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Re: [TCML] Spark dynamics on Jacobs Ladder
uh.. I do speak german, but I'll have to work on it. it's really tough to
hear what the dude is saying.
mainly what I got was his count-down to start the thing ;-)
from the posts: (lame cheezy fast translation)
(mvogt) (6 mos ago)
to understand: the wheel cant be closed, it has to have a gap in it so
that the electricity flows in a single direction otherwise it would just
stick
in the middle
then under that one:
mvogt:
(blah blah I studied there too TU in Darmstadt)
he's saying that somebody explained the thing incorrectly in class
that it was magnetism that caused it to move, but Alas! they were wrong
it's the lorenz force
-------------------------
also, I am fairly certain that Gleichsspannung = DC, so this thing is 3kV
500A DC
gleich = same, spannung = voltage
paul
----- Original Message -----
From: "Bert Hickman" <bert.hickman@xxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Friday, January 18, 2008 11:46 AM
Subject: Re: [TCML] Spark dynamics on Jacobs Ladder
Lau, Gary wrote:
I hope this isn't viewed as too off-topic - I'll argue that the same
physics apply to TC sparks ;-)
I was giving a demonstration of various HV toys to a 4th grade class
yesterday. Among the devices was a Jacobs ladder, powered by a 15/30
NST. The two 1/8" x 3 ft steel electrodes appeared to have been
excited into a mechanical oscillation, bouncing towards and away from
each other, at very roughly ~ 1Hz. One of the students asked my why
they were moving, and I had to admit that I didn't know the source of
the force that was moving them.
The period of the oscillation was much faster than the arc travel
time up the electrodes. It's clear that the period was that of the
free-standing rods, and that the exciting force between them varies
as a function of their separation, but I don't see the source of the
attraction or repulsion between them. Any theories?
Thanks, Gary Lau MA, USA _______________________________________________
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Hi Gary,
I've seen this on ladders where the lower part of the ladder is
mechanically fixed but the top portion of the electrodes are free to move.
I suspect that it's due to electrostatic attraction between the
electrodes. The attractive force becomes particularly strong during the
brief interval between one arc extinguishing at the top and the next one
restriking at the base of the ladder. The short time lag causes a brief
impulse of electrostatic force that can shock excite any mechanical
resonances of the electrodes. There may also be secondary effects due to
increasing electrostatic attraction as the arc climbs the ladder, since
the increasing positive column length causes a larger voltage drop across
the arc and increasing E-field between the electrodes. However, since the
open circuit voltage is considerably higher than the arc voltage drop, the
largest attractive force undoubtedly occurs during the brief interval
between quenching and reignition.
BTW, I have encountered some folks who think that one reason why the arc
rises in a Jacob's Ladder is due to Lorentz forces. Because of the
relatively short circuit current, I suspect that NST and even ballasted
pig arcs rise primarily via thermal effects. This is NOT the case for high
current arcs, such as phase-phase arcs on power lines. One very
interesting video clip shows a circular Jacob's Ladder created by a higher
current (3 kV, 500A) arc. The circular loop has a gap to prevent the arc
from "hanging" half way around. Any German speaking folks who can
translate the speech on the video?
http://www.youtube.com/watch?v=6hGiAIRcn98
Bert
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