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Re: Gap Dwell Times (formerly: Beating Solved)
Hi Bert, all,
> > > I did some research this weekend, pouring through a Corum brothers
> > > monograph and some old posts to this newsgroup and found out that the
> > > optimal dwell is 1/(k*Fr), *not* 1/(2*k*Fr). In other words, the spark
> > > gap should conduct for only 1/2 of the superimposed beat-frequency
> > > envelope. Primary current peaks at that point, and maximum energy is
> > > transferred into the secondary.
> >
> > I started from k approx dF/F, and ringup time = 1/2dF so you can see
> > how I derived that. The problem when cutting the gap off (if you
> > could) when Ip is maximum is that with k<1, most of the primary
> > energy is coupled to the primary. I tried doing exactly this with the
> > MOSFET gap and the spikes hit the roof. Virtually none of that energy
> > was coupled to the secondary. The spikes in a real gap would have re-
> > ignited it anyway. I wonder if they have actually tried doing this?
>
> <SNIP>
> Malcolm,
>
> It looks like they did - in the appendix of their booklet "Vacuum Tube
> Tesla Coils", page IV-10, they present a chart which shows experimental
> data points connected with a curve. Their system had Fu=123.33kHz and
> Fl=74.18 kHz, and k=.46(!). The predicted "best case" quenchtime was
> 1/(2*(Fu-Fl))=10.17 uS. They tested dwell times from slightly less than
> 5 uS through 55 uSec, finding that the peak secondary output occurred at
> the expected value of 10 uSec.
Well that sounds right. 1/2dF or 1/2kFr. Important to note though that
the time quoted is related to operating frequency. Even at k = .46,
quenching at the first zero crossing makes the transfer far from
complete. At this k they would have been quenching around the end of
the third primary half cycle. Funny k to use though. The transfer
while done in an integral number of half cycles would not go entirely
to completion IMO. Did they do that with a spark gap or some other
device in its place?
Malcolm
<snip>
PS - If Jim doesn't mind, I'm happy to have the pictures viewed. I am
hoping to take many more and better quality ones off the scope from
time to time for general viewing. The ones I sent were a first
attempt. I had no idea whether they would come out. We are just so
lucky to have this kind of gear available.
[ NOTE: This may be a duplicate. I got a mailer error for this message,
and I didn't recieve it myself, so I'm resending -- Chip ]