So if your on 240V AC, it goes to about 340 rectified DC so youll need a bunch of neutrals to match 2V by cell. By the way, 2V by cell is only a very good approximation to fall into high efficiency generator as, depending on the type of electrolyte you use, max efficiency is somewhere between 1,3 and 1,8 V. Theoritically to split the water molecule you need 1,25V any excess voltage will obviously result in more amp in the cell, so more HHO but also more heat and less efficiency. In practice though to get the reaction started good all over your plate you need a bit more(again depending on the e-lyte you use between 1,3 and 1,8V), so thats why 2V is the recommended voltage for Mr. Everybody. After you set the voltage to the value where is is the most efficient it's a matter of mixing e-lyte concentration to reach the amperage you want. take note that with NaOh max conductivity is at 20% by weight and with KOH it is at 28%. If you can concentrate to either of these levels you'll reach the max amp you generator at max efficiency, form there if you want more or less amp you need to vary the size of the plate.
So the resume the whole thing to get the best efficiency: get the best water conductivity with the less voltage between your cell to have only HHO and no heat. From there you can modulate the amp with an autoregulated or not "duty cycle variable pwm" (I am, having mine built at this moment as there is none available so far).
So to get back to the plate size, it is only a matter of how much HHO you want to produce at max efficiency. Also take note that stainless is a poor conductor so the if your plates are to big, youll have a good production near your connection and it'll decrease as distance increase from the connection. (A good way to see this effect is when you use SS wired coil like water4gas masson jar for generator) So if you plan to play in the 1,3 to 1,8V zone the plate size and where the connection on the plate is might become critical.
Last thing, I'll just want to let you know, how my next generator will be built: On my youtube channel there is one 3D animation that shows the channeled gaskets I will be using to have a good flow in the cell and no edge effect, my generator (the tohmahak 3,4 gen) will only have a 5in x 5in active surface. One cell (stack of 8 plate) will produce about 3 LPM max on 14V(car alternator). To get more production I will only add other cell in parrallele.
So let us know how everything will turn out! I hope this will help you out! Also all of what I said is based on my reading and experience, someone might have found something else, I do not pretend to hold the absolute truth on efficiency, I'm just sharing so take what you like and try the rest for yourself

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