New Coil Just Blew Cap
Subject: New Coil Just Blew Cap
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Thu, 5 Oct 1995 04:30:00 GMT
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Quoting msr7-at-po.cwru.edu (Mark S. Rzeszotarski, Ph.D.):
> Greetings Coilers,
> I finally got my first coil (4 inch diameter, #24 wire 4.5:1
> height/width ratio) put together and it works well using a 2kV
> microwave transformer.
Good Job! There is nothing better than the "First Spark".
> I hooked up my 15kV neon sign transformer and managed to blow
> my capacitors (lossy barium titanate doorknobs) with a
> simple twist of the variac control.
Ha! You paid your first dues! I have harped, and harped, and
harped, ad nauseaum, about the problems with these caps in Tesla
Tank circuit applications. The dielectric losses are very high.
These losses are imparted as heat. The capacitor design is not
equipped to dissipate heat, warm to the touch on the outside of
the cap translates to melting temps on the dielectric... The cap
> Now I will look seriously into building some caps myself.
Build or buy, good capacitance is an investment.
> It is amazing how much heat is lost in these capacitors (before
> they fail!).
Not when you consider the RF dissipation factors... another thing
I harp... and harp... and harp about....
> I also want to mention that I, too, stumbled across a supply of
> used Powerstat variacs here in Northeastern Ohio, U.S.A. The
> company has a few 22 amp 120 volt (about $65) and several 28
> amp 240 volt (about $125) models. The above prices are
> approximate, and are negotiable. E-mail me privately if you
> are interested, and I will put you in touch with the company.
Who would pay to ship? These prices are OK, but not excellent on
the surplus market, if you figure shipping costs. The 22 amp 120
volt variacs are $15.00 over "excellent" prices and the 240
volters are $25.00 over "excellent" prices. These suckers are
powdered iron and copper wire and end up difficult to move
(figure and literal) in a normal retail market. We are one of the
few groups interested in these components.
> Now on to my question:
> I wound a spiral primary which is tilted 30 degrees, rising up
> from the base in the form of a saucer so that the outermost
> turn is the most elevated. The coil looks something like
OK, pretty good ASCII art depeciting a "bowl" or "saucer" shaped
> It is wound on flat plastic supports in a star pattern using
> soft copper tubing. Does anyone have a formula for estimating
> the inductance of a coil of this form? The flat pancake coil
> formula overestimates the inductance by about 1/3, based on
> experimental data.
Yeah, calculate the values for a straight vertical helix and the
flat pancake. Add the two values together and divide the answer
by two. The results will put you in the ballpark.
... If all else fails... Throw another megavolt across it!
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