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wrote:
phatty mo wrote:

I've been wondering along similar lines..
I've been wondering how I could make a reasonable ~12V battery,cheaply
and easily.

I've done just what you talk about, so can offer a few details on mine.

Maybe some sal****er cells,built up in Tupperware containers?

Here you can buy flat multicompartment cases for £2, with 18 sections,
used for storing screws etc. These are ideal as long as you can keep
the thing horizontal while active. Tip it up and the water would run
between cells.

Assuming maybe 0.5V per cell,and (if they're large enough) perhaps 10AH?

I think people are underestimateing here. I used an M3 bolt and a bit
of carbon, which will fit into a roughly 1" bottle cap, and got 1v 0.5A
all day. Thats 5Ah or more. So a multicompartment tray would provide
several times the Ah at 18v.

Wow,I had thought about those little multi-compartment boxes,but I
didn't think a "simple cell" that size would have any real juice to it..
I have a couple here i could play with.

500ma? really? Nice!
What did you use for electrodes and an electrolyte,just sal****er?

24 containers in series,it would be fairly large!
If we can find some good electrode materials,the cell voltage may go
up,so we would need less cells/containers

Well... the more V you want out, the faster it corrodes. Mine gave very
little out after 24hrs, but scraping the steel renewed it, so I'd go
for long service life as far as poss. I reckon one could easily improve
on steel as an electrode, but its free in large amounts.

Salt and water are both readily available,and pretty cheap,so the
electrolyte could be replenished easily enough...(any ideas for
something better,that's easy to get,and fairly cheap?)

exactly

But,I'm not sure what would be best to use as "plates",keeping the
cheap,and easy concept in mind.(They will eventually corrode away,right?)

yes, thats the nature of batteries. The lower the whatnot of the plate
materials, the slower they corrode. So pick one plate as low as poss on
your electrowhatever it is scale, and the other will determine voltage
and life.

Perhaps some kind of setup with pipes-inside-of-pipes.
Pehaps you could then build the cells up inside of some lengths of PVC?

lot of work though, when you can just use scraps like food tins etc

True,But see below..

4 inch diameter PVC,maybe 3-4 feet long,with a copper pipe inside of a
steel pipe,inside of the PVC pipe?

holy ---, what are you going to power off this thing?

In short,as much as I can!
If the power goes out,and my main battery bank is drained,or i'm not
near it (away from home)it would be nice to have a 12V battery I could
run some lights,and a radio or something off of.A large capacity would
be a good thing.
10AH is just a starting point,if I could I'd like to build a (say)
50-100AH version. (the equiv of a car battery or two.)
Maybe run some CFL lights from an inverter in the house or something for
a day or two?
Perhaps the TV for a bit? My PC?
CB radio,scanner,cellphone charger,etc..?

Keep a bag of salt next to it,and when the power goes out,dump some salt
and water in the cells,and turn on a (LED) light or something for a
while.. could be handy.

whats needed is to scrape the electrode, not add salt. A steel bristled
brush works, but of course will corrode away rapidly itself.

Well,i was thinking of storing the battery "Dry" untill needed (and
possibly draining/rinsing it after use) that way the electrodes won't
dissolve away in the meantime..
So to use it,you'd pour sal****er (or other electrolyte) in there,and
connect a load.
Agitation is a good point though. I wonder if a small air pump would
help..maybe put a "bubble stone" for aquariums in the bottom of each
cell to help keep the electrolyte mixed,and help knock the 'crust' off
the plates?

I recall seeing an "emergency battery" that used sea/salt water for an
electrolyte..apparently it went through electrodes quickly..
But it had a decent capacity,and was fairly small,maybe half the size of
a car battery?
But I've no idea what exactly they used for electrodes.
It could be useful to have a "backup" battery with an infinite shelf
life,untill you fill it.

exactly.

Perhaps then you could just rinse it out,and store the electrolyte (or
not,sal****er is fairly non-toxic,shouldn't be an issue to dispose
of/dump.) and store it untill you need it again?

right, but bear in mind its not just salt water once its used. You'll
have FeCl in there as well, if you use steel.

Ahh,yes..good point.
Actually,I wonder..if FeCl could be useful for etching printed circuit
boards. ;-) (I believe thats what is used as an etchant?)

I'd actually like to build something like this,but at this point it's
just a half-thought bouncing around my brain.
If you have any ideas,I'd like to hear them!

These things work very well, but their one problem is very short
service life. And that renders them not the most useful IRL.

Yea,that might be okay though.In an "emergency" situation,it might just
be enough to get by with for a night or two.

NT