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Re: Smoking the Neons!
>>From huffman-at-fnal.govWed Oct 23 21:54:00 1996
>Date: Wed, 23 Oct 1996 11:08:49 -0500
>From: huffman <huffman-at-fnal.gov>
>To: tesla-at-pupman-dot-com
>Subject: Re: Smoking the Neons!
>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.
Dave,
I had a look at your schematics and simulation plots. Nice work! I
can verify what you see in the case where you have an L in the
circuit between your transformer output and the spark gap. I have
observed this with a high voltage probe and o-scope on my MTC system
which uses a dry pole pig type transformer, 12000 VRMS and a series
240 mH air core type RF choke in series to the rotary. At the point
the rotary gap closes I saw an enormous lower frequency than the RF
ringdown which had a peak to peak excursion exceeding the secondary
voltage of the transformer by a factor of at least two times! I
figured it was energy stored in the choke ringing back into the
transformer. I'm certain this is not good for my transformer, but so
far it hasn't caused any harm. My MTC system runs so darned well
that I wouldn't be suprised if this 240 mH isn't actually assisting
the operation in some way which I cannot say for sure at this time.
I really haven't had the time to scope this out and analyze it in
detail. I just looked at waveforms the only time I did this test
before, and didn't measure the voltage seen. Presumably this energy from
the choke wastes itself in the transformer secondary as heat and is
pretty much dissipated by the time the gap is quenched. This would
seem to indicate that the chok'es ringing energy _ is not_ being used to help
recharge the system cap after the quench. The choke's inductance
_does_ add directly to the secondary impedance of the transformer and
is therefore reflected back to the primary where it may work with
balancing against the primary series control reactor. It also might
be giving me a 60 Hz series resonant voltage boost that does in fact
help charge the system cap to a higher voltage than the transformer
alone could supply. I put it there only to assure that less system
fundamental RF voltage would get into the transformer secondary. I
still have a transformer, so I guess it is working.
On the deal with the neons, fragile as they are, who knows. Your
plots indicate that an RC is certainly better looking than an LC
protection circuit. Trouble is that an R wastes power. My own
experience is that a large L does not waste neons, but that is
without a bypass cap!
I would like to put a HV probe and o- scope on a neon output with and
without a 500 pF doorknob to ground bypassing the transformer
output, and compare the two waveforms carefully. One might be able
to see evidence of second and higher order harmonics riding on the 60
Hz fundamental with the bypass cap in place. You would probably want
to bypass both sides of the transformer to maintain symmetry although
you are only scoping one side to c.t. ground.
I agree that your spice analysis is probably correct, but I cannot
yet comment on how it actually applies to the real case with a neon.
I hope to do some Malcolm level scoping soon once I'm in the new lab
and have the shop space to conduct these tests. I will gladly share
findings when I have some.
regards,
rwstephens