hot, bright noisy sparks needed

Turn NPN/MOS-FET on.

When current in coil reaches 5A, turn NPN/MOS-FET off.

(So, besides a timer, you will need a current sensor for this to work properly... in my case I designed a custom ASIC for the task ;-)

Repeat at spark rate desired, no closer together than 3ms between sparks.

Voltage on cap will reach about 300V each cycle.

The NPN/MOS-FET is operated as a switch, so worst-case dissipation is

5A*VSAT/2 at max spark rate. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
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I love to cook with wine.     Sometimes I even put it in the food.

On the contrary, it offers the opportunity of even greater creativity to the O.P. He can find another way to achieve his ultimate goal of amazing/ entertaining/ people without doing anything with such a high risk (almost a guarantee) of fatality.

If you want something to start you thinking about alternatives, here are three examples:

1) For theatrical 'short circuits' I used a trembler-bell type of apparatus with a low-voltage carbon arc run from a small welder. A magnetic pickup on the welder choke fed sound into the theatre's P.A. system. The arc was inside a strong metal housing and was not directly visible, the light was reflected off crumpled aluminium foil. The power never exceeded 80v or 20A, but the crackling and buzzing noises were enough to convince the audience that something really powerful and devastating was taking place. 2) On another occasion I arranged a 'magic' sword fight between two marionettes. They stood on pieces of aluminium foil on a sheet of plate glass, wires from the soles of their feet led to their sword arms. The aluminium sheets were supplied with about 15kV from an old television EHT generator, allowing spectacular sparks to be drawn whenver the swords clashed. The current was limited to less than 1mA. and the operators were insulated from the supply by the puppet strings.

The power supply was fitted with a Yale-key-operated switch and the only key was held by a technically-qualified operator . In addition, a push button with a strong spring had to be held down to energise the generator; the operator had a good view of all the procedings. This was in the 1960s, long before the draconian Health & Safety laws were passed, but we took every precaution to ensure reasonable safety whilst still giving a spectacular show.

3) Quite recently I had to produce a portable 'spark transmitter' for a play about the First World War. The electrode balls were joined by a transparent tube which contained white and blue L.E.D.s. Each time the Morse key was pressed, an old contactor wired as a trembler made a raucous rattling buzz against a thin wooden panel. Simultanelusly a capacitor discharged into the white leds and the blue leds were illuminated in the usual way. By carfully scratching the inside of the tube, the light was diffused and appeared, from a distance, to be an electric arc. The whole thing was powered from a 9V battery.

I would strongly advise the O.P. against getting anywhere near high voltages with a current capability (either continuous or instantaneous) of more than 1mA. There are other way of achieving the required effects which do not pose this near-certain risk of instantaneous death.

--
~ Adrian Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
www.poppyrecords.co.uk

There's real reason. All the devices I've used to date to generate the requ ired spark also put out a tremendous amount of interference. I learned the hard way that the spark generator could not be anywhere near the processors that control the device, no matter how much shielding I tried to add. The field generated immediately knocks the processors for a loop, and while the way the circuit is designed, that immediately shuts down the spark, I deci ded I didn't even want a possible risk of the circuit somehow locking up wi th the spark stuck on. So the spark generator stays a few feet away from th e rest of the device, and since I don't want a HV source exposed, that mean s a backpack, several layers of shielding, special venting so the battery g asses never meet the HV source, etc. Yes, that gave me the problem of const ructing a cable that could safely carry voltage, but I have a working desig n for that and I've used it without incident quite a number of times.

he issue I'm having, and would like help on, is that I've been unable to fi nd any resource online that will teach me how to reliably generate 25-30kV at very low ma and 40Hz and aren't so affected by capacitance. I have faile d solutions, like the ZVS oscillator, which do not work. I need something t hat does. I do not want to use a taser because they are designed to generat e a lower frequency which is deliberately disruptive to the human body - it 's not just voltage that matters - and if someone DOES manage to squeeze hi s finger into the arc I would rather he got a skin burn and a painful but f orgettable lesson, than have him incapacitated on the floor in front of doz ens of people, and planning a lawsuit.

