Zapping my way to nitric with a Marx generator

[megalomania]

I found this nifty device ( <a href="http://www.netcomuk.co.uk/~wwl/marxgen.htm" target="_blank">http://www.netcomuk.co.uk/~wwl/marxgen.htm</a> ) that I think might be useful for zapping the air as a means of making nitric acid. Unfortunatly I don't know much about electronics, so I have a bit to learn before building such a thing. What I would like to know, if anybody can tell from the plans and pictures on that site, whether or not those individual gaps between the wires spark, or is it just the end of the device?

It would be nice to lay one of these inside a long piece of plastic tube and have it zap zap zap along the entire length. Push some air in at one end, and bubble the resulting slightly NO2'd air into a hydroxide solution at the other, instant nitrate maker. These don't look terribly hard to make and they could be quite fun by themselves. I would have to build the nitric device with clear tube just to show it off :D I could even make a big enough one (two) to send the spark from one end of the tube to the other. Sounds like a good science fair project too, to damn bad I am 15 years late in thinking of it.

If anybody has any other kind of suggestion as to making sparks, lets here em. I could try a line of spark plugs, maybe little tazer devices, who knows. I don't <img border="0" title="" alt="[Frown]" src="frown.gif" />

[xoo1246]

This is why we should cooperate with powerlabs, that way we would have the knowledge to assemble explosively pumped EMP weapons. <img border="0" title="" alt="[Wink]" src="wink.gif" />

[Anthony]

All the gaps between the wires spark.

It does look simple, although you do need a HV DC input. Although with up to 14" sparks as shown, you could place an electrode at either end of the tube with the air flowing through it and have sparks travel the length of it :)

[PYRO500]

There are several easy ways of making sparks that don't involve voltage multipliers, In fact I wouldn't recomend a marx generator beacuse they are hard to get in too many stages, in fact all the stages seem to light up at the same time although there is a tiny delay between them. The UV light generated from the first gap will help the others spark over too. I see probems with contact corrosion and possibly part corrosion with a marx generator. For another simple way to get HV you can make one of these <a href="http://63.229.238.60/kv2/kv2/hv/multiplier/" target="_blank">http://63.229.238.60/kv2/kv2/hv/multiplier/</a> witch are solid state and have no spark gaps (unreliable) to get in the way of doing somthing like cooling it in mineral oil.

You also could take a high voltage transformer and do this but it'd be hard on the transformer and would possibly get hot.

[McGuyver]

Oil Burner-10kv, Neon Sign-15kv, and microwave-1kv at 1 amp. These are all transformers that make about a 1 inch spark. The microwave transformer puts out the most power though, the other two only put out a few milliamps (not exactly sure how much). These transformers are easily obtainable. I got two free oil burners from a air conditioning repair place.

I also have built a tesla coil that makes a 12 inch spark. It's 400,000 volts but at barely any amperage.

I believe all electrical spark make ozone. I'm not sure if this affects anything but it's true. My tesla coil produces a shit load of it.

[PYRO500]

I wouldn't recomend oil burner transformers beacuse they have a tendency to get very hot as there only designed for short use. Also microwave oven transformers are very dangerous especially if you don't use current limiting. they will put out enough power to melt almost any electrode you have pretty fast and generate enough heat to melt glass.A neon sign transformer might work though. Voltage multipliers are easy, cheap and repairable if a part goes bad. also they can be cooled very efficently compared to big transformers.

[pyromaniac_guy]

a microwave oven tranny isnt going to be of too much use, because at such a low volatge you are going to need some way of striking an arc, also you are going to need to limit the current some how.. what would probably be a better way of doing things would be to use a chemical safe pump to flow hydroxide solution throught a water asperator.. the lower pressure will make it much easier to strike an arc (if you went low enough, you could simply point the magnitron at a low pressure tube, that way you dont have to worry about your electrodes melting off!).... a word of warning about microwave oven transformers, when it comes to electrocution, it only takes about 60ma... microwave oven trannys put out a good portion of an amp or more, so for all intents and purposed you might as well be working with an unlimited source of current... if you have an accident with a microwave oven tranny there is a very good chance of getting killed, especially if the curent path is through your chest...

neon sign transformers and oil burner ignitors are normally alwasy limited to about 15 or 30ma, making them much safer, even though you have to worry about high voltage saftey more....

as i have personally got hit by 7.5 kv @ 15mA i can persoanlly testify that this is NOT something you want to happen to you!!!!!!

as otheres mentioned oil burner tranys arent ment for continuous duty aplications, so a neon sign tranny would be best...

finally, i have noticed, in playing around that a dc arc will produce more o3 than an ac arc.. I'm not sure of the reason for this, or if it will apply to making oxides of nitrogen, but it's something worth looking into...

[Marvin]

Marx generators and tesla coils are good for a single blasts of high peak voltage and voltage multipliers are good for low current high voltage supplies but these are counter productive for generating nitric oxide. What matters is the total power into the arc, not its voltage or current alone. All of these devices sacrifice total power, for high voltage production.

