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RE: performance/tuning question
There are three known (at least that "i" know ;-)) "sweet spots" for cap
size on NST or shunted transformer systems that allow optimal power transfer.
The first is our old friend the "resonant" primary cap size. This tunes
the NST to resonate and effectively remove the current shunts from the
circuit so very high currents and voltage can be drawn from the NST. The
is a rather risky configuration since if the gap does not fire, the voltage
can skyrocket and blow the NST in an instant. The currents can also be
excessive and burn out the NST. This configuration is the one that kills
NSTs like flies...
The next is point about 1.5 times the resonant size (static gap) where the
NST list still able to charge the cap to the full NST rated peak voltage.
This is the "LTR" type coil we often speak of. The trick here is to charge
a large cap to a specified voltage and take advantage of the increased
energy. With a rotary gap, one can really tune the inductive kick effects
and use really large primary caps to get the full VA rating of the
transformer into the coil's primary. Unfortunately, this tuning is a bit
tricky but tunable multi-string MMCs have mostly solved this. My 15/60 LTR
coil uses a 24nF cap and my small 9/30 uses 27nF. The resonant size caps
would be only 10.7nF and 8.84nF. The 27nF cap stores three times the
energy and fires at 120BPS. The 8.84 cap would have to fire at 360BPS for
the same power through put. However, 360BPS does note "ring" well with the
60Hz line voltage so the throughput is worse due to erratic gap firing.
LTR coils were literally born from line frequency timing theory so they are
truly optimal in this respect. LTR coils do not over voltage the NST and
they only over current them a "little" (50%) which NSTs seem to take in
stride. If the spark gap on an LTR sync coil fails, the voltage actually
drops about 30%... It is interesting to note that the sync gap
configuration was "discovered" by computer modeling before the real
hardware was demostrated and "real" testing proved the computer's
prediction. No "seat of the pants" stuff there! :-))
There is a largely unexplored region where the current and power of the NST
are so great that the internal current limiting shunts saturate and no
longer limit the current. Thus, the NST "goes nuclear" and becomes sort of
a little pole pig. Unfortunately, this effect is more important to
"protect against" rather than "exploit" since the little NST will fry very
quickly in this mode.
It is difficult to compare the spark outputs of these different situations
since many of the coils characteristics change in each configuration.
Computer modeling and "my" experience definitely suggests that the sync gap
LTR coils are the most reliable and powerful configuration out there. You
"can" get more power at the expense of reliability and more reliability at
the expense of power. However, the highest powered (biggest streamer)
coils that will "not blow up" are the carefully engineered LTR types IMHO*.
Of course, people with pole pig powered systems can just turn up the power
until the fuse box explodes! :-))
*In My Humble Opinion
At 04:37 PM 7/26/00 -0700, you wrote:
>Mike, John, All -
>The Cp/Cs and Ls/Lp ratios are a dilemma when it comes to TC computer
>programs. Tests have shown that when the Ls has been increased such as
>increasing the secondary turns the output spark will increase. However, I
>have not heard of anyone making the proper tests to determine if when the
>primary capacitor is increased the spark length changes and if the input
>It is a well know fact that with a NST if the primary capacitor is a
>resonant type the spark will increase but the NST input current increases.
>Have you or anyone on the List heard of any of these tests?
>From: Tesla list [mailto:tesla-at-pupman-dot-com]
>Sent: Tuesday, July 25, 2000 5:45 PM
>Subject: Re: performance/tuning question
>Original poster: Hollmike-at-aol-dot-com
> To a point, this will likely increase the output - if something else is
>not the limiting factor. The output voltage is largely dependent of the
>Cp/Cs ratio(or conversely the Ls/Lp ratio which would be the same if the
>is tuned to the fundamental frequency of the secondary system and not a
>harmonic). There are of course other factors involved with spark
>propagation, but this is one way to possibly improve performance of a coil.
>It is certainly worth experimenting with if you have the caps to do it.
>> I was wondering, if I was to build a TC with the tank cap double or
>> the value derived from the formula used to match it with the impedance of
>> the power supply (say .01ufd or .015ufd instead of the matched value of
>> .005ufd) and decreased the primaries inductance appropriately so that the
>> primary and secondary would both resonate at the same frequency. What
>> affect would that have on the system and output compared to starting with
>> the cap matched to the power supplies impedance. Has anyone done this
>> would this have much affect on the streamer length and "look" (whiter but
>> less smooth, etc.)? BTW this would be in a rotary gap setup if that
>> Thanks experienced ones,
>> John M.