Part 12

DEVELOPMENT OF THE DYNAMO, 1840–1860

During the first few years after 1840 the dynamo was only a laboratory experiment. Woolrich devised a machine which had several pairs of magnets and double the number of coils in order to make the current obtained less pulsating. Wheatstone in 1845 patented the use of electro-magnets in place of permanent magnets. Brett in 1848 suggested that the current, generated in the coils, be allowed to flow through a coil surrounding each permanent magnet to further strengthen the magnets. Pulvermacher in 1849 proposed the use of thin plates of iron for the bobbins, to reduce the eddy currents generated in the iron. Sinsteden in 1851 suggested that the current from a permanent magnet machine be used to excite the field coils of an electro-magnet machine.

In 1855 Soren Hjorth, of Copenhagen, Denmark, patented a dynamo having both permanent and electro-magnets, the latter being excited by currents first induced in the bobbins by the permanent magnets. In 1856 Dr. Werner Siemens invented the shuttle wound armature. This consisted of a single coil of wire wound lengthwise and counter sunk in a long cylindrical piece of iron. This revolved between the magnet poles which were shaped to fit the cylindrical armature.

This dynamo was an improvement over others on account of the construction of its “shuttle” armature.]

THE FIRST COMMERCIAL INSTALLATION OF AN ELECTRIC LIGHT

In 1862 a Serrin type of arc lamp was installed in the Dungeness lighthouse in England. Current was supplied by a dynamo made by the Alliance Company, which had been originally designed in 1850 by Nollet, a professor of Physics in the Military School in Brussels. Nollet’s original design was of a dynamo having several rows of permanent magnets mounted radially on a stationary frame, with an equal number of bobbins mounted on a shaft which rotated and had a commutator so direct current could be obtained. A company was formed to sell hydrogen gas for illuminating purposes, the gas to be made by the decomposition of water with current from this machine. Nollet died and the company failed, but it was reorganized as the Alliance Company a few years later to exploit the arc lamp.

This was the dynamo used in the first commercial installation of an arc light in the Dungeness Lighthouse, England, 1862.]

About the only change made in the dynamo was to substitute collector rings for the commutator to overcome the difficulties of commutation. Alternating current was therefore generated in this first commercial machine. It had a capacity for but one arc light, which probably consumed less than ten amperes at about 45 volts, hence delivered in the present terminology not over 450 watts or about two-thirds of a horsepower. As the bobbins of the armature undoubtedly had a considerable resistance, the machine had an efficiency of not over 50 per cent and therefore required at least one and a quarter horsepower to drive it.

FURTHER DYNAMO DEVELOPMENTS

In the summer of 1886 Sir Charles Wheatstone constructed a self-excited machine on the principle of using the residual magnetism in the field poles to set up a feeble current in the armature which, passing through the field coils, gradually strengthened the fields until they built up to normal strength. It was later found that this idea had been thought of by an unknown man, being disclosed by a clause in a provisional 1858 English patent taken out by his agent. Wheatstone’s machine was shown to the Royal Society in London and a paper on it read before the Society on February 14, 1867. The field coils were shunt wound.

This machine was the first self-excited dynamo by use of the residual magnetism in the field poles.]

Dr. Werner Siemens also made a self-excited machine, having series fields, a paper on which was read before the Academy of Sciences in Berlin on January 17, 1867. This paper was forwarded to the Royal Society in London and presented at the same meeting at which Wheatstone’s dynamo was described. Wheatstone probably preceded Siemens in this re-discovery of the principle of self-excitation, but both are given the merit of it. However, S. A. Varley on December 24, 1866, obtained a provisional English patent on this, which was not published until July, 1867.

These were commercially used, their main feature being the “ring” wound armature.]

Wire coils, surrounding an iron wire core, were all connected together in an endless ring, each coil being tapped with a wire connected to a commutator bar.]

