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0.5*C*V*V vaild? (Was Output Voltages and Voltage/Length)



From:  D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent:  Saturday, February 07, 1998 1:24 PM
To:  Tesla List
Subject:  Re: 0.5*C*V*V vaild?  (Was Output Voltages and Voltage/Length)

to: Antonio Carlos

We use a pickup probe consisting of a 14 dia. old VDGRF sphere.  This
sphere is grounded to the coax shield.  A small copper patch approx 3 x 3
inches is glued to a piece of mylar which is glued to the grounded sphere. 
The copper patch is connected to the center of the coax.  The copper piece
is in effect insulated from the sphere and forms a capacitor.  This results
in a neat capacitive pickup probe that is then connected to a 10 microAmp
DC meter.  The other end of the meter is grounded.  Meter is protected from
excessive potential by connecting three 1N4007's in series and
anti-parallel across the meter.  The probe is placed near the coil usually
at twice the normal striking distance of the discharge spark.  The meter
will then indicate an exact tuning for the coil as the primary tap is
adjusted.  More current on the meter equals more spark discharge and this
is very helpful especially when adjusting large coil systems such as Greg
L. is constructing.  We use both a 10 uA and 50 uA meter depending on how
large/small the system is.

DR.RESONANCE-at-next-wave-dot-net



> From:  Antonio Carlos M. de Queiroz [SMTP:acmq-at-compuland-dot-com.br]
> Sent:  Friday, February 06, 1998 2:07 PM
> To:  Tesla List
> Subject:  Re: 0.5*C*V*V vaild?  (Was Output Voltages and Voltage/Length)
> 
> Mark S. Rzeszotarski wrote:
> 
> > I have also built a series of tesla coils with back-to-back
> > LED's placed every 2 inches along the length of the coil with various
H/D
> > configurations to examine the voltage rise in these rather heavily
damped
> > coil systems. 
> 
> LEDs connected in series with the coil would measure current, as the
voltage over a
> conducting LED is practically constant. LEDs connected in parallel with
the coil
> sections, with series resistors, would measure voltages. What connection
are
> you using? (The readings would be proportional, anyway.)
> 
> > 1.  The voltage distribution goes from a minimum at the base to a
maximum at
> > the top when tuned to the quarter wavelength of the coil system, even
in a
> > damped coil system.
> 
> This looks strange. I would expect more voltage at the base, where the
coupling
> is higher, or almost constant voltage along all the coil sections, that
is what
> the lumped model predicts. Is this coil a capacitor-discharge coil or a
CW coil?
> 
> > 2.  Adding a toroid or sphere to the top tends to linearize the voltage
rise
> > somewhat, so that the turn-to-turn voltage stress is lessened
especially
> > near the top of the coil.
> 
> Looking at LED lights is not a very reliable method for measuring
linearity,
> as LEDs are very nonlinear.
> 
> > Typical oscilloscope probes have 10-30 pF of
> > capacitance, which greatly affects the readings unless you have a huge
coil
> > system with a Csec of perhaps 10-20 times this or more.
> 
> Better to use a metal sphere connected to the oscilloscope and put near
the
> coil. Some calibration procedure is required.
> 
> > 4.  The Corum brothers suggest that the voltage rise in a helical
resonator
> > can be rather astronomical.  I disagree.  My measurements of the
maximum
> > possible voltage at the toroid tend to agree with the equation:
> > Vsec(max) = Vpri x SQRT(Cpri/Csec), or the equivalent:
> > Vsec(max) = Vpri x SQRT(Lsec/Lpri), which is essentially the lumped
circuit
> > model.
> 
> Can someone point where I can find a rigorous analysis of an helical
resonator?
> (Not the lumped model, that I know well. The distributed model, that I
strongly
> suspect that is not valid for any tesla coil of reasonable size...) 
> 
> >         There is an interplay of energy storage between the capacitance
(1/2
> > Csec V^2) and the inductance (L dIsec/dt), (as well as an interplay
between
> > the primary and secondary systems while the spark gap is conducting).
> 
> You can simulate this with a program that I wrote (lumped model):
> ftp://ftp.coe.ufrj.br/pub/acmq/teslasim.zip
> 
> I agree with the other comments.
>  
> Antonio Carlos M. de Queiroz
> mailto:acmq-at-compuland-dot-com.br
> http://www.coe.ufrj.br/~acmq
>