How many watts/sq inch?

[BeaverRat]

I am planning a new cell that can handle 50 amps at 12 volts (not 13.8). What power density is good so the cell will not deteriorate?

If I build it with 6x6 plates (reactive area of 5.5x5.5) than if it is configured as

-NNNN+NNNN-NNNN+NNNN-

I could run it at 50 amps with a power density of .5 watts per square inch. Is .5 a good power density? If not, what is?

[H2OPWR]

I am planning a new cell that can handle 50 amps at 12 volts (not 13.8). What power density is good so the cell will not deteriorate?

If I build it with 6x6 plates (reactive area of 5.5x5.5) than if it is configured as

-NNNN+NNNN-NNNN+NNNN-

I could run it at 50 amps with a power density of .5 watts per square inch. Is .5 a good power density? If not, what is?

With Stainless a good rule of thumb is no more than 1 watt per 4 sq inches of reactive surface area. That will allow a cool running cell with good plate life. Nickel or nano coated plates will allow much more but at a higher build cost.

Larry

[BeaverRat]

Dang... So I would need 2400 inches squared of surface area to run it at 50 amps 12 volts? Thats a lot of plates... WHat would happen if I did run it at .5 watts per inch rather than .25 like you recommend?

[Danger]

I think that nothing will happen. Your cell will run just fine. Your plates might start to show signs of wear a bit sooner, but overall they won't disintegrate overnight.

[BeaverRat]

Another thing is that it will have a short duty cycle. The longest time it will run is about an hour because it will not be going in the car right away...

[H2OPWR]

Dang... So I would need 2400 inches squared of surface area to run it at 50 amps 12 volts? Thats a lot of plates... WHat would happen if I did run it at .5 watts per inch rather than .25 like you recommend?

With extended runs your cell will get too hot and your water will turn yellow as your plates degrade. You need to trust me on this one. I was running 51 6X8" 316L plates to pull 65 amps at 13 5 volts. That was 48 gaps the way I had it set up. Each gap had 70 sq inches of reactive surface area. That was 3360 sq inches of reactive surface area total to run 877.5 watts. That was just over .2 watts per sq inch. The cell ran at around 100 degrees if it was left to run non stop. If I pushed it to over .25 watts per inch the heat would run away eventually and the cell would have to be shut down.

The hardest thing for everyone to accept is that there is just no way to get lots and lots of gas out of a small device with stainless. Like I said. I have found many ways to acheive the result you are looking for but they all cost way more money than just building the cell the proper size to acheive the results you are looking for.

Larry

[BeaverRat]

Ok... so if I limit the duty cycle to 1 hour or less, would .5 watts per square inch be allright?

I will be running 12 volts 50 amps, so 600 watts.

Oh, and is this 316L or just 316?

http://www.onlinemetals.com/merchant.cfm?pid=9858&step=4&showunits=inches&id=325&top_cat=1

[H2OPWR]

Ok... so if I limit the duty cycle to 1 hour or less, would .5 watts per square inch be allright?

I will be running 12 volts 50 amps, so 600 watts.

Oh, and is this 316L or just 316?

http://www.onlinemetals.com/merchant.cfm?pid=9858&step=4&showunits=inches&id=325&top_cat=1

One more time. You should never run more amps through your cell than the design can handle. The same things that make your cell heat up and leach minerals into your water happen from minute one. I know it costs more but feel lucky that you can learn from people who have already make the mistakes. Over amping your cell will eventually ruin it. Start with a design that can handle the current load you want to use.

Larry

[BeaverRat]

Ok, thanks... I guess I will just have to build it the right way!

Anyway, is that online metals the best place to get 316L sheets? Is that stuff I linked in my previous post even 316L because it is labled as "316/316L". What is that supposed to mean?

I am looking for as cheap as possible for 316L 20 gauge...

[Philldpapill]

Larry, have you ever tracked "Total Gas Production vs. Cell Life"? I assume what you are saying is that the relationship is non-linear. Probably something along the lines of e^-x type function, based on the reactivity at higher temperatures? Otherwise, you would always get the same total amount of HHO out of a cell, regardless of the current through it...

[IM2L844]

BeaverRat,

You don't want to mix up power density, current density and power dissipation. They are all different things and are not interchangeable. Power density is a volumetric variable that is measured in watts per cubic inch, centimeter, liter or whatever volume metric you want to use and has nothing to do with surface area. There is also weight based power density, but that is something else. Surface area is only used to calculate current density and power dissipation.

Unless you want to try and predict how hot your reactor will get, all you need to be concerned with is current density using only amps per square inch and the active surface area of one face of one plate. 0.25 AMPS (not watts) per square inch is the recommended operating parameter to limit plate degradation and 0.5 amps per square inch is the recommended absolute limit.

