Exploding Wire Project

[Centimeter]

My purpose is to create an art project in which a large capacitor bank is powered up by a hand crank generator until the voltage is enough to trigger a spark gap resulting in a tremendously loud and bright exploding wire. My basic concept is similar to that of an EBW blasting box. I purchased 12 2uF/2kV mica-paper polymer pulse type capacitors from Cornell Dubilier off of ebay, one tungsten spark gap, 2 high voltage diodes, and a 9kv DC transformer that steps up from 150v. I was planning on configuring the capacitors so that the over all bank rating would be 2uF at 12kv. Is this the optimal configuration of the 12 caps to produce the most pleasing exploding wire? I was planning on using a basic rc charging circuit. Do I need to use some sort of special high voltage resistor? Is making this thing powered by a ~6v hand crank generator feasible? I will of course be using a capacitor to step the voltage of the generator up to around 150v. Is there a problem with using DC as the input of the transformer and if so how do I adress this? I was planning on measuring when the capacitors are fully charged by including a conductivity meter in the circuit. Do I need to use a special high voltage ahmeter or will the average multimeter work? Also, where in the circuit should the meter go? Amazing1 uses a capacitor bank of 96uF at 4.5kv in their exploding wire machine and RISI says that only a capacitor of 2uF at 2kv is neccesary for an EBW blasting box. So basically I am wondering if my capacitor bank is capable of producing an extremely loud and bright explosion. I will be using a ~0.5 inch long hair thin piece of copper or nichrome wire as the bridge wire. I get the feeling that the amazing1 device is intended for very long or thick strands of wire. I know that many of these questions are quite simple and indeed I believe that I know the answers to most of them. I just want to be sure about everything so that I can best prevent destroying my expensive equipment. ;) Any and all help is greatly apreciated!

[Zerstoren Sie]

"Do I need to use some sort of special high voltage resistor?"
Yes, arc-over can occur if not. If it's not possible to find a single resistor rated for the voltage, then put several in series, being sure to keep them insulated, a non-conductive tube with oil could do the trick.

"Is making this thing powered by a ~6v hand crank generator feasible?"
Yes, but maybe not practical, it may take a good bit of time for the bank to charge.

"I will of course be using a capacitor to step the voltage of the generator up to around 150v."
Capacitors alone do not step up voltage.

"Is there a problem with using DC as the input of the transformer and if so how do I adress this?"
Yes, transformers do not transfer energy with a DC input. It must be alternating current.

"Do I need to use a special high voltage ahmeter or will the average multimeter work?"
An average meter can work, if you have a high-voltage probe to lower the voltage. Otherwise, it'll probably cook the meter.

"Also, where in the circuit should the meter go?"
If you wish to measure the voltage at the capacitor bank, it goes across those terminals.

"I get the feeling that the amazing1 device is intended for very long or thick strands of wire."
Thick wire is very difficult to explode without many thousand or tens of thousand joules.

I would STRONGLY suggest reading much more than you have before building any pulse-discharge device. A capacitor that's 2uF charged to 12KV stores 144 joules of energy. (E=1/2 cv2) That's not something you wanna mess around with, especially if you dont have any experience with high-voltage. The spark gap could switch that 144 joules in a microsecond, turning that 144 watts discharged in one second to 144,000,000 watts in 1us!!

Here's a link to a page that'll be a good start in learning about high-voltage apparatus. http://www.kronjaeger.com/hv/

Also, why is it you want to charge it with a hand-powered generator??

[Child-of-Bodom]

Aside from your beginner questions, which Zerstoren Sie already perfectly answered, there is already a thread of this stuff....http://www.roguesci.org/theforum/showthread.php?t=3425 (CLICK)

Don't go for the data used in the RISI doc, they have tested with equipment there, which you can never obtain with home-improved swiches and normal cables. Read the linked thread carefully, it is very interesting...

Ow, and please place some enters in your posts, that makes it much more readable.

