Hi William,
Quarter-wave resonance is a myth perpetuated by the fact that some nicely-proportioned TCs
have an amount of wire on the secondary that turns out to be close to 1/4 wavelength, and
that a TC behaves, to a first approximation, like a 1/4 wave resonator in terms of voltage and
current distribution. Careful empirical studies of the last 50 years no not support the 1/4
wavelength of wire hypothesis. However, those whose scientific knowledge comes from the
back pages of tabloids and ads for "secret knowledge" still promote this "Truth" since for
them faith always trumps fact.
Hope this helps,
Matt D.
-----Original Message-----
From: William Howard <snakeprior@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Sat, Nov 1, 2014 11:01 am
Subject: Re: [TCML] Technical Tesla Coil Questions
Dear Paul,
Thank you for your concise explanation.
I forgot that adding a topload lowers the resonant frequency of the coil.
So there is no way to match the topload to the secondary. Tuning is done on
the primary side.
A follow up question: are the primary and secondary oscillating at the same
frequency or at a 1/4 wavelength?
I get confused because I often see the 1/4 wave mentioned. JavaTC seems to
supply numbers for a matched resonance.
Is there a way to get a Tesla Coil to operate at 1/4 wave or do you need to
build a 3 coil system?
I have been battling to get longer than 30cm arcs from my VTTCs. It's
mainly due to my impatience and incompetence but hopefully there is a way
to improve the current system.
I don't have any toroids unfortunately. Will have to get one!
Cheers!
-Wil
On 31/10/2014 7:39 PM, "paul" <tcml88@xxxxxxxxxxx> wrote:
>
> > is the topload acting as a capacitive transmitter?
> > I mean is it transmitting using a dielectric effect
> > rather than electromagnetic.
>
> The electric field dominates, therefore mostly capacitive
> coupling to surroundings. Far field is negligible which
> is why you don't need a transmitting licence.
>
> > does the topload turn the secondary into a parallel or
> > series LC network?
>
> The TC is either parallel and series resonant - depends on
> your viewpoint. Looking between top terminal and ground
> you see a parallel resonance. Looking into the base of
> the coil you find a series resonance. Same when you add
> a topload but with increased C.
>
> > could the secondary topload be sufficiently sized to match
> > the inductance of the secondary?
>
> Not sure what you mean by 'match' here? Coil and topload will
> form a resonator with whatever L and C they happen to have.
> If you want a particular frequency then you must choose the
> topload to have the correct C to achieve your target frequency.
>
> But usually F is not a design target.
>
> The topload protects the top of the coil from high field
> strengths, and matches the output of the coil to its load
> (usually a spark loading). These considerations determine
> the size and shape of topload. That fixes the topload C.
> In combination with the coil, that determines resonant
> frequency. Then you design a primary to match that F.
>
> > ...Tesla used an elevated capacity. Was this for transmission
> > purposes
>
> Probably the intention was to extend the E-field as far as
> possible.
>
> > ... or could it act as a delay line between the inductor
> > and capacitor?
>
> No significant delay.
>
> If the topload is too far above the coil it wont be able to
> protect the top of the coil. Can consider two toploads, one
> toroidal just above the coil and another of any shape which
> can be placed remote from the coil.
>
> Formation of long sparks requires short very rapid bursts of
> charge delivered into the developing streamers. The coil only
> provides charge slowly (compared with the streamer formation
> timescale), so the topload needs to act as a charge reservoir.
> A sphere is the worst possible shape for this - for a given
> size and voltage a sphere is the shape that stores the least
> amount of charge. A sphere is also poor for controlling the
> field around the coil top. Toroids are good in both respects.
>
> I'll just add that there is no formula to calculate the ideal
> topload size/shape to give max spark length for some given
> power level. Coilers have discovered over the years that
> large is good, and larger can be even better. But there must
> be an optimum size - too small and not enough charge stored,
> too large and not enough E-field to push out the streamers.
>
> --
> Paul Nicholson
> --
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>
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