Fun with HV

[Active8]

On Sun, 16 May 2004 02:29:58 GMT, Rich Grise wrote:

"UncleWobbly" <hendy@talk21.com> wrote in message
news:40a6495f$0$4584$db0fefd9@news.zen.co.uk...
Once the air is ionised it will conduct very well, this warm air rises,
and
thus leads to the arcs... until the point where they no longer represent
the
"best" route, either due to a rise in resistance (shutting the arc down)
or
a new arc forming effectively "shorting-out" the more resistive route.

I would imagine the exposure of this photo takes in several of these
"cycles" so we see the rats nest at the top.

This was used as a special in old frankenstein films where the mad
professor's lab had the electrical arcs moving up between two wires that
gradually move apart.

I pray to differ - what you're talking about is a "Jacob's Ladder".

I think yer right. That was the most facinating demo in 7th grade
science. A oil furnace transformer with 2 coat hanger wires secured
to the terminals (yes, it was an old one. These days, the xfmr
swings closed and the contacts, well... make contact - sheesh! not a
profound concept, eh?) Any way, the wire were bend in to 1 cm apart
near the terminals and diverged like TV VHF rabbit ears.

This
is much prettier.

Absolutely!

The stuff that really turns me on is the corona -
Is that just stressed air ionizing?

In any case, it's gorgeous.

An understatement. It's friggin' art!

Thanks!
Rich

--
Best Regards,
Mike

 

[Guy Macon]

Active8 <reply2group@ndbbm.net> says...

Have you rotated and resized/croped it yet. Did it work out?

If anyone has a nice 1024x768 version, I sure would like a copy.
email is engineer [at] guymacon [dot] com...

 

[UncleWobbly]

"Rich Grise" <null@example.net> wrote in message
news:GmApc.203353$L31.169153@nwrddc01.gnilink.net...

"UncleWobbly" <hendy@talk21.com> wrote in message
news:40a6495f$0$4584$db0fefd9@news.zen.co.uk...
Once the air is ionised it will conduct very well, this warm air rises,
and
thus leads to the arcs... until the point where they no longer represent
the
"best" route, either due to a rise in resistance (shutting the arc down)
or
a new arc forming effectively "shorting-out" the more resistive route.

I would imagine the exposure of this photo takes in several of these
"cycles" so we see the rats nest at the top.

This was used as a special in old frankenstein films where the mad
professor's lab had the electrical arcs moving up between two wires that
gradually move apart.

I pray to differ - what you're talking about is a "Jacob's Ladder". This
is much prettier. The stuff that really turns me on is the corona -
Is that just stressed air ionizing?

In any case, it's gorgeous.

Thanks!
Rich

I was attempting to explain why the arc is not in a straight line... the
reason I believe is the same as what makes the arc rise in a JL.

However, thinking about this again, this does not explain why lightning
forks... hmm... random fluctuautions in the electro-chemical "mix" of the
air ????? dunno.

 

[Scott Stephens]

Rich Grise wrote:

"UncleWobbly" <hendy@talk21.com> wrote in message
news:40a6495f$0$4584$db0fefd9@news.zen.co.uk...

Once the air is ionised it will conduct very well, this warm air rises,
and
thus leads to the arcs... until the point where they no longer represent
the
"best" route, either due to a rise in resistance (shutting the arc down)

I pray to differ - what you're talking about is a "Jacob's Ladder". This
is much prettier.

I thought the reason arcs were arcs was because of the Lorentz force
from the magnetic field.

The stuff that really turns me on is the corona -

Is that just stressed air ionizing?

Yes, but there is a difference between the ionization of plasma in an
arc and a corona. Gas ionization, plasma, is nonlinear. Coronas are
diffuse, and as current increases the diffuse discharge pinches into the
narrow discharge of an arc. The ubiquitous plasma-globe is a great
demonstration of how diffuse discharges can pinch into arcs.

--
Scott

**********************************

DIY Piezo-Gyro, PCB Drill Bot & More Soon!

http://home.comcast.net/~scottxs/

**********************************

 

[Winfield Hill]

Kevin McMurtrie wrote...

Winfield Hill wrote:

On Sat, 15 May 2004, Kevin McMurtrie wrote...

