RE: NST power rating con

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

Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> 


Harvey -

If you do the tests and make the graphs as I mention in my post to Gerry I
think you will get the answers to all of your comments.

Note that the resonant charging has little to do with the NST maximum output
power. Resonant charging has more to do with maximum sec voltages. The
impedance matching for NST maximum power is different than the impedance
matching for resonant charging. They are both determined in different ways.

The LTR capacitor can be any capacitor that is greater than the resonant
capacitor. As the capacitor is made larger the resonant voltage reduces to a
certain amount. The 1.5 times higher value is a good compromise. The 80 KV
60 Hz voltage normally mentioned is a fictitious voltage that could never be
supported by the typical electric service entrance size. A much lower
voltage "transient" is all that is needed to kill NSTs. These transients are
also caused by the operating gap and can easily be eliminated by the proper
protection gap and RF chokes.

John Couture

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


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Saturday, October 04, 2003 8:33 PM
To: tesla-at-pupman-dot-com
Subject: RE: NST power rating con


Original poster: Harvey Norris <harvich-at-yahoo-dot-com>


--- Tesla list <tesla-at-pupman-dot-com> wrote:
  > Original poster: "John H. Couture"
  > Harvey -
  >
  > I don't believe this is a verification of the
  > maximum power transfer
  > principle. The tests indicate that the maximum power
  > available from a NST is
  > only about one quarter not one half of the nameplate
  > rating. Note that one
  > half the voltage and one half the current gives one
  > fourth the power.

Hi John.

I was not arguing the point that the transformer
should deliver its stated short circuit amperage ALSO
AT its stated voltage rating.  To me this sounds
nonsensible.  A 24 inch neon placed across my 15,000
volt rated NST will only show about 500-600 volts
across it, and also at less then the short circuit
current rating.


You had stated;
The maximum secondary watts output  was 59.3 watts,
3900  volts, 15.2 ma.
  >From this comment I had deduced that you tried a
variety of combinations, and it was this one that gave
the best results. It was from that standpoint that I
made the comment that this sounds like the principle
of maximum power transfer.
Here is some background info on the principle;
I will cite from Herbert W Jackson's Introduction to
Electric Circuits.(3rd edition) I have found his
descriptions very consise, and here he gives 4
statements concerning the matter of how internal
resistance of a stator emf influences the conductions
on the load.

1. Maximum power output (into the load) occurs when
R(L) = R(int)
Also when R(L) is selected for maximum load power
I = 1/2 I (short circuit current)
V(L) = 1/2 E (open circuit voltage)
This is also 1/2 maximum efficiency
Note that maximum power output does NOT coincide with
maximum efficiency. When a load resistance is selected
for maximum power input, there is an equal power
dissipation inside the source of emf.

2. If we want to increase the efficiency, a load
resistance of from two to three times the internal
resistance of the generator results in appreciable
reduction in wasted power ( as heat in the generator)
for only a small reduction in power output.

3. A load resistance less than the internal resistance
of the generator not only results in a reduction of
power output, but also causes a very high dissipation
within the generator. In practice, this condition of
operation is termed OVERLOAD and must be avoided.

4. If we are interested more in voltage output than
power output (as in transistor and vacuum-tube
amplifiers), the load resistance should be high in
comparsion to the internal resistance of the source
of emf.

What I was doing here was to simply compare the NST
secondary as if it were a generator source of emf.
This may be a mistaken approach, but it seems apt.


  > The other problem with NSTs is that the TC input
  > impedance is generally
  > never equal to the optimum needed to get the maximum
  > power out of the
  > transformer. To my knowledge no coiler ever tests to
  > find the optimum
  > impedance for the NST he is using and then designing
  > his TC input impedance
  > to match.
I thought this whole aspect was dealt with in the
subject of resonant recharging, where then this
impedance matching is precisely what takes place. Also
the inherent dangers involved led to the idea of using
LTR, (larger then resonant) C values which are
estimated to be 1.5 times the impedance matched
values.
Obviously then the primary coil must be designed for
the values of capacity being selected by that
strategy.

Some former list coments below...

Re: LTR question
I have been reading a lot of posts lately about LTR
(lower than resonant)  capacitors. This term does not
make sense to me. Any capacitor in combination  with
an inductor will form a tank circuit which will
resonate at a frequency  determined by the values of
the L and C. Is LTR refering to some sort of  stagger
tuning where the primary tank circuit is resonant at a
slightly  different frequency than the secondary tank
circuit? If so, to what end?
A reply:
The confusion results from the fact that the cap is
resonant with two different coils.
1. It resonates with the primary coil of the TC to
produce the HV RF energy.
2. BUT it also has a resonance with the secondary of
the NST (or other transformer) It is THIS resonance at
~50-60 Hz that the term LTR refers to. It is the ~60Hz
resonant rise that will kill your power supply, caps,
etc.
Terry's reply;
Larger Than Resonant cap sizes refer to the 60Hz
resonance between the NST's secondary winding and the
primary cap. This circuit is also a resonant circuit
just like between the primary coil and the primary cap
but it runs at 60Hz (50 Hz) instead of the hundreds of
kHz of the primary circuit. The primary cap and NST
can resonant up to like 80kV if the system is not
drained by the main gap firing. Traditionally, the
primary cap size was selected to be exactly resonant
with the NST's inductance. A 15kV/30mA NST has an
output impedance of: 15000 / 0.030 = 500000 ohms At 60
Hz, a capacitor with this same impedance is: 500000 =
1 / (2 x pi x F x C) Where C = 5.305nF By selecting
the capacitor at this exact resonant size, you can get
a very high power transfer through it. However, there
are two big problems. It is far too easy to keep
widening the gaps or turning up the variac in such a
system which gives greater and greater arcs but it
ends when the NST or primary cap blows up. Second, if
the main gap fails and does not provide a place for
the resonant energy to go, the voltage will skyrocket
to around 80kV. That will destroy something instantly!
Long time coilers remember well the many many
complaints of NSTs blowing up... LTR coil use a cap
size about 1.5 X higher value than the resonant size.
This allows the NST to charge to full working voltage
but the capacitance is so high the voltage will not go
much higher. This removes all the dangers and problems
with resonant rise effects that have destroyed so many
NSTs. Since the cap size is larger, it stores more
energy which makes up for loosing most the resonant
effects. You have the same arcs but without many of
the dangers to the NST and cap. LTR coils tend to have
better arcs but they may be due to more careful tuning
and cap sizing. LTR coils like this are typically used
in static gap systems and the BPS rate is around 200.

Sincerely HDN