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hydrogen power

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: rp181 » Wed Dec 26, 2007 11:04 am

im only using 12v because thats the only voltage i could find with a decent current, I didn't know batts could supply that much current. Im a noob at electronics, would a resistor reduce current proportionally?
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Unread postAuthor: jimmy101 » Wed Dec 26, 2007 5:57 pm

rp181: A resistor will drop both the voltage and current. You need a fairly low valued, high powered resistor for this type of setup. You might try a 50 or 100 Watt light bulb in series with your cell. (A 100 Watt light bulb is roughly 150 ohms, a 50W about 300 ohms.)

Do you know that the cell is actually drawing ~5A or is that just the output rating of your power supply? Based on your description of the cell, I wouldn't think it is drawing that much current.

Another way to drop the voltage is to use several electrolysis cells in series. With four cells in series, and a 12V supply, each cell is getting 3V.
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Unread postAuthor: sgort87 » Wed Dec 26, 2007 6:09 pm

Everything here is proportional. If you move the electrodes further apart, it's the same as adding cells. There's no need to add more cells if you do that.

We can't give you an accurate resistor value to use unless we know the resistance between the two electrodes. This is going to depend on what's in your water and how far apart the electrodes are from each other. If you have a multimeter, connect it to your electrodes where the transformer leads touch them and read the Ohmic value and let me know what it is.

By the way, you can get all kinds of stainless steel parts from www.mcmaster.com.
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Unread postAuthor: jimmy101 » Thu Dec 27, 2007 1:31 pm

sgort87 wrote:Everything here is proportional. If you move the electrodes further apart, it's the same as adding cells. There's no need to add more cells if you do that.

Sgort is right, but increasing the separation between the electrodes will drop the current significantly (as will adding an external resistor). The nice thing about adding multiple cells is that more of the power goes into the electrolysis process and less is wasted as heat.

sgort87 wrote:We can't give you an accurate resistor value to use unless we know the resistance between the two electrodes. This is going to depend on what's in your water and how far apart the electrodes are from each other. If you have a multimeter, connect it to your electrodes where the transformer leads touch them and read the Ohmic value and let me know what it is.

In other words, measure the resistance of your cell, with the power source disconnected. You would like the resistance of the cell to be as low as possible unless you are trying to step down the voltage. In general, the more current (the lower the resistance of the cell) the faster it will produce hydrogen and oxygen. You can decrease the cell's resistance by;
1. Increasing the salt concentration.
2. Increasing the surface area of the electrodes.
3. Decreasing the distance between the electrodes.
4. Vigorously stirring the solution (usually not very practical).

The voltage across the cell has almost no affect on how fast it will produce hydrogen and oxygen as long as the voltage is above the redox potential for the cell.

sgort87 wrote:By the way, you can get all kinds of stainless steel parts from www.mcmaster.com.

You really don't need stainless steel, though stainless will work well. If you use a strong base as the electrolyte you can use pretty much any old piece of sheet metal. Galvanized metal roof flashing works well, is cheap, and will give a large surface area for the electrodes. Check your local hardware store for drain cleaners, many are mostly either sodium hydroxide (NaOH) or potassium hydroxide (KOH). Concentrated solutions of NaOH and KOH are a bit hazardous (read the label on the drain cleaner), much more so than a concentrated solution of bicarb, so be careful. Sometime people use Drano (the powdered kind) since it is readily available but Drano also contains aluminum shavings and various other things.
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Unread postAuthor: rp181 » Thu Dec 27, 2007 2:32 pm

For some reason, i cant get a reading of the resistance, i did before with plain tap water, but now i cant. Works with other things though. I was going to try a NaOH, but its a bit dangerous. I read somewhere it targets protiens in human cells :shock:
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Unread postAuthor: paaiyan » Thu Dec 27, 2007 3:24 pm

NaOH, sodium hydroxide, is a very strong base which can cause sever chemical burns. I would assume that when undergoing electrolysis, it produces sodium, hydrogen, and oxygen.
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Unread postAuthor: jimmy101 » Thu Dec 27, 2007 3:39 pm

paaiyan wrote:NaOH, sodium hydroxide, is a very strong base which can cause sever chemical burns. I would assume that when undergoing electrolysis, it produces sodium, hydrogen, and oxygen.

"Strong", in reference to an acid or base, is a dependent on the concentration. The "strengthen" of the solution is proportional to the conentration. A 10% solution of NaOH is very caustic, a 1% solution less so, 0.1% even less.

NaOH really isn't all that bad. You can handle the pellets with your bare hands for a brief period. A quick wash with water afterwards is all that is needed. Splashing a bit of 10% on your hands isn't going to cause you to flop onto the ground and die. You do want to avoid splashing a bunch of it into your eyes.

Electrolysis of NaOH in water produces hydrogen and oxygen, just like the electrolysis of pure water. It is just much more efficient with the added salt, and the high pH of the solution does a lot to protect metal electrodes from corrosion.

