Re: DC/AC sparks

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

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:

> Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

> Tesla list wrote:

> > Original poster: "rheidlebaugh by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

> > A tesla coil is not a simple oscilator with contiouous AC power.
 
> A continuous-wave coil is.
 
> > 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.

	Perhaps.
	Max voltage depends on (among other things) drive voltage AND
	leakage from terminal.  Toroid minimizes leakage.
 
>>If you have an unbalanced + pulse a charge will build up on a
>> "static" charged surface and will grow with each pulse, just like a
>> VANDEGRAPH charging a sphere.

	Or....
	Even if the charge voltage is an arbitrarily symmetrical wave
	form, be it undamped, or damped, a DC component can appear
	IF the top terminal, by shape, causes partial rectification.

> "Van de Graaff". A capacitor-discharge Tesla coil does -not- accumulate
> and "DC" charge at the terminal.

	cf above.
	And a number of people report residual charges, consistent
	with DC from 'somewhere'.
 
> During the energy transfer process, the charge there swings a few times
> between positive and negative values, until the electric field around
> the terminal is high enough to cause breakdown and start a spark.

	It is well documented, that, for any terminal (and especially
	a sharp one) the max voltage achievable (or the leakage from,
	which is the same) VARIES WITH POLARITY.

> The spark is then fed by the charge at the terminal at this instant, and
> if it connects to a grounded object, it discharges the terminal with a
> spark very similar to the spark of a VDG. There are differences, however.
> If there is still energy in the magnetic field of the secondary coil, a
> continuous current will keep the spark active for some time, until most of
> the energy in the system is drained.

> > an antenna sensing the wave shape using a scope dosen't see the DC part
>>of the build up. You must use a space charge mesuring detector to read
>>the total charge.

> True, but there is no DC buildup.

	It 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.

> Even if there were, the charging is fast enough for an oscilloscope to
> see everything correctly.

	A small (on the 100s KV scale) DC offset is easy to miss.

>> I don't hear anyone trying to measure this level. Time after time I
>>see postings of streamer size, but no one measures the voltage of the
>>static charge required to make that streamer.

	Streamers can be nicely made by AC.
 
> It's quite difficult to make these measurements, but Terry, for example,
> has voltage measurements in his web site.
 
> > You get a streamer when the AC builds up a DC component to a point
>>that the air breaks down and the total AC & DC fires through the space
>>of your play area.

	Or when the AC does it....

	(DC measurements at the base would be intriguing, even instructive.
	Also challenging...)

	best
	dwp