Re: Oil insulated secondaries (fwd) (Are they worth it?) (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Tue, 11 Sep 2007 09:19:20 -0700 (PDT)
From: J. Aaron Holmes <jaholmes@xxxxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Oil insulated secondaries (fwd) (Are they worth it?) (fwd)

I don't doubt that an epoxy coating can provide some
measure of corona suppression, but the fact that you
get corona in the air bubbles does not strike me as
especially compelling evidence of its insulating
qualities.  No matter what you paint, coat, or wrap
your coil in, if you miss a spot, that spot seems much
more likely to suffer corona breakout.  In fact, it
seems reasonable (to me) to suggest that, by coating
your coil, you are in fact increasing the likelihood
that corona (e.g., in an air bubble) will cause
damage, because it will be concentrated in a few spots
versus distributed, as it would otherwise have been.

Also, as I indicated below, there are plenty of
opportunities in Tesla coil design to avoid the
requirement of extreme insulation of your secondary
(e.g., oil immersion).  Most of these have become
well-known "rules of thumb" by now.  Unless you have
gone out of your way to disregard these rules of
thumb, leaving only an epoxy coating to save you, it
seems unreasonable to hold the success of your own
coils up as evidence that epoxy coating is a good
insulator.  Much more likely, in my opinion, is that
your design side-stepped the need for extreme
secondary insulation, either consciously, or by
application of what has come to be known as "common
sense" in coil design.

