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Re: TSG instability
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