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A word about internal primary coils
Original poster: Finn Hammer <f-h@xxxx>
All,
The idea about internal primary coils come up from time to time, and
I was an advocate for the idea myself, a couple of years ago.
It is entirely possible, and coils built this way, by myself, are
running daily in museum environment. One of these coils is a 1-turn
primary OLTC, which lends itself nicely to internal coils, the other
2 are SSTC`s. These coils are configured to produce short bursts of
up to 54 ringdowns @500BPS which means that they only operate 1/10th
of a second with seconds of rest in between.
The purpose of this driving scheme is to make the discharges look
like lightning bolts.
Provided that this "macro duty cycle" is kept low, no problem.
But if you run the coil flat out, with coupling coefficients in the
competitive range, problems develop.
The voltage gradient between. primary and secondary becomes large
enough to produce corona at the primary coil, and this corona starts
to burn the coilform internally, until there is a spot of carbonized
PVC internally, adjacent to the point where the corona is most
intense. Usually the end of the top turn.
This spot of carbon is in corona contact with the primary, and in
capacitive contact with the secondary.
Something interesting happens now.
Capacitive contact from the secondary winding couples trough the PVC
former, _without puncturing it_ (*I have checked*), and the carbon
spot starts to grow upwards towards the top of the coil. It looks like this:
http://home5.inet.tele.dk/f-hammer/tracking.jpg
With any air in the area btwn. primary and secondary, this problem
will arise, I wonder how Greg avoided it in the Electrum. Probably by
making the coil so big, that sufficient clearance btwn. primary and
secondary was possible. This could bring the voltage gradient down to
reasonable levels.
To my knowledge, in smallish coils, the only way to get around it is
to introduce potting material btwn. the coils, to avoid corona.
More experiments, pending the acquisition of a vacuum laboratory, is
needed to verify this.
Cheers, Finn Hammer
Tesla list skrev:
Original poster: "Breneman, Chris" <brenemanc@xxxxxxxxxxxxxx>
Hello,
There's been some discussion about internal primaries lately, and I
was wondering if there are any other primary designs which could
possible be easier to build or more efficient than a classic flat
spiral or helix.
For example, could a primary wound externally on the same former as
the secondary but several inches below where the secondary winding
starts work? Or what about a primary actually wound on top of the
lower part of the secondary windings, sufficiently insulated? What
are the consequences of such schemes and would they work at all?
Thanks,
Chris
-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Thu 4/12/2007 4:34 PM
To: tesla@xxxxxxxxxx
Subject: Re: Tesla coil on Ebay; 80-300' lightning?
Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
Not very well. Larger secondary diameters are needed. Given turn
requirements to meet inductance's needed, 8" is too small to be
practical. You would end up trying to wind a 6.5" diameter coil and
it would have to be helical adding to the difficulty with coupling,
placement, and mechanical winding. Either external or internal is
electrically/magnetically equivalent, but practicality is best
external with that small of a coil.
Take care,
Bart
Tesla list wrote:
>Original poster: "david baehr" <dfb25@xxxxxxxxxxx>
>
>
>Hmmm, would a internal pri work with a smaller coil , say 8" dia. ????
>
>
>From: "Tesla list" <tesla@xxxxxxxxxx>
>To: tesla@xxxxxxxxxx
>Subject: RE: Tesla coil on Ebay; 80-300' lightning?
>Date: Tue, 10 Apr 2007 19:33:17 -0600
> >Original poster: "Hans Schattenmeister" <klugmann@xxxxxxxxxxx>
> >
>
>. The coil was 5' in diameter, had an
> >internal primary and stood about 25' tall.
> >
> >
> >
> >
> >
> >
>
>
>
>----------
><http://g.msn.com/8HMBENUS/2734??PS=47575>MSN is giving away a trip
>to Vegas to see Elton John. Enter to win today.
>
>