RE: Primary current feedback on the DRSSTC-3

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Shad Henderson <sundog@xxxxxxxxxxxx>

I've seen this exact effect on a tube coil that James H. owns, plus a
tube coil of my own.  Here's what happens.

You tune the primary low, and basically "bully" the coil into breakout.
Once the coil detunes to a certain point, it "snaps" into resonance with
the primary. This is marked by a audible pop from the streamers, plus
the input current settles down a bit as the pri-sec impedance match
becomes a bit more reasonable.  What's interesting, is that once the two
are running at the same frequency, I can generally back the variac down
to just a bare brush discharge and it won't fall out of that operating
mode.  IE, I run the variac back up and no "pop" as it jumps frequency.

It doesn't surprise me that SS TC flavors exibit this behavior.  I'm
interested to know if there's an increased amount of RF trash on the
primary until the system snaps into resonance.  I believe that all TC's
exhibit this behavior, but with all the crash and bang of SGTC's, it's
almost impossible to tell when it happens.

Interesting!

Shad




On Mon, 2005-02-14 at 09:24, Tesla list wrote:
> Original poster: "Steve Conner" <steve.conner@xxxxxxxxxxx>
>
>  >im getting about 30" sparks
>
> Wow, that is hardcore stuff considering the small size of your DRSSTC-3. I'm
> really not surprised that it detunes by 22% :-o
>
>
>  >i noticed the primary
>  >current had a much nicer linear ring up, instead of the choppy looking
>  >current ring up when tuned in the middle
>
> The transient simulation I have predicts this. It also says that the lower
> tuning you're using produces less output voltage for a given primary
> current. That explains why you have to turn the DC bus voltage higher to
> achieve breakout, and also explains the "snap" effect. When the streamers
> form, they pull the secondary down to match the primary which has the effect
> of increasing the output voltage, hence reinforcing the streamer growth. So
> your streamers explode out all of a sudden.
>
> They don't keep growing infinitely because pulling the secondary down lowers
> the primary current too (and also the real part of the streamer load damps
> the resonance)
>
> You need to be careful going down this road. You'll probably find that the
> tuning for best eventual streamer output produces insanely high primary
> currents prior to breakout. I expect the pre-breakout primary current will
> be what limits how far you can go with the detuning thing. Eventually you'll
> reach a point where the IGBTs explode before any sparks appear at all.
>
> Steve C.
--


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