[Centimeter]

Wonderful links! I shall thoroughly digest them as soon as school allows me. I do realise that this device is extremely dangerous and believe me I am trying to learn everything possible to make my experience safe. Worry not Zerstoren...I will read that entire site before even attempting to assemble anything. I wish to make it hand crank powered because I want the subsequent explosion to be the result of one's own energy. As I said, it is for an art project; I plan on integrating it into my own little jack in the box. It is intended to represent the false order that is so evident to me in our society. I want the viewer to get involved in the chaos and to see the manifestation of anger and frustration. That's about as good of an explanation as I can give you at this point. If you want I can provide a more thorough explanation once I fully think things through. I did try to post in that EBW thread as well as another thread on tools and techniques however both aparently did not pass the moderators. Thus I decided to bring it to the water cooler as I realy must have these questions answered for both my safety and the future of my project.

After re-examining my capacitor bank, I don't think that I would be able to achieve 12kv/2uF. At such a voltage, the capacitance would be MUCH lower correct? I think it would be around .6uF. I have a variety of ways to configure my caps and I was wondering what configuration would be best for my purposes. In other words, do I want high voltage or high capacitance?

From my research I found that RC circuits must have a farely steady current and voltage. This is obviously a problem when using a hand crank generator. How would I go about evening things out? I thought that a small cap would even the current out but how would I make the generator produce a farely constant voltage? Also I found that converting the DC into AC shouldn't be a problem at all and stepping the voltage up to 150V shouldn't be a problem either with a common wall transformer. Also, I plan on constructing a flywheel generator to make the powering up process less labor intensive.

Can you explain the high voltage ameter a bit more?

Thanks! :D

[warmage]

Dear Centimeter

I think you need to do a search for info on two circuit arangements; one is the "Cockcroft-Walton voltage multiplyer" and the other is the "Kelvin-Varley divider".....whyle your at it do at least a Google on "Flukemeter"
I believe that will at least get you started, further on look into the procedings of the IEEE.

[Centimeter]

Well I finished reading all of the links and I did a bit of research on what you recomended warmage. I am not sure how the Cockcroft-Walton voltage multiplyer applies to my project. Perhaps I could implement my caps into it to take full advantage of the capcitors, however this would involve a lot more time and space and I am not sure if it would work. I guess I could try to use it for stepping up the hand crank generator.

For the resistor, can I just use a normal ceramic resistor of the desired value and place it in oil? The voltage is realy not all that high and there will only be a current for a short period of time. Would there still be overheating problems? If nothing else, I will go with a water resistor.

What I realy need to know now is whether a high voltage or a high capacitance will create the best EBW. I need to know whether or not I should cancel my order of the transformer. Actualy I may not need to send it back at all. Here is a link to the transformer; http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3844675708&ssPageName=ADME:B:EOAB:US:6

It talks about a tap and from the picture it says it has two outputs. One seems to say 9,000vDC and the other says 300vDC. I can't seem to figure out what the deal is with the tap. Does this mean that I can vary the voltage some how?

While I am at it, I guess I might as well show you guys the caps I bought. http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3844152725&ssPageName=ADME:B:EOAB:US:6

In the description it even says that they can be used for EFI devices, which is some what motivating.

I think that I did not properly explain the meter thing. I want to use an ammeter to display the current that is coursing through the system. As the caps charge up, the current will fall until finaly reaching zero, indicating that the caps are fully charged. Perhaps I could use a regular ammeter if I put some resistors on the probes?

[Zerstoren Sie]

The transformer on ebay has two outputs, one at 300V and the other at 9000 V, both these are listed DC so I assume there is an internal rectifier. Notice that the input is 120V AC.

What are the detials of the hand-powered generator?? That really should be the first place you start. If you can find a hand generator that puts out 120V AC, you could directly power that transformer, and then use its output to charge a bank rated for it's output. The 300V terminal would not be used however, and should be covered and insulated somehow. Also, if the hand-powered gen. does not output a full 120V, but say 90V AC, you can just proportionally figure out the HV output(assuming that is just a transformer with a rectifier) and design you capacitor bank accordingly.

