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Most efficient way to get a high voltage DC source

Red Squirrel

Red Squirrel

No Lifer
I need a DC source that is of relatively high voltage, like 120V. What is the best way to get this? I was doing research on bridge rectifier and it seems like the easiest way, but high voltage diodes are not exactly something you can just pickup at a store. OR would a typical small diode found in a piece of electronic equipment actually be able to handle 120VAC?

For those curious, I want to make a small electrolysis machine, just for fun.
 
lol 120V «high voltage».

I foresee redsquirrel zapping himself though. You need isolation transformer.
 
...don't you need high current / low voltage & current control?


and uh don't be hooking up a diode bridge directly to a wall outlet.
 
PottedMeat said:
...don't you need high current / low voltage & current control?
Click to expand...

Yup.

50V is more than enough for demo purposes.
If you want efficient electrolysis, you want less than 10V. You need huge electrodes to go anywhere with such low voltages.
 
OP should read up more on electroysis and electrochemistry. I detect an undercurrent of "more is sure to be better, so I need more voltage". That is dead wrong, and other posters have pointed out that the direction probably is low voltages and large currents, requiring large apparatus and electrodes. You'll begin to understand why this is so if you learn more about the process itself.
 
You can actually buy relatively cheap, small-scale electrolysis kits online. Of course, if you are just interested in building your own, that won't help, but if you're more interested in puttering around with the process, I'd recommend this route.
 
so low voltage will be ok, but does the current need to be higher? I'm sure a bank of 9 volt batteries or a 12 volt wall adapter is probably not going to do much good or will it?

And yeah I'm not sure how yet but I want to spread it as much as I can. I'm leaning towards some kind of plates that are very close together but not touching where + - alternates. I've done electrolysis before with straight 120VAC but since it's AC, you get a mix of O and H on both sides. Then again, looking at the bubbles is the fun part. 😛 I have not tried 240v yet.
 
RedSquirrel said:
so low voltage will be ok, but does the current need to be higher? I'm sure a bank of 9 volt batteries or a 12 volt wall adapter is probably not going to do much good or will it?
Click to expand...

The amount of gas you get is proportional to charge (current x time).

Voltage is irrelevant (unless you go below the electrolysis voltage of 1.2 V- when electrolysis cannot take place at all), except for the fact, that the higher your voltage, the higher your current (for the same electrolyte concentration and electrode configuration).

Because voltage doesn't affect the amount of gas produced per Coulomb (1 Coulomb = 1 Amp for 1 second), the most efficient electrolysis is obtained at 1.2V, and efficiency rapidly decreases as voltage increases. (If you do electrolysis at 120 V, then your efficiency is about 1% - the remaining 99% goes to heat).

To get a lot of gas, you need a lot of current. That means big, closely spaced electrodes, and a suitable electrolyte (e.g. 5% sulfuric acid).
 
I always used old car batteries for electrolysis and electroplating. They are around 13vdc and can provide around 20A of current for a couple hours before needing a recharge. Don't do this with a good car battery as they are not designed for a constant drain and it will warp the plates inside and degrade the battery. I get them from people whose battery has failed and give them $5-$10 they would normally get off the core charge fee. They normally have a dead cell or two so it might be as low as 10Vdc but they are still good for stuff like this.


edit:
For electrodes break open 6volt lantern batteries, they have some nice graphite electrodes inside. Some of the D cells do to, but it varies more. Be careful, graphite is really easy to break.
 
Is foil a good material for electrodes? I know anything works, but some are better then others. I once just put a cut power cord in water as a kid to watch all the bubbles. But it was probably not really efficient. Is the graphite in batteries the same as I'd find in a pencil? I have ton of those I could split in half.

As for voltage, so it sounds like low voltage high current is what I need. Come to think of it, if you use AC and get a mix of oxygen and hydrogen at same time, would it still be flamable? Oxygen is combustiable so technically it should make the hydrogen burn faster.
 
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RedSquirrel said:
Is the graphite in batteries the same as I'd find in a pencil? I have ton of those I could split in half.
Click to expand...

The graphite in pencils is usually mixed with clay or other materials to make it harder so it is less conductive and varies with pencil brands. It will heat up more than the graphite in batteries as it will act as a resistor. I would get some cheap D size batteries , zinc carbon , not alkaline batteries and use those. They are usually the cheapest batteries in the stores.

Just for comparison , a piece of graphite rod I pulled from a AA battery has .7 ohms resistance for 1 inch measured from end to end
 
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If you just want to watch the bubbles, you could look into a variable transformer. They can output a lot (relatively) of amps and you vary the voltage by rotating the knob. Jameco Link You can get bigger ones than those, also, for around 150 or 200, also. Of course the output is still AC.
 
