Re: DC secondary components

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

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Paul and all,

Greg Leyh actually did this experiment a couple of years ago using one
of his large coils. He used a high energy capacitor bank charged to a
high potential to elevate the base of his secondary. The RF base
currents easily passed through the bank to ground. 

While it's not clear that there was any significant change in the
behavior of the unconnected leaders and streamers, there was certainly a
large amount of follow-through current whenever the leaders power arced
to ground. The resonant frequency of Greg's large secondary combined
with the bank capacitance resulted in low frequency audio oscillations
during the resulting high current power arcs. Greg may be able to share
further details.

I suspect that you'd need to elevate the secondary DC potential to a
significantly higher potential  (many 10's of kilovolts positive) before
you'd actually begin to see changes in streamer behavior. 

Best regards,

-- Bert -- 
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com


Tesla list wrote:
> 
> Original poster: "Paul Nicholson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
> 
> Jim Lux wrote:
> > Corona discharge isn't a particularly high current phenomenon
> > ( a few mA),
> > ...Without giving it much thought, I would expect the DC average
> > current to be in the microamps,
> 
> Hmm, indeed. The corona only a small fraction then of the topload's
> displacement current...so the DC component of the corona will be
> another small fraction again, so yes, it might be only a few tens of
> uA. That *is* a tricky one.
> 
> You can see in the fourier spectrum in
> http://www.abelian.demon.co.uk/tssp/tfss270501/
> a small low-frequency blip from slight rectification of the beat
> envelope, which is how we would expect see the DC component.  But in
> this case, the signal was a fairly low voltage using a solid state
> gap and thus no corona, so it must have come from non-linearity in
> the recording.  Just shows that any attempt to detect this must be
> very highly linear to succeed.
> 
> > One approach might be to run the secondary current through an
> > electrolytic cell and measure the amount of metal added or removed
> 
> A cunning solution!
> 
> Or perhaps a minute deflection of a compass needle close to the
> secondary.  Anyone got an aurora detector?
> 
> > Most of the spark theory says that the charge for a free air
> > streamer moves back into the source as the spark collapses,
> > leaving essentially neutral (net) air behind (it might be ionized,
> > but there's an equal number of + and - ions).
> 
> in which case we would see no DC leakage at the base.  Any that we
> do see must then be due to charge leaking permanently away from the
> topload - beyond recall, so to speak, by the next half-cycle.
> I guess we'd only see these currents, if they exist at all, when
> the topload is close to arcing to something.  A reliable detector
> might make a neat warning device or automatic cut-off.
> 
> dwp wrote:
> [DC build-up on the topload]
> > ...has been widely reported, for varying designs, that there is.
> > It appears to be on the order of a few KV, rather than the
> > 100s of KV associated with the nominal output, however the
> > DC does seem to be there.
> 
> You'd better tell us just exactly where this has been 'widely
> reported' because it's obviously wrong.  A few kV of DC on the
> topload would give a constant (few kV)/(few tens of ohms) amps
> through the secondary, and the wire would quickly melt. And if
> that's not good enough for you, consider: a dc base current
> component cannot be bigger than the ac base current, since it
> must come (somehow) from rectification of just a fraction of it.
> Thus, even if the entire coil base current was somehow rectified
> at the topload, the top voltage DC would only be a few tens of amps
> times a few tens of ohms.  Those are two real good reasons why you
> should seriously question any claim of DC on the topload.  Static
> charges evolving on the surface of dielectrics, or on floating
> conductors placed near to the coil or topload, are quite another
> matter, and these may be one source of faulty observations.
> 
> [Applying a DC pedestal to the coil base]
> Jim wrote:
> > an intriguing idea.  Especially if you were to make the voltage a
> > significant fraction of the topload voltage during breakout,
> 
> I was wondering if it might help preserve the remnants of streamer
> channels between bangs, thus enhancing subsequent growth.
> 
> > You'd want a good RF bypass cap across the power supply
> 
> A non-trivial component, I imagine.
> 
> > You'd want a small TC (low voltage) for this so you could really
> > make a difference. A few kV out of 500 kV on a big coil might not
> > make a difference.  10-20 kV out of 75-100 kV though...
> 
> Hope someone rises to the challenge, to see what a DC supported
> breakout looks like.
> 
> --
> Paul Nicholson
> --