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

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 12 Sep 2007 08:05:46 -0700
From: huil888 <huil888@xxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Oil insulated secondaries (fwd) (Are they worth it?) (fwd)

Aaron -

I probably should have been more specific ........ the "pinhole with corona" 
was present only on one of my first epoxy-coated secondary's, and that 
subsequent refinements to the coating process essentially eliminated 
pinholes.
After initial testing of the coil revealed the presence of the pit in the 
coating, the defect was repaired using a toothpick to apply a tiny droplet 
of epoxy to fill the pit. That ended all corona discharge from the pit, and 
the secondary ran corona-free thereafter.

During the last stages of the epoxy coating process, the secondary is 
turning very slowly on the winding/coating jig, and every inch of the 
surface can closely inspected for any thin spots or bubbles. Bubbles are 
"popped" using a hot air gun to locally heat the epoxy, causing it to become 
less viscous and the bubble to expand, which causes the bubble to pop or 
collapse. In the coil that exhibited corona, there was not a real bubble of 
trapped air in the coating, but a "pit" where a bubble had popped but the 
epoxy had not flowed back into the pit. Also, when coating larger coils 
where more than 2 pints of epoxy are used, I vacuum-degas the epoxy after 
mixing. Even a small vane-type vacuum pump/compressor (like used with an 
airbrush) will pull enough vacuum to effectively degas the epoxy, although 
it will froth up to 2X or 3X its initial volume as the bubbles initially 
expand. If you are very careful while applying the epoxy to the coil, very 
few additional bubbles will be generated.

I should have clearly stated that the pinhole/corona was present on only one 
secondary, and that it was repaired as soon as it was detected. It wouldn't 
make much sense to go through the effort to epoxy coat the secondary, and 
then leave a near-microscopic but easily repaired defect that would affect 
the reliability of the coil.

Regards,
Scott

----- Original Message ----- 
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Tuesday, September 11, 2007 12:36 PM
Subject: Re: Oil insulated secondaries (fwd) (Are they worth it?) (fwd)


>
> ---------- 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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