Cheers,
Aaron, N7OE

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> 
> ---------- Forwarded message ----------
> Date: Mon, 10 Sep 2007 21:11:57 -0700
> From: huil888 <huil888@xxxxxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: Re: Oil insulated secondaries (fwd) (Are
> they worth it?) (fwd)
> 
> Aaron -
> 
> I've got to disagree with your position that epoxy
> coatings don't provide
> effective electrical insulation. I've been using
> epoxy to coat every
> secondary I've wound over the last 8 years or so,
> and I can assure you that
> a heavy (.050" or thicker) epoxy coating provides
> extremely effective
> electrical insulation, as well as providing the
> mechanical protection you
> mention.
> 
> Since I started using epoxy coatings, I have never
> had a secondary damaged
> by external arcing or flashover, even when used with
>  helical primaries with
> very high coupling factors. Exactly how much
> electrical insulation is
> provided can be seen when there is a tiny pinhole or
> near-microscopic bubble
> in the coating anywhere in the upper 1/2 of the
> secondary. Once the coil is
> tuned and operating at near peak power, corona and
> thin spidery arcs will
> flow out of the pinhole like a leak in a pressurized
> garden hose.
> 
> I fully agree that aside from the novelty factor,
> its hard to justify the
> additional complexity and probability oil seepage
> with an oil-insulated
> secondary for a conventional Tesla coil.. A
> correctly applied epoxy coating
> will give the appearance that the secondary is
> encased in a perfect glass
> sleeve, an effect that you just can't get with
> concentric acrylic tubes with
> oil in between.
> 
> The only place that I can think of where this
> additional complexity is
> likely to provide any real benefits is in a
> magnifier setup, where the
> extremely tight pri-sec coupling makes it very hard
> to prevent corona and
> flashover.
> 
> Regards,
> Scott Hanson
> 
> 
> 
> ----- Original Message ----- 
> From: "Tesla list" <tesla@xxxxxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Monday, September 10, 2007 7:37 PM
> Subject: Re: Oil insulated secondaries (fwd) (Are
> they worth it?) (fwd)
> 
> 
> >
> > ---------- Forwarded message ----------
> > Date: Mon, 10 Sep 2007 09:53:09 -0700 (PDT)
> > From: J. Aaron Holmes
> <jaholmes@xxxxxxxxxxxxxxxxxx>
> > To: Tesla list <tesla@xxxxxxxxxx>
> > Subject: Re: Oil insulated secondaries (fwd) (Are
> they worth it?)
> >
> > Epoxy coating is not about electrically
> insulating,
> > it's about physically protecting and preventing
> the
> > windings from sliding off.  That's it, really. 
> Oil
> > does neither of these things, and is instead all
> about
> > electrical insulation.  HOWEVER, whether it's any
> > advantage at all depends on what other aspects of
> your
> > design you hold constant, and given that most of
> these
> > other aspects are usually controllable in such a
> way
> > as to avoid the necessity of oil insulation, I'd
> have
> > to agree that oil insulated secondaries are
> moderately
> > to extremely silly in most cases.  They are
> > undoubtedly "interesting" and "cool", though.  I
> loved
> > the look of Terry Blake's coil, and decided to add
> my
> > own twist".
> >
> > All else being equal, I'd expect oil insulation
> would
> > make the secondary less susceptible to secondary
> > breakout, primary-secondary strikes, racing arcs,
> and
> > internal arcing.  This, in turn, might permit the
> use
> > of higher-than-average coupling, larger toploads
> > (which would otherwise tend to encourage secondary
> > breakout), and generally a bit more power,
> achieving a
> > higher-than-average streamer-to-secondary length
> > ratio.  But we'll see!!  Again, I doubt if it's a
> very
> > practical way to accomplish these things, but it
> is
> > nonetheless a fun twist.
> >
> > Cheers,
> > Aaron, N7OE
> >
> > --- Tesla list <tesla@xxxxxxxxxx> wrote:
> >
> >>
> >> ---------- Forwarded message ----------
> >> Date: Sun, 9 Sep 2007 18:22:33 -0700 (PDT)
> >> From: Yurtle Turtle <yurtle_t@xxxxxxxxx>
> >> To: Tesla list <tesla@xxxxxxxxxx>
> >> Subject: Re: Oil insulated secondaries (fwd)
> >>
> >> I'm just curious why oil would be better than
> simply
> >> potting it in epoxy. I realize it would look
> cooler.
> >> Seems like an oil tight seal would be harder to
> >> accomplish than one that only needs to hold up
> until
> >> the epoxy hardens.
> >>
> >> Adam
> >>
> >> --- Tesla list <tesla@xxxxxxxxxx> wrote:
> >>
> >> >
> >> > ---------- Forwarded message ----------
> >> > Date: Sat, 8 Sep 2007 16:22:58 -0700 (PDT)
> >> > From: J. Aaron Holmes
> >> <jaholmes@xxxxxxxxxxxxxxxxxx>
> >> > To: Tesla list <tesla@xxxxxxxxxx>
> >> > Subject: Re: Oil insulated secondaries (fwd)
> >> >
> >> > Hey there, Dave!  I'd be interested in any tips
> >> > here,
> >> > too, however I suspect the number of amateur
> >> coilers
> >> > who have built oil-insulated secondaries can be
> >> > counted on one hand, maybe less ;-)  The only
> >> > functioning amateur oil-insulated coil I've
> ever
> >> > seen
> >> > pictures of is Terry Blake's:
> >> >
> >>
> >
>
http://www.tb3.com/tesla/teslathon2003/tb_tc/tb_tc.htm
> >> >
> >> > It was his coil that inspired me to start
> building
> >> > my
> >> > own oil-insulated coil.
> >> >
> >> > I've also heard of a few oil-insulated research
> >> > coils,
> >> > and seen drawings illustrating their
> construction.
> >> >
> >> > For about the last year, I've been slowly
> >> gathering
> >> > the pieces for a medium-sized oil-filled
> >> secondary.
> >> > For lack of any real guidance on oil-insulated
> >> > construction, I've decided to strike out in
> what
> >> > seems
> >> > like a new direction:  I'm building the
> secondary
> >> > inside an oil-tight ceramic insulator that used
> to
> >> > house a 115kV capacitor:
> >> > http://silicon-arcana.com/cap/cap.jpg
> >> > (on left)
> >> >
> >> > It's about 4' tall and will accomodate a 6" x
> 30"
> >> > coil
> >> > form quite nicely.
> 
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