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Re: Optimal Quenching Tests Subject: Optimal Quenching Tests

Tesla List wrote:
> 
> Subscriber: FutureT-at-aol-dot-com Sun Jan  5 21:42:27 1997
> Date: Sun, 5 Jan 1997 16:36:43 -0500
> From: FutureT-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Re: Optimal Quenching Tests
> 
> <<
>  Subscriber: bert.hickman-at-aquila-dot-com Sat Jan  4 21:54:49 1997
>  Date: Sat, 04 Jan 1997 19:34:26 -0800
>  From: Bert Hickman <bert.hickman-at-aquila-dot-com>
>  To: tesla-at-pupman-dot-com
>  Subject: Optimal Quenching Tests
> 
>  Hi all!
> 
> >I had a few more thoughts on quenching after answering John Freau's post
> >today.
> 
>  >The bottom line:
> > Existing methods for estimating proper quenching time predict
> > excessively long quench times.
> 
> > Why:
> > We can define "ideal quench" as the point at which we have transferred
> >all the energy we can from the primary to the secondary. We let the
> > one-way primary->secondary transfer go to completion, but prevent the
> > reverse from happening. However, quenching too early leaves some energy
> > stranded in the primary. Quench time, k, and Fo are inextricably
> > intertwined.
> 
> >The current method uses k and Fo to compute optimal "dwell":
> 
> >      Toptimum = 1/(2*Fo*k)
> 
>  >However, this does not take into consideration the impact of gap losses.
>  >During the time the primary-to-secondary energy transfer is taking
> > place, we are also losing significant energy through gap dissipation.
> 
> > This means that the first notch of minimal primary energy actually
>  >occurs significantly earlier than predicted by the above calculation.
>  >After some further analysis, I conclude that the actual quenchtimes
> > should be adjusted by a factored of 80% [for k <= 0.18] or 85% [for k =
> > 0.22 - 0.28]. This reconciles certain quenchtime measurements I'd made
> >on both my 6" and 10" coils which showed earlier than predicted times
> > for minimum primary energy.
> 
> > Example (for 10" coil):
>  >  Fo = 90.4 kHz
>   > k=0.209
>   > Predicted Toptimum = 1/(2*90400*0.209) =      26.5 uSec
>   > Adjusted Toptimum = 0.85*Predicted Toptimum = 22.5 uSec.
> 
>  >FWIW.
> 
> > Safe coiling to you!
> 
> > -- Bert --
> 
>  >>
> Bert,
> 
> True, the Toptimum formula you mentioned above will give quench times that
> are too long since they do not account for losses.  The formula is useful
> only as a "rule of thumb" in TC work.  My experimental results agree closely
> with your experimental findings above, regarding the required shortening of
> the quench time.
> 
> However,  the Corums' theories, as expressed in TC Tutor and elsewhere, do
> account for spark-gap losses.  Their TC tutor program shows this nicely;  if
> you change the primary resistance value, the 1st beat notch "time of
> occurance" will change accordingly.  In one of my tests, experimental
> observed quench  time was ~ 8 uS.  I  plugged in a value of 10 ohms for the
> primary losses, and  the program gave me a ~ 8 uS quench time.  If I plugged
> in a 1 ohm resistance, the program gave me a ~ 10 uS quench time.   I of have
> no idea what my actual primary resistance is, but it seems reasonable to me
> that it is about 10 ohms.  Thus, I find complete agreement with my
> experimental findings and the Corums' quench time theories.
> 
> Happy coiling,
> 
> John Freau

John,

Thanks for the update. I don't have the TC Tutor program, but do have
their "Vacuum Tube Tesla Coils" book. When I did an indirect measurement
of my primary alone, by measuring Q under high power, then back-figuring
the "effective" series resistance of the gap, primary, and associated
wiring, I got a value of about 8 ohms. Plugging this into a PSPICE model
for my coil, I get results which are in the same ballpark. Malcolm did
some earlier spark-gap measurements which indicated that, in reality,
the gap's non-linear characteristics could actually result linear,
rather than exponential, decay if primary current.
 
Safe ccoilin' to you!

-- Bert --