I'm sure everybody knows of Dennis Klein and Stanly Meyes, daniel dingle, "joe" from Australia, the guy in new zealand with the motorcycle. And before them Garrett, the inventor of the street light. All claimed to have working cars which ran on water.
How did they do it? Why have subsequent attempts failed? These questions have bothered backyard inventors for years.
My hypothesis:
what is needed to crack water is a high voltage low amperage dc pulse followed by a low voltage (really low about 2 volts for the average cell) pause until the next pulse.
What goes wrong 99% of the time: either the low voltage is too high and it generates too much heat, making h2 instead of browns gas, or at some point through the cycle, the voltage goes below 0 and polarity switches, locking the water molecules back together.
If I had a water cell right now, I'd connect it to a battery in series with a low bandpass filter or telecom loading coil, and connect a high voltage high frequency source to a rectifier, and connect the outputs from the rectifier to the water cell (in parallel with the battery/coil.) The coil should block the hf and protect the battery while the high voltage pings will break down the dielectric properties of the water like a spark breaks them down in air, and the power flows through the cell unimpeded.
I would supply my high voltage high frequency from a transformer with equal resistance on the primary to a speaker, and hook the primaries to the amp instead of the speaker, this way you can experiment with different frequencies.
Enough of what I think, here's what is on paper so far:
Patents:
Stanly meyer had a bunch of patents
# ^ a b U.S. Patent 5,149,407 : Process and apparatus for the production of fuel gas and the enhanced release of thermal energy from such gas
# ^ a b c U.S. Patent 4,936,961 : Method for the production of a fuel gas
# ^ U.S. Patent 4,826,581 : Controlled process for the production of thermal energy from gases and apparatus useful therefore; U.S. Patent 4,798,661 : Gas generator voltage control circuit; U.S. Patent 4,613,779 : Electrical pulse generator; U.S. Patent 4,613,304 : Gas electrical hydrogen generator;U.S. Patent 4,465,455 : Start-up/shut-down for a hydrogen gas burner; U.S. Patent 4,421,474 : Hydrogen gas burner; U.S. Patent 4,389,981 : Hydrogen gas injector system for internal combustion engine
quote from:
http://en.wikipedia.org/wiki/Stanley_MeyerThe only patent which really matters is 5,149,407. And the main points of that patent boil down to a cell and 2 circuit diagrams:

Note the coild in the cell circuit. Meyer relied heavily on resonance, maybe not the wisest idea, but it worked.

This transformer is described in the patent as a 1 1/5 inch diameter pressed magnetic powder core (non-magnetisable) ring wrapped with the wire. What isn't mentioned but was discovered later is that this transformer is bifilar wound.

Sized to resonate with the system.
I think this design relies too heavily on the system resonating which is always a tricky business.
But it has worked. It was run on TV news, that is more than I can say for any design I may come up with.
Then there's this guy:
http://www.youtube.com/watch?v=Pu6RvCSJrawHe seems to be making water split into hydrogen, and then burn by exposing it to a magnetron. is he extracting energy from the water or only from the power company? It is well known that microwaves make plasma. It would be nice if a simple magnetron could make water split with minimal electricity, but I'd think that probably has already been tried. A safer way to experiment is to electrolize water in the presence of a powerful wifi device. wifi resonates with water, but is not powerful enough to kill you (right away)
I haven't tested, but cabletv or phone lines with dsl traffic might have the right signal (high frequency dc pulse on top of flat dc, no polarity shift)
Cabletv and telecom guys have the best chance of cracking this nut.
http://www.peswiki.com is a good site dedicated to the pursuit of alternative energy.
I'd like to hear what others have done in the hydrogen experiments realm?