The Turn Of The Century Electrotherapy Museum
http://www.electrotherapymuseum.com
(C) Jeff Behary 2007

4" Multilayered Pancake Coil


Coil winding arrangement.  Many many many thanks to Frank for the silk-covered magnet wire.
Its a must-have for Pancake Coils.  The silk acts like a wick and absorbs the wax making an air-tight seal around and
between the wires.  The interleave material is 2 1/2" wide drywall seam paper.  The coil form is seen to the right.  Its just
a piece of hexagonal PVC scrap.  The hexagonal shape allows a round form with plenty of room for wax to flow.

25 turns per layer were used.  Interleaves  were secured using electrical tape.  The tape was never allowed to overlap
the windings, as this might interfere with the wax insulation.

The silk covering provides a mechanical separation of the windings without space-winding them.  It also provides
a 360 air-tight insulation around each wire when the wax is poured.   


Mejla isn't wrecking havoc at the moment.

The finished coil is approx. 3 7/8" in diameter - 20 layers, 500 turns. 
The primary was 3 1/2 turns of 1" copper ribbon, insulated with a single thickness of
the drywall interleave material.

The coil was centered in the bottom of a 6" ABS drain pipe and filled with a mixture of paraffin wax and boiled oil.
1" of solid wax surrounded the entire coil and filled all of the interstices.
The discharge post was another hex PVC, and the discharge ball only a 5/8" diameter ball bearing.


The transformer was 4000V, adjustable current.  .048 mfd was used.  A single 1 1/4" Tungsten Quenched Gap was used, the tungsten being
mounted to 6" diameter aluminum heat sinks.

The purpose of the this coil was to produce the Phantom Streamers.
At low powers, 50 - 200 watts, 1 - 4" showers of sparks were produced.   The "Phantom" Streamers darted out
a visible distance of 6" but could be felt nearly a foot away from the ball.

I then tested the unit the same with a 5kV 120mA Cold Cathode Transformer, and a 6" spark came out of the bottom of the casing to the ground, arcing across the white PVC bottom plate and burning the 3/4" phenolic plate below that (and to the ground a few inches lower).  Lesson learned, when you insulate
with 1" of wax make sure its on the bottom of the coil too!!!!



I had to repour the coil with new wax and set the discharge post an inch higher to avoid sparks through the bottom to ground!


At 5kV 120mA the unit produces a 4-6" hot discharge depending on the setting of the spark gap.
The effects in studying the Phantom Streamers are much more interesting though.  A power supply will be built that consumes only around 200 watts.