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Re: [TCML] Re: Position of baffle inside secondary

Hi Herr, all,

I have only experienced the HV tracking carbonization
of the inside of a secondary coil form once and that was
with an Information Unlimited BTC1 kit coil that I pur-
chased (I'm telling on my age here ;^), probably 22 or
so years ago. It was a small OBIT driven coil with an
appr. 3" x 12" secondary form, and the best spark length
that I ever got out of it was in the 6 to 8" range, so no-
thing big and spectacular in power or performance ;^\
Anyway, as I got more and more practical Tesla
coil building experience under my belt (learned mostly
through the school of hard knocks - this was before
the days of the TCML or even the Internet, for that
matter), I started installing internal baffles in my second-
aries. However, since my machining tools (and abilities)
have been pretty challenged, I have never been able to
cut out disc that made a perfect fit inside of the second-
ary form. Yet I have still never experienced an internal
flashover (to my knowledge) since that original incident,
so I am really wondering if the internal baffles are really
even necessary? That IU BTC1 kit was barely achieving
spark lengths of even half that of the secondary coil length
and yet it suffered the internal flashover. My large Green
Monster system typically produces spark lengths of 3X the
49" long secondary coil and although I did install 2 inter-
nal baffles, I can assure you that they are nowhere near
air tight fits, and I have never experienced internal flash-
over with this pole pig driven beast (external flashovers/
racing sparks - unfortunately yes, on occasions, but never
internal flashovers). Yes, I have used the silicone sealant
to seal around the edges of the baffle discs but I really fail
to see where that little 1/4" bead of sealant would stop a
HV spark that easily travels in the 150" linear point/point
range outside the coil.? Thoughts, anyone?

David Rieben

----- Original Message ----- From: "Quarkster" <quarkster@xxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Sunday, July 12, 2009 3:36 AM
Subject: Re: [TCML] Re: Position of baffle inside secondary

Peter -

I've always used an internal baffle near the top of my secondary coils, 2-4 inches down from the end of the form (depending on form diameter). I run the top end of the secondary wire through the sidewall of the form, and secure it to a standoff insulator mounted in the center of the baffle. Then, I run a separate conductor from the standoff insulator up to the topload. This way, the secondary wire is always mechanically strain-relieved, and the baffle eliminates any risk of internal arcing down to the grounded end of the secondary.

Regular hardware-store silicone RTV sealants release acetic acid during the cure cycle (that's why they smell like vinegar). Acetic acid residue is not a good thing to have inside a secondary form, so I use an "electronics grade" RTV that releases alcohol during curing rather than acetic acid. General Electric makes several different electronic grade RTV products, including RTV 160, RTV 162, and RTV 167. Dow Corning also makes electronic grade RTV sealants. There are also some automotive grade RTV sealants that are marketed as "safe for oxygen sensors" that do not use the acetic acid cure system.

I make the baffle so it is a light press-fit in the ID of the secondary form, and first apply a heavy bead of RTV inside the form, about 1" above the desired location of the baffle. When the baffle is pressed into place, it pushes the bead of RTV in front of it, creating a nice, uniform 360-degree fillet. After this RTV has cured, I apply a second fillet of RTV on the top side of the baffle, ensuring that the baffle is 100% hermetically sealed to the coil form. If there is even a microscopic void or gap, eventually the HV will find it and arc around the baffle.

I started using baffles after I lost a small secondary to internal arcing long ago. Coil performance started out fine, but output gradually diminished to near zero. Careful examination of the coil relealed a deep, carbonized arc track inside the secondary.

Herr Zapp
----- Original Message ----- From: "Peter Terren" <pterren@xxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Saturday, July 11, 2009 1:07 PM
Subject: [TCML] Re: Position of baffle inside secondary

I need to position a single baffle inside a TC. My guess is that voltage stresses are greatest the base as that is where racing arcs are, so a baffle near the base would be best.
Any comments? Hey even a noob has a 50% chance of being right here.
I think when tuned that voltage is lowest and current highest near the base, but in a racing arc situation things may break down more at the base

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