HHO, hydrogen generator

The 80% efficient hydrogen generator produces mixed hydrogen and oxygen gasses when powered by DC.  The oxyhydrogen gas is a stoichiometric mixture of hydrogen (2 parts vol.) and oxygen (1 part vol.).  The hydrogen generator uses KOH electrolyte to split distilled water into hydrogen and oxygen.  The series-cell is very efficient as it allows the cells to operate close to their optimal cell voltage (1.47V). The hydrogen generator runs fairly cool, at about 30-50 C depending on the current and electrolyte. The hydrogen generator has 6 cells with a target input voltage of about 12.9-14.1Vdc which makes the cell voltage about 2.0V.

Pulsing (PWM) or modulation of the input voltage waveform increases performance, as it is known that in the beginning of each pulse larger current flows than in the steady state condition, thus lowering the cell voltage needed to push thru a certain amount of current and increasing the efficiency slightly.

The seven electrolyzer plates are stainless steel (316L grade). A gas vent hole is drilled in each plate. The electrolyte level is always about 25mm below the gas vent hole. There are 3mm diameter liquid level equalization holes drilled in the bottom corner of each plate in such a way that adjacent plates have holes in opposite corners. Staggering and using small holes minimizes any efficiency loss due to current leakage between cells, but makes electrolyte refilling and level equalization significantly easier.  The two end plates (electrodes) have a small SS piece protruding at the top for electrical contact.

The finished hydrogen generator is equipped with a bubbler. The bubbler is absolutely essential to prevent backfires from blowing up the electrolyzer. The bubbler may be filled with 20% alcohol to prevent freezing of the bubbler water.  The KOH electrolyte does not freeze.

Gas production is directly proportional to the current draw only. You need approximately 12 Amps for each Liter Per Minute.

The ideal cell voltage would be about 1.48V, and anything above it is wasted efficiency. The lowest practical cell voltage seems to be around 1.8V-2.0V. The voltage is only needed to push the current thru the cell, it has no relation on the amount of gas produced. The cell overvoltage (above 1.48V) is determined by electrode materials, current density, electrode spacing and conductivity of electrolyte.

Power or total efficiency of the hydrogen generator is defined as the amount of watts needed to produce one LPH. Series-cell designs seem to have the best efficiency in the range of 2.5-3 Watts per LPH.

Many people build simple single-cell car hydro-booster type electrolyzers and control the amperage by using weak electrolyte. The cell voltage is often around 13V, and they put just enough electrolytes to pass 5A or so. 5A creates only 3.5 LPH of gas, so the efficiency is very bad at 18.5 Watts per LPH. Properly designed 6-cell series electrolyzer would produce 6 times that amount or 21 LPH gas at the same input power.

The cell voltage is also dependent on the current density (current / electrode area). Smaller cell area is less efficient because it requires higher voltage to pass the same amount of amps. Good practical current density is around 0.5A/Sq.inch or 0.1A/cm^2.

The smaller the electrode spacing the lower the cell voltage. In practice 3mm electrode spacing is good up to about 10A. At higher currents the electrolyte starts foaming and crawling up the plates (reduces efficiency) and the electrolyzer starts spitting electrolyte foam out. For 10-40A use 5mm-8mm spacing.

Best electrolyte is KOH (28% by wt). These give the lowest practical cell voltage.

The bubbler is absolutely essential to prevent backfires from having an explosion in the hydrogen generator.  Adding a flashback arrestor to the system as well as bubbling the gas thru a water bath is the only safe way to prevent backfires, provided that the bubbler is strong enough to contain any backfires and that the water level in the bubbler is high enough.

The hydrogen generator will not be able to take any pressure without leaking. For pressurized operation use a pressure-proof shell (metallic).  If you need to store oxyhydrogen gas for a short period of time, put a large balloon on the bubbler exit gas nozzle. The balloon will store the gas at atmospheric pressure and will not be very dangerous if it explodes due to a backfire. Remember to wear hearing and eye protection.

Caution:  Oxyhydrogen is a very explosive gas.  Do not store in any containers.  If the gas is stored and ignited, a “grenade” effect could be experienced in which the storage container is turned into shrapnel and shards of metal or plastic could cause harm or damage to a person or property.

The Hydrogen Generator (Electrolyzer) should be connected to a 12 or 24 volt 30 amp circuit at the ignition switch or a suitable source that is activated and deactivated when the engine is turned on or off. This will prevent the Electrolyzer from operating when the engine is turned off for safety concerns and prevent damage to the unit or components.