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Re: Optimal Quenching Tests
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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