For our purposes, heat is not a real factor in plate degradation and it can get very complicated trying to figure in all the other necessary variables required to determine how hot your reactor will get such as ambient temperatures, air flow, thermal condutivity of all the materials and the percentages each material will contribute to the whole heat dissipation picture. You don't even want to try and go down that road.

Looking at your opening post, your predicted 50 amps will be divided among 4 stacks with 12.5 amps going to each stack and you will have a surface area of 30.25 square inches...so 12.5 amps divided by 30.25 square inches gives you a current density of 0.41 amps per square inch. That's below the absolute limit, but well above the recommended safe limit. With your configuration you should shoot for a total amp draw of 30 amps or so to play it safe.

[BeaverRat]

So power density doesn't matter... only current density shows the deterioration status of the plates?

If I configured the cell as

-NNNN+NNNN-NNNN+NNNN-NNNN+NNNN-

That is 31 plates with each one a reactive area of 5.75x5.75 inches (33 inches squared) (will 1/8th inch gaskets work?)

50 amps split between 6 stacks is 8.33 amps per stack. 8.33/33= amp density of .25

This setup can safely run 50 amps at 12 volts, correct?

[IM2L844]

That's right. More than likely, however, you will probably have about 13.2 volts most of the time which will give you 2.6 volts per cell and with that I expect it to pull more than 50 amps. You will need a PWM, but with that voltage per gap, I'm guessing 1/8" gaskets should work just fine. Depending on your vehicle's electrical system, you could see voltages and amp draws even higher than that.

[Philldpapill]

Well, power density does kind of matter, but not the density you're thinking. The voltage per gap isn't what is important, but the voltage potential from plate surface to electrolyte. The REAL power density is this voltage potential, times the current.

However, since you're using stainless, the voltage potential is going to be a constant, so the equation simplifies down to the only changing variable - current density.

In other words, what IM2L844 and Larry have said... LOL

[BeaverRat]

It actually will be exactly 12 volts (not 13.8) because it is running off of a converted ATX PSU. That is why I am using 4 Bi-polars instead of 5.

Oh, and I did it again... I meant 1/8th gasket width to allow for a reactive area of 5.75x5.75 versus 5.5x5.5. Not Gasket thickness.

[BeaverRat]

Ok, I am even more confused now. Larry mentioned power density as to not go over 1 watt per inch squared of total plate area including both sides of the plates. IM2L said that you only need to worry about the current, not the watts. IM2L said to not go over 1 amp per 4 inches squared on one face. WHich is correct, 1 amp per 4 square inches or 1 watt per 4 square inches? They are completely different.

[H2OPWR]

Ok, I am even more confused now. Larry mentioned power density as to not go over 1 watt per inch squared of total plate area including both sides of the plates. IM2L said that you only need to worry about the current, not the watts. IM2L said to not go over 1 amp per 4 inches squared on one face. WHich is correct, 1 amp per 4 square inches or 1 watt per 4 square inches? They are completely different.

From all my testing 1 watt is the rule of thumb. 1 amp is very different depending on voltage.

Larry

[BeaverRat]

How exactly do you calculate your power density?

[BeaverRat]

Shane, did you mean power? because amps X volts is watts. What method is used to calculate how many plates you need? Power density, or amp density?

IM2L says to use current density (amps/inch squared) to determine how many amps can travel through a certain cell without damaging i. The amps in one stack, divided by the surface area of one plate face. For instance, If you have a cell with plates that are 1x1" (excluding gaskets) configured as -NN+NN-NN+NN- running off at 12 amps, then the current density would be 12 amps divided over 4 stacks, or 3 amps per stack divided by the surface area of one plate face (1 square inch). So, it would be 3 amps per square inch which is terrible, he recommended .25 amps per square inch.

HHOPWR says to use power density (watts/inch squared) to dictate how much amp draw can go through a cell without deteriorating it. You achieve this by taking the total surface area or (total plates - 2) X (Surface area of one face) X (2) + (2 X one plate face surface area) and then doing Watts/Total surface area. He says to use 1 watt per 4 inches squared.

Which one is correct?

[IM2L844]

I don't know where this watts per square inch thing, in the context of the electrolysis of water, originated, but there are tons of reference materials from all the generally accepted authorities (i.e. Bob Boyce, Tero Ranta, et al) going back many years clearly stating that current density (Amps/sq. inch) is the correct metric to use. A quick search of Bob's Hydroxy group forums turned up more than 200 references over 4 years that agree with me, but I would suggest that you research it for yourself rather than taking any one person's word for it.

Later, I'll see if I can find a couple of links to get you started.

[richard_lyew]

you cant just ask for a amp per square inch, you have to take into consideration the gap space, the thickness of the plates, the electrolyte percentage to water(and what kind of water), how much volts per gap, what kind of plates, the list goes on and on.......... :D

[BeaverRat]

Well, I already know all of the other factors and I am using a well known material (SS316) so I figured I would just ask about current density since it was the factor I was unsure about...