Nicholas Callan - Induction Coil

Induction Coil

Influenced by William Sturgeon and Michael Faraday, Callan began work on the idea of the induction coil in 1834. He invented the first induction coil in 1836. An induction coil produces an intermittent high-voltage alternating current from a low-voltage direct current supply. It has a primary coil consisting of a few turns of thick wire wound around an iron core and subjected to a low voltage (usually from a battery). Wound on top of this is a secondary coil made up of many turns of thin wire. An iron armature and make-and-break mechanism repeatedly interrupts the current to the primary coil, producing a high-voltage, rapidly alternating current in the secondary circuit.

Callan invented the induction coil because he needed to generate a higher level of electricity than currently available. He took a bar of soft iron, about 2 feet (0.61 m) long, and wrapped it around with two lengths of copper wire, each about 200 feet (61 m) long. Callan connected the beginning of the first coil to the beginning of the second. Finally, he connected a battery, much smaller than the enormous contrivance just described, to the beginning and end of winding one. He found that when the battery contact was broken, a shock could be felt between the first terminal of the first coil and the second terminal of the second coil.

Further experimentation showed how the coil device could bring the shock from a small battery up the strength level of a big battery. So, Callan tried making a bigger coil. With a battery of only 14 seven inch (178 mm) plates, the device produced power enough for an electric shock "so strong that a person who took it felt the effects of it for several days." Callan thought of his creation as a kind of electromagnet; but what he actually made was a primitive induction transformer.

Callan's induction coil also used an interrupter that consisted of a rocking wire that repeatedly dipped into a small cup of mercury (similar to the interrupters used by Charles Page). Because of the action of the interrupter, which could make and break the current going into the coil, he called his device the "repeater." Actually, this device was the world's first transformer. Callan had induced a high voltage in the second wire, starting with a low voltage in the adjacent first wire. And the faster he interrupted the current, the bigger the spark. In 1837 he produced his giant induction machine: using a mechanism from a clock to interrupt the current 20 times a second, it generated 15-inch (380 mm) sparks, an estimated 60,000 volts and the largest artificial bolt of electricity then seen.