Some electronic knick knacks powered by water.

[dieter]

That's interesting, thanks a lot. It seems there is more to it then, than a simple voltaic cell.

[pomodoro]

Every single electron coming out of that battery is from oxidation of magnesium and the corresponding reduction of water at the copper. At those current levels , distilled water has enough salts still in there to allow some conduction. You need to use triple distilled water or special milliQ water and it must be kept under nitrogen gas. Carbon dioxide from the air immediately makes  the water conduct  as it forms carbonic acid. Any oxygen present is easy reduced , more so than water and gives a maximum current limited by its diffusion in the water.  There are many unseen factors even in such an easy cell.

[spacecowboy]

Agrees, strange but amazing. Ill tell you another type of water battery I tried. I used magnesium flint rods, people use them to start fires. They worked but were very problematic. and they erode way to fast. But I did get it to work, but it took 2 of those kinds of water batteries in series to run a wall clock. Where as in my other water batteries using pure magnesium only took one water battery. Also noticed that one of the problems with magnesium flint rods, other then the fact they did not contain enough magnesium. Was when the tiny bubbles that form on those rods, if a few bubbles crossed over from the bar and touched the other electrode, the copper. That shorted it out. But then a tap knocking the bubbles out would then make the battery work again. I never had those problems using pure magnesium rods. But using magnesium flint rods are problematic.

[dieter]

That is most likely due to the iron in the flint, as Mg is only an addition, as far as I know.


Useful is the "Voltage Row" of elements (don't know the correct english term, anyhow), by using one element with a high negative and an other with a high positive potential, you can get up to 5.91 Volts per cell.( Fluor and Lithium) Easily obtainable materials are eg. Calcium (as in plaster, cement, concrete) with -2.87V (Magnesium has -2.36V, Copper +0.16... I have no idea how this boils down to your 1.5V). So, some concrete, a paper tissue as a membrane and a bunch of tooth paste should give you a juicy battery as well. Not for years, but maybe a month. I think John Hutchison did that.


I also like extremly available materials that you would find everywhere, such as some scrap iron trash and a bunch of coal from your camp fire.


But I don't wanna get too far offtopic.

[spacecowboy]

The flint rods will work, but they are to problematic later on as they erode way to fast. Best to stick to just the pure magnesium rods, they last for years to decades even, and have the least problems, Ive had some powering a few things over ten years. The occasional once a year cleaning of the electrodes is recommended. And of course you must add water when needed.