RE: performance/tuning question

["John H. Couture" <couturejh-at-worldnet.att-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Terry -

Many thanks for all that information on the NST "sweet spots". I had heard
about these possible conditions but had little specific information. I would
be interested in more information so these special conditions can be
incorporated into a TC program. The resonant cap is no problem but how about
those other "sweet spots". At present it looks to me like they are not
changing Tesla coils outputs very much.

For the resonant cap I use the following equation.
    C = 10^6 * I / (6.283 * Hz * V)

For a 15/60 900 watt NST - 60 Hz
    C = 10^6 * .06 / (6.823 * 60 * 15000) = .0106 uf

The gain in current or wattage is about 2 to 3 times normal.

I agree it is difficult to compare spark outputs for these special
conditions. However, with a TC program you show something approximate based
on the available empirical data. Hopefully coilers who have coils will test
them so more information is available.

What is the LTR line frequency timing theory?

The people with pig powered systems do just the opposite. They do not want
and can not handle the possible full output power of the transformer when it
is short circuted by Tesla coil operation. They limit the potential current
that can be over 50 times normal or 50 times KVA! Fortunately the limiting
by the electric service, ballasts, etc, saves coilers from desaster. Coilers
should be aware that this type of hazard can cause their electric service to
explode as you pointed out.

John Couture

------------------------------

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, July 26, 2000 6:51 PM
To: tesla-at-pupman-dot-com
Subject: RE: performance/tuning question


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

Hi John,

	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! :-))

Cheers,

	Terry

*In My Humble Opinion