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Tesla Coils and more (fwd)
---------- Forwarded message ----------
Date: Sun, 2 Aug 1998 18:05:37 EDT
From: RWB355-at-aol-dot-com
To: Tesla List <tesla-at-pupman-dot-com>, alfred.skrocki.sr-at-juno-dot-com
Subject: Tesla Coils and more
Hi Alfred and all,
Thanks for correcting me about the bug zappers. I never really took one apart,
so my reply to Dave was just a train of thought.
I have been fooling around (without being foolish) with high voltage / high
current for a pretty long time now. I love man-made lightning. I guess itīs
because of my dad (God bless his soul). He was a prof (physics & astronomy) at
U.C. Long Beach. He built his own unique plasma lab, where students could
really work with plasma not just bla bla about it. Everything was self built,
from the plasma chamber to the vacuum pump, filaments and high voltage supply.
The filaments were heated by using two "Minute-Man" starter units rated at 28
volts and 800 Amps for a total of 1600A. The high voltage supply had a rating
of 25kv-at- 100 (one hundred!!) Amps. In fact the faculty had to wire up his lab
seperatly with 3 Phase 440 Volt mains wiring (1MW power capability). Now
thatīs what I call p o w e r!! I have built all types of welders for my own
needs including MIG/MAG, stick & TIG welders with all options included. They
are simply to expensive (esp. TIG units) to buy and as I am unemployed at the
moment this holds true even more so. Besides itīs fun when a home-made device
works and is as good or better than a bought unit (for much less $$$$$).
I have built quite a few small Tesla coils with less than 1.5kW input rating.
However, I plan to build a bigger one next. I want to get 55" to 60" sparks
from this baby and keep the frequency high enough to stay out of danger. I
have a few questions to you coilers out there.
1.) The power supply will look something like this: I will be using 10 units
of furnace burner xformers 15kV-at-20mA (voltage & phase matched) wired in
parallel to get 15kV-at-200mA. I will pull these babies out of their shell and
emerse the whole set in a plexiglas container filled with castor oil. Does
this sound okay? Over here (in Germany) you canīt get hold of neon sign
xformers. The people who sell them are rare and they want big bucks, even for
used ones. The same holds true of pole pigs. You will get strange looks from
power companies when you tell them what you want and what it will be used for.
I though of using MOTīs but I canīt get a hold of enough of the same sort to
make my needed 15kv and I donīt need 700mA of power. The 2.3Kv-at- 700mA seems to
be a common type in german microwave ovens. They pull power like crazy. My
2.3kV-at-700mA unit pulls almost 15A-at-230v under full load (Okay really its
overloaded because it doesnīt limit the current. It does have a thermal fuse,
however). This means if I wire up seven of these xformers to get my 15kV I
would need a 100A slow blow fuse in my primary side. Wow man, I donīt have
6mm2 wiring in my house (other than the wire that comes from the electric
company, itīs 10mm2) Of course I could use a current limiter in the primary,
but who wants unnecessary heating and why use more parts than necessary. The
primary side will be controlled by some sort of non holding (meaning you have
to press & hold the button) fused remote controller. What about x-ray xformers
from x-ray machines or x-ray viewers ? I know x-ray machines are pulsed, so I
would suspect that they probably will burn out after a time if they are
operated continuesly. However, I donīt know how x-ray viewers are constructed.
They probably donīt have a high amperage output, but they should provide
35-40kV at least. Or is this too much, so that you have corona problems on the
primary side of the TC ?
Circuit description of my planned Tesla coil:
2a.) The mains enter the circuit via a switch, fuses and a power "on" light
and have a hefty varisistor connected across them. The next step is the remote
control box. Across the mains and in series there will be a voltmeter and
ampmeter (respectivly) A simple non holding relay with big amp capacity from a
high frequency generator for a DC TIG tourch. (300A capable) will switch the
current to the HV xformer. The coil is 24 volt AC and will be activated by a
separate small xformer.
2b.) Next the mains will pass through an over dimensional RF filter consisting
of two caps connected in series across the mains and their center-tap
grounded. The center tap (the iron core) of the HV xformers will also be
grounded. The next step are two chokes in each leg of the mains wound on
ferrit toroids. Behind the chokes there is a second set of caps connected in
the same way the first are. Now we enter the set of HV xformers.
