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about things that interest me.

Tag Archives: tesla coil spark gap


Shell condenser   Testing brings no joy.

It appears that I have a major error in the coil lay out design.

The outer ring of the disk seems to be a short in the field that limits the rim to 485vac instead of the 80,000 that I was aiming for. The design of the coils was for a 600 volt per turn field. 485 volts is about right for the coils fully loaded sag.



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Tesla remarked in his “Boulder Colorado Notes” that with air coils, any 3rd coil aligned with and within the influance of the primary field would react with the same per turn voltage as the primary.

Note that this drawing of Tesla’s transmitter, the top toroid is covered with dimples. In the Wycliffe design the dome was covered with “scales” that did not touch but were connected in a star pattern at the center of each panel to prevent current circulation.

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Pictorial schematic 03

Guess I should have paid better attention.

My present layout has all the power coils in axial alignment with the disk.  The skin of the disk acts as a short.

The naked main coil would light up florescent tubes 3 feet away.  The unpainted Disk over the coil limited the tubes lighting up to about 6 inches. The metal paint seems to be preventing enough radiation to cause any light up of the tubes. To solve this problem all the coils will be removed and used remotely for testing while a new coil system is designed.

A poly phase coil driver set is contemplated.  Most likely star configured and laid out axially between the frames 90 degrees from the disk axis.  pg


Smoke Test!

Circuit Smoke Test!

I could no longer stand it. Time to apply power and test the circuits.

Things were put away well enough and the floor cleaned. Other work caught up, So I hooked up the power supply and turned on the switch. The spark gap hissed nicely and there were no loud noises. I took out an old florescent tub, turned off the lights and  examined the fields. Emm……….. kind of weak. Turned things off after 10 minutes and had a late lunch.

Later in the evening, turned the lights off. Now dark and tested again. Discovered illumination inside the disk. After some crawling around found an arc, a short between the back of the pin cushion and the shell coil ground wire. Almost the center of everything, Damn! now I must take things apart and reroute a wire and seal the old route.

At least this design can be taken apart and changed.  pg

Upper Disk 2

Getting the form Right

Raw FRP shell

Raw FRP shell condenser shell form

shell form

Condenser shell form

I April 2012

The raw FRP ( Fiberglass Reinforced Polyester) shell form needs to be repaired and trued before the actual condenser can be created on it. Due to working alone there are starved areas in the FRP where there is not enough polyester resin to float the fiberglass. These white streaks are weak areas and need to be ground out and refilled with FRP before the shell can be built up and trued. There are many high areas that must be ground down to a minimum thickness and all other areas built up to obtain a smooth and true curve with little or no ripple under the capacitance foils.

After the minimum thickness is true and strong and stable, the low areas that remain can be filled with resin fillers and further trued. It took most of 6 weeks to get to this point. Now the edge must be trued to the center point so the curvatures are even and smooth.

Electron fields concentrate at points of sharpest curvature and we want the fields to maximize at the disk edge with the least loss. The more true and smooth this surface is the better the quality of the capacitance layers to be created on it.  Any high areas can result in thin dielectric and possible failure. Any low areas will result in loss in capacitance.

marking the shell form

marking the shell form for truing

To obtain a true edge a wire is connected to the top center point and used to draw concentric circles that are tested with the template that is a cut and marked piece of heavy corrugated card board. The use of this shows the areas that need to be ground down or built up to achieve a true shape. After nearly 3 gallons of filler the surface is very true. Now layers of polyester resin are applied and sanded to create a smooth surface, each more smooth and true then the last.  Now I need to clean the work area as everything is covered with a thick layer of polyester dust.  😥

Now to add the coils

The great coil and plasma jet in place

The 130 turn spiral wound high voltage coil has been cut out of the old device and mounted under the disk frame with the plasma jet pointed down.

The black coil around the spiral coil is the 24 turn  primary coil,  and the white coil above it is the bundle of driver coils for the twitch coils.

Inside of the central frame cage is the shell field driver coil that is connected to the groundplain in the rim and to the surface field cap on top of the coil and the outer skin of the shell.


Center coils inside disk

The shell field coil is induction driven 165 turns of 12ga tw covered wire and should create a 100,000 volt field on the shell capacitance due to the 600+ volt per turn field strength.

The shell field coil and twitch coils are loosely coupled to the main field and are jointly connected to the groundplain to make their operation independent of any back EMF from the spiral coil and primary driver that are connected together as an autocoil.

