abc@unh.UUCP (Avinash B Chopde) (02/10/88)
A question about stepping down voltage. I went into a Radio Shack shop to get a transformer (primary 240V, secondary 120V) so that 120V equipment can be run off 240V AC supply. I thought only the wattage should be important in such a transformer, but the salesman told me that the 1000W unit they have will work only for hair-dryers, and cannot be used for motors (food processors, etc) even if they are of lesser wattage. Does this have something to do with resistive/inductive loads ? Anybody have a simple answer (non-technical! - am an electronics ignoramus!), or, (better still) a refutation of the salesman's talk ? A specific question : will there be any burnouts if I use a 1000W convertor specified to be used for hair-dryers for audio equipment instead ? Thanks in advance for any replies. -- ================================= Avinash Chopde (abc@unhcs.CSNET) =================================
todd@uop.edu (Dr. Nethack) (02/11/88)
Slightly unrelated, I recently purchased some copper wire for some
lights I was rigging. The sales girl tried to talk my Father into buying
stranded #12 wire, (more expensive than solid core)...
"Because it makes the electricity go faster"
---
...rutgers!retix!\
...ames!ucbcad!ucbvax!ucdavis!uop!todd
...uunet!lll-winken!cogent!/
Remember, Dr. Science has a Master's Degree, in *Science*max@trinity.uucp (Max Hauser) (02/11/88)
In article <1055@uop.edu> todd@uop.edu (Dr. Nethack) writes: > ...I recently purchased some copper wire for some lights I was > rigging. The sales girl tried to talk my Father into buying > stranded #12 wire, (more expensive than solid core)... >"Because it makes the electricity go faster" Good one! Of course, she was "only a sales clerk," not supposed to be knowledgeable about these things. This stands in marked contrast to authorities we can find here on the Usenet -- rec.audio, for instance -- many of whose explanations of the electrical physics, in just such situations as solid vs. stranded wire, are a world apart from this, dazzling in their clarity and substance. Aren't we Usenet readers lucky, since we need not rely on such dubious sources as sales clerks for advice, but instead can harness the power of an expensive intercontinental computer network... Don't know about you, but I can just barely stand it. Max Hauser / max@eros.berkeley.edu / ...{!decvax}!ucbvax!eros!max "And was Jerusalem builded here / Among those dark Satanic mills?"
hes@ecsvax.UUCP (Henry Schaffer) (02/11/88)
In article <204@unh.UUCP>, abc@unh.UUCP (Avinash B Chopde) writes: > > A question about stepping down voltage. > > I went into a Radio Shack shop to get a transformer (primary 240V, ^^^^^^^^^^^ > secondary 120V) so that 120V equipment can be run off 240V AC supply. > > I thought only the wattage should be important in such a transformer, ^^^^^^^^^^^ > but the salesman told me that the 1000W unit they have will work only for > hair-dryers, and cannot be used for motors (food processors, etc) even if > they are of lesser wattage. The problem is that everyone concerned seems to be assuming that a 240->120 volt converter has to be a transformer. A transformer does work fine and can run anything, but tends to be big and expensive in the high current/wattage sizes. For much less money and in a much smaller package you can put a half-wave rectifier rectifier which will give you the same effect - *for loads which don't care about the wave-form*. Note that this generally includes resistive loads (such as heaters - which is where the high wattage is important) - but doesn't generally include audio equipment. Some motors will work, others won't (vagueness intentional :-). > ... > ================================= > Avinash Chopde (abc@unhcs.CSNET) > ================================= --henry schaffer n c state univ
dmt@ptsfa.UUCP (Dave Turner) (02/11/88)
In article <204@unh.UUCP> abc@unh.UUCP (Avinash B Chopde) writes: > >I went into a Radio Shack shop to get a transformer (primary 240V, >secondary 120V) so that 120V equipment can be run off 240V AC supply. > >I thought only the wattage should be important in such a transformer, I'll bet that if you open one of RS's power "converters" you'll find a high current diode rather than a transformer. I've just started looking for a 1000 Watt (VA) 115v - 115v isolation transformer and expect to pay from $50-$100. The 1000 Watt RS converter is $14.95. Herbach & Rademan, Inc. 401 East Erie Ave. Philadelphia, PA 19134 lists a 500 Watt 230v - 115v step-down transformer in their latest catalog for about $50. The catalog is home so I can't give you the exact price. Sorry. -- Dave Turner 415/542-1299 {ihnp4,lll-crg,qantel,pyramid}!ptsfa!dmt
bownesrm@beowulf.UUCP ( Stowaway aboard the Long Shot) (02/11/88)
In article <204@unh.UUCP>, abc@unh.UUCP (Avinash B Chopde) writes: > > A question about stepping down voltage. > > I went into a Radio Shack shop to get a transformer (primary 240V, > secondary 120V) so that 120V equipment can be run off 240V AC supply. > > Does this have something to do with resistive/inductive loads ? > Anybody have a simple answer (non-technical! - am an electronics ignoramus!), > or, (better still) a refutation of the salesman's talk ? > Mostly the 240-120 converters (at leasst the one I bought from RS a few years back) work by using an SCR to hack the wave up. This results in some squarish waves instead of a nice smooth sine. When you run this high delta Voltage through a transformer (like an AC motor) it tends to produce some really nifty destructive spikes. The rule is, "When in doubt, use an isolation transformer." When we moved to N. Ireland, we had a set of circuits in the house wired to a 2.5 KvA transformer. Solved all our problems. (Incidentally, most hair driers have DC motors. This chopped