Re: one turn heating

Subject:     Re: one turn heating
      Date:  Sat, 07 Jun 1997 20:45:23 -0500
      From:  Chuck Curran <ccurran-at-execpc-dot-com>
        To:  Tesla List <tesla-at-pupman-dot-com>
References:  1

Tesla List wrote:
> Subject:  Re: one turn heating
>   Date:   Fri, 6 Jun 1997 13:33:39 -0400
>   From:  "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
>     To:  "Tesla List" <tesla-at-pupman-dot-com>
> Two other plausible causes:
> 1) A short between turns. The short can be *triggered* by ocassional
> side sparks that erode the insulation. A true short will get real hot
> real quick!
> 2) Not a short, but just sparks/corona issuing from this location.
> Both of the above can be *triggered* by scratches, direct hits from
> discharges, and by splitting, which is a result of
> over-coupling. If you have ever had sparks down the side of the coil,
> then you may have had tiny punctures develop. These then become the
> *prefered* points for future discharging.
> AS SOON as I see any side sparks on my coils, I apply another layer
> or two of varnish. If caught early enough you can prevent major
> damage.
> The most important thing, of course, is to eliminate the CAUSE of the
> sparking, which is usually overcoupling. Notice that as you pump
> more power into your primary, you will usually experience more
> symptoms of over-coupling.
> If a spark gap is opened too wide, you may *also* experience symptoms
> very similar to over-coupling.
> If you use space-winding then you get less of this over-coupled
> arcing, but you *may* find degradation of discharge length.
> If the damage is extensive, you may have to do some minor surgery.
> Since you have a fairly large gauge wire, this will not be *too*
> difficult. You can cut the wire right at the break and carefully
> unwind 1/2 turn above and below the cut point. Cut and trim wires so
> they meet in the middle. Carefully tin the ends of the wire, solder,
> and then make an ohmmeter check to make sure they are actually
> soldered. Then cover with Behr Build or whatever insulation you
> prefer. Richard Hull has another method for repairing damaged
> windings. Perhaps he will share it with us again.
> Fr. Tom McGahee

Fr. Tom:

Another update with my repair efforts from this morning.  I did cut into
the damaged section with my Dremel tool using one of those little 3/4"
diameter saws.  Boy that was tough to do after all that work!  I peeled
out two wires all the way around to start and yes, it was a clear short,
complete with a specific spot that appeared to be the starting point. 
Bert Hickman and I briefly discussed a spot on the coil that was bubbled
slightly maybe 1 1/2" long and 3/16" wide after the initial very brief
runs.  It turns out that this is where all the action apparently
started.  I clearly either damaged it during fabrication or something
else occurred to mess it up.  I thought that my overcoupling arcs had
been about 6" lower, but that is really a guess from 30 feet away.  It
easily could have been the result of the primary secondary arcing that
had been evident on my third test night.  Well, tomorrow I'll lay in the
repairs and keep my fingers crossed!  Next I'll have to modify the
vacuum gap construction to eliminate melting of the acrylic plastic
electrode housing.  That will be pretty straight forward.
I hope to get it back up in order to start the actual tuning process,
curious about the final efficiency, from a spark distance per Kw
standpoint--not good now.
Chuck Curran
Cedarburg, WI