Maker Pro
Maker Pro

hot, bright noisy sparks needed

S

Scott M

Jan 1, 1970
0
...But...given the size that "taser" type circuits can be shrunk to (and

the truth that they are pretty much exactly what you are building, no

matter how uncomfortable that makes you), no real reason to run HV along

your arm.

There's real reason. All the devices I've used to date to generate the required spark also put out a tremendous amount of interference. I learned the hard way that the spark generator could not be anywhere near the processorsthat control the device, no matter how much shielding I tried to add. The field generated immediately knocks the processors for a loop, and while theway the circuit is designed, that immediately shuts down the spark, I decided I didn't even want a possible risk of the circuit somehow locking up with the spark stuck on. So the spark generator stays a few feet away from the rest of the device, and since I don't want a HV source exposed, that means a backpack, several layers of shielding, special venting so the battery gasses never meet the HV source, etc. Yes, that gave me the problem of constructing a cable that could safely carry voltage, but I have a working design 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 find 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 failed solutions, like the ZVS oscillator, which do not work. I need something that does. I do not want to use a taser because they are designed to generate 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 his finger into the arc I would rather he got a skin burn and a painful but forgettable lesson, than have him incapacitated on the floor in front of dozens of people, and planning a lawsuit.

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

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

Scott M

Jan 1, 1970
0
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.

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.
 
For an art project, ...

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

Martin Brown

Jan 1, 1970
0
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.

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

Greegor

Jan 1, 1970
0
Adrian Tuddenham: Your descriptions showed
some creativity, but Scott M's does not.
I hope he doesn't nominate himself for the Darwin prize.
 
S

Scott M

Jan 1, 1970
0
Thank you all for your suggestions. I'll look into coaxial cable with thicksilicone insulation; that seems like a practical solution and might be allI need. If not, I'll do the research necessary to create a voltage source with the frequency, voltage and current characteristics I need.
 
A

Adrian Tuddenham

Jan 1, 1970
0
Greegor said:
Adrian Tuddenham: Your descriptions showed
some creativity, but Scott M's does not.
I hope he doesn't nominate himself for the Darwin prize.

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.
 
G

Greegor

Jan 1, 1970
0
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.
---

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.
 
W

Wimpie

Jan 1, 1970
0
El 02-11-13 13:10, [email protected] escribió:
RG-8 is rated at 20,000 volts.

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.
 
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.

RG-8 is surprisingly robust. My experience is that is lasts a lot longer than 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 high voltages where failure is life threatening.

Dan
 
J

josephkk

Jan 1, 1970
0
RG-8 is rated at 20,000 volts.

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.

?-)
 
G

Greegor

Jan 1, 1970
0
dca > RG-8 is rated at 20,000 volts.

G > Would you like to buy a good used bridge?

http://home.earthlink.net/~jimlux/hv/hvwire.htm

"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 first is the level of insulation necessary to prevent arcs to adjacent components or wiring. The second is the diameter (or effective diameter) necessaryto reduce corona losses. Reduction of corona is important because a commonfailure mode for insulation is the formation of small defects (i.e. pinholes) 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 field for air is around 71 kV/inch, this provides a 7:1 safety factor.

Popular insulation materials for hookup type wire are polyethylene, PTFE, rubber, and silicone, particularly the latter. Neon signs are a cost sensitive application, so inexpensive wire ($.15/ft) rated at 15 kV with polyethylene insulation is widely available. Rubber is popular for test leads at the5 kV level, although many rubbers degrade in the presence of ozone, which is often present in HV equipment. High quality high voltage wire has silicone insulation which is quite flexible and high temperature resistant.Typical 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 surrounded by a semiconducting sheath, which in turn is surrounded by the insulation. The semiconducting sheath effectively increases the diameter of the wire, reducing the tendency for corona discharge. Suppliers of such wireinclude Belden, Caton, Tally, etc.

Coaxial cable of the RG-8 (RG-213) family is often used as high voltage cabling for several tens of kV. Grounding the outer shield makes the field distribution inside the cable very even, reducing the field concentrations that start corona. RG-8 is rated at 5 kV RMS, however, the polyethylene insulation is (.285-.01??) .120 inches thick which corresponds to 120 kV breakdown. I suspect that the 5kV rating (7 kV pk) allows for a substantial VSWR intransmission 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, the field strength at the inner conductor is higher than that at the outer conductor

Equation here.

Having the outer surface of the cable at ground potential also confers somesafety advantages. Don't forget though, that in systems with sufficient stored energy, the coax can literally explode in the event of a dielectric failure. 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 the nitrogen used to make the foam has a much lower breakdown than the PE. The same goes for RG-59 cable TV remnants, because they are usually foamed insulation (cheaper and lower loss).

Coaxial cable also has the advantage of low series impedance in pulsed circuits, as does other types of transmission lines such as twinlead and quadroline.

The so-called UHF connector (SO-279, PL-259) can be modified as a high voltage 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 jackat the end. The jack can be modified by mounting the threaded outer housing (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 for automotive use. The more common variety has a resistive core (used to slow the rise time reducing EMI) of a few kOhms per foot. A less common variety, called solid core or copper core, the conductor is normal wire. Spark plug cable typically has a very rugged silicone or hypalon jacket, as well as a fibrous armor layer. Spark plug cable costs about $1/ft

Copyright 1997, Jim Lux/ hvwire.htm / Back to High Voltage Main Page / Back to home page / Mail to Jim ([email protected])
 
J

Jasen Betts

Jan 1, 1970
0
On Sunday, November 3, 2013 4:30:51 PM UTC-5, Wimpie wrote:

RG-8 is surprisingly robust. My experience is that is lasts a lot
longer than 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 high voltages where failure is life
threatening.

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

Greegor

Jan 1, 1970
0
dca > I would certainly not use it for high
dca > voltages where failure is life threatening.

The OP apparently intends to run this coax
along a human body to project power beyond a hand.
 
J

John Devereux

Jan 1, 1970
0
Greegor said:
dca > I would certainly not use it for high
dca > voltages where failure is life threatening.

The OP apparently intends to run this coax
along a human body to project power beyond a hand.

What could possibly go wrong?
 
G

Greegor

Jan 1, 1970
0
dca > I would certainly not use it for high
dca > voltages where failure is life threatening.

G > The OP apparently intends to run this coax
G > along a human body to project power beyond a hand.

JD > What could possibly go wrong? -- John Devereux

< cringe >
 
Top