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RE: [TCML] RE: Splicing wires - Secondary Coil
All,
A couple of years ago, during a Teslathon, I accidentally miss-connected
the primary on Zotzilla (big coil)to the wrong tap (fo too high). During
the pursuant demonstration, the secondary flashed over and burned the
winding in two spots: almost exactly one third and two thirds of the way
up. I imagine a harmonic may have been responsible for the location of
the damage. Not sure. With a ton of eager help on hand, we removed two
turns at each location, cleaned the carbon spots with lacquer thinner,
soldered the wires back with a smooth ball of solder, slipped several
small pieces of phish paper over and around the "splices", added a few
layers of ten mil tape, re-tapped the primary, and much to everyone's
surprise, the coil has never worked better since. Strange, isn't it?
Oddly enough, I'm almost afraid to re-wind the secondary "to make it
look pretty again", because I may lose the gains in performance acquired
after it burned up in the first place.
Explain that.
Hank
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Steve Ward
Sent: Monday, May 03, 2010 11:10 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] RE: Splicing wires - Secondary Coil
Hey Dan,
Can you please elaborate on how they "failed"? Do you mean the
oscillating
frequency was wrong? or you had electrical breakdown? If it were *only*
breakdown of the winding, then it sounds like the simple answer was that
the
insulation was compromised, or the e-field stress was higher due to the
discontinuity in *geometry*. Seems perfectly plausible. But if the
oscillating frequency of the self-resonant system changed due to this
splicing, and yet the coil still measures the same L as a non-screwed-up
coil, then im still confused by this.
I guess its possible the point fails right away with a short, which
would
certainly change the Fres.
Steve
On Mon, May 3, 2010 at 7:20 AM, McCauley, Daniel H <
daniel.h.mccauley@xxxxxxxx> wrote:
>
> Steve,
>
> Well, first of all don't, don't assume. I never said anything about a
> reflection or anything regarding secondaries behaving like
transmission
> lines. I simply stated it was an impedance discontinuity at the point
of
> splicing. This could be as simple as a bad solder joint, poor
connection,
> etc... at the splice due to poor workmanship. Or maybe its the sharp
point
> as you mentioned that causes some break-out and makes the system tune
to
> that point.
>
> And I don't have any measurements handy, but I have plenty of bad
> experience with splices. Just last year, I had a magnetics house down
in
> Mexico wind 100 small coils for a customer of mine. These were for a
small
> self-tuning SSTC coil. After having each of the first (5) coils I
tested
> fail about 85% up the coil, i began to suspect that something was
amuck.
> Upon close inspection of the coils, i noticed a splice point. After
some
> discussions with the manufacturer, it was determined that the coils
were all
> wound initially, but too short, so they decided to splice and continue
> winding the coil to spec.
>
> Now electrically (with LCR meter), these spliced secondaries measured
just
> fine, and from visual inspection, you would never even notice the
splice
> unless you used a magnifying instrument. But when connected to a
> self-tuning driver, they all failed at that splice point.
>
> Now I certaintly don't claim to know all the theoretical and
mathematical
> explanations to why this occurred, and I'm *certaintly* open to
suggestions
> from other people regarding this, but I do know that they were all
failing
> at this point, and the only thing I can think of is some sort of
impedance
> discontinuity due to the splicing causing this problem.
>
> So again, its my opinion that if you have a self-resonant system, i
don't
> recommend splicing your secondaries.
>
> Daniel McCauley
> http://www.easternvoltageresearch.com
> DRSSTC, SSTC, Flyback Kits and Components!
>
>
> >If you are going to make your point #2, i demand to see some
> >measurements (or even simulations, >or even supporting math),
otherwise i
> dont believe it for a second. Of course i have seen the instability
during
> ground arcing of a SSTC, but that really is a BIG change in impedance
which
> >DOES cause the mode of the system to change. And this was always
with
> secondary coils that didnt have any splices in them, so we cant blame
it on
> that.
>
> Steve
>
> On Sat, May 1, 2010 at 6:46 AM, McCauley, Daniel H <
> daniel.h.mccauley@xxxxxxxx> wrote:
> > 2. If you are running a self-resonant (antenna or current feedback
> > based) coil, then it is NOT recommended to splice the wires.
> >
> > The reason for this is that with a self-tuning system, there will be
> > some impedance discontinuity at the point of splicing. And the
> > self-tuning feedback network has a high probability it will detect
> > this continuity and tune the coil accordingly making that
> > discontinuity the node where voltage is maximum. What happens next
is
> > that your coil is now tuned at that point, and high voltage peaks
and
> destroys your secondary at the splice point.
> >
> > This is one of the drawbacks with self-resonant systems.
> >
> > Which makes me think, maybe some sort of notch filter in the
feedback
> > network would prevent this. Hmmmm . . . sounds like an idea!
> >
> > Daniel McCauley
> > http://www.easternvoltageresearch.com
> > DRSSTC, SSTC, Flyback Kits and Components!
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
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