commgrp@silver.bacs.indiana.edu (05/13/87)
In article <5924@shemp.UCLA.EDU>, mitch@CS.UCLA.EDU writes: > I'm building a cabin in a remote area in Arizona, and I > plan to use 12-volt dc power for lighting. > > Can anybody tell me how to convert standard shop-lite > florescent fixtures for this application? Is it practical > to do this myself, or should I just pay the $80+ for > the commercial variety? 12-volt DC fluorescent light fixtures for recreational vehicles are available from Warshawsky/JC Whitney auto parts of Chicago, and from other suppliers of RV accessories. These are quite inexpensive (cheaper to buy than build) however, there are some disadvantages: 1) Their internal construction is VERY crude. 2) Some types produce a DC component (see below) which causes one end of the fluorescent tubes to blacken. The effect can be minimized by periodically rotating the tubes end-for-end. 3) They produce radio-frequency interference which totally obliterates AM radio reception. (Many 12vdc-to-115vac inverters also produce RFI.) 4) Most operate at ultrasonic frequencies but the transformers in some types emit obnoxious squealing noises. -...- Historical note: Gas-discharge lamps were used for lighting in the 19th Century. Jules Verne equipped his intrepid cavers with electric "Ruhmkorff" lamps in JOURNEY TO THE CENTER OF THE EARTH, an adventure which begins in 1863, well before Edison's 1879 lightbulb. After a lengthy search, I found a reference to Ruhmkorff in A HISTORY OF ELECTRICITY AND MAGNETISM by Herbert W. Meyer (MIT Press, 1971. JOURNEY was first published in Paris in 1864, followed by a beautifully illustrated edition in 1867. The description of the lamps has changed and lost vital details in English editions (as have other aspects of the novel, especially in the movie version). The following translation by Indiana University history professor B. G. Martin is from the list of cave gear and scientific equipment on page 58 of the 1867 French edition: ...Two Ruhmkorf apparatus which, by means of electric current, give a very portable light, sure and little encumbrance. footnote: The Ruhmkorf apparatus consists of a Bunsen battery which is activated by potassium bichromate and has no odor, and an induction coil which produces electricity from the battery, connected to a special lantern in which is found a serpentine glass, exhausted and containing a residue of carbon dioxide or nitrogen gas. When the apparatus operates, this gas becomes luminous, producing a continuous whitish light. The battery and coil are held in a leather bag which the adventurer carries over the shoulder. The lantern, placed outside, very sufficiently illuminates the profoundest darkness, and permits the adventurer, without fear of explosion, in the presence of extremely inflammable gasses, and is not extinguished even under the deepest water. M. Ruhmkorf is a learned and able physicist. His great discovery is the induction coil which permits production of high-voltage electricity. In 1864, he received the five-year prize of 50,000 francs which France reserves for the most ingenious application of electricity. Verne spelled the name with one f. "Ruhmkorff coil" is an archaic term (actually, a brand name become generic) for what Americans commonly call "Ford coils," i.e., dc- powered high-voltage transformers with vibrating interrupters, small versions of which were used for ignition in Model-T Ford cars. Ford coils are still available from JC Whitney for about $35. Ruhmkorff coils were "Hi-tech" in Verne's time, a golden age of learning in France during which fundamental laws of electricity were discovered. Studies of electric gas-discharge phenomena were in the forefront of mid-19th-century science. A succession of breakthroughs ensued from investigations of light produced by static electricity in the vacuum above the mercury column of a barometer. This fascinating "quest for fire" is chronicled in the PBS TV series and book CONNECTIONS by James Burke. Meyer writes, "H. D. Ruhmkorff of Paris began making induction coils about 1851. He was familiar with the work of...others who had already produced powerful coils... Ruhmkorff was an excellent craftsman, and made coils of great refinement and excellence, so that the term Ruhmkorff coil was synonymous with induction coil for many years. In order to overcome the difficulty of internal sparking, Ruhmkorff divided the secondary winding into sections, which were well insulated from each other and from the primary winding." "Ruhmkorff...coils were probably the finest made anywhere. He engaged in their manufacture on a large scale and was therefore often considered as the inventor of the induction coil. One of his largest coils made in 1867 gave sparks of 40 centimeters, or about 16 inches." "Theoretically, the discharge from an induction coil should be AC. Actually, however, the secondary voltage is so much higher when the circuit is broken by the interrupter than when it is closed that the secondary output is almost unidirectional." Induction coils were instrumental to the discoveries of cathode rays by William Crookes (1860's), X-rays by W. K. Roentgen (1895), and to the work of Tesla, Hertz and other radio pioneers. They were used in spark-gap radio transmitters well into the 20th century. Meyer does not mention Ruhmkorff lamps, but reports that Geissler tubes were produced in great numbers around the mid-19th century. These partially-evacuated tubes, often of convoluted shape, contained mercury or various rare gasses, and sometimes were made of glass containing fluorescent metallic salts, or had double walls filled with fluorescent liquid. Geissler tubes powered by induction coils are still among the most spectacular physics-classroom demonstrations. They also appear as props in old Flash Gordon and Frankenstein movies. Bunsen batteries, widely used in the 19th century, had carbon and zinc electrodes and dilute sulphuric acid electrolyte. A porous cup surrounding the carbon contained chromic acid depolarizing agent. The lamps in the 1958 MGM movie were powered by hand cranks. The wonderful windup lamps were waterproof, but failed when salt got inside them and "corroded the induction coils." Although they have moving parts, Ruhmkorff coils aren't mechanically powered, and require batteries. A related device, the magneto, IS mechanically driven. Spring-powered magnetos were within the technological capabilities of Verne's day, and would have been an attractive alternative to the expensive and primitive batteries then available. Gas-discharge lamps powered by induction coils or magnetos would probably have been inefficient light sources, but desirable for their then-unique advantages over open-flame lights. Verne also mentions Ruhmkorff lamps used underwater and aboard the Nautilus in 20,000 LEAGUES UNDER THE SEA (1870). 19th-century gas-discharge lamps survive today as neon signs. Although Ruhmkorff lamps were elcipsed by incandescent bulbs, fluorescent technology has steadily advanced. We may say that Verne correctly predicted that electric fluorescent lights would be ubiquitous in the future world except, ironically, among cavers and divers. References ---------- 1. Verne, Jules VOYAGE AU CENTRE DE LA TERRE (vignettes par Riou). Paris: J. Hetzel et Cie, 1867. 2. Burke, James. CONNECTIONS. Little, Brown & Co., 1978. p. 209. 3. Morgan, Alfred P. THE BOY ELECTRICIAN. New York: Lothrop, Lee & Shepherd Co., 1913, 1929, 1948. 4. Armagnat, H. THE THEORY, DESIGN AND CONSTRUCTION OF INDUCTION COILS New York: McGraw Publ. Co., 1908. -- Frank Reid reid@gold.bacs.indiana.edu