Two twisted wires charged with pulsed HV at the threshold of arcing:
http://www.pixelmemory.us/Photos/Nerd/Wire%20Corona/Violet-Corona.jpg

I can't believe that the insulation on this cheap Radio Shack wire
didn't burn through. It was enduring so much ozone and capacitive
losses that it nearly melted during photographing.

Did you take that picture? It's damn spectacular! Please tell us
more about how you took it, some of the photographic details, etc.

Thanks!

I took the photo last night. I've made other attempts at this kind
of thing but the insulation usually burns through in a few seconds.

The HV source is two opposite-phased ignition coils driven by two
parallel NTE2385 MOSFETs. The device started out as a "Jar-Jar-Q"
joke but, with some circuit upgrades, became reliable and useful.
A pair of insulated pots adjust the on-time and off-time of the
pulsing. For this photo, the off-time was at minimum and the on-
time was set to the threshold of arcing across the top.

I kid you not - My small tripod tips over when I take profile
orientation photos. The Art of Electronics and a Nesquik carton
helped hold the camera in place.

Other appearances by this device:
http://www.pixelmemory.us/Photos/Work/Women.com/JarJar-Q/
http://www.pixelmemory.us/Photos/Nerd/Propane/


EXIF details from the original photo:

[snip]

Camera Model Name: Canon EOS DIGITAL REBEL
Shooting Mode: Manual
Tv(Shutter Speed): 83
Av(Aperture Value): 7.1

OK, what does a shutter speed of 83 mean?

Also, what wire size did you use?
How far apart were the exposed ends?

Thanks,
- Win

(email: use hill_at_rowland-dot-org for now)

 

[Wayne Shanks]

Hey Guys

Dielectric breakdown in Air occures when the electric field across the
mean free electron scattering distance is sufficient to allow electrons
to accelerate to ionization energies. One electron is accelerated and
knocks off another electron. In this way you get an avalanche breakdown.
In air at STP the Mean free scattering distance is a about 1 micron.
Air is mostly Nitrogen and it takes about 1eV to liberate an outer
electron. This puts the breakdown field strength of air at 1 million
volts per meter, or 25 kV/inch. All throughout the air there is a small
population of free electrons liberated by cosmic rays, and background
radiation. The random distribution of free charge in air is what allows
the breakdown to start, and also what gives it its distinctive random
path. Note that the random path of a spark has a 1/f, not a white
distribution.

Kevin is using an induction coil to generate the HV, so I suspect that
the output is actually composed of short HV pulses at the rising and
falling edges of the primary waveform. As such, the HV is able to
ionize the air, but no significant current flows before the voltage
drops and the arc is extinguished. Because no significant current
flows, the air is not significantly heated up and a long-lived plasma
channel is not created. In saturable core transformers like those used
in Neon signs, and oil furnaces, the output is not fast pulses, but 60
Hz AC. With 60 Hz HV, significant current can flow in the breakdown to
produce the more flame like arc of the Jacobs Ladder

By the Way Kevin…. Excellent Ignition Coil HV supply. I spent many
years playing with HV and it all started when my uncle gave me a car
ignition coil and a 6V lantern battery. He says with a smile to my dad
(his brother) “you KNOW it can’t kill him” (they worked on cars
together). I must say that your take on this classic circuit is Excellent!

Wayne Shanks



Rich Grise wrote:

"UncleWobbly" <hendy@talk21.com> wrote in message
news:40a6495f$0$4584$db0fefd9@news.zen.co.uk...

Once the air is ionised it will conduct very well, this warm air rises,

and

thus leads to the arcs... until the point where they no longer represent

the

"best" route, either due to a rise in resistance (shutting the arc down)

or

a new arc forming effectively "shorting-out" the more resistive route.

I would imagine the exposure of this photo takes in several of these
"cycles" so we see the rats nest at the top.

This was used as a special in old frankenstein films where the mad
professor's lab had the electrical arcs moving up between two wires that
gradually move apart.


I pray to differ - what you're talking about is a "Jacob's Ladder". This
is much prettier. The stuff that really turns me on is the corona -
Is that just stressed air ionizing?

In any case, it's gorgeous.

Thanks!
Rich

--
"Anyone over 27 years of age that's not married is a menace to society"
Brigham Young

"Dam Right"
Wayne Shanks