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Re: Smoking the Neons!

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Robert/All,
Something here doesn't seem right. I remember the discussion stating that
RF going into a neon can cause a 'hot spot' and burnout the winding, but
one would think that an LC would remedy the situation. I did some spice
simulations and got some surprising results. (This may be one of those
theory/actual conflicts.) 
I have included pictures of the results which can also be found at
ftp:\\d0huffman.fnal.gov\ftp
It appears that if a simple RC is placed between the neon and the primary,
very little of the tank oscillation is seen at the terminals of the neon.
If the R is replaced with an L, a large oscillation is seen at the neon
terminals. This lower frequency oscillation could over voltage/current the
neon and seems to be (Roberts comments below) quite destructive. Even a 1H
inductor will not help, it may in fact make this worse since the higher
voltage (now a lower freq.) is there for a longer time.

TeslaLC1.jpg Schematic of LC filter
TeslaLC2.jpg Waveform of input/output
TeslaLC3.jpg Closeup of LC2
TeslaLC4.jpg Inductor=1H
TeslaRC1.jpg Schematic of RC filter
TeslaRC2.jpg Waveform of input/output
TeslaRC3.jpg Closeup of RC2

Can this be right or am I way out of line here?
Dave Huffman
Stick and stones may break my bone, but flames will never hurt me.

snip
> >You also should add series inductors, caps to ground, and safety gaps to
> >ground for reducing RF coupling to the transformers, and to provide a
> >path to ground for any secondary "hits" that may couple into the primary
> >circuit. 
> >
> >Safe coilin' to ya!
> 
> >-- Bert --
> 
> Bert,
> 
> I do not concur with the advice to use RF bypass capacitors to 
> ground from the terminals of a small shunted transformeer such as a 
> neon.  Any capacitor large enough to be a good RF bypass (low 
> reactance) at a few hundred kilohertz will also be so large as to compete
bigtime
> with the system capacitor for the meagre charging power available 
> from the high impedance secondary winding of the transformer..  My
experience
> using merely measly 500 pF doorknobs on a 10kV -at- 23 mA funace transformer
> is a failed transformer in about 45 seconds of operation into nothing
else but 
> the bypass caps! I did this twice, the first time with 500 pF an they 
> second time with only 250 pF.  Both times I heard sizzling inside as they

> failed. This has been discussed on the list before.  It seems that 
> the voltage does not distribute itself evenly along the secondary 
> winding and resonant effects caused by external capacitance loads can 
> cause crest points within the winding space and a hot spot followed 
> by insulation failure.
> 
> rwstephens

[ Note: the pictures will be sent to those who can recieve large image
files. -- Chip]