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Re: [TCML] understanding DRSSTC

On Feb 1, 2013 8:40 AM, "Herwig Roscher" <herwig.roscher@xxxxxx> wrote:
> Steve,
> Thank you so much for sharing your insights.
> Checking whether I got it correctly:
> 1. Unlike standard LC-oscillators having a light coupling coefficient and
running at a
> single frequency, DRSSTCs have a tight coupling and run at two frequencies
> simultaneously.

Im not sure what exactly you mean by "standard lc oscillators" but this
phenomena of 2 pole frequencies comes about with any doubly resonant
configuration.  The coupling factor determines how far apart these
frequencies split apart so low k along with low Q can trick you by looking
like a single frequency.

When operating at the upper pole the coils have current in opposing phase
so the secondary field is cancelling the primary field which makes the
inductance look smaller so it rings faster.  At the lower pole the coils
are in phase so the mutual inductance adds with the primary inductance
making it look even bigger so it rings slower.

> 2. If the primary circuit is tuned slightly below the natural frequency
of the secondary
> circuit, its "hump" becomes bigger than that of the secondary circuit and
the circuit
> runs at the lower pole frequency mainly.

You can also tune the primary just above the secondary resonance and it
will make the upper pole response bigger.

> 3. The lower the primary is tuned, the bigger its hump becomes and the
more energy it
> gets. Tuning lower and lower is limited by starting racing sparks of

Well i think you've touched on an interesting point.  Tuning can greatly
change the behavior of the tesla coil under streamer loading.  If the
primary is tuned very low then the voltage gain of the system could
continue to rise as the streamer grows and puts the secondary in tune.  If
the impedance of the system is too great then you would actually observe a
collapse in primary current as the streamer clamps the maximum voltage that
the coils can ring up to.  If the system impedance is still low enough that
driving the spark is not limiting system Q by too much, then the coil will
simply go out of tune and voltage gain will be limited by impedance once
again .  Ground discharge behavior can be quite different depending on
tuning.  I think the lower pole dominant tuning makes the system build to
higher levels of current as the impedance of the secondary looks lower at a
lower frequency (inductive loading).  If the primary is tuned for upper
pole operation then the secondary will be driven at a higher frequency
because the higher primary tuning and so the secondary impedance could
potentially limit the current more.

How you exploit these tuning options seems to be the hard part.


> Are these assumptions true?
> Kind regards,
> Herwig
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