How Does a Tesla Coil Work?

by Ezmeralda Lee

If you've ever watched an old science-fiction movie, you're probably familiar with a Tesla coil. Invented by Nikola Tesla late in the nineteenth century, a Tesla coil is a device that can generate massive voltages of electricity and produce huge discharges. But how does a Tesla coil work?

For most basement or garage electronics enthusiasts, the workings of a Tesla coil start very simply with a common household electrical plug. From there, the current is carried to a step-up transformer. This transformer steps the household current up from 120 volts to several thousand.

From the transformer, the current moves into a capacitor. A capacitor functions as a sort of short-term storage battery for the electrical energy. Once the capacitor is fully charged, the current then moves into a spark gap.

The spark gap functions as a switch that rapidly turns the current off and on. As technology has developed, some people have used vacuum tubes or solid-state components to serve this function. The spark gap fires, releasing the current into the primary coil.

The primary coil is usually found at the base of the secondary coil. This coil can be saucer shaped, conical or helical. It is usually made of heavy-gauge copper wire or copper pipe. The movement of the current into the primary coil creates a magnetic field that collapses and discharges back into the capacitor. The current passes across the gap switch from the capacitor to the primary coil and back again. The exchange between the capacitor and primary coil can happen hundreds of thousands of times each second.

Each time the current passes from the capacitor to the primary coil, the secondary coil picks up some of the current. The secondary coil is made up of many turns of wire of a smaller gauge than the primary coil. Normally, the secondary coil would increase the coil by the multiple of coils in the secondary coil to the primary coil. For example, if there are 10 coils in the primary coil and 1,000 in the secondary, the voltage would increase 100 times. Due to the resonance of a Tesla coil, however, it is possible for much higher voltages to be reached.

The final component of the Tesla coil is the terminal capacitor. Usually, this is a terroid or sphere. This is positioned at the top of the secondary coil, and is where the visible action takes happens. When charged, it releases its energy into the surrounding air. The resulting spectacular display of sparks and corona discharge are what make the Tesla coil so popular as a special effect in movies.

Although there is currently no practical application for a Tesla coil, Nikola Tesla hoped that someday his invention could be used to transmit electrical power and information over vast distances without the use of wires. Tesla built his largest coil in Colorado Springs, Colorado. The device was reported to produce sparks 130 feet long and could transmit substantial amounts of electrical energy more than 25 miles.

More Articles