You're trying to perform electrolysis on water I take it? Current is what you're after... I'm sure you could do it with however many 9 volt batteries or a small wall charger but in my experience you want something like a sealed lead acid battery (they sell small 12V ones at radio shack that work nicely)... any kind of foil for an electrode is going to corrode eventually, that's why it's nice to use carbon/graphite. I built a setup like this with some carbon electrodes in a u-tube and it worked nice for visual purposes (and even to fill up some hydrogen balloons!). If you add an electrolyte to the fluid it will speed up the process immensely. It's the contaminants in water that make it conductive... pure water is actually a pretty poor conductor. You want to be careful what electrolyte you add though because they can produce harmful byproducts.

An alternative to pulling electrodes out of batteries is a welding supply store or any store that sells welding supplies should stock some small graphite rods, that's where I picked mine up

Adding simple table salt for instance will drastically speed up the process but will produce chlorine as a byproduct... you want to be careful whenever performing electrolysis to properly dispose of the fluid after. Since you don't know the exact make up of the water, you won't know what kind of god awful chemicals can be formed post-electrolysis. You'll need to dig around a bit but I'm sure there are some electrolytes you could obtain easily that won't be quite so nasty.

Also now that you will be producing more hydrogen and oxygen, remember that hydrogen is extremely explosive and oxygen is a powerful oxidizer. You don't want the two mixing because that can lead to spontaneous combustion.
 
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I was thinking, would a computer PSU be more effective? Trying to stay away from batteries just because this is probably very hard on them. Can I actually combine rails in a PSU for more current? Like put all the 12V rails in parallel. I have a feeling I can't do that, so I'd just have to pick one, or maybe even put multiple in there at once.

I was thinking of filling a hydrogen balloon too just for fun. Do they actually float? I would imagine so.

And yeah oxygen + hydrogen + source of spark = ouchie! Can probably be fun to play with in small quantities though.

I'm thinking of building this with a jar and some pex tubing and electrodes. I could put the carbon electrodes inside the pex so the bubbles rise up, and there would be valves at both ends where I can connect to whatever I want.

I was also reading up on the nasties behind using salt. Though this brings something interesting. I can probably get all sorts of different results by using different electrolytes.
 
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There are guides online on how to adapt a computer PSU for desktop power supply usage but I'm not sure what that really entails. Personally I prefer using batteries because I'm more confident they won't burn my house down. A little sealed lead acid battery will do the job just fine for a plenty long time and you can charge it with a 1 amp trickle charger or something like that.

Hydrogen balloons float much better than helium balloons, since they are half the density. In fact hydrogen was the predominant gas for balloons and airships before the hindenburg....There are some other very fun things you can do with hydrogen balloons because they are flammable, but I'll leave that to your imagination. I'd recommend against using a glass jar because in case something does explode you'd probably prefer not to have glass shrapnel. I used clear acrylic tubing with some PVC elbows to make my u-tube, and added some ball valves to enable me to fill some balloons.

Hydrogen on it's own is quite volatile... hydrogen and oxygen together are extremely volatile. I'd recommend not making very big quantities. Have fun and be careful

P.S. If you want something else fun to do with your finished electrolysis rig, find a cheap fuel cell! 😀

In fact a prefabbed fuel cell may be just what you're looking for, many of them work both ways (can perform electrolysis very efficiently if you apply charge, or generate electricity if you supply hydrogen and oxygen) I built a fuel-cell-car in high school using one of these types of kits and it was quite fun:
http://www.amazon.com/gp/product/B0..._m=ATVPDKIKX0DER&pf_rd_r=01HTFEQ5NTQT086PJ90A
 
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I've seen videos of people lighting a hydrogen baloon on fire, always fun. 😀

I think they used to use that for blimps too, now that I think about it, but it was too dangerous. That's a HUGE amount of hydrogen.
 
Are you looking for browns gas? Or just to split out H and O? If it's browns gas you are after, than an AC voltage at around 1khz gets you quite a bit. If you want H and O separately than DC is the way to go with seperate collection voids. Careful with the H side.

You'll basically need to construct a capacitor. The closer you get the plates/electrodes the more current, which = more gas. It's a function of current so batteries work best.
 
I didnt think that DC was a killer. It might burn you or start a fire, but 60 cycle AC is the issue as the frequency is near that of the human heart.

If youre really serious about this, then just get yourself a car alternator (with the diodes built in/onboard) out of the junk yard (like say for an old Caddi or Lincoln) & run it via a V belt using a wash machine motor. The alternator will be able to supply mucho current (probably 50 amp) at 15 - 18 volts DC basically continuously (24/7). You could put the whole thing together for less than $50.
 
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