DC secondary components was Stop the nonsense

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

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Robert Heidlebaugh wrote:
 
> A tesla coil is not a simple oscilator with contiouous AC power. It
> is a pulse fed circuit. That is why a charge builds up on the
> toroid. If the drive was pure AC of a balanced sign wave the use
> of a toroid would be a waste of time.

Rubbish. Take the trouble to look at the secondary waveform of a TC.
There are loads of them documented on the web.  For eg Thor.

The purpose of the toroid is to shape the electric field to prevent
undesired breakdown near the top of the secondary, and to store a
useful amount of charge (for the duration of each half-cycle only!)
to help with streamer formation. 

> If you have an unbalanced + pulse a charge will build up on a
> "ststic" charged surface and will grow with each pulse, just like a
> VANDEGRAPH charging a sphere.an antenna sencing the wave shape
> using a scope dosent see the DC part of the build up.

No, you've got a DC path from the toroid to ground (via the secondary
winding), so any DC build-up will leak away within the LR time
constant of the secondary - a few microseconds, and will not
accumulate like in a van der Graff.

The best you'll get is a small DC component to the base current
resulting from asymmetrical conduction (partial rectification) within
the topload discharge.

Can anyone remind me what polarity that will be?  I'd dearly like
to know if/how this DC base current relates to streamer length,
bang size, etc.  Does the current increase from bang to bang within
a burst?

You shouldn't think in terms of an unbalanced pulse.  The DC
component of the pulse waveform, ie its average value, has to be
zero because it is being evolved by magnetic induction in a winding.

There is no DC coupling between primary and secondary, so only the
AC components can get through.  Any DC component present in the
secondary must therefore be due to non-linearity of the secondary
load, or of the ground return circuit.

> You must use a space charge mesuring detector to read the total
> charge. I don't hear anyone trying to measure this level.

For the reasons above.  No point in looking for it unless you can
first give a plausible reason why any DC charge displacement forming
between toroid and earth won't immediately discharge via the
secondary winding.

Static charge building up within the dielectric of the coil former
is another matter altogether, as a few know to their cost!

> I only see "OH goody Oh goody I got a big streamer". You get a
> sreamer when the AC builds up a DC component to a point that the
> air breakes down and the total AC & DC fires through the space of
> your play area.

If you look into the literature on streamer formation, for example
Bert Hickman's explanatory notes in the list archives, you'll find
that a DC component to the electric field is not at all necessary.
Streamer formation takes place in stages, advancing a little more
with each half-cycle, during the decaying beat envelope of the
secondary.   Under favourable conditions (whatever they are?)
consecutive bangs evolve streamers along paths in the air made by
earlier bangs, which explains the changes in streamer length  with
BPS.  Nowhere along the way does a DC charge appear necessary,  if
it were, it would be safe to stand very near to an overhead power
cable.

> That is why most TUBE tc are less impressive. Yes total power is
> less, 

Its the lack of peak power capability that makes the CW coils less
impressive, in one sense at least.  Personally I'll trade streamer
length for those nice sheets of flame any day. I just love the
evil seething hiss of all that power going through...Hh Hmm, where
were we...

> But pure AC dose not build up a charge.
> There must be a DC component to build a charge.BOTH !!!

Where are you getting these notions from?  Someone's been feeding
you porkies here.

But another interesting thought comes to mind - what would happen if
you replaced the secondary base connection with a DC blocking
capacitor?  Anyone venture a guess at the DC component which would
form across it during streamer breakout?

What happens if you put a DC supply - several kV, in
series with the base, to provide a genuine DC component to the
topload charge, in the way that Robert describes - does that do
anything to enhance the performance?  

So many TC frontiers...so much real work to do.
--
Paul Nicholson
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