The primary and spiral coils should drive the plasma jet pincushion to about 100,000 volts.  At some time the primary coil can also be connected to the groundplain if needed for testing.

Twitch coils in place in disk edge

The primary coil is a bundle of 24 turns of stranded 12ga THWH inside polyethylene tubing and is powered by the 15,000 volt spark gap set. This should set up a 600+volt per turn field inside of all the coils

The twitch coils are mounted and connected to the groundplain.  2 turns per twitch coil are bundled into the white twitch coil driver necklace above the primary coil to independently provide 1200 volts to each twitch coil LC set. The twitch coils are 90 degrees to the other coils so are nearly independent of the main field.

FRP shell with cap in place

Every other segment is connected to the groundplain and bottom of the shell field coil. A coil/shell cap with carbon fiber whip has been created and covered with aluminum foil to act as the connection from the top of the field coil to the shells’ upper aluminum covering. The upper third needs to be trued by grinding and filling to the finished level as I prepare  to apply the inter condenser copper foil.


Construction of the Actual Shell Condenser

Inter Layer of copper foil


The FRP shell is ready for the addition of the copper foil segments that act as the inter layer of the shell condenser. Each segment connects to one side of the twitch coil behind it

Next, add the shell condenser  copper foil inter layer on the shell form. After several attempts I have found a way to apply a satisfactory copper foil layer to the form.

WOW!  This is starting to look impressive! If nothing else this is a work of Art or at least of PG.   😎    When the outer shell is finished this will be stunning! even if it doesn’t move.

The blue level is tape to hold the foil segments against the wires from the interior circuits. This is removed as I create the outer edge.

Outer edge formed

The outer edge form is done .




Fiberglass gores in place on shell

The outer edge shape is done and I am ready to build up the FRP shell over the inter condenser foil level. The Resin needed is on hand and the fiberglass mat is on its’ way. Hurrah! the end is in sight.

The Fiberglass mat has arrived and is being applied. Gores of mat are cut and taped in place with a slight overlap, then catalyst treated resin is poured on and rolled into the mat until the glass “floats” and air bubbles are eliminated. Fast work is necessary to complete the fill all the way around before the resin sets. To successfully make this, by myself, it is done in 3 layers. Each layer of mat requires the application of 3 and a half gallons of treated resin.

finished shell with aluminum skin

The shell shape is complete and covered with aluminum foil gilding.

A few coats of polyester and sand it smooth.

I just, have to, smoke test this!! Chase a few electrons around and around! light up some old florescent tubes.

It has been nearly 20 years since I energized the great coil

27 February 2013

Golden Shell Condenser

Polyester coated Shell condenser outside the hanger area.

The polyester coated shell is well cured and has been moved outside the hanger area. Now I have a lot more room to work and I have the greenhouse back  😎 for early spring grow out.

NOTE: Be sure to click on the pictures for a better view and more information in comments.  pg

Next see Condenser Disk and  Hurrah!

Primary driver

Primary Coil Driver

Primary Coil Driver

Primary Coil Driver

The primary coil driver set is assembled and ready to go. Left to right, Ganged condenser to drive the primary coil, spark gap attached to aluminum heat sink, chokes for suppression of back EMF to protect the neon transformer and most important part an OFF switch! see spark gap condenser test

The yellow wire is high tension ignition wire. This will allow me to operate the power supply 20 feet remotely from the very high voltage coils and any fields generated on the surface of the disk.

Primary Driver top view

 Driver set top view

When a neon transformer is used it must be protected from the possibility of a high energy kick back from the magnetic collapse of the field in the secondary coil.  A properly sized choke will easily pass current at the 60 cycle frequency of the transformer but strongly resist current at the high frequency of the primary LC  circuit of about 18,000hz.The frequency of the LC tank circuit (inductance/capacitance) of the primary is caused by the charge / discharge of the capacitor through the spark gap and the coil.

side view of primary coil driver

side view of primary coil driver

Driver set side view

The spark gap is to force the charge voltage from the transformer to rise to the break down point of the gap,  current in the circuit has inertia so it will over discharge the capacitance and cause the current to reverse flow. This back and forth flow will continue until the voltage in the circuit is too low to cross the gap. If the circuit is designed correctly the gap will break down early enough in the 60 cycle to bridge the time that the transformer has low voltage from its’ 60 cycle output. This is electronics on a massive scale.

be sure to click on the pictures for more information in the picture comments.  pg

