Re: LTR capacitors

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi,

I dug this from an old post:

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. 

Resonant - The first is our old friend the "resonant" primary cap size.
This tunes the NST to resonate and effectively removes 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... 

LTR - 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 demonstrated
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!
:-)) -------------------------------------------- 

Cheers, 

	Terry 


At 05:03 PM 11/28/2001 -0500, you wrote:
> What is the meaning of LTR when referring to an LTR tank capacitor?
>