As for the ammeter, it may be much easier to measure the voltage, instead of current.
With this method, you simply monitor the capacitor banks voltage, and when it is at the voltage you intend to use, well, use it. Now if the spark gap you have is just a simple two conductor gap, the distance of the gap will determine when your cap bank will fire, not how much your cap. is charged. This of course is based on the voltage breakdown of air. You just distance the gap to fire at the time at which it has most charge, takes a bit of experimentation, but once it's set, you won't need to set it again. Also, if you "want the viewer to get involved in the chaos and to see the manifestation of anger and frustration" that will be wonderful, as they won't know when the bank will fire, and it surely will startle them.

The voltage multipliers warmage speaks of can also be used to charge the bank directly, these can be ran on either DC or AC. They can be configured to put out the 8-12KV that I'm assuming your charging your caps to. Since your looking to get the transformer, I suppose that be the way to go. Either way can work, as long as you find a hand-crank generator to supply the power with. If I remember right, military hand crank phones output 90V or so, can't remember if its AC or DC, but that'd be great if it's AC, that could power it all directly.

If you get a generator that meets your needs, what I see in your circuit is this:
Hand-Crank Gen. (120 VAC)
Transformer (120VAC in, 9000VDC out)
Cap Bank (Built for 9 or more KV, at however much charge you can afford :) )
Spark gap (Gapped to discharge around 8-9KV)
Test Load (wire)

That's the order the parts would appear in the circuit, I'm assuming you can picture the connections.

[Anthony]

You could just measure the current being produced by the hand generator. The voltage at this stage would be easily handled by a cheap multi-meter.

[Centimeter]

The current at the generator would indicate when the caps are charged? I would think that current would still exist on that coil of the transformer even when the caps aren't fully charged. I will probably end up going with the volt meter as I only want to use the meter when setting up the spark gap any way.

As you mentioned, the non-predictable spark gap is a very important part of the design. It is inteded to be my own version of a jack in the box. My only worry is that it will cause a heart attack.

I was planning on getting the system running before designing the hand crank generator. I was just going to make my own out of an electric motor as I couldn't find a place on the net that sold hand crank generators with flywheels. Perhaps someone can recomend a place? I feel that a flywheel is essential so as to even out the voltage as much as possible. It will also feel more natural and should require less labor to power the system up.

I don't mean to be impatient, but I still need to know whether a high voltage or a high capacitance is better for EBW devices. I am not exactly sure why it would matter as no matter what configuration, it will produce the same amount of joules right?. I would assume that a higher voltage would produce a brighter explosion. If I have calculated correctly, my capacitor bank will store 48 joules correct? Although I am not planning on charging them up to 12kv as that is the maximum before the dielectric breaks down. If I only charge them up to 9kv it would store around 24.3 joules. Is this enough to make a VERY loud and bright explosion accross a 1/4" long strand of 38 gauge nichrome wire?

On a side note, my caps just arrived. The whole thing weighs ~5 pounds.

Once again, thanks for all the help guys. I can't possibly explain how much it means to me.

[Zerstoren Sie]

If you use a volt-meter, again, be sure to get a HV probe for it. I once ran a digital multimeter at around 700-800 Volts, and it started to make some funny sounds internally. Surprizingly, it still works, but I wouldn't be doing it again. If you don't wish to buy a HV probe, it's not all that difficult to set the gap. Simply move it to a position where it discharges, and slowly space the gap until it doesn't work. Just before that point will be the highest voltage. Of course, don't try setting the gap distance while the powers on!! A good practice is to have the power cord in your hand unplugged, so there is no way it is plugged in or someone could do so. Really setting the gap shouldn't take more than a few minutes.

