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Re: The 1500t secondary myth (long)

Original poster: FutureT@xxxxxxx

In a message dated 12/5/04 12:57:25 AM Eastern Standard Time, tesla@xxxxxxxxxx writes:


But could you quantify each of these conditions?
     What constitutes an "outrageous" top load? In his widely-posted
article, Hull wrote: "We further found that the moderate sized toroids then
used could be increased by one full order of magnitude and the result would
be a fantastic increase in the amount of energy handling capacity of a
relatively small system!" This is something I'm leaning towards myself,
after a modest amount of experimentation.



Phil,

Below I'll discuss some things about coils and magnifiers.

It's true that a large topload is helpful.  For example my small
TT-42 TC normally runs with a 4" x 13" spun toroid and gives
42" sparks.  However when I installed a 6" x 24" toroid which
barely permitted breakout, I got 44" sparks.  This is using
a 12/30 NST.  Obviously the toroid must not be so large that
the spark cannot breakout.  Breakout points can be installed
to permit a too-large toroid to breakout, but this tends not
to increase the sparklength.  I like to make the toroid about
1/4 to 1/3 the sparklength.  Hull did the same thing.  His
Nemesis coil used a 5 foot diameter toroid and it produced
15 foot sparks.  This is the general proportions that are popular
now-a-days anyway.

     How high is "very high" potential for a charging transformer? Hull
wrote, "Only one rule applies here. The voltage must be as high as
possible!!!" Of course, I mentioned that maybe we should be focusing SGTC
efforts on how to charge the primary caps to higher voltages. What kind of
relationship exists between primary voltages and streamer length, all other
factors equal?



I did some tests comparing various input voltages and found only
a minor improvement by using for example twice the voltage.  I tried
using voltages up to about 50kV, but didn't see much difference.  It is
true however that higher voltages are theoretically more efficient,
and are likely to give slightly improved performance.  A lot depends
on the coils original design.  For example if a coil has too few
primary turn in use, it will tend to be lossy.  Then if a much higher
voltage is used, it will permit more primary turns to be used
(because a smaller capacitor must then be used).  This will
reduce losses and help some.  But if the coil already has quite
a few primary turns in use (high inductance and high surge
impedance), then the high voltage won't help as much.  In other
words, one must look at the entire situation when thinking about
these issues.



     How small are "small" caps? Again, Hull said: "When we hear of a
builder that uses more than 0.1 uF of capacitance, we wonder about the
builder. Our 10Kw Nemesis used only 0.09 uF of capacitance and produced
straight line, point to point arcs of 14-15 feet." Yet we have folks on
this list right now advocating caps at least 0.1 uF to produce these kind
of sparks.



Richard eventually changed his mind about this and added more
capacitance to Nemesis for a total 1.1uF value.
The view on cap values has changed since Hull's Tesla days.  It is
now generally accepted that larger caps are better provided enough
turns are used in the secondary, (actually high enough inductance
in the secondary would be a better way to describe it).  It has also
been found that basically what's good for a classic TC is also good
for a magnifier;  low breakrate, large capacitors, high inductance
primary, large topload.  Consider that back in Hull's Tesla days, it
was considered *excellent* if a 12/30 NST coil produced 20"
sparks.  Now that's considered to be super wimpy.


     And what makes a "very good" rotary? Hull wrote :"We have designed a
special series arc rotary quench gap that can actually quench faster than
required (also a bad condition)." If this is of the utmost importance, how
exactly was this done? The only picture I've seen of a TCBOR rotary was a
good-sized "propeller" gap. And how does one tune a rotary for precisely
the correct amount of quench?



Hull used a series quenching rotary.  This design has a number
of electrode pairs all in series.  This makes the gap both a rotary gap
and a multiple gap in a sense.  It's true these types of gaps quench
a little better.

There is something that must be considered when designing
a magnifier and that is the coupling.  It is sometimes stated that
magnifiers have a very tight coupling, and that this demands the use
of a special type of gap.  In reality the actual overall coupling of
a magnifier is very similar to that of a classic coil.  It's only the
driver coupling that is tight.  This is because the secondary and
extra coil of a magnifier "work together", and the coupling of the
secondary and extra coil combination must be used to determine
the actual coupling.  Because the overall coupling is not that tight,
a normal spark gap can be used.  Note:  There are special magnifier
designs developed by Antonio DeQueroz, that may give better
performance and may need special spark gaps, but these have
not been demonstated in spark-producing applications.

     I'm just deathly curious about how the TCBOR made magnifiers with such
small resonators (which represent a huge cost and space savings) that
produced arc lengths of up to 7 times their height.



In reality there is no space savings.  One must consider the
entire Tesla coil.  When the size of the driver unit is considered along
with the resonator, the whole thing is about the same size.  The
arrangement can be more convenient to move around or store, etc.
There really nothing mysterious or special about the magnifier
design using a small resonator.  Consider this;  suppose you
used a tiny resonator just 1" tall and with 10 turns, and fed the
energy from a large driver to this.  Then place a large toroid on
top of this 1" tall resonator.  Then you could say that your
sparklength was 150 times longer than the resonator.  In the
magnifier you're basically just dividing up the resonator into
two sections of arbitrary size.  The secondary is one section,
the resonator is the other section of this "resonantor combo".

I don't know about

everybody else, but I'd rather build a giant toroid than wind a giant
secondary (bringing this post back on topic :) ).



Well you can build a small resonator for the magnifier, but you'll still
need a bulky driver to drive it.  In any case you'll need a large toroid
for good performance whether it's a classic TC or a magnifier.



I'd also rather build a

MMC of much smaller value but slightly higher voltage rating. BTW, I read
that Gary Lau has gotten best results yet by going to a much smaller cap.



I haven't heard about those results.  The last I heard Gary got his
best results by using a somewhat larger cap than most folks would
think of using.  The resonant value for his system is 0.01uF, often
LTR values of 2.5 or 3.3 x reso are recommended, but Gary got
his best results using a 0.04uF cap.  He got about a 70" spark or
so.  This is using a 15/60 NST.  Gary demonstrated this coil at
Ed Wingate's last Teslathon.



     So what do(did?) all the current design programs have to predict about
the performance of the TCBOR coils such as Nemesis and their last magnifier?



There is absolutely nothing special or unusual about the Nemesis coil
or Hull's magnifier.  They perform exactly as the design programs would
predict.  Hull in general used higher breakrates which permitted the
use of smaller capacitor values.  Hull never experimented with low
breakrate 120 bps synchronous rotary spark gaps.

Cheers,
John Freau


-Phil LaBudde