Re: the back of secondary winding

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>

(great thread; I was wondering about this myself)

I was watching a friend's coil this weekend, and his
secondary suffered an interesting yet unfortunate
fate:  All of a sudden, a bright spot of light
appeared on the side of the secondary.  After turning
off the coil and approaching, it was observed that a
nice little hole had burned in the winding.  It did
not appear to have resulted from a strike or racing
sparks or anything quite so obvious.

His secondary was coated with fiberglass.  One
possibility I was thinking of was that an air bubble
allowed corona to form near that point, and because it
was trapped, that corona became very hot very quickly,
eventually burning through the windings.  Is that a
possibility?  I had never thought about using
fiberglass before, and I wonder if the viscosity is
such that it would tend to trap air rather easily,
thus welcoming issues such as this.

Anyway, this made me wonder if coating a coil might
actually be *more* apt to produce failures than not
coating it.  I have also often wondered about making
an oil-insulated secondary.  That is, take a piece of
PVC and use a threading jig on a lathe to cut coarse
threads in the PVC in the opposite direction as the
coil would be wound (so the wire doesn't actually go
into the threads).  Wind the coil on this threaded
PVC, then immerse the whole assembly in a
larger-diameter pipe filled with transformer oil.  The
threads will ensure that the oil gets in behind the
windings, making them impervious to corona.  Hmmm...

Regards,
Aaron, N7OE

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

> Original poster: Tim S <stm800@xxxxxxxxxxx>
>
>
>
> Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: Russell L Thornton
>
> snip>
> If we were doing this for
> insulation purposes I would like to put a layer of
> varnish on the
> form mounted to the winding mechanism and while
> still wet wind the
> wire. What's up here?
>
> Russ,
> Monitoring Lightning at the Cape
>
> this is the way i do it.just like you said.wind it
> while adding varnish.
> squuezes between turns.it just seems to work out
> very good and holds
> things together better.
>
> i have been using helmans spar urethane lately and
> works good.
> just let it cure outside in the sun/heat before
> firing it up..
> p.s. use plently of ventillation the fumes are heavy
> and lay on the floor.
> becareful of any sources of sparks or open flame.
> tim
>
>
>
>
>