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Re: spark gap
Original poster: "Qndre Qndre" <qndre_encrypt@xxxxxxxxxxx>
Hey, Barton.
If your spark gap operates, electric energy is drawn from the circuit
due to "losses" in the gap. This energy is actually converted into
thermal energy which is then stored in the copper of the electrodes.
You can compare the thermal behavior of the gap with an electrical circuit:
If the electrodes are huge and solid, they act like a capacitor being
charged by electrical current. It's just that it's not charge which
is stored in them but heat. The longer you operate the gap, the
hotter they get. The longer you charge a capacitor, the more charge
is stored in it. If the electrodes get too hot, they vaporize. If a
capacitor is overcharged, dielectric breakdown occures. If you choose
a cap with a large capacitance, it will take longer till dielectric
breaks down but if you continue charging, it WILL break down. If you
use solid copper, it will take longer till the electrodes vaporize
but they WILL vaporize if you continue operating your coil. If you
add a load resistance to your capacitor, it will discharge and
breakdown might never occur. If you make the surface area larger,
more heat will be radiated and the gap might never vaporize no matter
how long it is run.
Regards, Q.
----Original Message Follows----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: spark gap
Date: Sat, 21 Jan 2006 06:22:30 -0700
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Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
Hi Jim,
Surface area is certainly important for cooling, but mass is also a
major factor. A tube has little mass and as a result, transfers heat
very quickly (heats up quickly, cools quickly). It also has the added
surface area inside the tube for heat dissipation. A solid round
stock will heat much slower and only has the outer surface to
dissipate heat, but, the mass of the object has more "mass" to
transfer within itself. This lowers the overall heat the object will
need to dissipate and will require less cooling on the outer surface.
For our spark gap coils, we can certainly build gaps with tubes or
solid stock and achieve stable running temperatures. In either case,
it's a matter of just enough air to keep the gaps at a stable
temperature, and in both cases, this can be achieved.
BTW, polished brass electrodes are very cool! After I drill and tap
a hole in the end of the solid round brass stock, I simply thread in
a 2" long threaded stock and attach it to a high speed hand drill.
Then place a wad of steel wool in my hand and spin the electrode in
the steel wool. The result is a polished electrode.
Here's a pic. The image is old and the connection terminals have
since been changed, but it does show the electrodes.
http://www.classictesla.com/temp/bba_brass_v2.jpg
The inside (white) tube which the electrodes are mounted to will
slide out of the main gap tube attached to the fan. Thus, another set
of electrodes can easily just be inserted (I ran across some larger
solid brass stock on ebay for cheap and will probably make another
insert). Haven't had the motivation yet to make the electrodes. I
don't have machining tools, so everything I do is always with a vice
and a hand drill. The baffle on the front is just another simple
gizmo which directs airflow across only the electrodes.
Take care,
Bart
Tesla list wrote:
Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
When it comes to heat transfer (which is what you're doing here),
surface area is the thing. The tube has area on both the inside and
the outside through which air can flow to carry the heat away.
Increased mass may keep it cooler for a time, but it's like a big
capacitor, it just delays the inevitable.