I have been kind of thinking along the same lines.
If you use Nicholas LeBlanc's list of electrolytes and voltages required to produce Hydrogen...
Zinc Sulphate............2.35V
Cadmium Sulphate.........2.03V
Cadmium Nitrate..........1.98V
Zinc Bromide.............1.80V
Cadmium Chloride.........1.78V
Orthophosphoric acid.....1.70V
Nitric acid..............1.69V
Caustic soda.............1.69V
Caustic potash...........1.67V
Lead Nitrate.............1.52V
Hydrochloric acid........1.31V
Silver Nitrate...........0.70V
And you use the concept that Neutral plates (un-wired plates?) to reduce the voltage down. Then you get something like:
Plate Setup _________ | Volts/Cell @ 12VDC | Volts/Cell @ 13.5VDC | # Neutral Plates | # Cells | Electrolyte
+- __________________ | ___ 12 ___________ | ___ 13.5 ___________ | ___ 0 __________ | __ 1 __ |
+N- _________________ | ___ 6 ____________ | ___ 6.75 ___________ | ___ 1 __________ | __ 2 __ |
+NN- ________________ | ___ 4 ____________ | ___ 4.5 ____________ | ___ 2 __________ | __ 3 __ |
+NNN- _______________ | ___ 3 ____________ | ___ 3.38 ___________ | ___ 3 __________ | __ 4 __ |
+NNNN- ______________ | ___ 2.4 __________ | ___ 2.7 ____________ | ___ 4 __________ | __ 5 __ | Zinc Sulphate
+NNNNN- _____________ | ___ 2 ____________ | ___ 2.25 ___________ | ___ 5 __________ | __ 6 __ | Cadmium Sulphate, Cadmium Nitrate, Zinc Bromide, Cadmium Chloride
+NNNNNN- ____________ | ___ 1.71 _________ | ___ 1.93 ___________ | ___ 6 __________ | __ 7 __ | Orthophosphoric acid, Nitric acid, Sodium Hydroxide, Potassium Hydroxide
+NNNNNNN- ___________ | ___ 1.5 __________ | ___ 1.69 ___________ | ___ 7 __________ | __ 8 __ | Lead Nitrate
+NNNNNNNN- __________ | ___ 1.33 _________ | ___ 1.5 ____________ | ___ 8 __________ | __ 9 __ | Hydrochloric acid
+NNNNNNNNN- _________ | ___ 1.2 __________ | ___ 1.35 ___________ | ___ 9 __________ | __ 10 _ |
+NNNNNNNNNN- ________ | ___ 1.09 _________ | ___ 1.23 ___________ | ___ 10 _________ | __ 11 _ |
+NNNNNNNNNNN- _______ | ___ 1 ____________ | ___ 1.13 ___________ | ___ 11 _________ | __ 12 _ |
+NNNNNNNNNNNN- ______ | ___ 0.92 _________ | ___ 1.04 ___________ | ___ 12 _________ | __ 13 _ |
+NNNNNNNNNNNNNN- ____ | ___ 0.86 _________ | ___ 0.96 ___________ | ___ 13 _________ | __ 14 _ |
+NNNNNNNNNNNNNNN- ___ | ___ 0.8 __________ | ___ 0.9 ____________ | ___ 14 _________ | __ 15 _ |
+NNNNNNNNNNNNNNNN- __ | ___ 0.75 _________ | ___ 0.84 ___________ | ___ 15 _________ | __ 16 _ |
+NNNNNNNNNNNNNNNNN- _ | ___ 0.71 _________ | ___ 0.79 ___________ | ___ 16 _________ | __ 17 _ | Silver Nitrate
I am seriously thinking about trying the silver nitrate.
Hopefully the formatting is better now...
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Some days I get the sinking feeling that Orwell was an optimist!