As for the capacitor bank, note that E=1/2CV2, therefore, the voltage is critical in determining the number of joules the bank will store. Much moreso than C, considering that V is squared in the formula. I would go with high voltage, matching it to the transformers output is the easiest way to go. Also, having the bank rated at 12KV and running at 9KV is good here. The rectified output probably isn't well regulated and there will still may be voltage peaks higher than 9KV. Also, the nichromes wire will play a part in capacitive discharge, as that wire has reasonably high resisitance. A higher voltage will allow more energy to flow through at a given time. This also shortens the pulse time, and allows for more peak power.

[Anthony]

Yes, as the caps become charged, the voltage at the generator will rise, and the current will fall. It won't fall to zero due to leakage current in the caps, charger and step-up transformer.

[Centimeter]

My transformer finaly arived. I set up the capcitor bank and charged the caps up and when I shorted the circuit hardly anything happened...just a small small spark. I got frustrated so I turned it off and started shorting the caps to make sure they were empty and each and every cap I shorted created a pretly large and loud spark. Why on earth did the caps not all discharge at once? It doesn't make any sense what so ever! They are obviously set up alright as they all charged so what the hell's going on?!?

[ProdigyChild]

Strange behaviour, really. If you're using alligator clamps, make sure, they work. Half of my alligator clamps are sh1t - the innocent guy who made them focussed on mechanical properties rather than electrical ones and the cooper wire inside the cable touches the clamp only by accident :mad:

If it's not the clamp, then things become difficult to explain.

One possibility could be, that the power supply exceeds the input voltage AND your transformer has a overvoltage protection, that switches of in that case. If you switch off the transformer, the voltage of the input capacitor drops into operation voltage and the thing charges with some remaining energy of the input cap.

Or (one of) your caps is over-driven, resulting in an inner temporary short circuit and voltage drop. Known as self-healing. When you switched the transformer off, it accidentally charged the cap just below its maximum voltage.

All plain theory of course and quite unlikely to happen.
Try to debug step by step. Don't make any assumptions about your devices that you haven't proved, even if proving them seems to be stupid (alligator clamp example).

[Centimeter]

Well, I looked though it and found that I haden't wired the caps properly. I rewired it and got the thing working and man am I happy. It makes such a loud report! My hearing goes completely blank for a few seconds...of course I am doing this all in my narrow hallway. Probably wouldn't be so loud if it were outside. Anyhow, I am bipassing the exploding wire entirely because the spark gap produces a more than satisfactory report. I placed a piece of paper folded 4 times over inbetween the spak gap and it blew a centimeter wide hole through it!

Off of a wall outlet, the thing takes around 15-20 seconds to trigger the gap. Is it even worth trying to put a hand crank generator on it? Also, I can't find any decent flywheal hand crank generators on the net. They are all just these dumb children's chemistry things or cell phone chargers. Dose anybody know if the cell phone chargers have flywheals on them? I might just buy a hand crank radio and salvage the generator from there. I have been looking through my EE books and I can't find any sort of circuit that would stabilize the voltage out of the hand crank generator. Will it matter all that much if the transformer is given varying voltages? Also, I tried using a voltmeter on the input side of the transforer to see if there was any indication of the caps charging up. I did not observe anything.

Thanks guys for all your help! If anybody wants I can try to post a movie of the thing in action. My video camera doesn't record the report all that well but you would get the idea.

[ProdigyChild]

Yes, make a short video (I have low bandwidth). I'm interested in it. But please include a centimeter mark so we can get an idea of how big that tay is.

It confuses me a bit, that the arc produced as much sound as the bridgewire. In my experiments, bridgewires are always MUCH louder.
Try some different length perhaps to maximize percussion. Just for the fun, long wires are better sometimes. And Aluminium ones are better (for the show) as copper ones). But still keep them extremely thin.

I've posted a few photos of my experiments yesterday (EBW thread). Long term exposures with a digicam. Looks cool, too ;)

[powdermunkey]

Centimeter- if you hook all the caps in parallel, they will make a dandy EBW driver. At the lower voltage this will yield, you will probably have better results with a triggered spark gap switch, although I realize this violates the artistic principle of surprise. A couple of 1/2 inch copper pipe caps with a piezoelectric cigarette lighter makes a good triggered gap. Google around for "triggered spark gap" to get the idea of how this works.

