Re: [TCML] Baffle tally (was Secondary Troubles)

["DC Cox" <resonance@xxxxxxxxxxxx>]

Yes --- this effect is due to the fact PVC is somewhat hygroscopic ---
attaching h2o molecules to it's atomic structure.  That's why it is always
good to sand and apply 2-3 coats of AC-43 to both the interior and exterior
of the tube prior to winding.

We used PVC on some large Van de Graaffs and it totally quit working
(excessive leakage currents down the column) at 600 kV.  Had to switch to
acrylic to overcome this obstacle.  For TC coils, PVC works fine up to a
certain potential level, then we switch to short-fiber fiberglass with resin
for our large 24" and up size sec coils.  Even with coating of AC-43 we hit
the leakage current limit of around 100 uA at 600 kV DC.  RF tracking is
even more pronounced as compared to DC.

Dr. Resonance




On Sun, Jul 6, 2008 at 1:56 AM, Frosty <frosty90@xxxxxxxxx> wrote:

> Not strictly about internal baffles....but.....:
>
> i have noticed some times that if a PVC coil form (or support or other) is
> exposed directly to corona (like the top  wire of the secondary before the
> toroid) sometimes this corona can slowly sort of 'work its way back' along
> the secondary creating a carbon track lichtenbourg patern as it goes, and
> slowly works its way down the inside of a coil form. Has any one else
> actually seen this happening? its pretty interesting to watch, but i would
> think (just from watching this actully happen on a piece of PVC)  that
> internal baffles would have absolutely no effect in stopping this occuring,
> and i think (again, going only by what ive observed) that the most
> important
> thing in stopping carbon tracking (and hence flashover) would be to keep
> the
> coilform clean from dust etc. so endcaps might actually stop the dust
> collecting in the coilform and hence prevent corona/tracking.
>
> Just for the record ive built a 4" and a 6" coil both with no end caps or
> baffles and have never had an 'internal' flash over.
>
> I would suspect that most internal flashovers could be prevented by simply
> keeping the 'inside' or the coilform empty....(i.e no wires or bolts/nuts
> protruding inward from the top load etc).
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