1ma over the heart is enough to cause arrest, so all of these machines are potentially fatal. Neon sign transformers are good for high voltage current limited applications like tesla coils and jacobs ladders, but for nitric you want as much raw power as possible which leavs only microwave oven transformers. Clever electrode arangements can overcome the striking problem and they will only overheat if the current drawn is too large. This may sound obvios, but this would generally be caused by an impedence mismatch, which would result in very little of the power being dissupated in the arc. Its very important the furnace design is calculated to avoid this.

Playing with powered magnetrons is very likley to leave the player with interesting additional problems, only a small power leak is enough to cause cateracts and high power will quite happily cause maasive internal as well as external burns. Making microwaves go where you want is very difficult without resorting to black arts like waveguides.

[Anthony]

Why is the magnatron coming into play? Only the transformer that powers it is required if you're making an arc.

You're right that a MOT will put a lot more power into an arc than a marx generator, neon sign transformer etc. 1.5Kw continuous shouldn't be a problem. Although it would be a lot more hazardous than other suggestions.

Also, HV would let you deliver more power at lower currents, which should mean fewer heat problems and less electrode wear.

But is the MOT required if we were to use (relatively) low voltage? Straight 240v mains would deliver more power and there'd be no transformer to overheat. It'd be a damn lot safer too.

[Marvin]

pyromaniac_guy suggested using the magnetron to provide an arc with no electrodes in a low pressure gas, which is not a bad idea in theory.

Using 240v mains with no transformer would be safer?!?!?
I dont think so somehow and there are unavoidable problems that come with no current limiting at all. Arc impedences are inherently unstable and depend on the current flowing at the time, no limiting and an effectivly very low impedence power supply would cause the arc to thermal avalanche and blow fuses.

A jacobs ladder in a bell jar is a good way to start nitric oxide experiments, but a microwave oven output voltage is too low to make this work dispite the high potential arc length at full extension, 5-6inches potentially, and the lack of magnetic flux limiting.

For applications that require &lt;9kv at 3kw or more its possible to wire 4 microwave oven transformers together, primaries in parallel, secondaries in series, hotcoreing two of them with external insulation from ground, such that the insulation rating of any one isnt exceeded. This is an example of when a much more useful voltage is produced, without sacrificing the total power of each unit.

Low pressure sparks/arcs yeild more acid for a given amount of energy, but its essentially impossible to setup a system that gives as much throughput as a power arc at atmospheric pressure.

[Anthony]

Ok, I didn't recall pyromaniac's suggestion of the magnatron.

You probably would require some form of current limiting if using mains, but there must be an easier to cool method than a transformer.

I've had a belt off the mains, and know plenty of other people who have. Before multimeters became widespread, electricians used to detect the presence of mains with their fingers. They could tell the difference between live and neutral by the sensation of the shock.

I've never heard of anyone who's taken a shock from the secondary of a MOT, and it's not something I'd bet my life on trying!

[Marvin]

Ive worked on a fair amount of high voltage equipment in the course of experiments, and had shocks ranging from 12AC, about the lowest I can feel with damp hands, to 20kv at 1ma. The only 2 times Ive been shaken enough to count my own pulse afterwards, was one particular shock from a MOT, and one particular shock from mains. Voltage/current make a big difference, but not as big as external circs, such as how damp your skin is (3 orders magnetude change in conductivity), what you are standing on in what shoes, and what your other hand is touching at the time. I'm not drawing conclusions from this other than mains and MOT Voltage/current combinations both scare me a lot, and about the same.

I'm sure a lot of engineers used to get away with testing live by touch, but keeping one hand behind back, and with good shoes the shock itself would be much reduced. Most sane engineers from what Ive been told used the neon/resistor trick before multimeters became common, and this is now included in a lot of screwdrivers. Youve probably seen this before, but an added bonus you might not have learned, is in DC HV systems, wiring it over an unknown supply also tells you which is the anode/cathode from which element of the neon lights up.

All neutral wires are grounded before they enter the house, a few volts or more between neutral and earth is indicative of an earth fault. Live only should be capable of giving a shock, so its a little less subtle than youve been told. Its at this point the big advantage that MOT have that more direct methods dont becomes more obvios. Transformers are inherently isolating, so you can construct a circuit where no single point to earth is a hazard, youd physically have to touch both sides of the MOT secondary circuit at the same time to get a shock. Since earth is everywhere an unisolated circuit is much more likley to give a shock with no aparent second connection. One of the stated tricks of HV engineers is to work with one hand in a pocket, or behind their back which vastly reduces the chance of an accident in the event that the circuit is improperly disconnected/discharged. Large high voltage capacitors are on another level of safety entirly.

