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Re: Question regarding synchronous gap driven coils



Tesla List wrote:
> 
> > Subject: Question regarding synchronous gap driven coils
> 
> Subscriber: bert.hickman-at-aquila-dot-com Sat Feb  1 21:09:42 1997
> Date: Fri, 31 Jan 1997 23:34:02 -0800
> From: Bert Hickman <bert.hickman-at-aquila-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Question regarding synchronous gap driven coils
> 
> Tesla List wrote:
> >
> > Subscriber: sgreiner-at-mail.wwnet-dot-com Thu Jan 30 22:23:48 1997
> > Date: Thu, 30 Jan 1997 13:48:42 -0800
> > From: Skip Greiner <sgreiner-at-mail.wwnet-dot-com>
> > To: tesla list <tesla-at-pupman-dot-com>
> > Subject: Question regarding synchronous gap driven coils
> >
> > Hi everyone
> >
> > I address this post mostly to those of you who run synchronous rotary
> > gaps but will certainly appreciate responses from anyone.
> >
> > Here is a quick description of my latest creation although the question
> > also applies to my previous smaller TCs.
> >
> > Secondary:240 turns #14 ga wire on a 14" x 30" skeleton acrylic frame
> >
> > Primary:6 turns 3/8" copper tubing spaced 3/8" apart solenoid wound on
> > 18" diameter acrylic skeleton frame tapped at 5 turns
> >
> > Neon:15kv -at- 120ma
> >
> > Toroid:8" x 18" mounted 2" above top turn of secondary
> >
> > Primary top turn is even with lowest turn of sec giving k=.25(about)
> >
> > Rotary synchronous break -at- 1800rpm giving 1 break per half cycle of the
> > mains at about peak of the sine wave
> >
> > Discharge length over 60" point to point limited by room dimensions
> >
> > Although the discharges maximize at the fifth turn tap, a variation of
> > +/- 1/2 turn has very little effect on the discharge length although
> > changing to the sixth of fourth turn has more effect. The connecting
> > wires between the gap, cap and primary are from 6" to 12" max.
> >
> > In reading various posts it appears that those of you running static
> > gaps and non-synchronous gaps obtain very definite peaking when tuning
> > the primary. My question is: do those running synchronous gaps see the
> > same sharp tuning or do you see the much broader peaks which I
> > encounter. Also is it possible that the broader tuning is due to the
> > fairly large diameter primaries and secondaries which I use or is it due
> > to the synchronous gap.
> >
> > Skip
> 
> Skip,
> 
> Any idea how long your gap is actually firing (true dwell)? If you're
> able to actually quench before the secondary can begin transferring
> power back into the primary, the primary frequency current spectrum will
> be quite broad, and will still very effectively couple to the secondary
> - even if the low power primary center frequency is significantly
> different than the secondary center frequency.
> 
> However, this will be mostly a function of how your rotary is
> constructed, and the resulting dwell time. What diameter, electrode
> size, are the electrodes offset, simple or series, and are you running
> any static series gaps in addition to the rotary?
> 
> -- Bert --

Bert,

The electrodes on this rotary are 0.25" in diameter, NO offset. There
are actually four gaps,in series, each with a spacing of about 0.030".
There are no static gaps. The electrodes are on a 3.5" radius and the
rotor spins at 1800 rpm. With these parameters, I calculate that the
electrodes have a presentation (dwell ?) time of about 1100 usec. Assume
that the TC frequency is about 250khz or a period of 4 usec. If this is
true, there is a lot of oscillation going on while the gaps are
"closed". There has to be some quenching going on because this system
puts out some pretty good discharges ( 60"(+) at 1800va input).

I guess my next natural question is :How do I measure the actual dwell
time? I am too chicken to put the scope directly on any part of the HV.
Is there any other way to look at the dwell time remotely? I have looked
at the secondary current in the base lead using a small toroid around
the ground lead but that doesn't appear to offer any incite.

Skip