RE: Capacitor in series or parallel?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Harvey Norris <harvich@xxxxxxxxx>



--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
>
> I think both you guys are right.  With the xfmr
> across the cap, the xfmr
> will see a lot of RF at the tank frequency, and with
> the xfmr across the
> gap, the xfmr will see HF-rich step functions.
> Also, during the
> zero-current crossings when the gap briefly turns
> off, there will be VHF
> transients at the self-resonant frequency of the
> primary and other
> paracitics, peaking at TWICE the tank capacitor
> voltage.
>
> But the important thing is that while R-C filters
> don't do a great job
> at filtering the main tank frequency (i.e. they
> won't help much if the
> xfmr is across the cap), an R-C filter will do an
> excellent job
> attenuating the VHF transients and step functions
> seen across the gap.
> When using an R-C filter, running with the xfmr
> across the gap is
> better, as both hazards are eliminated.  If you're
> not using an R-C
> filter, choose your poison.  I couldn't say which is
> worse.
>
> Regards, Gary Lau
> MA, USA
(From CSN Marincic commentary)
The first record Of Tesla's high frequency coupled
oscillatory circuit with an air cored transformer is
to be found in patent 454622 of 23 June 1891 under the
title "System of electric lighting". The oscillator
converts low frequency currents into "currents of very
high frequency and very high potential" which then
supplies single terminal lamps. (from Aleksandar
Marincic's CSN preface) The arc gap in this schematic
is within the tank circuit, something later abandoned
as the best method.

On July 2,1899 Tesla notes the reasoning for this; In
a
schematic showing the break within the tank circuit he
comments... "the scheme of connections has the
disadvantage that the primary discharge current passes
through the break hence, the resistance of the latter
being large, the oscillations are quickly damped and
there is besides a large current through the break
which makes good operation of the latter difficult. To
prolong oscillation in the primary and increase
economy one of the schemes before considered may be
resorted to." He then refers to the conventional
approach of allowing the break to be shunted across
the hv secondary outputs where he comments.. "in this
arrangement the currents through the break device are
much smaller and the oscillations started by the
operation of the break device continue much longer."
Tesla makes no comment concerning the idea of placing
an inverse tank circuit on the other side of the break
in the first example for a center tapped high
frequency transformer. In that situation two (180
phased) primaries would recieve their oscillations
from a single arc gap. The problem of the arc
containing the entirety of the currents is then
circumvented by the pathway established along the
sides of the newly configured figure 8 LC quantities.

Further comments:
The above descriptions may sound quite vague without
resorting to an actual perusal of July 2, CSN notes.
The first diagram shown there; refered to as the break
or arc gap within the tank circuit: shows the C and L
primary elements being connected in parallel; and the
break device put between this LC loop, on the top half
of the schematic in this case. The C value is arranged
as the closest branch to the transformer. Since the
tesla primary  circuit is considered to be
predominantly capacitive reactance, if the gap is not
firing, the transformer current output is then limited
by that capacitive reactance. In this instance however
once the gap fires another comparatively low impedance
pathway, practically resembling a short since primary
L reactance is minimal, this low impedance pathway is
now in parallel with the much higher impedance C
branch pathway: hence once the gap fires, a large
current should ensue. Hence Tesla's comment, "there is
besides a large current through the break which makes
good operation of the latter difficult." In the next
schematic the gap appears next to the transformer
outputs, or as a shunt or short to its outputs. The
CpLp loop remains the same as before, further attached
as parallel branches downline from this gap, but now
an extra C value has been added on one of the lines
leading to this loop, thus effectively current
limiting the amount of current to be made available to
this loop. (apparently this is no longer a practice in
TC primary designs) In these schemes the practice of L
and C being in series: with a  transformer shunted arc
gap is not shown. Now in the first abandoned arc gap
scheme, if a mirror image tank were attached on the
other side of the gap, and the input connections were
to be expanded to the new connections of this added
tank, this would resembling a voltage doubling Marx
type scenario. This would then (possibly) eliminate
the objection of the current through the gap being
unnecessarily large and difficult to control.
Schematically it might appear thus;
                          1
C
L
``````````````````````ARC
GAP``````````````````````````
L
C
                          1

Now each branch is current limited by its C values,
but also each cap is being charged oppositely, serving
as a voltage doubler a la Marx type circuit.

A variac was employed to an NST and a narrow gap set
for a conventional tesla primary using permissible
arbitrary L and C values. The firing voltage was
noted. Then the second set of L and C values was added
inversely in parallel as noted in above schematic,
(if no translation problems develope in that writing)
It was noted that the inverse tank addition allowed
that gap to fire at half the voltage that the
conventional gap required for firing, thus indicating
its action as a voltage doubler.

Past references from
Tesla on Lightning/ Bifilar Marx Tank Primaries as 3rd
Schematic Possibility. Mon Dec 9, 2002
http://groups.yahoo.com/group/teslafy/message/561
"The fact that a voltage doubling must take place is a
consequence of the fact: THAT BOTH THE AMPERAGE AND
THE VOLTAGE ARE 90 DEGREES OUT OF PHASE WITH THE
SOURCE FOR A CAPACITIVE REACTANCE. A tesla coil
primary is exactly that, a capacitive reactance with
respect to its source frequency. If we then make two
of these; each charged in opposite directions or
polarities from the source, we then have two
opposite 90 degree capacitive reactance voltages on
each capacity, thus with resect to each other, they
are closely 180 degrees out of phase. For the Marx
Tank, similar to the Tesla Tank, the L and C
quantities must be tuned to that of the imagined
secondaries resonant frequency.[If these dual
primaries were placed together in mutual inductance to
excite a single secondary. Other options using two
secondaries obviously also exist where these
complications would not be so problematic,for a
totally different type of bipolar twin tesla coil
system](not merely placing the primaries in series,
but also exciting them oppositely). This is then the
great complication involved with tuning a Marx
Tank,[for a single secondary] because we must also
account for how each primary changes in relation to
the other by mutual inductance.
[Adjacent spirals are known to have a higher mutual
inductance]

This then is the analogy of a ferromagnetic center tap
transformer applied to a air core transformer.

Sincerely Harvey D Norris

Tesla Research Group; Pioneering the Applications of Interphasal 
Resonances http://groups.yahoo.com/group/teslafy/