RE: compact oil insulated secondaries?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Thomson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <dave-at-volantis-dot-org>

Hi Jolyon,

I have constructed such a secondary using the type of construction you plan
to use.  I call it a jacketed coil and it can be seen at:
http://www.tesla-coil-builder-dot-com/images/magnifierT2001.jpg

In the coil pictured I have used the jacketed coil in combination with a
flat secondary spiral, the two coils are connected in series with the wire
length of the jacketed coil being exactly 3 times longer than the wire of
the flat spiral secondary.  This coil arrangement puts out considerably more
amperage in the terminal than a regular all solenoid coil arrangement.  The
trade off is in the spark length.  But the gain is in the distribution of
the spark.  Instead of one or two streamers coming off the terminal, there
is a spray of streamers
http://www.tesla-coil-builder-dot-com/images/chiron032302a.jpg

I have been contemplating building a primary to fire just the jacketed coil
to see what type of streamer length it would produce.

The jacketed coil was necessary for my combination coil design as an
unjacketed coil shot out 8" streamers from the side of the solenoid.  Some
of these streamers arced to the primary.  The jacketed coil completely
arrested all leakage from the solenoid.  An interesting effect, however, is
that an enormous electrostatic charge builds up around the outside of the
plastic jacket during coil operation.  This electrostatic charge pulsates
and remains well after the coil is turned off and can continue to dimly
light a fluorescent tube for several minutes after power is turned off.

I use transformer oil to fill in the jacket.  In my first attempt I used
silicon sealers and plastic pipe cement to seal off the ends.  But the
transformer oil eventually ate through and it leaked.  I solved the problem
by sealing with polymer coating inside the tube.  To keep the polymer
coating from leaking through I used silicon sealer.  The silicon sealer kept
the polymer coating in until it set and after the polymer set, there haven't
been any further leakages.  This coil is still in excellent condition about
a year and a half later.

Instead of using rings cut out to plug the top and bottom, consider using
PVC end caps with holes cut in them.  The end cap should fit the outer
diameter of pipe and the hole should be just large enough for the inner
diameter pipe to slide through.  In the first photo above the end caps are
made of black PVC and contrasts the white PVC pipe.  All materials in my
system are schedule 40 pipe.

Keep in mind that if you drill holes in the inner pipe to feed your wire
through, keep the upper hole above the oil line and seal it with epoxy or
some other non-degrading material.  Keep the lower hole just below the level
where the polymer will fill.  This will help to prevent future leakage.

I used 3 coats of polyurethane on the coil windings before sealing it in the
transformer oil.  I wanted to make sure the wire didn't come loose in the
oil later on.  It probably wouldn't come loose anyway due to the tightness
of the winding, but I just wanted to be safe.

Dave
 > -----Original Message-----
 > From: Tesla list [mailto:tesla-at-pupman-dot-com]
 > Sent: Wednesday, April 23, 2003 9:06 AM
 > To: tesla-at-pupman-dot-com
 > Subject: compact oil insulated secondaries?
 >
 >
 > Original poster: "Jolyon Vater Cox by way of Terry Fritz
 > <teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
 >
 > Dear List,
 > I am considering building an oil filled secondary
 > to improve durability and increase compactness in a small TC in
 > which I am
 > currently using a secondary of 880t of 32swg enamelled copper
 > wire wound on
 > a former measuring 10.875" long x 2.98 diameter.
 >
 > My reason for doing this is because I am planning to double the number of
 > turns by winding a new secondary using 40swg wire on the same former
 > and there may be insulation issues to be considered here.
 >
 > What is envisaged here is a double-walled cylinder made from two
 > plastic  tubes of dissimilar diameter the winding wound on the smaller
 > inner tube with the oil contained between this and the larger outer tube.
 > the ends of the tubes plugged with rings cut from a polythene chopping
 > board and sealed with silicone.
 >
 > I am anticipating cutting the rings from the board using a  hole
 > saw driven
 > by an electric drill with cutting blades of different diameters-
 > will this
 > be OK?
 >
 > Has this method of construction been tried before and  is
 > containment/leakage of the the oil likely to be a major problem?
 >
 > More importantly, what is effect of the oil on primary-to-secondary
 > capacitance -are there tuning issues to be considered with this?
 >
 > Jolyon
 >