[Prev][Next][Index][Thread]

Re: Optimal Quenching

Subject: 
        Re: Optimal Quenching
  Date: 
        Fri, 14 Mar 1997 14:34:15 -0500 (EST)
  From: 
        FutureT-at-aol-dot-com
    To: 
        tesla-at-pupman-dot-com


Malcolm, All,

I agree that maximum energy should be transfered at ~1/2kF, and this is
why I
didn't trust my original results.  I did some more work last night on my
transistor "gap" system, and my original concerns were well grounded,
indeed
various flaws were uncovered. The tuning of the system was incorrect in
the k
= .22 arrangement, and this helped to throw off the results.  Also, the
"biasing" of the bipolar transistor was incorrect, causing weird voltage
spikes in the primary.  Under these conditions, the generator may have
been
driving the coil directly, to some degree, instead of allowing the
primary to
ring at its natural frequency.   Another problem was that too much of
the
primary energy was bypassing the (turned off) transistor and ringing
down
through the power supply -- I had to add a larger choke to stop this,
but
there's still some leakage.  After making these changes, the system
behaved a
lot better, but I still don't trust it too much.  But at least now, I
got the
best secondary output using a ~9 uS quench which is much more in line
with
expectations.  Center frequency is 240 kHz, and side frequencies (which
show
up at longer quench times) are as reported previously.

Malcolm, thanks for your comments, it sounds as if your experiments were
more
sophisticated than mine.  I'd be interested to hear a description of the
test
set-up you used for your experiments.  Some time ago, I had a discussion
with
Bert H. regarding just when splitting occurs.  His PSPICE models showed
NO
splitting before ~1/2kF.  Are you saying that splitting occurs at or
beyond
1/2 cycle, but that it does not become "troublesome" (noticeable, or
possible
racing sparks, etc.) until after ~1/2kF?  Is it a matter of degree?  Is
PSPICE correct?  I'd be most interested to hear your views.

Towards optimal coiling,

John Freau


<< Hi all,
>          Having done experiments with a MOSFET "gap" system last 
> year, I'd like to make a few comments on John Freau's post and ask a 
> few questions.
>     First, why do sidebands occur (and increase as quench time is 
> increased)? If you look at a quarter cycle of ring, it has a well 
> defined amplitude, right? No change in amplitude = no sideband 
> production. If you look at a half cycle, you now see a change in 
> amplitude. Spectrally decomposing this there are now several 
> frequencies present, the centre frequency and two sidebands of rather
> low amplitude. As the time over which you examine the 
> amplitude-changing-waveform increases, the sideband amplitudes 
> increase at the expense of centre frequency amplitude until you 
> decompose a complete beat envelope at which point, the centre 
> frequency is entirely suppressed and the sideband amplitude hits a 
> maximum. This spectrum is not intuitively obvious when you look at 
> the waveform in the time domain. What you see there is the centre 
> frequency whose amplitude is changing.
 
>     I did exactly what John did and increased the dwell time 
> progessively. What I saw was the secondary amplitude increase in 
> proportion to the dwell until the point (1/2kF approx) at which no 
> energy remained in the primary to be transferred. At no stage did I 
> see the secondary reach that amplitude when cutting the dwell time 
> shorter. I didn't expect to because loose coupling kept a high 
> proportion of the primary energy more closely coupled to the primary
> than the secondary. On cutting dwell time to that of a quarter cycle, 
> I got enormous spikes across the parasitic primary capacitances as 
> the energy still coupled to the primary coil dumped itself into those 
> strays when the cutoff gap disconnected Cp from the primary coil. It 
>never coupled into the secondary for the most part. Cutting 
> conduction time off at half a cycle left a reversal on the 
> cap as I described in the SCR post.
 
>     Question: Did you (John) manage to get all primary energy into 
> the secondary in just 1/4 cycle of oscillation despite the loose 
> I think I'll repeat those expts over the Easter break when I'll 
> have time.
 
> Malcolm
  >>