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DC on Tesla coil
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From: D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent: Thursday, March 26, 1998 12:06 AM
To: Tesla List
Subject: Re: DC on Tesla coil
to: Vivian
On regarding the strange potentials storage. The basic definition of a
capacitor is a conductor separated by an insulator (dielectric) and then
another conductor. Sometimes the "other conductor" isn't always a high
visibility item, and that's where the strange properties usually begin.
Any parallel traces on a board would fit this description, but equally
important would be any traces on the opposite side of the board. With
regard to TC's the primary circuit can store energy especially if you run a
cap in each leg of the power circuit. This type of circuit is commonly
referred to as an "equi-drive" configuration which denotes caps usually of
equal value in series with each power leg, ie, there is no ground on one
side of the circuit as both legs contain power -- classic example would be
a NST powered coil. Usually there is no storage when a single cap bank is
used and is only run in series with one leg of the tank circuit. The
secondary circuit consists of each turn which is separated by the
insulation of the wire, hence the definition of a capacitor is again
brought into play. There is also capacitance to ground, to terminal, and
turn to turn all which contributes to the potential to store energy if the
circuit is switched off an the correct time and the quench was good on the
gap. Quenching and secondary ringing effects are very important but
equally important is the waveforms themselves especially with regard to
constructive and destructive interference effects which allow powerful
resonant buildups or can severely reduce the output depending on their
exact nature. The standing waves generated are very complex and explains
why careful adjustment of coefficient of coupling is necessary in any
system to achieve optimum outputs. Coefficient of coupling adjustments and
careful attention to quenching (switch-off) timing usually results in
improved performance in most systems. The convential TC must be loosely
coupled to prevent the formation of two sideband resonant frequencies which
will beat against the central freq and create potentials at undesireable
points up the sec coil other than the top. You might read up on this in
the ARRL Radio Amateur's Handbook as they discuss it clearly and in great
detail.
DR.RESONANCE-at-next-wave-dot-net
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> From: Vivian [SMTP:V.C.Watts-at-btinternet-dot-com]
> Sent: Tuesday, March 24, 1998 2:46 PM
> To: Tesla List
> Subject: DC on Tesla coil
>
> Hi All,
> On Saturday I was demonstrating my TC to a good friend when due to a
> pull on the ground cable unbeknown to me my secondary became disconnected
> from earth. When firing it up sparks ensued from around the base and from
> Primary to Secondary. So I shut it down very quickly. Now when I
> re-connected the secondary to the ground I got a large spark just before
> contact. So the secondary had stored charge. Question is was it a
static
> charge in the sense of formed by the insulation of the coil as proposed
on
> the list or is their a tendency for a level of DC to be built up but
> naturally bleed away by normal connection to ground. If a spark ensues
to
> an object and the connection is terminated at the peak of the Oscillation
> then will a charge be retained?
>
> Before the idea is dismissed outright one might like to consider another
> experience I have had. I use to work for a company making automatic test
> equipment to test bare circuit boards (no components fitted) for shorts
and
> opens. We charged up a track on the circuit board to 500V or so and
> measured how long it took at a known source impedance. If it took longer
> than expected it was either directly shorted to something else or was
> leaking via high resistance to another trace. Times measured were in
nano
> seconds and detection of shorts to another trace measuring only 0.02 pf
> could be resolved or resistance's up to 1000MOhms.
>
> One of the power planes on the board would be grounded. The problem we
> experienced was that if the circuit board had multiple power planes,
testing
> one plane i.e. charging it up to 500v would induce a voltage on another.
OK
> so far, but the machine always discharged the plane being tested, before
> proceeding to test another. But now here's the difficult thing, the
other
> power planes retained their charge. The consequence was that when that
> charged plane came to be tested it blew the electronics away. Even a
Spice
> model showed a charge build up with no rectification and yet all that was
> happening was another part of the board was first charged up then
> discharged.
>
> The consequence of all this was that after discussing this experience
with
> my friend I now know less than I thought I did.
>
> Here's a few more questions some kind sole might like to put my thoughts
> back on track.
>
> 1/ When the gap fires the current in the gap will be from the
transformer
> and from the capacitor. What current is hardest to quench? For the
period
> of one half cycle the transformer current could be considered like DC but
> the
> capacitor current will be AC. Is one harder to quench than another.
>
>
> 2/ I have read descriptions like ... "When the Gap is quenched the
energy
> goes into the secondary". Is it really breaking the tank circuit and
thus
> removing the lossy gap from the circuit, increasing Q and allowing the
> secondary to ring true that gets the sparks going?
>
> 3/ Are the oscillations, when the gap fires, like a carrier with two
> sidebands until the gap quenches and then become a single carrier.
>
> 4/ Why does the conventional TC have to be loosely coupled. Why can't
we
> get more bang by increasing coupling if the insulation could stand it.
>
>
> With Brain Ache
>
> Viv Watts UK.
>
>
>