Leclanche wet cells, back to the future ?

[adam2]

In a number of recent posts, the shelf life of various types of battery has been discused, together with posible concerns about future supplies in the event of a crash. Manufactueres shelf lives, from production not sale, are typicly
Lithium, 15 years
Alkaline, premium makes, 7 years
Alkaline, cheaper makes, 4 years
Zinc/carbon, 2 or 3 years

Rechargeable batteries can of course be re used numerous times, but most sorts have relatively short shelf lives.

If planning for the long term, it might be worth considering a return to the old technology of wet lechlanche cells.
These were used to power bells, telegraphs, and railway signals up until at least the 1960s.
Such cells are very low technolgy, and no rare, expensive or highly toxic materials are needed.
When run down, only the active materials require replacement, not the complete cell. Large stocks may be held at little expense.
The components should keep indefinatly.

The cell consists of a porous pot of unglazed ceramic, containing a carbon rod, the pot being filled with powdered maganese dioxide mixed with powdered carbon.
This porous pot is placed in an outer container of glass, this being filled with ammonium chloride solution, and containg a zinc rod.
The zinc and carbon rods are fitted with terminals, or sometimes short pieces of wire.
A lid is desireable to exclude dust and slow evaporation.

The voltage is about 1.5 volts, the capacity depends on the size, I think it was about 100 A/H for the common 4 pint size.
In use, the zinc rod is consumed and should be replaced when largely consumed.
If the cell fails to work properly, then the electrolyte should be dumped and replaced with new.
The carbon rod, the manganese dioxide, the porous pot and the outer container should last indefinatly.

3 or 4 cells could power a torch bulb, or LEDs
Signal bells, radio equipment, and intruder alarms could also be powered.

[the mad cyclist]

Last time I had anything to do with a lechlanche cell was at school, but I shall investigate them further.
I have thought about storing a few lead acid batteries without the acid.

[adam2]

Leclanche cells are still manufactured, primarily for school science lessons, though these tend to be expensive.
They may still be used for railway signalls in remote places, though I have not found a supplier.

All the materials are readily available.
Porous pot, earthenware flower pot.
Outer container, any suitable glass or rigid plastic container.
Carbon rod, extract from an old zinc carbon dry cell.
Zinc rod, readily available from marine suppliers for use as anodes.
Amonium chloride and manganese dioxide are sold by many chemical suppliers, these should be handled with care, but are lower risk than many materials in regular household use.

[woodburner]

I think super-capacitors would be a better choice. They have practically unlimited shelf life, and long service life.

[adam2]

I think super-capacitors would be a better choice. They have practically unlimited shelf life, and long service life.

Different products for different purposes.
A super capacitor is not a source of electricity, but is a means of storing it.
The storage capacity is very limited when compared to rechargeable batteries, but as you point out, supercapacitors have a long shelf life and cycle life. The stored energy may be released very quickly, making supercaps useful for engine starting.
A source of electricity is required to charge supercaps.

A leclanche cell actually produces electricity and requires no external source for charging.
A considerable qaunity is produced before the active materials require renewal, but the discharge rate is very low.
Lechlanche cells are ideal when a very small current is required continually, as for railway signaling or intruder alarms.
Or a small current for many hours a day as for LED lighting or transistor radio use.
Larger currents, up to about one amp can be supplied briefly as for bell ringing and similar purposes.