In 1870 Gramme, a Frenchman, patented his well-known ring armature. The idea had been previously thought of by Elias, a Hollander, in 1842, and by Pacinnotti, an Italian, as shown by the crude motors (not dynamos) they had made. Gramme’s armature consisted of an iron wire core coated with a bituminous compound in order to reduce the eddy currents. This core was wound with insulated wire coils, all connected together in series as one single endless coil. Each coil was tapped with a wire connected to a commutator bar. His first machine, having permanent magnets for fields, was submitted to the French Academy of Sciences in 1871. Later machines were made with self-excited field coils, which were used in commercial service. They had, however a high resistance armature, so that their efficiency did not exceed 50 per cent.

The armature winding was entirely on the surface of the armature core, a principle now used in all dynamos.]

Von Hefner Alteneck, an engineer with Siemens, invented the drum wound armature in 1872. The wires of the armature were all on the surface of the armature core, the wires being tapped at frequent points for connection with the commutator bars. Thus in the early seventies, commercial dynamos were available for use in arc lighting, and a few installations were made in Europe.

RUSSIAN INCANDESCENT LAMP INVENTORS

In 1872 Lodyguine, a Russian scientist, made an incandescent lamp consisting of a “V” shaped piece of graphite for a burner, which operated in nitrogen gas. He lighted the Admiralty Dockyard at St. Petersburg with about two hundred of these lamps. In 1872 the Russian Academy of Sciences awarded him a prize of 50,000 rubles (a lot of real money at that time) for his invention. A company with a capital of 200,000 rubles (then equal to about $100,000) was formed but as the lamp was so expensive to operate and had such a short life, about twelve hours, the project failed.

The burner was made of graphite and operated in nitrogen gas.]

In this lamp the graphite rods operated in a vacuum.]

Kosloff, another Russian, in 1875 patented a graphite in nitrogen incandescent lamp, which had several graphite rods for burners, so arranged that when one failed another was automatically connected. Konn, also a Russian, made a lamp similar to Kosloff’s except that the graphite rods operated in a vacuum. Bouliguine, another Russian, in 1876 made an incandescent lamp having a long graphite rod, only the upper part of which was in circuit. As this part burned out, the rod was automatically pushed up so that a fresh portion then was in circuit. It operated in a vacuum. None of these lamps was commercial as they blackened rapidly and were too expensive to maintain.

A long graphite rod, the upper part of which only was in circuit, operated in vacuum. As this part burned out, the rod was automatically shoved up, a fresh portion then being in the circuit.]

THE JABLOCHKOFF “CANDLE”

Paul Jablochkoff was a Russian army officer and an engineer. In the early seventies he came to Paris and developed a novel arc light. This consisted of a pair of carbons held together side by side and insulated from each other by a mineral known as kaolin which vaporized as the carbons were consumed. There was no mechanism, the arc being started by a thin piece of carbon across the tips of the carbons. Current burned this bridge, starting the arc. The early carbons were about five inches long, and the positive carbon was twice as thick as the negative to compensate for the unequal consumption on direct current. This, however, did not work satisfactorily. Later the length of the carbons was increased, the carbon made of equal thickness and burned on alternating current of about eight or nine amperes at about 45 volts. He made an alternating current generator which had a stationary exterior armature with interior revolving field poles. Several “candles,” as they were called, were put in one fixture to permit all night service and an automatic device was developed, located in each fixture, so that should one “candle” go out for any reason, another was switched into service.

This simple arc consisted of a pair of carbons held together side by side and insulated from each other by kaolin. Several boulevards in Paris were lighted with these arc lights. This arc lamp is in the collection of the Smithsonian Institution.]

In 1876 many of these “candles” were installed and later several of the boulevards in Paris were lighted with them. This was the first large installation of the arc light, and was the beginning of its commercial introduction. Henry Wilde made some improvements in the candle by eliminating the kaolin between the carbons which gave Jablochkoff’s arc its peculiar color. Wilde’s arc was started by allowing the ends of the carbons to touch each other, a magnet swinging them apart thus striking the arc.

This dynamo had a stationary exterior armature and internal revolving field poles. Alternating current was used for the Jablochkoff “candle” to overcome the difficulties of unequal consumption of the carbons on direct current.]