2c.) On the high voltage side I want to set up a safety spark gap using 3 ball
bearings (dia. 3/4") with the middle one grounded to an RF (real earth stuff)
ground. Is this okay ? I would rather use this setup than a set of RF-
supressing "safety caps" like they are on the primary side of the HV xformer
in my circuit. Who knows if the caps will stand up to a real backward blow
from the tank circuit!!
2d.) Moving on to the primary coil of the Tesla circuit: The next step will be
two chokes (short, thick wire on ferrit toroids). These will be connected to
the spark gap which lies parallel to the hv xformer. Please read note 5.
2e.) My caps goes in series (see note 5) with secondary of the HV xformer and
the primary of the Tesla coil. The caps have a safety spark connected parallel
to them. Or does this pose a danger in case of a kickback ? In effect the
capacitor is no longer present in the circuit, should the safety gap fire (for
the time of the arc at least).
3.) Can I use a plexiglas tube as a capacitor carrier ? The capacitor will be
self made and the plexiglas tube will contain caster oil, too. This way I can
keep up on the insides and also be able to show the capacitor. Both caps of
the tube will contain small holes plugged with a rubber "skin" as a safety
valve, that can rupture if necessary. Somewhat like a "real" capacitor safety
valve.
4.) What kind of spark gap should I use. Rotary or stationary? I have never
used (needed) a rotary spark, but I do have a lathe and it should not be a
problem to design one. If I used a stationary spark gap it would be a multi-
gap (4 gaps in series) to distribute the load and get richer harmonics. As
electrodes I would use 3/16" thorium free tungsten TIG electrodes. The rotary
gap would contain a synchron motor and tungsten electrodes. It would also
contain a fan to de-ionize the air and carry off the heat.
5.) Corresponding to 2d & 2e I have a question about the tank circuit. I have
seen numerous different configurations. I even saw an oddball with a center-
tapped primary (tc) that is grounded. I couldnīt figure out what this is
supposed to improve. Does anyone know ? They other configurations can be
divided into the following two basic catagories:
a.) Looking from the HV side of the HV xformer: The spark gap is
connected
parallel to the HV xformer and the "tank-caps" are in series with
the xformer
and the primary of the Tesla coil.
b.) Again looking from the HV side of the HV xformer: The capacitor is
now
connected parallel to the HV xformer and the spark gap is in
series with the
xformer and the primary of the Tesla coil.
Does it make any difference (I have always used the "A" version) ? If so, why?
and what would be better for my Tesla coil.
6.) What kind of primary should I use on my Tesla this time. Up to now I have
always used a (single) helical coil. I am thinking of adding a strike rail
(that is RF grounded) between the primary & secondary in order to prevent the
sparks (from the secondary of the TC) from hitting the primary coil. Is this
idea any good ? Does it make a difference where (along the length of the
secondary) the primary is placed. Of course I mean somewhere along the bottom
of the secondary coil.
7.) My RF ground and my ground on the primary side of the HV xformer are not
connected. The secondary has itīs "cold" end connected to the RF ground.
8) What is better on top of a Tesla coil: a sphere or a toroid. I have never
used either because I could not get hold of something good looking AND cheap.
Of course the sparks which my Tesla were making were not the maximum possible
length because the charge "evaporated" before it could reach itīs maximum. So
this time I will use an "extra capacitor" (sphere or toroid). But which is
best? From the physics point of view I canīt imagine how a toroid made from a
dry hose (as a lot of people shown on the internet have) could work all too
well because the surface is not as smooth (because the hose is flexible) as
possible which in turn lets some of the charge leak off.
One last question:
Does anyone have a cool "Danger High Voltage" sign for me (or at least a scan
of it) ? The "Hochspannung !! Lebensgefahr !!" sign from Germany is pretty
boring.
If so and if anyone has any ideas, corrections or improvements for my Tesla
coil please send them to me at:
<A HREF="">RWB355-at-AOL-dot-com</A>
Thanks and keep coiling,
Reinhard