Inductive Kick Effects - was- Re: cap firing voltage scope measurements question (tests)
Subject: Inductive Kick Effects - was- Re: cap firing voltage scope measurements question (tests)
From: Terry Fritz <twftesla-at-uswest-dot-net>
Date: Fri, 18 Jun 1999 19:05:30 -0600
Hi John, Malcolm, Richie, All,
Well, I finally get it too! Richie sent me an excellent model that made
the effect simple enough for me to understand too :-)) Basically, the gap
switching is changing the system from a resonant charging circuit to more
of an inductive kick charging circuit. It is storing energy in the
inductor and then the switching action allows a sudden high voltage kick
right after the gap opens that charges the cap up to a higher voltage than
the circuit would normally produce. This works much like those power
supply ICs that switch current across an inductor to get -15 volts from +5
The real key is the energy that is stored in the inductor when that gap
fires. I made this table of stored energy in my new LTR coil just before
the gap fires.
Neon Primary 24.95 J
Neon Secondary 23.75 J
Filter Caps 0.2 J
Primary Cap 5.97 J
Primary Inductor 0.0J
Obviously, the neon transformer is storing an overwhelming amount of
energy. At only 80 mA across each of it's giant 3700H inductances, a
secondary winding stores 1/2 x L x I^2 = 11.84 Joules per side!! I never
considered this before. The computer programs just crunched this factor
with everything else but I was oblivious to this giant energy being stored.
The neon is acting much like a current source do to the giant inductance
and will push current into the cap as it pleases causing the cap voltage to
skyrocket!! It is possible to get up to 100+ kV if one really tries! Of
course, the smaller the primary cap, the more voltage the inductor will
push it to...
This is apparently the mechanism behind the LTR coil's ability to charge
larger cap values than one would normally expect. I knew from computer
simulations that the effect was there but I never really understood why
Consider this; If a cap were charged continuously at a rate of 60mA, what
value cap could one charge if the end voltage were 21.2kV? V = 1/C x I x T
so 20000 = 1/C x 0.06 x 1/120. C=23.6nF which is just what an LTR coil
with a 60mA neon likes to run! Perhaps this is a governing equation for
LTR coils given and available RMS current level? Perhaps this can be used
to very easily calculate what size cap a give power transformer will
I was hoping this would also explain why some filter resistors like to get
super hot while others stay cooler depending on yet unknown things.
However, I don't see how this would explain this mystery... The filter
resistor's values may be more important in such a circuit than I originally
thought. Their resistance keeps the transformer from seeing a dead short
when the gap fires, thus possibly saving the stored inductive energy from
being lost to the gap... Have to think more on that...
Many thanks to Richie for helping me to see all this!! This whole LTR
things just became much more clear but now has added factors to consider...
At 09:50 AM 6/18/99 -0400, you wrote:
>Terry, Malcolm, Richie, all,
>I found my voltage breakdown table, and after interpolating for my
>voltage, etc., the table shows very good agreement with my scope.
>Just a further verification of the voltages I'm seeing. It seems from
>your comments, that the 2X rise is not un-expected. It looks like what
>I had heard in the past was wrong. Well, the Tesla coiling world is
>full of myths anyway, looks like I got caught in one this time. I'll be
>doing some more work with the set up.