Please let's assume that I want to live and am going to continue to take ex cessive precautions to insure that I do. I take responsibility for my own s afety.

As to the legality of the RF output - folk, this device is used at Steampun k conventions. It does put out RF, but you'd be hard pressed to find it amo ng the Jacob ladders and suchlike toys that are staples at these events. Mi ne is at least somewhat shielded. I won't be the FCC's first interviewee.

I'm all in favor of HV, very low mA designs. It doesn't take many mA to generate a bright spark, so if you can give me a circuit diagram of a design that generates exactly this, I'm all ears.

Since it's only an art project, you can consider simulating an arc by break ing it down into the sound and visual components: an audio generated spark sound synchronized with some sort of flash tube. This would have the potent ial of creating a more intense effect than anything you could do safely usi ng a real spark.

You don't seem to have much clue how few mA it takes to kill at these voltages. There are no safe bright noisy large sparks except perhaps chemical ones and they are not safe but at least they won't kill you.

--
Regards, 
Martin Brown

aking it down into the sound and visual components: an audio generated spar k sound synchronized with some sort of flash tube. This would have the pote ntial of creating a more intense effect than anything you could do safely u sing a real spark.

Yep. Or, low-current r.f. high voltage. That way you only fry your skin (and corneas). Use the spark current to generate an audio signal, and an audio amplifier to pump out the sound.

Cheers, James Arthur

Adrian Tuddenham: Your descriptions showed some creativity, but Scott M's does not. I hope he doesn't nominate himself for the Darwin prize.

Thank you all for your suggestions. I'll look into coaxial cable with thick silicone insulation; that seems like a practical solution and might be all I need. If not, I'll do the research necessary to create a voltage source with the frequency, voltage and current characteristics I need.

That was my fear. I hope he treats our warnings seriously and does not continue with his present course of action.

I have seen animals electrocuted with voltages and currents lower than he proposes using and it is the kind of sight which haunts you for the rest of your life.

--
~ Adrian Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
www.poppyrecords.co.uk

ck silicone insulation; that seems like a practical solution and might be a ll I need. If not, I'll do the research necessary to create a voltage sourc e with the frequency, voltage and current characteristics I need.

--- Where are you going to get coax with insulation rated for that kind of voltage? Normal coax might do 600V and would most definately have breakthroughs at the kind of voltage you're talking about. In addition the outside insulation of most commonly available coax would not be safe. If whichever side of the flyback coil you hook the center conductor to has a breakthrough to ground somehow, then handling the outside of the coax becomes a death trap. There is no learning curve on this.

RG-8 is rated at 20,000 volts.

Dan

Would you like to buy a good used bridge?

Dan

Hello Dan, that 20kV may be true for a DC test to destruction, but when you apply AC high voltage, the smallest air void in the insulation, or clearance between metal and insulation, will lead to partial discharge.

At 50/60 Hz the cable may survive for some days or weeks, however when you apply 200 khz or more (as that is safer for the human heart), the insulation may very likely break down within seconds or minutes.

--
Wim 
PA3DJS 
www.tetech.nl 
Please remove abc first in case of PM

RG-8 is surprisingly robust. My experience is that is lasts a lot longer t han you think it will. Good RG-8 will not have any air voids in the poly. At 200 khz , ] would be concerned that the voltage would be higher at some places because of standing waves. And I would certainly not use it for hig h voltages where failure is life threatening.

Dan

Some of it is, provided the connectors support that as well. Generally i see 1500 V as well 4500 V & 5000 V. Generally 2000 V and above requires special insulation, termination and splicing techniques.

?-)

dca > RG-8 is rated at 20,000 volts. G > Would you like to buy a good used bridge?