It is not possible to generate sodium metal in a water solution since it reacts with water to produce Na<sup>+</sup>, OH<sup>-</sup> and H<sub>2</sub>.
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Unread postAuthor: paaiyan » Thu Dec 27, 2007 3:46 pm

Uh, I beg to differ jimmy. When I say strong, I reference the PH scale, which places NaOH at 14... the top of the scale with 1 being most acidic, 7 neutral, and 14 most alkaline. Yes, the strength, not strengthen, of the solution is dependant on concentration, but I'm not talking about that. I'm saying sodium hydroxide is one of the strongest bases that exists, and is not to be played around with.
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Unread postAuthor: jimmy101 » Fri Dec 28, 2007 2:47 pm

paaiyan wrote:Uh, I beg to differ jimmy. When I say strong, I reference the PH scale, which places NaOH at 14... the top of the scale with 1 being most acidic, 7 neutral, and 14 most alkaline. Yes, the strength, not strengthen, of the solution is dependant on concentration, but I'm not talking about that. I'm saying sodium hydroxide is one of the strongest bases that exists, and is not to be played around with.

Actually no. NaOH is not one of the strongest bases that exist. Many, many things are much much much more basic than NaOH. NaOH is one of the strongest hydroxide containing base. But NaOH is really only a strong enough base to remove a proton form an acid or from water. Stonger bases, like LiAlH<sub>4</sub> will remove the proton from something that is a much weaker acid, for example, an alcohol.

The only thing that matters when a strong acid or base is dissolved in water is the concentration of the final solution. The pH is just based on the concentration. A 1% solution (0.25M) of NaOH in water has a pH of about 13.4. An 0.1% solution about 12.4, an 0.01% solution 11.4.

Oh and you don't reference a pH scale when discussing the strength of an acid or base, you reference it's pKa or pKb (assuming your are discussing a protic acid/base and using a Bronsted-Lowry Definition). The pKb of NaOH is about 0.2, the pKa of hydrochloric acid is about -4. HCl is a much stronger (~10,000x) acid than NaOH is a base.

There is really no reason a person can't "play around" with NaOH. It ain't that dangerous. Heck any noob can walk into the local grocery store and buy it by the pound for a couple bucks.

Or, take a couple pounds of wood ash and boil it in water. Filter off the crud and you get a solution that is a couple molar in NaOH and KOH with a pH ~14.
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Unread postAuthor: rp181 » Fri Dec 28, 2007 3:16 pm

im going to try the NaOH, but will regular galvanized steel work?
i converted the gun into a low pressure (60 psi) pneumatic, and will try to make an all-metal one with improved electrolysis cell.
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Unread postAuthor: jimmy101 » Sat Dec 29, 2007 11:31 am

rp181 wrote:im going to try the NaOH, but will regular galvanized steel work?
i converted the gun into a low pressure (60 psi) pneumatic, and will try to make an all-metal one with improved electrolysis cell.

Galvanized steel should be OK. It'll corrode over time but should have a useable life. Stainless steel would be better. You could even chop up a large can, like a coffee can, for the electrodes.
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Unread postAuthor: jonjr » Sun Dec 30, 2007 12:01 pm

i have a :idea: for a gun that will have a perfect mix and can control the amount of mix. this is by taking a T connector for water and the chamber then goes to the barrel. in the water will be two electrodes called an anode and cathode. just so u don't have to wait so long use a car battery or two. i know this much if hydrogen is used in mass quantities. so if u leave it in there for say 5 min then it should not blow your hand off. now if u leave it to where you get a good 20 psi then your asking for trouble. one way to make this safe regardless is to put it underground and have the barrel sticking out and what ever else is needed to fire it. then just fire from a good 15ft. so i don't care what you make it out of it will work. please go easy on me this is my first post. i have just been doing some heavy research on the hydrogen fuel cell side and thought it would go nicely in a gun. the hydrogen if made right should only get up to a good 100 to 200 in a combustion engine and that is a fire ever second or more a second. so a fire every 10 min there is cool down time.
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Unread postAuthor: jonjr » Sun Dec 30, 2007 12:19 pm

o if you guys want a deadly mix. acetylene is deadly if put in pvc and safer in metal but i still go to the underground method.
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Unread postAuthor: sgort87 » Wed Jan 02, 2008 8:31 am

Sorry, I forgot to reply a few days ago, but the reason you can't get a resistance reading must be that your transformer leads are still connected to the electrodes. Not only does the power need to be off, but the transformer needs to be disconnected or else you will read the resistance of the transformer coil in parallel with the water's resistance, which is approximately zero Ohms.
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Unread postAuthor: rp181 » Wed Jan 02, 2008 9:16 pm

nope, everything was disconnected. I got a box of baking soda from the dollar store, and aton of it dissolved into the water. Couldve done te whole box, but decided to save it. 300ma is getting me the same amount as before O.o

When i mixed the soda in, no co2 comes, i know its not supposed to. But when i put in the carbon rods, it start bubbling. I thought it needed something like vinigar to bubble?
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