 at 09:39
Can it be done? I tried stacking cells made with 1€ coins + 50c coins separated by some tissue soaked in sea salt but didn't measure any voltage
with the multimeter.
The problem is every coin except the brown ones consist mainly of copper and the brown ones are steel plated with copper. Heres the composition of
Euro coins:
1c, 2c and 5c: Copper plated steel
10c, 20c and 50c: 89% copper, 5% aluminium, 5% zinc, 1% tin
Centre of 1€ and ring of 2€: 75% copper, 25% nickel
Centre of 2€ and ring of 1€: 75% copper, 20% zinc, 5% nickel
Steel is mainly iron but the brown coins are plated with silver so it doesn't matter what the core is made of does it? My inspiration for making a
voltaic pile came after watching an episode of Breaking Bad where the battery of their caravan goes dead out in the desert and they manage to get it
started with a voltaic pile made from change. You'd probably need a pile the height of a house to get 12V but I like the idea of being able to produce
voltage with coins all the same.
Contrabasso - 22-8-2010 at 22:46
It may work in the movies! Also it's certainly an offence to deface coins.
ScienceSquirrel - 23-8-2010 at 04:05
I think that the voltage would not be a problem but the amperage would be.
I bought my nephew a science kit that had a build your own voltaic pile from zinc and copper discs.
The current produced was tiny, it lit a small LED.
I doubt you could generate the hundeds of amps needed to turn over a motor and start it from a primitive cell like this.
peach - 23-8-2010 at 13:31
First off, you're right that the voltage isn't going to be very much at all even with a few coins.
The squirrel is also correct in that the current capacity of that stack will be minute. If you're using a cheap multimeter, it may have a hard time
picking up the voltage on the scale. Multimeters all need some level of 'drive current' to produce the reading, because the circuit or coil that
measures it doesn't have a perfect, 100% resistance. On analog meters, it's called the FSD current; full scale deflection, the current needed to move
the voltage needle to the end of the scale. Digital ones have something similar.
Why not try a squirt of lemon juice?
In terms of getting a caravan going with one... 
I have enough trouble getting
the car going with something that's a pain to pick up and designed for the purpose. Starting a car needs a big jolt of amps. On that note, I always
wondered why people didn't stick a capacitor in parallel to supply the pulse as the battery impedance rises (it dies).
Copper plated steel? Yuck. 
bbartlog - 23-8-2010 at 14:22
Calculate the size (and cost) of the capacitor required and I think you'll have your answer...
peach - 24-8-2010 at 02:08
This is fairly big and cheap
I don't know the precise starting current or energy, but such a vast amount of capacitance over the cell drastically reduces the impedance.
It's impedance that kills batteries, as opposed to a lack of potential energy. Well, it's a combination of the two to some degree, but the inactive
materials in the battery blocking the current path drastically reduce it's current carrying capacity. That's why Maxwell and the like have started
producing these super capacitors. These audio fans are trying to get kW of current through the amps.
The capacitor wouldn't need to supply the full start energy / current, just bypass some of the cell's impedance.
When in doubt, add ten more batteries
And a stack of bypass
[Edited on 24-8-2010 by peach]
Contrabasso - 26-8-2010 at 09:06
With any primary cell the electrodes are of specified elements for the typical cell voltage. Alloys usually do not work. In fact Al - Cu forms a
destructive cell on the one plate of the attempted cell. That's why sunken aircraft don't last as wrecks because the high performance alloys corrode
to destruction in water.
[Edited on 26-8-2010 by Contrabasso]