Giant Tesla Coil Unveiled

SAN FRANCISCO--Bolts of artificial lightning more than 10 meters long shot up into the night sky here Friday when a local electrical engineer switched on the world's largest tesla coil, charging it to nearly 3 million volts. Although smaller tesla coils are commonly used to accelerate the photons in a TV set and to start up the arc in a welding torch, this one was built for aesthetic purposes only: as a piece of art for a New Zealand ranch.

The tesla coil, invented in 1891 by Serbian physicist Nikola Tesla, is essentially two long coils: one attached to an oscillating electrical power source that generates charge and a second, surrounding the first, that accumulates charge. As the primary coil spins, its capacitors switch on and off rapidly, creating an oscillating charge. When the frequency of that charge is the same as the natural resonant frequency of the electrode of the other coil, it will induce a higher and higher charge. With nowhere else to go, the charge on the electrode eventually conducts into the air around it as bolts of electricity. Electrical engineer Greg Leyh built the record-setting coil with Eric Orr, an artist hired by a New Zealand arts patron to make a lightning sculpture.

Last week, Leyh conducted the first public demonstrations of the finished product--a 13-meter cylindrical fiberglass-covered steel tower, topped by a spherical stainless steel coil--the electrode. A crowd of several hundred, notified only by word of mouth and Leyh's Web site (, gathered at the decommissioned Hunter's Point Naval Shipyard to see the coil powered up to 70% of its capacity. The machine whirred like a turbine as a coil made of 90 kg of copper and aluminum began spinning to generate the current. When the turbine approached its top speed of 483 km per hour, writhing lightning bolts cracked from the sphere and branched into trees of lavender light. Today Leyh will begin dismantling the coil for shipment and installation on the patron's 100-hectare sheep ranch near Auckland, New Zealand.

Experts confirm that Leyh's is the largest and most powerful tesla coil of its kind ever built. "Greg seems to have exceeded all the specs," says Richard Hull, an engineer and tesla coil designer in Richmond, Virginia. But Leyh has even bigger tesla dreams: an amusement attraction consisting of twin towers, each 30 meters tall and 100 meters apart, connected only by the artificial lightning they generate. Such a toy, Leyh says, could also be used to lightning-test planes or land vehicles.