PowerLabs 1kW Tesla Coil


Side view of transformer with a close up of the labelA French-Made 10000V 100mA (1kW) Center Tapped Neon Sign transformer, measuring 18 X 14 X 39cm (7.4 X 5.7 X 16″), and weighting a mere 25kg ((67pounds): It is potted in tar). This is one of the finest neon transformers that can be obtained in Europe, as the law in most European countries states that transformers there may output no more than 8kV at 30mA. Below you can see a picture of the transformer with the two heavily insulated silicone/vinyl wires coming off the front, and a close up of the label on the side. The gray object next to it is a 30cm-ruler, for size comparisons.

View of the transformer with top removedHere the transformer is seen with the top cover removed (it is attached by a butterfly nut). As can be seen from the “O” ring seals around all wires going into the transformer, and from the rubber seals around the top, this unit was designed to be run outdoors and is completely water proof. This transformer will have a triple point grounded safety gap set for exactly 14kV on top of it, and will be controlled by a 5A 250V variac with 41uF of PFC, and a full RCL fused filter network.
I got this transformer for free from my friend Reinier Heeres, who in turn obtained it from a neon sign shop in Holland. THANKS REINIER!
Because of this I am naming the coil “RWH”, as that is his internet nickname.

Tank Capacitor:

 0.03uF (that’s larger than resonant, in order to increase the energy per spark, and also increase the step-up voltage of the coil somewhat), at 20Kilovolts. The design currently being discussed is MMC (A series/parallel arrangement of several smaller PP “snubber” capacitors). When charged to the transformer’s peak voltage (15kV) it will store 3.375Joules (quite a respectable amount of energy!), and its expected rate of discharge (DV/DT) is in the order of 800amperes! Each individual capacitor will be inter connected by a 5mm thick copper bar, and the whole bank will be protected by individual equalizing resistors, and a triple point grounded safety gap set for 15kV.

Primary Coil:

  Will sit on top of a 3mm (.12″) thick, 45cm (18″)diameter acrylic disk, which will in turn be glued to the 5mm (.2″) thick acrylic top of a 45 X 45 X 25cm (18 x 18 x 10″) box housing the transformer, tank capacitor, series static gap, safety gap, and all the H.V. and mains filtering (RCL and PFC) and fusing system. From this box a single plugged wire will part which will go to the 5A 250V (1250W) variac (voltmeter integrated). The coil itself will be wound with 6mm dia (1/4″)  thin wall annealed soft copper tubing, with 5mm (.2″) inter turn spacing which will make 13 turns around the coil (tuning calculated at turn 9.9). 13 meters of tubing will be used, and the coil will sit 11cm above the base at its highest point. An 8mm (0.33″) diameter copper tube forming an open loop 45cm (18″) in diameter 2cm (.8″) above the top turn of the primary will form the strike rail for this coil.
Specs are as follows:
16cm (6.5″) inner diameter
43cm (18″) outer diameter
15cm (6″) average radius
6mm (0,250″) wire diameter
5mm (0,200″) inter turn spacing
13 turns total
0,0334mH inductance
15degrees slope
0,0305uF of primary capacitance to form a resonant circuit at 157,7Khz

Secondary Coil:

 1000turns of AWG 23 (0.287mm dia) wire wound around a 12cm diameter (4.9″), 70cm high (28.6″) clear acrylic tube (60cm (25c”) winding height). 400 meters (1300′) of wire used. A 15 X 25 x 0.1mm copper rectangle will be glued to the base 3cm below the first turn for the ground connection and the coil will be given 3 turns of two-part (catalyzed) PU (Polyurethane) varnish, with fine sanding between the second and 3rd turn. 10 turns of varnish will be given to the base, in order to prevent pri-sec strikes.
Specs as follows:
12cm (4,90″) diameter, 6cm (2.45″) radius, 37.8cm (15.4″) circumference.
60cm (24.5″) winding height.
Wound with 1000turns of 23AWG (0.287mm) wire (assuming 98% effectiveness, with 17 turns/cm (42 turns/inch).
Wire length is 400m (1300ft)
Height/Diameter aspect is 1:5
Inductance = 2.43mH
Resonant Frequency = 337.19khz, 157.7khz with 35.47pF topload.
Self Capacitance = 9.93pF

Spark Gap:

 Multi section vacuum quenched linear spark gap. 10 sections each one made of 10cm (4″) long, 2cm (0.8″) diameter thick copper pipe. All held in a 12 X 12cm (5X5″) clear acrylic box with two 1cm (.4″) thick, 2.5cm (1″) wide, 22cm (9″) long TEFLON  bars between them and the box walls. Teflon (PTFE) retains its excellent physical (extremely high tensile strength) and electrical (very low dissipation to high frequency electricity and very high standoff voltage) properties at over 260C, so it is the perfect choice of material to be in contact with the gap sections.

Top load:

 For better electrostatic field control two toroids will be used: The first one with 8cm tube diameter and 50cm outer diameter, and the second one with 1m outer diameter and 10cm tubing diameter. Top load capacitance will be in the 45pF range. Both top loads will be made of flexible aluminum ducting wrapped around acrylic disks and covered with heavy duty aluminum tape, smoothened to perfection.


 Allright, here is where the science breaks down… As can be seen from the design specifications, I am building this coil to perfection, and I’m not saving a dime to do it. Final cost when finished will probably run at +-500USDollars, so this project might take a while to be completed, as it is competing for funding with my other projects, equally important 🙂 Nevertheless, the design is complete and construction is already started. Within the next few weeks I hope to have the secondary, the toroid, and the HV / LV filter network done. The tank capacitor and primary coil will take longer, as they will be the most expensive parts in the system.
Given the input power and the overall design of the coil I am guessing (note, guessing is the word here) that it will put out close to half a million volts when unloaded, maybe around 350kV with the toroids in place. At break rate it will be running, sparks averaging around 1.3meters (4.5 feet) should be possible. Maybe more if my design and construction techniques, make it as efficient as my previous coil… Than as much as 150cm (5′) might be possible… Either way, the beautiful, compact construction of the coil and its high power level should make it an astonishing tool for demonstrating the dramatic behavior of electricity at high frequencies and powers to large audiences. At lower powers it is well suited for any kind of high voltage experimentation, including ion engines, remote electrostatic charging, e-field mapping, and more.
With the experiences earned in this coil POWERLABS plans on ending its research on Tesla Coils until larger facilities become available (working in an apartment has proven highly frustrating as power restrictions, noise considerations, walls, ceilings, and lack of a proper RF ground constantly get in the way of larger sparks), which would allow the continuation of its research onto higher powers. Who knows what the future will hold? Maybe a 10000Watt Tesla Coil putting out 4 meter long sparks? A Tesla Magnifier?… Time will tell.

 Before this project is completed, the following projects must also be completed and video taped for the POWERLABS archive:
Mini Tesla Coil (Currently having its primary coil redesigned).
Twin Tesla Coil (the primary for the twin coil is halfway done, but videos for one of the towers running should be available this week.)