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Re: Gap Dwell Times (formerly: Beating Solved)



Tesla List wrote:
> 
> > Subject: Re: Beating Solved
> 
> >From bturner-at-apc-dot-netWed Sep 25 21:01:09 1996
> Date: Wed, 25 Sep 1996 03:21:51 -0700
> From: open_minded <bturner-at-apc-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: Gap Dwell Times (formerly: Beating Solved)
> 
> Tesla List wrote:
> >
> > >From MALCOLM-at-directorate.wnp.ac.nzTue Sep 24 22:28:55 1996
> > Date: Wed, 25 Sep 1996 10:04:47 +1200
> > From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> > To: tesla-at-pupman-dot-com
> > Subject: Re: Beating Solved
> >
> > snipola
> 
> Malcolm -
> 
>   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 hope this is correct...perhaps
> Richard H. can jump in on this one....????)

You are correct in your understanding of what the Corums have said.  The 
gap should come on and extinguish prior to the first zero crossing of the 
first tank circuit ring wave. (1/2 cycle)  Richard Hull
> 
>   While I don't have the exact specs (yet...) as far as k and the beat
> freq for my coil, 40uS is a bit long for a 230KHz (approx.) coil, unless
> my coupling was in the dumper, which it isn't. 40uS at 230KHz yields
> a k of only 0.108, which definately would be in the 'dumper', and the
> coil would probably NOT toss out it's healthy 6-footers.
> 
>   Yeah, *any* timing on a rotary gap *will* work, as the idea is to
> create the RF oscillations. Worst thing to happen is that the coil
> isn't running at peak efficiency, and more line inductance (current
> limiting) is needed.
> 
>   Problem is that most coilers go with what they can get their hands
> on, and make the coil run as best as possible with the stuff on hand.


There is nothing wrong with this and it works OK for getting one's "feet 
wet".  Somewhere about the sixth coil, we all start to better the 
arrangement with our own unique ideas.  Richard Hull


> For me at least, that meant using the 1800-RPM motor which was already
> laying around, and 3/8" tungsten-carbide tips which I was able to
> purchase dirt cheap. It works. Not optimally, but it works. 66+ inches
> from a 22" tall winding ain't to shabby, even if the dwell is "exactly
> wrong".
> 
>   I could have re-designed the gap, and used 5/16" tungsten rod instead
> of the 3/8" tips. At 1800 RPM, that would have given me the 20uS dwell.
> By staying with the 3/8", and moving to the 3600 RPM motor, I not only
> get the dwell, but also increase the BPS from 240 to 480. Thus, *twice*
> as much energy is commutated into the system, which hopefully will
> result in hotter (not necessarily longer) sparks.
> 
> - Brent