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Re: [TCML] DRSSTC ring-up

Steve Ward wrote:

It turns out another efficient tuning is to leave the coils more or less
"in tune" with eachother, but have a driver thats smart enough to drive it
at the upper pole frequency (which might be significantly higher).  This
can excite just the one resonance (upper one) after enough cycles, and i
find in my latest experiments that driving at the upper pole while
"detuned" for streamer loading is much more efficient than driving at the
lower pole with streamer detuning.

The reason for this has to do with the location of the poles. If the primary
is tuned lower than the secondary, the lower pole will be located somewhat
below the primaries resonant frequency. The upper pole will lie a bit above the
secondary resonance.
The upper pole is much closer to the secondary resonance than the lower pole,
so running at the upper pole frequency will make your coil much more efficient.
Effciency in this context means a low current to achieve a given
secondary voltage or power transfer to the secondary.
The problem of having to generate a lot of primary current to get the streamer
started in the case of running at the lower pole is circumvented.

Running at the upper pole won't help, if your secondary is tuned below the primary.
In this case the upper pole will be the one which is far away from the secondary
resonance. In terms of efficiency the role of the poles is reversed then.

From simulation it seems, that a coil which does simple primary zero current switching,
will ramp up with a mixture of both poles, if primary and secondary are tuned close.
This will show up as a beating, i.e. an oscillation of the current amplitude.
If there is a considerable difference in primary and secondary resonant frequencies,
the coil will ramp up mostly with the pole, which is close to the primary freq.
That leads to less beating.

Sadly, this is just the "wrong" pole in the light of the above. So some special
electronics is needed to achieve the nice effects Steve described.

Herwig Roscher wrote:

In the meantime I've found that my TC runs at the upper pole if both coils are in tune and have tuned the primary a little bit lower therefore.

I find this surprising, since you have tuned your primary lower than the sec.
I can only imagine this to happen, if streamer loading pulls your secondary f below
primary f very early during rampup.
Do you know, how far the primary was tuned low? And how do you know, that
you're runnig at the upper pole?

It would be nice if someone came up with an idea to ramp up at the "right" pole
with a simple driver.


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