RE: Early versions of Tesla's coil

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

Original poster: "John H. Couture by way of Terry Fritz <teslalist-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


Ed, All -

There are dozens of different wiring diagrams for the devices we are talking
about and they all work differently. In my comments below I am referring
only to the wiring diagram on page 75 of the book "My Inventions" by Nikola
Tesla and edited by Ben Johnson.

This diagram has been the subject of many confusing posts in the past. It is
my understanding that the above wiring diagram is used for the antique coil
shown in the RMC photograph and also for many Leak Detectors. The circuit is
a combination of the induction coil circuit and the Tesla coil circuit. This
Induction/Tesla coil combination is very difficult to design for optimum
operation because it involves both electrical and mechanical design. I have
built and tested many of these circuits and I still do not have what I
believe is the best optimum design method. Maybe Antonio has a good design
method. My operating description of a combination (Induction Coil/Tesla
Coil) below is an elaboration of what Ed has said.

It should be noted that the buzzer inductance coil system will produce a
spark all by itself when the coil is energized and the contact opened. This
is normally called an induction coil system as in a Ford spark coil and
produces pulse wave type sparks. This induction coil can be used to power a
Tesla coil. The Tesla coil primary is energized by the inductive kick
current from the induction coil and the TC would produce dampened sine
waves.

In the diagram I am referring to the induction coil capacitor is also used
for the Tesla coil primary capacitor as Ed has pointed out. The Tesla TC
primary coil is in series with this capacitor. The diagram does not show the
TC secondary coil. The input current is very busy in this combination of
circuits. At the start the buzzer contact is closed and the current from the
main source energizes the buzzer coil. This opens the buzzer contact and the
HV current from the buzzer coil flows thru the TC coil and the capacitor
back to the source. If the TC system design is properly coordinated with the
induction coil all of the energy will be absorbed by the TC at this time and
the cycle will then be repeated similar to the standard TC operation.
However, the cycling will depend on the contact characteristics not on the
source frequency.

If the TC system does not absorb all of the energy on the first cycle the
capacitor will be charged and there will be a resonant current flowing
between the buzzer inductance and the capacitor. The frequency will be
determined by the LC values. This alternating current will also be flowing
thru the TC primary and the current will be quickly absorbed in losses and
the TC system. The cycle will then be repeated.

The energy flow is as follows. At the start the buzzer contact is closed and
the input energy from the source flows into the buzzer coil. This opens the
buzzer contact and all the energy flows into the TC circuit and the cycle
repeated. This cycle would depend on the mechanics of the contact with a
maximum of about 1000 CPS. If all of the energy is not absorbed (poor
design) on the first cycle the energy (current) flows back and forth between
the induction coil and the capacitor at the LC frequency as Ed mentioned.

The buzzer contact will not close and open at each LC cycle because this
cycle frequency would be too high. The contact cycle will be limited by the
contact inertia, etc. (good design problem). The contact will close only
when the alternating energy in the buzzer coil is too low due to losses to
keep the contact open and the cycle will be repeated. Because of the added
losses after more than one cycle the spark length will be much shorter
compared to the one cycle operation (difficult design problem).
Comments welcomed.

John Couture

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


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Monday, July 07, 2003 9:43 PM
To: tesla-at-pupman-dot-com
Subject: Re: Early versions of Tesla's coil


Original poster: "Ed Phillips by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<evp-at-pacbell-dot-net>

Tesla list wrote:
  >
  > Original poster: "John H. Couture by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>
  >
  > Ed -
  >
  > Why would there be two energy storage sources, one as the buzzer coil
  > (contacts closed) and one as the capacitor (contact opened)?  That would
  > only increase the losses. The energy in the buzzer coil cannot be used
twice
  > in the TC primary as this would imply over unity energy. I would be
  > interested in reading Curtis's description of this operation.
  >
  >   In fact I believe this device would work without the capacitor but not
as
  > well. Only the energy from the buzzer coil is needed to energize the TC
  > primary coil. I believe the capacitor only protects the contacts and they
  > last longer.
  >
  > John Couture

	The law of conservation of energy is not defeated and no "over unity"
is involved.  Not permitted on this list anyway!  The actual voltage
across the capacitor will be the final current in the buzzer inductor
times the square root of L/C, where L is the buzzer inductance and C is
primary capacitor for the TC.  I haven't made any measurements on the
coil I have, but make this guess:

	Suppose the inductance of the buzzer is 0.1 henry (it's probably a lot
more) and the primary capacitor is 5 nf.  If the current flowing in the
buzzer just before the contacts open is 0.5 amp (another wild guess) The
resultant voltage across the capacitor will be about 2200 volts.  If the
contacts close again at the right time (Antonio can help on this) that
capacitor voltage will be discharged through the TC primary.  About the
same as charging the capacitor from a 2200 volt (peak) transformer.
Note that there are two separate resonant circuits involved, both
involving the same capacitor.  The first and lowest resonant frequency
is that of the buzzer inductor and the primary capacitor, while the
second is that of the primary capacitor and the TC primary inductor.

	I haven't made any waveform measurements because I'm very reluctant to
have the thing running near my scope.  Maybe Terry could make the
appropriate measurements on one of his (he certainly is adequately
equipped) and report the results.

Ed