"RG-8 is rated at 5 kV RMS, however..." That's from YOUR OWN reference! It doesn't mention deformation from age. It does warn against foam insulated varieties. It also warns about pinholes. The part about grounding is interesting since the OP apparently intends to run this out to the extremities of somebody's body, probably in close contact. Arcs inside the cable could easily disintegrate shielding. If somebody dies from this it had better be the creator themself and not some victim of the creator's depraved indifference. High Voltage Wire and Cable

There are two issues which need attention with high voltage wiring. The fir st is the level of insulation necessary to prevent arcs to adjacent compone nts or wiring. The second is the diameter (or effective diameter) necessary to reduce corona losses. Reduction of corona is important because a common failure mode for insulation is the formation of small defects (i.e. pinhol es) in the insulation due to corona discharges within the insulation.

With bare conductors, air is the insulator, and clearance distances can be calcuated using standard values for the breakdown of air. A common rule of thumb which is very conservative is 1 inch per 10 kV. Since the breakdown f ield for air is around 71 kV/inch, this provides a 7:1 safety factor.

Popular insulation materials for hookup type wire are polyethylene, PTFE, r ubber, and silicone, particularly the latter. Neon signs are a cost sensiti ve application, so inexpensive wire ($.15/ft) rated at 15 kV with polyethyl ene insulation is widely available. Rubber is popular for test leads at the 5 kV level, although many rubbers degrade in the presence of ozone, which is often present in HV equipment. High quality high voltage wire has silico ne insulation which is quite flexible and high temperature resistant.Typica l prices for silicone insulated wire range from $.20/ft for 10kV rated to $

2.00/ft for 50 kV rated.

Corona resistant wire is typically constructed with a central copper core s urrounded by a semiconducting sheath, which in turn is surrounded by the in sulation. The semiconducting sheath effectively increases the diameter of t he wire, reducing the tendency for corona discharge. Suppliers of such wire include Belden, Caton, Tally, etc.

Coaxial cable of the RG-8 (RG-213) family is often used as high voltage cab ling for several tens of kV. Grounding the outer shield makes the field dis tribution inside the cable very even, reducing the field concentrations tha t start corona. RG-8 is rated at 5 kV RMS, however, the polyethylene insula tion is (.285-.01??) .120 inches thick which corresponds to 120 kV breakdow n. I suspect that the 5kV rating (7 kV pk) allows for a substantial VSWR in transmission line use without breakdown. Certainly, many systems use RG-8 at 25 kV, and I have seen some at 50 kV using RG-8 as a conductor. Also, th e field strength at the inner conductor is higher than that at the outer co nductor

Equation here.

Having the outer surface of the cable at ground potential also confers some safety advantages. Don't forget though, that in systems with sufficient st ored energy, the coax can literally explode in the event of a dielectric fa ilure. If you have several tens of kJoules stored up, the energy has to go somewhere. At least you won't get shocked, just burned.

Coaxial cable using foamed dielectrics (e.g. RG-8X) are not useful, since t he nitrogen used to make the foam has a much lower breakdown than the PE. T he same goes for RG-59 cable TV remnants, because they are usually foamed i nsulation (cheaper and lower loss).

Coaxial cable also has the advantage of low series impedance in pulsed circ uits, as does other types of transmission lines such as twinlead and quadro line.

The so-called UHF connector (SO-279, PL-259) can be modified as a high volt age connector for use with RG-8 family coax by drilling out the center and extending the center conductor (of the plug) into a tube with a banana jack at the end. The jack can be modified by mounting the threaded outer housin g (drilled out) on a block of insulator (acrylic, G10 glass epoxy).

Photo here

Another ubiquitous source of high voltage hookup wire is spark plug cable f or automotive use. The more common variety has a resistive core (used to sl ow the rise time reducing EMI) of a few kOhms per foot. A less common varie ty, called solid core or copper core, the conductor is normal wire. Spark p lug cable typically has a very rugged silicone or hypalon jacket, as well a s a fibrous armor layer. Spark plug cable costs about $1/ft

Copyright 1997, Jim Lux/ hvwire.htm / Back to High Voltage Main Page / Bac k to home page / Mail to Jim ( snipped-for-privacy@earthlink.net)

200Khz standing wave,RG8,20 pounds: impossible.

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For a good time: install ntp 

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