Condenser / Sparkgap test

Condenser / Spark gap test

Condenser & spark gap with 15,000vac transformer

  Main condenser

Top picture is of main condenser, spark gap and neon transformer. This test of the main condenser was its’ first “smoke test” to see if my design would function as planed. Condenser is made up of aluminum foil lined PET plastic jars set up similar to Leyden Jars fixed end to end and paralleled to create a bank,  .0196mfd – 40,000vac condenser to power the primary coils through the spark gap. The power at this time is supplied by a 15,000 vac 30ma center tapped neon illumination transformer. ( built in 1940s)

Spark gap

  Spark gap

This second picture is of the spark gap and transformer. To the left is an electrode from a Leyden jar as well as a 4 inch pocket wrench. The spark gap is constructed from two engine XL spark plugs that have had the grounding electrode and some of the threaded shank removed. These are threaded into an extruded aluminum form,  so that the central electrodes face one other, to provide a base as well as a heat sink. The spark gap can be adjusted from as small as 3/8 inch to as large as 1 inch.

Spark gap without condenser

 Spark gap powered

This is being directly powered by the neon transformer with no load. The arc is small thready and produces a lot of heat and not much light. It is also quiet, just a light crackle.

You may have to look closely, click on the image or do an enlarge to see the arc.

This is the first time in 16 years that I have powered up this transformer, good to see that it still works.

Spark gap with condenser

 Spark with condenser

I hooked up the condenser in parallel and turned the thing on, real smoke test. WOW! very hard arc, very bright and white, lots of UV and very loud hiss, not much heat! I am pleased with this spark gap design and the output of my home made condenser.

The Tesla Coil Builders need to see this as the spark gap is the most difficult part of a tesla coil device.  I’m pleased with the outcome of this test, I will continue & assemble the primary driver   😎  pg

History of my flat spiral coil

Post about origin of my Flat wound Tesla coil

Flat spiral wound tesla coil with central pincushion termination

 History and details of this device.

This Tesla Coil was created in 1994 as the base of my first test device. A spiral of 14 gauge copper magnet wire was welded onto a deck of half inch polypropylene with over a mile of  5/32 polypropylene rod, 5 turns to the inch, for a total of 120 turns and 1200feet of wire. The insulation was tested with a HV 40,000 volt weld tester over every inch of the coil weldment, for a high”Q” coil that can withstand up to 5,000,000 volts of stress. A spiral wound coil is the Tesla design that creates the highest stress at the coil center with the perimeter at “ground” for the safest design as well as the sharpest voltage spike is at the center due to magnetic field collapse pinch. This center termination is a pincushion 8 inches in diameter with 16 pins per square inch. This is inside a polypropylene forcing cone for a plasma conduit / jet. This was circled with a capacitance / inductance necklace that served as the primary that was driven at first with a 15,000 volt, 500ma neon transformer. The bulge rings around the coil deck were the capacitors for this neckless and the some of the wiring can be seen within the right inside of the top ring.  This was setup with the plasma conduit pointed up and the driver transformer hooked up directly to the primary coil to operate the main coil in transformer mode, about 500,000 volts. All of this device was created of welded polypropylene.

During a test of overall fields with a hand held 8 foot florescent tube, a wire from the neon transformer came loose and the device went into full Tesla mode and violet plasma shot up out of the plasma conduit at least 6 feet into the air near my head. Not a big spark of lightning but a real jet 2 inches in diameter. While I was trying to figure out how to get down from the device onto the concrete floor to unplug the driver, without electrocuting myself, the loose wire came off totally and the thing went dead……………………………………………………………………………………………whew.

That event damaged the built in capacitance and I was unable to repair it successfully and continue the testing of that device.

I am now cutting away the capacitance rings and turning the coil deck over to reuse it in the new configuration.

This coil will be operated at less then 300,000 volts initially.

PG’s Experiment

FRP covered dish

A  HIGH VOLTAGE  experimental to attempt to confuse inertia/mass with rich magnetic fields that move in 3 dimensions. This is a paper skin over a light wood frame. It has been covered with FRP ( fiberglass reinforced polyester) and will be covered with a metal foil skin. Under the disk is a flat wound Tesla coil of 14 ga. copper wire  that will terminate at the top skin. At the center termination there is a 8 inch pin cushion inside a plasma conduit that vents down. There are 12 secondary twitch coils around the rim that are powered by the main field.  links to pages of additional information on primary coil driver and pictorial-schematic-of-device

25 February2012, Those white streaks are weak, resin starved areas and must be ground out and relaid. WHAT a disagreeable job! Hopefully I will have this done in an other week and then be able to start the metal work.

This post will be an on going project for a while  pg