2 Day Coil


(From September, 2011)

Although my DRSSTC project is slowing inching forward, I found myself yearning for larger, scarier sparks than my prototype coil could give, so I grabbed a high voltage transformer and some pulse capacitors and the primary and secondary coils from my DRSSTC and in a couple days of work, this is what I came up with:


I won’t reprint the “standard” Tesla coil schematic here, I’ll only give the specifications of my coil:

Power Supply-
Mystery Raytheon HV transformer, probably 10 – 15kVRMS @ 1kW (power factor was too horrible for the clamp meter to give an accurate reading)

Primary Capacitor-
3 series string of 50kV Maxwell pulse capacitors for 80nF at 150kV

Primary Coil-
Several turns of 1/4″ copper tube

Spark Gap-
5- 0.5″x3″ copper tube unquenched multiple gap

4.5″x20″ of 32AWG wire

~16″x5″ aluminum duct toroid

With a few improvements like a rotary gap instead of an unquenched static gap and a slightly larger secondary, I think this coil could push another 1 – 2 feet of sparks. I plan to find out!


The coil is not assembled on a permanent base because I built it to make quick sparks rather than as a long term demonstration setup.

An IEC power connector from a computer power supply is held onto the power transformer with thick gauge wires.

The capacitor bank is zip-tied together and connections are make using wires with ring terminals.

The spark gap is made from several 3″ segments of copper tube zip-tied to a block of wood and glued to the zip tie that holds the capacitor bonk together. Using zip ties to secure the spark gap electrodes made it surprisingly easy to adjust, so unlike the standard “Richard Quick” segmented gap design, it doesn’t require a tap.

Connections are made to the primary coil via a heavy duty alligator clip tap from the capacitor bank and a similar alligator clip connection from the inside of the primary to the spark gap:


This coil worked quite well the first time I turned it on and with some tuning, I was able to achieve 3 foot spark length, which is an impressive feat for an unquenched spark gap coil of this size. Unfortunately, the series string of Maxwell pulse capacitors is too much of an overkill to justify boxing up this coil into a portable demonstration setup. They could easily work in a coil of up to several kilowatts without failing, so it seems wasteful to permanently use them in this <1kW setup.

Powerful ground strikes captured in a demonstration near the MIT museum on Mass. Ave. in Cambridge:

Free air streamers (2 – 3 feet):

Another ground strike, this time indoors:


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