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Re: Question regarding synchronous gap driven coils



Tesla List wrote:
> 
> > > Subject: Question regarding synchronous gap driven coils
> > Subject: Re: Question regarding synchronous gap driven coils
> > > Subject: Question regarding synchronous gap driven coils
> 
> Subscriber: sgreiner-at-mail.wwnet-dot-com Sun Feb  2 17:59:31 1997
> Date: Sun, 02 Feb 1997 15:58:08 -0800
> From: Skip Greiner <sgreiner-at-mail.wwnet-dot-com>
> To: tesla-at-pupman-dot-com
> Cc: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: 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

Skip,

One way, mentioned earlier by Richard Hull I believe, is to use the
light off the gap itself, piped through a fiber optic cable, to a high
speed phototransistor or PIN diode. The actual dwell will be the same as
the length of time the arc is "lit". 

Based upon the description of the rotary gap, I suspect that any
quenching you're seeing is primarily attributable to heavy streamer
losses, and not from the rotary forcing a quench. Under these
conditions, its not the gap that's causing the broad tuning range you're
seeing. However, if you're running with fairly large tank capacitance,
you may still be getting rather consistent and heavy breakout. Once this
occurs, you'll lower the secondary's Q, and thereby broaden the "tune"
of the system. That was probably as clear as mud, right?? :^)

Safe coilin' to you, Skip!

-- Bert H --