More melted stuff

To: tesla-at-poodle.pupman-dot-com
Subject: More melted stuff
From: Tesla List <tesla-at-stic-dot-net>
Date: Mon, 07 Apr 1997 07:27:47 -0500
Approved: tesla-at-stic-dot-net
Subject: 
        More melted stuff
  Date: 
        Mon, 7 Apr 1997 06:26:03 -0500 (CDT)
  From: 
        Bert Pool <bertpool-at-flash-dot-net>
    To: 
        tesla-at-poodle.pupman-dot-com


Wild Bill came over to my place yesterday, and we tore down my magnifier
secondary.  I had noticed some heavy inter-turn arcing during my last
run,
so I thought I'd better check it out.

It was not a pretty sight.  The inter-turn arcing had been 10 to 12
inches
long in places and had melted holes a foot long completely through the
30
mil poly that was wrapped around the secondary.  The secondary wire had
multiple punctures with severe carbon deposits around the punctures -
usually 3 or 4 adjacent turns in one area were damaged.  A lot of the
arcing
had occured beneath the windings.

We removed all the wire and sanded the entire form down to virgin
plastic
and rewound it with h.v. test prod wire that has a 10 kv rating. 
Because
this new wire is only about 14 gauge, I decided to go ahead and wind a
second layer on top of the first and parallel them for higher current. 
I
know that bifilar winding works on Tesla coils, because I've done that,
but
no one on the list serve last week said that they had ever tried using a
coil that had two layers of wire. (Typically, bifilar winds are two
wires
wound side-by-side, which does reduce the dc resistance by half, but
your
turns count drops by half as well.)  When you wind a second layer on top
of
a first, the second wire ends up being somewhat longer than the first. 
I
know at high frequencies this small difference in length could end up
being
a significant fraction of the operating wavelength so that the phase
difference between the induced currents in the two wires could result in
large voltage differences between adjacent turns.  However, at typical
magnifier frequencies, the operating wavelength is miles long, so the
phase
difference between two adjacent wires, one somewhat longer than the
other,
should be insignificant. One can theorize all day long that a two layer
coil
might work, but there is only one way to know for sure!

We measured the inductance of each of the windings.  They both measured
9 mh
within 1/4 mh.  Paralling them resulted in a final measured inductance
of 9
mh.  The old secondary was 10 gauge wire and measured 6.67 mh.  Our
turns
ratio on the driver will be higher with the new coil.

I will be buying some new 60 mil poly whicj I will use to insulate the
secondary later this week, and I may get to test the new driver
secondary
this next weekend.  I'll post the results of the two layer coil as soon
as I
run it.


Bert Pool
bertpool-at-flash-dot-net