Re: TC Electrostatics

Tesla List wrote:
> >From rwall-at-ix-dot-netcom-dot-com Sat Dec  7 22:13:53 1996
> Date: Sat, 7 Dec 1996 13:57:07 -0800
> From: Richard Wayne Wall <rwall-at-ix-dot-netcom-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: TC Electrostatics
> 12/7/96
> Conclusion:  The Tesla Coil is a major electrostatic device.
> A series of experiments were preformed measuring TC base current as
> measured with a Weston Thermo-galvanometer and various components in
> series.  The meter and all components were placed in series with the TC
> base.  Again, the square root of meter reading was not taken, even
> though the meter measures I^2.
> The variac was adjusted (~60 vac) for 90 ma meter reading.  The spark
> discharge appeared the same as with no meter in series.  Forward
> conducting, reverse conducting and back to back blocking diodes were
> placed in series with the meter and TC.  The spark discharge appeared
> unchanged and meter currents were 80 - 90ma.  The diodes were checked
> with DC and appeared good afterwards.

Hmm.. based upon the results you saw with NO base ground (later on in
your post), I suspect your diodes were breaking down. The 80-90 MA was
clearly the integrated average value of the damped-wave current pulses
exiting from the base. If your diodes were actually blocking, the
current should have gone to 0. 

> A 22 uH ceramic roller inductor was place in series.  The spark
> discharge appeared the same as originally and meter currents were 90 -
> 95 ma.  This coil was off axis to the TC secondary and did not appear
> to affect tune or TC output.

The secondary inductance is typically tens of milliHenries, so that the
major impact of the additional base inductance would be minor: small
detuning and a decrease in Q due to added groundpath impedance.

> A 50 pF 35 kV fixed vacuum capacitor was placed in series.  Spark
> output decreased markedly and meter current read 20 ma.  This was off
> axis capacitance for the TC secondary and did not participate in the TC
> field.  Attempts to retune the TC primary made little change in output
> and base current.

This would have severely limited the maximum AC current that could be
removed from the base of the coil. I'm somewhat surprised you didn't run
into flashover problems with this configuration. 50 pF is probably
fairly close (factor of 2?) to the sum of your secondary self-C and
toroid capacitance. Much of the current that would have gone directly to
ground instead was charging your vacuum cap and elevating your coil base

> The coil was fired without a secondary ground connection and Richard is
> right that the TC seeks ground/counter poise with a vengence.  The base
> of secondary arced ~ 3" - 4" over a plexiglas barrier to the TC primary
> coil.  Of course, this is a straight shot to the neon secondary.  I
> stopped it immediately.  Neon still fires, for now anyway.

This is what your back-to-back diodes would be trying to block!

> Assessment:
> Blocking EM base current with diodes has little affect on the coil
> output.  

Most likely because the diodes are not, in fact, blocking the current.

> My next experiment is to confirm with a current shunt and
> scope that EM is truely blocked with the diodes.  If the diodes blocked
> any EM and EM is the major electricity (really basic term) responsible
> for TC output, then there should have been some indication of decreased
> output. This doesn't appear to be the case.  Note, as in measuring TC
> output with the ESVM, it appears that diodes permit passage of
> electrostatic charge.

I'd suggest the following::
Connect the meter directly in series with the coil base. Then shunt the
meter with a diode polarized first one way, then the other. Do NOT
attempt to BLOCK the base current in either direction... you will not
succeed with commonly available semiconductor diodes. Steer the current

> Adding series inductance made no real change.  It is off axis and did
> not appear to change tune, spark output or base current.  Inductance
> should imped EM current at RF frequencies and if EM is responsible for
> TC output the output should have decreased. 

Yes, but only if the inductance is significant versus the secondary
inductance. 55 uH at 200 KHz is only about 70 ohms of impedance...
probably not enough to have any visible effect on coil output.

> The output did not
> decrease.  The inductor should easily conduct DC and presumably
> electrostatic charge.  Since base current and coil output were
> unchanged with increased inductance it is good evidence electrostatics
> may be involved.

While there may be other evidence that electrostatics are involved, the
above measurement does not demonstrate this.

> My first impression of decreased spark output and decreased base
> current using the 35 pF capacitor in series was that the coil was out
> of tune.  Retuning didn't change much.  It's noted that the capacitor
> is off axis and does not participate in the TC field or function.  It's
> my impression that this added capacitance just gets lumped in series
> with the earth capacitance.  The cap presumably should conduct most of
> the EM current, but block DC current and presumably electrostatic
> current.  Again, if EM current was primarily responsible for TC output,
> the output should not have decreased so drastically.

However, the relatively small value of capacitance versus that of the
coil self-C and toroid makes a BIG change in how efficiently energy
couples into the secondary system, as well as detuning the system. If
you would have used a 5000 pF cap, the results would have been markedly
different. A 50 pF cap represents 15k Ohms of capacitive reactance at
200 kHz - this makes for a _very_ lousy AC path to ground, and would
kill coil efficiency even if you WERE in tune.

> These findings are qualitative and preliminary.  Much work and
> verification must be done.  Correct tuning with and without added
> capacitances and inductances must be verified.
> It appears there are two basic currents in Tesla coils.  The TC
> secondary is coupled to the the primary driver and of necessity energy
> is transferred primarily by electromagnetic induction.  Resonating coil
> energy and TC ouput appear largely electrostatic in nature with a
> secondary EM component.


I agree with the first statement regarding electromagnetic induction.
The experiments you've conducted are certainly creative and interesting,
but they have not, as yet, demonstrated that TC output is primarily
electrostatic in nature. There certainly appears to be some
electrostatic effects, however... The trick is to be able to actually
measure what is thought to be measured.

Conceptually, your experiments are definately headed in the right
direction. If you shunt across your thermal RF meter with a diode one
direction, then the other, you should be able to _safely_ measure any
difference in magnitude between the positive and negative portions of
the average coil-base current.
With further measurements, you may indeed be able to provide stronger
evidence for a significant electrostatic component. Different magnitude
of + vs - base-current current measurements may be demonstrating that
toroid breakout ( and subsequent discharge current) is more favorably
initiated when the terminal potential is negative than when it is
positive. If negative half cycles "conduct more", then this may be part
of what is being measured in the coil base AND by pickup plates... 

Interesting stuff, for sure!

Safe coilin' to ya!

-- Bert --