Re: TSG instability

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 2/27/02 11:01:57 AM Pacific Standard Time, tesla-at-pupman-dot-com
writes:


>
> Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <Gary.Lau-at-compaq-dot-com>
>
> I have been making slow progress with my triggered gap experiments.  I use
> a modified Jon Tebbs zero-crossing detector, driving a capacitor-discharge
> circuit to power an EG&G trigger transformer.  The circuit works well,
> delivering a consistent 3/8" spark regardless of the phase control setting.
> All of my experiments so far have been done using an array of halogen
> lamps to serve as a dummy-load in place of my primary coil.  This works out
> well as the lamp brightness directly indicates the phase "sweet spot" and
> is far less subjective than streamer length.
>
> While I'll ultimately be interested in finding the least lossy electrode
> configuration, I've been stumped by instability when approaching the timing
> sweet spot.  Just as with a mechanical synchronous RSG, the lamp brightness
> increases as the trigger delay increases, approaching the sweet spot.  The
> sound of the gap is a strictly even drone.  Scoping the gap waveform, the
> gap is firing as the gap/cap voltage is still increasing.  Increasing the
> delay, the lamp brightness continues to increase and the gap fires as the
> waveform crests.  But now, every second or so, the gap misfires.
> Continuing to increase the delay, the brightness increases considerably and
> the gap fires as the waveform is on the downswing, but the frequency of
> misfires increases correspondingly with the delay setting.  Clearly, from a
> performance perspective, the gap should be firing at this point, but the
> misfires cause dangerously high voltages across the cap.  If I was using my
> primary and secondary rather!
> than a dummy load, racing sparks would surely result.
>
> I wanted to ask other TSG users what their experience has been with regard
> to this instability.  I don't think my trigger circuit is misfiring when
> the NST is drawing maximum current and causing the mains to droop.  The
> 300V capacitor discharge power supply dips only a few volts when the
> instability is at its worst.  I have verified that the timing is stable
> across a wide latitude of AC input voltages.  That the timing vs.
> power-delivered and stability is so similar to a mechanical SRSG, it makes
> me wonder if there is some mechanism inherent in sync gaps that can't be
> overcome.  But I don't want to believe this.
>
> I'm using a 15/60 NST with a .03uF cap, for about a 3X LTR factor.  Since
> the instability seems most evident when the timing is beyond the crest of
> the cap voltage (optimal for LTR operation), it seems that LTR operation
> may be a factor.
>
> Regards, Gary Lau
> MA, USA




Gary,

Your instability problem again shows a good reason to keep a safety gap across
the TSG.  The specific transformer / cap combination may be the cause of the
instability - but I don't understand why.  Have you repeated the test with say
a .01 or .02 ufd cap?

Ed Sonderman