Xref: utzoo rec.travel:18625 rec.radio.amateur.misc:1054 sci.electronics:18873 Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!att!bellcore!epic!karn From: karn@epic.bellcore.com (Phil R. Karn) Newsgroups: rec.travel,rec.radio.amateur.misc,sci.electronics Subject: Re: large 110->220 transformers Message-ID: <1991Mar28.211132.3521@bellcore.bellcore.com> Date: 28 Mar 91 21:11:32 GMT References: <1991Mar28.190723.9681@athena.cs.uga.edu> Sender: usenet@bellcore.bellcore.com (Poster of News) Reply-To: karn@thumper.bellcore.com Organization: Packet Communications Research Group (Bellcore) Lines: 79 European power differs from American power in three ways: the voltage is different (220/240V vs 110/120V), the frequency (50 vs 60 Hz) and the plug (the UK has one type, the Continent another, and both are quite different from the North American style). Converting plugs is easy; converting voltage is harder (you usually need a transformer) and converting frequency is hardest of all (you need a motor-generator set or AC/DC/AC rectifier/inverter combination - impractical in most cases.) Whether a given American appliance can be operated in Europe (with or without a transformer) depends very much on that appliance. Given the international nature of the appliance market, more and more units are built in a common "export version", with a switch for operation on either 110V or 220V. These appliances are by far the easiest to deal with, requiring only a plug adaptor (or new line cord) to mate with European outlets. Much modern computer equipment (PCs, AC-powered disk drives and printers, but NOT modems and monitors) use switching power supplies, and many (if not most) of these supplies are readily operable on 220V 50 Hz. Just throw the line voltage switch and connect up a cord with the appropriate plug. Modern switching power supplies invariably rectify and filter the power line directly, so they are not at all sensitive to line frequency. The line rectifier is usually designed to operate as a full-wave bridge on a 220V line and as a voltage doubler on a 110V line, so all it takes is a SPST switch to select the mode of operation. This design seems to be universal in personal computers. One of the characteristics of a switching power supply is the ability to operate efficiently over a wide input voltage range. This feature has been taken one step further in the development of 110/220V supplies that do not require manual switching; they are simply designed to operate over a 2:1 input voltage range. This design is becoming common in laptop computer power supplies. Monitors and modems generally do not use switching supplies, so they have power transformers. If the unit has a 110/220V switch and is rated for 50/60 Hz operation, no problem. If the unit is for 110V operation only it MAY be safely operable from a stepdown transformer; I say MAY because some transformers intended for 60 Hz operation may overheat when operated at 50 Hz. The rest of the unit probably won't care about the line frequency because the output of the power transformer is rectified and filtered to DC anyway. (If the filter caps are marginal, you might have increased hum problems at 50 Hz). TV sets generally do not have power transformers (they rectify the line directly), so they should operate okay from 110V 50 Hz. Unfortunately, US TV sets use the NTSC standard while television in Europe is either PAL or SECAM, so your set wouldn't be of much use over there except for playing back NTSC tapes on your NTSC VCR. Stereos, CD players and most ham gear are similar to computer monitors in that they usually have power transformers; the same considerations apply regarding the change in line frequency. Hair dryers, incandescent lamps, brush-type motor power tools, etc, can be operated off 220V through those small "travel converters" that are simply high power rectifiers. They produce a strong DC component, but that will not bother these appliances. NB! Do NOT use one of these converters on anything that has a power transformer! (Many travel kits have two adapters, a 1KW diode model for the aforementioned appliances and a 50W model that uses a step down transformer. When in doubt, always use the transformer model if it can handle the required load.) Alarm clocks or other devices with synchronous motors (e.g., turntables and analog tape decks) will NOT operate properly off European power even with a transformer, as their motor speeds are determined by the power frequency. (This may not be true for ALL alarm clocks, turntables and tape decks as some may have internal crystal clock references, but without knowing the design you can't be sure.) Note that CD players are not a problem here as their internals are always driven from a crystal reference, not the AC power line. So the bottom line is that it's not easy to make generalizations about how easy it is to operate a given US appliance in Europe. Unless it was clearly designed to operate off either 120 or 240V power, you can't really tell for sure without a look at the schematic. Phil