There is no denying the similarity in appearance of Van de Graaff generators and Tesla coils. Both produce high voltage electric arcs. However, the comparison stops there.

Van de Graaff generators are electrostatic devices. A potential is gradually built up through friction from a rubber belt and collects on the accumulator until it discharges to a grounded object, i.e., a ground rod or you. The rate of discharge is inversely proportional to the distance the arc has to jump. The spark is thin and makes a mild snap when it flies. It carries almost no current and is harmless (unless it's twenty feet high). Typical generators might produce 200,000 to 400,000 volts depending on the relative humidity. They are safe to touch while operating.

The Tesla coil is a dynamic device. High voltage radio-frequency current is produced at the rate the spark-gap fires. 120 times a second would be typical. Maximum arcs are produced in profusion immediately and continue for as long as the coil is left running. The sparks, poorly visible in strong light, appear quite strong in subdued lighting conditions. The arcs are purplish to whitish depending on whether they are allowed to go to the open air or are drawn to a nearby grounded rod or wire. A ground wire held close produces very intense sparks.

Tesla coils are not harmless toys. One must constantly be watchful of what is touched. It is said that the r.f. current from the coil flows over the surface of the skin, and is therefore not capable of killing. However, it is also known that contacting a high-powered discharge can cause burns and is extremely painful. The primary circuit of the coil is where the true danger lies; plenty of voltage and amperage here. An inadvertant touch of a fully charged primary capacitor, even with the coil *off*, can kill you. Primary voltages run up to 15,000 volts, but the discharger puts out anywhere from a quarter-million to a couple million volts depending on the input power.

Tesla coils are not quiet, humming generators like Van de Graaff machines. The spark gap is extraordinarily powerful and sounds like an unmuffled chain saw. Hearing protection is a must. The gap must also be shielded from the eyes. Then there is the ozone problem.

The bottom line is, if you want a toy, build a Van de Graaff machine. If you want raw, unadulterated power that will make your skin crawl, then go with the Tesla coil.


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Luke Mester and I are experimenting with a "bargain basement" type coil. It is 3½" ×19" wrapped with a plastic coated, stranded, termi-wrap wire of unknown origin on a cardboard core. The winding length is 16½". The discharge terminal is a 5½" diameter styrofoam ball covered with aluminum tape.




Taken on VHS-C and dubbed to full size VHS, this AVI was captured at 8 fps in a 320×240 format. The file is 2 Mbytes long and runs for 18 seconds.
Download now .
Our coil is powered with two 15,000 volt / 30 mA. neon-sign transformers. The primary is a flat spiral made from #12 house wire. Twelve wine cooler bottles in a foil-lined dishpan make up the saltwater capacitor. Its value is .00865 uf.

Smaller files are available.

This one is of the same run as the larger one above. Captured at 7 fps in a 160×120 format and more highly compressed, it is 680 kbytes long. Running time is 16 seconds. Download now.
Xing compatible mpeg version. (284 kbytes)


Spark lengths shown here reach 13" but this coil produced 15" 
sparks before the inner turn of the primary was cut out to alleviate an
arc-over problem while playing with the coupling.





This is a different run and is 619 kbytes long.
Running time is 14 seconds. Download now.


Our highest quality AVIs.


These videos were taken on a Super-VHS camcorder and captured from the original tape. They are 8 frames per second in a 320×240 format. A high quality compression setting was used.

Tesla coils don't always take the shortest path as seen here. Note the corona spray from the ground wire. File size is 1.8 Mbytes and running time is 21 seconds.
Download now.
Fully encoded mpeg version. (959 kbytes)

For those who desire a shorter file, here is an 11 second version and it includes the sequence shown above. 970 kbytes. Download now.




We got our 15" sparks back with a new primary!

Infantile attempt at humor. No, the arc isn't striking the flourescent tube. Captured at a jerky 4 fps to shorten file size, this AVI runs 17 seconds and is 880 kbytes. Download now.
We will soon be replacing the saltwater capacitor with a polyethylene rolled-cap and adding a third transformer. Continue to watch this page.


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