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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