larry@uunet.uu.net (Larry Lippman) (03/29/91)
In article: <telecom11.247.5@eecs.nwu.edu> uccxmgm@unx2.ucc.okstate. edu writes: > I wonder if they used electrolytic rectifiers back then to handle > that kind of current? A liquid electrolytic rectifier was indeed used for small PBX applications during the 1920's. It used one electrode of tantalum and one electrode of lead in an electrolyte solution of sulfuric acid. A floating layer of mineral oil prevented evaporation. The maximum current per device was limited to several amperes, though. One manufacturer of this device was Fansteel Products. Such electrolytic rectifiers were rapidly superceded by copper oxide rectifiers, which were available in capacities up to 20 or so amperes. By the 1940's copper oxide rectifiers were largely superceded by selenium rectifiers. However, even selenium rectifiers, which were used in new product designs until the advent of silicon rectifier diodes during the 1950's, were limited to about 100 amperes in capacity. From the *very* early days when telephone company central offices produced their own electric power from steam boilers, generators were used to create the DC necessary for charging batteries. By 1900 most telephone company central offices used commercial AC power, but to run motor-generator combinations. In fact, one of the benefits from using batteries was the filtering of AC noise created by the commutators of DC generators. AC motor-driven generators used to create DC for battery charging were still in service in a few Bell System central offices as of the early 1980's! The last ones I saw were for +130 and -130 volts used to power vacuum tube carrier and microwave apparatus. Chances are they were not replaced because the associated apparatus had very little remaining service life, and 130 volt battery installations were primarily associated with such old vacuum tube apparatus. Newer apparatus which required 130 volts generally relied upon solid-state DC/DC converters powered by the -48 volt DC battery. Starting around World War I, mercury arc rectifiers came into vogue, but only for smaller central offices. Mercury arc rectifiers were limited to about 50 amperes per device, although multiple devices could be paralleled for larger loads. Many mercury arc rectifiers for smaller central offices were updated during the 1960's through the use of solid-state devices which were plug-in replacements for the rectifier tubes. I feel certain that a few of these updated rectifiers (like the WECo 110A) are still in service today in small SxS CO's. For larger multi-thousand ampere battery plants, AC motor-driven generators were still the only way to go until the 1950's when large silicon rectifier diodes became available. No other rectifier method prior to this time could compete with motor-driven generators for ampere capacity. Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 [note: ub=acsu.buffalo.edu] uunet!/ \aerion!larry