Another reason Id prefer ~2Kv peak from a MOT rather than 240v is becuase the latter is only just capable of making a spark at all, I suspect the only way to make that work in practice would be to strike an arc by shorting the electrodes. I really dont like this method. The oven transformer is only just capable of striking an arc of a few mm long, and not really a large enough gap to be carried by air alone. A high impedence strike electrode over a large gap might work, but Ive learned of these long after my old jacobs ladder attempts. Wiring more than one transfomer together (Up to 4 as Ive said before without overspec) could well completly avoid these problems.

In the Birkland Eyde furnace a large magnet was used to turn an arc into a disk air could be blown through directly, which is very cunning and Id have liked to try this. I still dont quite understand how maximum arc length is affected by voltage/current effects and I have no experience at all at the low voltage end of the spectrum. In an arc welder we have about 50v at often over 50A, which should be inherently safe from shock hazards but does anyone know how far an arc can be pulled with one of these? With my best MOT I got an inverted catenery of about 5 or 6 inches total length, but didnt have the equipment to determine if the voltage, the current, or the air flow were the main limiting factors.

[Bander]

Here's a few nice diagrams of MOT stacking like Marvin suggested. <a href="http://www.altair.org/projects/MOTstack.gif" target="_blank">In parallel</a> and <a href="http://www.altair.org/projects/MOTstack2.gif" target="_blank">in a series</a>. With a setup like this you could achieve quite high currents for the voltages you'd need. Plus I've found that you can get nice MOTs quite cheaply.

[EDIT]Oh, and someone that has done that exact thing: <a href="http://www.kronjaeger.com/hv/hv/exp/no/index.html" target="_blank">Jochen's High Voltage Page: Nitric Oxides</a>

<small>[ December 07, 2002, 03:19 PM: Message edited by: Bander ]</small>

[Marvin]

Some nice searching, but as ever the internet must be regarded as suspect as a source of information.

Some comments, both MOT stacking methods are in series, with the primaries in parallel. The difference is in the way they are isolated, assuming the MOT core is or isnt wired to one side of the secondary output. Both versions use external isolation, which isnt really needed if the problem is thought through properly, and the limit of 4 MOTs isnt exceeded.

In the second one, each MOT has one end of the primary wired to the core, which we would automatically assume is a bad thing, but not so. Thats how they are supplied for use in MO's and we could rewire them, but this turns out to be counter productive in the long run.

The second diagram uses 4 MOTs to both isolate and bias each half of the supply. The design assumptions here are that the insulation between the core and the primary isnt up to 2kv, which is rather overly conservative. The isolation section takes its bias from the the 4 transformers wired secondary to secondary, but this is attampting to be overly clever, it would be simpler to use 2 isolating transformers, ground the 2 cases in the stack wired head to head, and take the bias of both tails, at least in the case only 4 in series are needed. Another problem in this design is that power is limited becuase of the underperforming isolation setup. An advantage if you dont need the full power but we do since more power = more nitric and that will be rather slowly produiced as it is. The technical term for the method used here is 'an utter fucking waste of 4 transformers', but if you need 8 in series, multistage isolation of some kind is the only way to go.

Ok, the 4 transformer trick. Assumptions, the secondary is wired to the core at one end (The head), the output of the transformer is 2kv, which means there is 2kv strong insulation between the tail and the primary, and 2kv strong insulation between the core and any part of the primary. Pretty safe bets for a MOT, but we can stick to these numbers to avoid overstressing anything. The normal way the trnasformers would be wired is straight head to tail all the way down, but this provides only a single ground point, and one of the transformers is automatically overstressed. If we wire the middle two head to head however, we can ground both cores, adding the other two on either end tail to head provides two symetrical high voltage cored transformers which need to be insulated from everything else to 2kv. There is only ever 2kv between the primaries and cores, and only ever 2kv between the core and tail end of the secondary. No attempt should be made to use this method for more than 4 transformers, but I suspect the max output power of 4 will bring enough cooling problems of the arc chamber.

This looks very simple in a diagram, but wiring transformers head to head, or tail to tail, as done in both this and the other two above, requires absolute certainty the primary is connected to mains the right way round (the oppasit way to before), which with real MOTs can be rather confusing. If this is done it will result in a lower output voltage/power but should not damage itself as its only transformer EMF canceling out.

I will sort out a diagram for this setup at somepoint. I would advise trying a much lower power device first and working your way up. I should point out 2 things here, this idea isnt mine, I got it from some tesla coil builders, and that I havnt tried 4 MOTs together myself. I am educated in EE (in addition to chemistry), and this circuit does seem sane and safe (Well about as safe as any method for producing around 8kv@3kW) or I wouldnt be suggesting it, comments welcome.

[MnkyBoy]

Here is the effects of several Marx Banks in use, all directing their energy into a tiny center.

http://www.sandia.gov/media/images/Z02.gif

Note: The arcs-n-sparks seen in the pic above is only 5% of the energy being discharged. What you see is just the LOSSES!

If your want the full run down Z-Machine (http://www.sandia.gov/media/z290.htm)