I was very excited to find this thread (no electrical pun intended) as this is a project in which we are actively engaged. We're building a pontoon boat (poly, not aluminum pontoons, before anyone gets exercised) which will be electrically driven. Short range manouvering using the 1 hp (about 755 watt/12v motor) will be via deep cycle cells charged by solar panels, but for longer trips we are trying to build a "big dumb battery" primary cell which could be staged down when not in use. The battery is composed of 1/2 gal cell containers and uses bundles of copper and aluminum tubing as cathode and anode, respectively, the aluminum being sacrificial. I'll try to attach some photos if I can, or you can go over to the forum on the grindlebone.org site and see them (please do). There's also some over at overunity.com under "salt water battery" on the forums.
Before I go on, to get some things out of the way: This is an experiment. YES I know getting an outboard would be easier, yes I know I could just expand the deep cycles we have and add more solar panels, yes I know sulphuric acid is a better electrolyte than salt water, yes I know magnesium might be a better anode, yes I know adding sodium hydroxide or another alkaline would probably increase output. We wanted to see if we could make THIS work, and I'd love the forum's help in doing so.
Thus far we built a single cell (and are collecting materials for the full 24 cell battery) which produced .54 volts up to a maximum of .74 volts using a wick with the cathode (copper) which I guess technically makes it an aluminum-air cell. We did a month long corrosion test at no load and discovered no voltage variance over the period, which means the cells are relatively stable even in the salt solution when not under load. In terms of earlier discussions here, agitation or bubbles help maintain the voltage, but I think most of the problem is the accumulation of hydrogen and oxygen bubbles from electrolysis on the electrodes which inhibits the chemical reaction. Shaking them off restores voltage. Certainly, cells on a boat would be subject to a degree of native agitation.
So here are my questions: is there some formula for this to calculate current (amps) and the destruction of the anode? I have no idea what the amp output of the cells are, but a discussion over on google (
https://groups.google.com/forum/#!topic/sci.chem.electrochem.battery/7o4xBWjWNg8) seems to indicate a rather higher output than I'd considered.
Would love to hear suggests, ideas, rants, vents, and brilliant solutions from the board
(btw the multiple leads coming off the cathode were an attempt to drive a tiny motor with the cell and have nothing to do with the voltage reading)