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Re: [TCML] DRSSTC ring-up

Hey Udo!

On Tue, May 28, 2013 at 6:02 AM, Udo Lenz <udo_lenz@xxxxxxxxxxxxxx> wrote:

> 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.

This is something i suspected but still have difficulty proving.  Have you
done any formal analysis to share on the subject?  My subjective view was
simply that spark performance remained similar to the lower pole design
(which had the same operating frequency) but the primary current went from
~300A to ~200A in my case.  But i still cant come up with a proof that says
one pole is better than the other in a general sense.  This is something i
should work on :-).

> Effciency in this context means a low current to achieve a given
> secondary voltage or power transfer to the secondary.

Yes exactly.  Of course there are many "efficiency" measurements that can
be talked about, but this one is of most interest to *me* at this time ;-).
 To me this is sort of an efficiency associated with the Tesla transformer
itself, which is good because it can be thought of independently of the
driver efficiency.

> 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.
Yes exactly.  Its as if the Tesla coil stores less energy with the higher
pole tunings, which implies less primary amps.  But as i said before, ive
yet to formally prove this idea to be true.. its all just instinctual.   I
wouldnt be surprised at all that you can make the numbers work in favor of
either pole, and that its just more practical to get the tuning right for
the upper pole.  In fact, maybe the poles only make a difference until the
system is sufficienty loaded, and then the CW efficiency is purely related
to the tuning (being out of tune causes the primary current to build up
higher to make up for the lower power transfer to the spark).  Its silly
that i havent settled all this for myself yet :-).

> 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.

This is an important observation about the tunings, and my thought is that
its simply because a streamer always *adds* capacitance and lowers the
natural frequency of the TC, so you want to bias the tuning to accomodate
that.  So for the case of operating at the upper pole, it means the primary
should be tuned below the natural resonance of the secondary (as you said).
 As previously stated by me, the simple self-oscillating driver will then
excite the lower pole resonance (as its more "in tune" there) more than the
upper pole, and will eventually reside at the power pole frequency in CW
mode.  However, with a "smarter" TC driver, you can ring up the upper pole
frequency at start up causing the self-oscillation to end up at the upper
pole, which the tuning was set up for and consequently the primary current
should be lower.

>  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.
I hope to some day release my newer driver design for sale, but i think its
sufficiently complex that it would be sold as a completed unit to avoid too
many assembly issues.  More on that when its closer to being releasable.


> 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.
> Udo
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