[Centimeter]

Using the EBW is about as loud, however it produces a much more impresive visual effect. The only problem with the EBW is that I would have to replace it every time the thing is used. It is much better to have it just be the spark gap as it can continuously be used by people in a gallery. I will try to post a video, however it will take a while because I must order some software. The thing is sort of predictable because it starts to buzz quite a bit before it triggers. Perhaps it could be said that it just adds to the tension and results in a more startling experience. I am going to drop by the mall tomorow and pick up a hand crank radio. I'll check back with the results.

[Centimeter]

I am going to purchase this military generator; http://www.armyradio.com/arsc/customer/product.php?productid=1533&cat=86&page=1
It will geneate about 7.5 Watts. In order to attach it to the tranformer I need to also buy an inverter. Most inverters have an input of 12VDC so I will probably step down the voltage. Will this work and about how long would it take to charge the capacitor bank up?

Edit- OMG!!! I just checked out the HV caps on ebay and look what I found... http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4662&item=3850312181&rd=1
That's 2 150uf 6kV energy discharge caps. That's 5400 Jules!!!!!! To think that mine is a paltry 24.3 Jules. I can't even imagine how fantastic an EBW those things could make. Think of the lasers! You could almost crunch a refrigerator with those!

[Centimeter]

In order to make the transformer work, I must have a generator that puts out AC, thus I must have an alternator. There are no alternators on the market suitable for hand cranking so I am going to make one. I purchased 30 NdFB magnets and a spool of 32# wire. So far I have wound 12 400 turn coils and I am going to assemble the rest this week (hopefully). All I need to do is set the coils in resin and then make the two magnet panels. In case you haven't guessed already, I am making a single phase co-axial alternator. I expect it to put out ~60VAC at 120RPM. The transformer says that its input is 115VAC 60Hz. My alternator will not put out 60Hz...is this a problem? If it is, how can I go about making it 60Hz? Considering that it is not going to put out 115VAC, I need to step the voltage up. Such a unique output will most likely require me to make the transformer. Anyhow, that's what I have been doing up until now. I will be back with another update once the alternator is finished.

[Boomer]

Why not use one from a bike light? They are AC, they are small, and even at only 3 VA and 50% charger efficiency, it will take under 20 seconds to charge your cap to 20J.

Or what about using the DC generator to power either a CCFL driver or a flash unit with voltage doubler? Or one of the 12V -> 115/230V converters for camping (car adapter) between generator and HV transformer?

Why do you want a hand-crank system BTW? It is much bulkier than a battery, and more suspicious.

[Centimeter]

Well...the purpose of this device is not for detonating explosives. It is for an art project in which the viewer puts their energy into the eventual discharge. Hence the alternator. After discharging the caps outside, I realised that they aren't all that loud after all. After further contemplation, I think that capacitance is more important than voltage when it comes to making loud sounds. After all, the average static spark one experiences from touching a light switch is probably around the same voltage as my caps, yet it is no where near as loud. Thus I purchased a 6000uFD/250v electrolytic capacitor from Amazing1.com This should store just about 120joules when charged to 200v. 120J vs 2.43J...I assume this will be MUCH louder. Furthermore, the 120J is being discharged in a much smaller area do to the lower voltage. If it doesn't work, I could always just use it in a coil or rail gun. :D Imagine, the 2.43J cap bank cost me over 100USD where as this 120J cap cost me 35USD. :rolleyes:

[Anthony]

How are you going to make 200V jump across a spark gap? Or are you going back to the idea of an exploding bridge-wire?

[grammarless]

I have a 600 Joule electolyte capacitor bank and the discharges are pretty ridicoulous. Steel wool explodes in a shower of sparks, but when the discharges are compared to my 44 Joule 1000volt capacitor they are louder but longer. The electolyte discharges go boom but the higher voltage capacitor makes a nice pop. I doubt the electolyte will make a good EBW because slow rise times, but it will make an excellent noise maker.