Making your own tesla coil


The devices described on this page may cause lethal electrical shocks or serious injury! Any adaptation of the described devices will be at your own risk!


Some time ago I came across a book named "Elektrotechnik für Jungen" ('Electrical Engineering for Boys') published in 1947. First I was interested in building a spark inductor which was described in the book, but gave it up, as coiling up 10 km of wire didn't seem to be very exciting. There was also a description for constructing a tesla coil, but it used the spark inductor as high voltage supply. Then I got a high voltage transformer which was used as ignitor in an old oil heating. It transforms normal 230 V AC to 10 kV at max. 20 mA (technical information). But as I had forgotten about the tesla thing in the book, I just played with the transformer itself (and nearly killed myself). A year later I started studying physics and was inspired by a demonstration of a tesla coil during a lecture. I got the book again and started building.
As capacitors I 'borrowed' two glass jars from my grandma, on which I pasted aluminium foil to obtain Leyden Jars. The primary coil was made of 5 turns of thick (2 mm) copper wire, the secondary was coiled on a paper tube. Even simpler was the spark gap, it just consists of a metall plate and a pointed screw. These parts are connected this way:
Note: It is better to swap spark gap and capacitor (i.e. spark gap in parallel to transformer and capacitors in series). This causes lesser stress for these parts.

The measures of the parts in detail:
Transformer: prim. 230 V AC sec. 10 kV AC at max. 20 mA
Capacitors (Leyden Jars): 1. inner diam.: 9 cm, height covered with alu foil: 14 cm; 2. inner diam.: 10.5 cm, height covered with alu foil: 17 cm (together 2.7 nF)
Primary coil: diam.: 10 cm, height: 13 cm, turns: 5
Secondary coil: diam.: 4.5 cm, turns: 300

Leyden Jars
Note: the spark gap shown in the overview is now replaced by this one:
Spark Gap (scheme)
Spark Gap (photo)
Coil in action
Close-up of the corona
Discharge tube made by my father after my plans (well my father is a glass-blower)

Further information:



Tesla Coil Ring
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Created by Christoph Baumann May 1997
Last change: Oct 22 2016


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