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Re: Colorado Notes and laser caps
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> From: Tesla List <tesla-at-poodle.pupman-dot-com>
> To: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: laser caps
> Date: Friday, February 07, 1997 2:25 AM
>
> Subscriber: gweaver-at-earthlink-dot-net Fri Feb 7 00:17:33 1997
> Date: Thu, 06 Feb 1997 08:39:52 -0800
> From: Gary Weaver <gweaver-at-earthlink-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: laser caps
>
> see attachment
>
> [ Part 2: "Attached Text" ]
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> Today at the scrap yard I found what I think is a power supply for some
type of laser. The tag said Laser Products, Mesa, Arizona. The power
supply has 28 door knob type capacitors. They are mounted in 2 groups of
14 caps each in parallel. Each group is mounted side by side and the ends
of the caps all have a single spark gap on the end connecting each cap of
one group to the matching cap of the other group. It has 14 spark gaps.
The caps and gaps are mounted inside a 1/2" plastic case with 4 fans on the
side of the case for air flow. All 4 fans are 4" box fans also sometimes
called muffin fans. The case also has a small freon type cooling system
built inside. On top of the case is a high voltage transformer, some type
of amplifier device, another control box, a 40,000. volt .06 uf plastic
cap, several high wattage resistors, a choke coil, a high voltage ignition
coil device simular to a car ignition coil large orange plastic, gas flow
control valves and guages and lots of other items. The thing weive never
seen anything like it and I have never thought of making such a device. I
have not given it any thought yet but it may be useful in TC applications.
Enclosed is a circuit drawing.
>
> Gary Weaver
> [Part 3, Image/GIF 7.7KB]
> [Unable to print this part]
Gary,
The 14 spark gaps may indicate that the caps are wired in what is sometimes
called a Marx configuration. Are there any coils connecting the caps? If
there are, then what you have is a form of high voltage Multiplier circuit.
Many people are familiar with the Marx multiplier circuits that use
capacitors and rectifiers. Well, there is a form of the Marx multiplier
that uses coils and capacitors. The way it works is this: The capacitors
are initially connected in parallel with one another via the
inter-connecting coils. (the coils can be just a couple of turns of wire...
it doesn't take much!). When the capacitors reach a certain critical
voltage at least one of the spark gaps conducts. What happens then is very
interesting. ALL the spark gaps will fire simultaneously and the currents
will cause the coils to build up a very high opposition to this current
spike. The result is that for a fraction of a second the capacitors that
had been in parallel now ACT like they are in series. Since the voltage
drop of the spark gaps is LOW when they are conducting, this results in a
VERY HIGH output voltage pulse.
Now, before everybody starts thinking "Off the Topic, what has this got to
do with Tesla Coils?" let me say that in 1964 I saw a very large Tesla coil
that was part of a traveling science show. The coil threw about six foot
sparks, which was quite good for a Tesla coil in those days. After the show
I pestered the people responsible for the show until they reluctantly let
me look at the thing up close. Inside a big metal box was a bunch of coils
and capacitors. When I asked the guy what all that was about, he explained
to me that it was a coil-capacitor Marx multiplier used to step up their
couple of KV main transformer voltage up to 30KV. I should mention that
another thing that made this Tesla coil somewhat unconventional was the
fact that the resonating capacitor was connected directly in parallel with
the primary of the Tesla coil. The Marx multiplier would dump a nice big
bunch of energy into the L/C primary circuit, and then the primary would
happily ring away until it was hit again by the next dump of energy. Note
that this strange Tesla coil was a pulse-driven design with no topload
other than a flat copper plate on the top. And *that* was there so that the
performer could stand on top of the coil and throw sparks off of metal
electrodes on his hands. If these guys had bothered to put a toroid on this
baby, it probably could have done much better. Also, this was the *only*
Tesla coil that I had ever encountered that had a capacitor connected
directly in parallel with the primary. When I got home I pulled out my most
prized possession, a book published in 1956 on the occassion of the 100th
aniversay of Tesla's birth by the Nikola Tesla Museum in Beograd,
Yugoslavia. This book is a huge compendium of Tesla's lectures, patents and
articles, entitled "Nikola Tesla * Lectures * Patents * Articles" that
comprises about 600 pages of material written by Nikola Tesla. It is not a
book about Tesla, but rather ALL of it is material written BY Tesla.
Excellent stuff! Anyway, at the absolute end of this huge book is a
photograph of a page from Tesla's Colorado Springs notebook. And there is a
hand drawing by Tesla of a Tesla coil circuit in which one capacitor is
used to produce the disruptive discharge, and the other is placed directly
in parallel with the Tesla primary.
I was reminded of this L/C arrangement by a recent remark made by Richard
Hull in one of his postings here on the Tesla list. And then today this
Laser power supply with its multiple spark gap thing reminded me of the
first time I ever saw such a circuit, and how I had thought the designer
must have made some sort of mistake, because their Tesla coil was so
different from all the ones I had information on, only to discover that
Tesla had done the same thing many years earlier.
There is still room for fruitful modern research based on such little
things from the past. We may be tempted to just pass by, look at it with a
shake of our head and say "boy, those guys weren't as smart as us." Some of
them, like Tesla, were even smarter than we think. And that includes those
of us that think he was a genius.