up wave won't cause a problem there.) > A specific question : will there be any burnouts if I use a 1000W convertor > specified to be used for hair-dryers for audio equipment instead ? > It depends on what it is. I ran a stereo cassete deck off an SCR type converter but I looked at the schematics first to make sure the ac went straight to a rectifier. > Thanks in advance for any replies. > -- No problem. I have LOTS of experience dealing with this. If any of the aforementioned techno-babble was confusing, send me mail. Bob Bownes, aka iii, aka captain comrade bob | Since I AM my employer, Function Consulting, Albany, New York, 12203 | I guess these opinions are (518)-482-8798 voice (518)-482-9228 (anon uucp) | those of my employer bownesrm@beowulf.uucp | my houseplants, and my TR-6. ------------------------------------------------+------------+------------------ PS/2: Yesterday's Hardware Today. | Stolen from Jerry OS/2: Yesterday's Software Tomorrow. | Pournelle in OS/2 Extended Version: Yesterday's Software REAL SOON NOW. | InfoWorld -------------------------------------------------------------+------------------
wolfgang@mgm.mit.edu (Wolfgang Rupprecht) (02/11/88)
Expires: Sender: Followup-To: Distribution: In article <4591@ecsvax.UUCP> hes@ecsvax.UUCP (Henry Schaffer) writes: > The problem is that everyone concerned seems to be assuming that a >240->120 volt converter has to be a transformer. [...] > For much less money and in a much smaller package you can put a >half-wave rectifier rectifier which will give you the same effect - *for >loads which don't care about the wave-form*. Henry you are clearly on the right track, but be careful, you are missing a power of two. For resistive devices the power disipated is (E^2)/R. Doubling the voltage from 120v -> 240v will quadruple your power. If you use a diode to cut out a half cycle every cycle, then you will only end up reducing your power by a factor of 2, not the factor of 4 that is required. The cheap scr/triac ("light dimmer") type systems that one sees sold as transformerless 240v adapters actually take a significant chunk out of each waveform, infact, roughly 3/4 of each waveform gets eaten. (The actual on time is chosen so that the integral of E^2/R over the on part of the cycle is exactly 1/4 of the integal over the whole cycle.) As a side note, you can actually see 50 hertz flicker from a half vave rectified light bulb quite clearly, if you observe it out of the corner of your eye. The center of vision appears to have a bit slower response, which prevents one from seeing the 50hz flicker. The US line frequency of 60 hz, is just barely fast enough that a half wave rectified bulb flickers slightly, but not annoyingly so. (Is this how 60 hz got chosen as the standard I wonder?) I have seen 3 way lightbulb sockets wired with a diode between the extra contact and the normal center contact. This hack lets a normal single filament bulb act like a "3 way" bulb, with an off, dim, and full on setting. Problem is, the dim setting flickers a bit. .---. / \ o----------------------( < o > ) three-way socket | | / 120v +------+-----+ | in | | | dim o +---|>|-+ <----- this diode added to socket base. o---------> | full o--------------+ --- Wolfgang Rupprecht ARPA: wolfgang@mgm.mit.edu (IP 18.82.0.114) 326 Commonwealth Ave. UUCP: mit-eddie!mgm.mit.edu!wolfgang Boston, Ma. 02115 TEL: (617) 267-4365
henry@utzoo.uucp (Henry Spencer) (02/15/88)
> ... the salesman told me that the 1000W unit they have will work only for > hair-dryers, and cannot be used for motors (food processors, etc) even if > they are of lesser wattage. If you look carefully at the Radio Snack converters, you will find that there are two kinds: a low-wattage type for motors and such, and a high- wattage type for heaters and such. Only the low-wattage one is really a transformer. The high-wattage one is just a diode, which does a really sloppy job of conversion that is only good enough for things that don't care about the details. Most anything electronic will care, as will many motors. A high-wattage transformer will not be cheap, or small, or light. You also need to worry about another problem. I assume you are thinking about the flavor(s) of 240VAC found overseas, not here. If so, note that those awful furriners also run their power at 50 Hz rather than 60 Hz. There is likely to be a little label on the back of your equipment giving things like voltage and power requirements. If it says something like "47-63 Hz", as many of them do now, you're in the clear. If it says "60 Hz", then you are gambling if you hook up to 50-Hz power: it might work, it might overheat, it might fail completely. There is no easy fix for this one. -- Those who do not understand Unix are | Henry Spencer @ U of Toronto Zoology condemned to reinvent it, poorly. | {allegra,ihnp4,decvax,utai}!utzoo!henry
koko@uthub.toronto.edu (M. Kokodyniak) (02/16/88)
Some appliances have universal motors (with brushes) while others have induction or synchronous motors (without brushes). Appliances that do not care much about line frequency (since they have universal motors): electric shavers hair dryers small kitchen appliances power tools vacuum cleaners Appliances that do care about line frequency (since some have induction or synchronous motors): major appliances: refridgerators dishwashers washers dryers all analog clocks (with dials) some digital clocks (except those with battery backup) some phonograph turntables (especially older automatic ones and ones with orange-neon stroboscopes built in) some reel-to-reel taperecorders Clocks usually use the line frequency to keep time, since the utilities keep the long-term average line frequency accurate. Cheaper turntables use an induction motor, to keep constant speed, as do some cheaper reel-to-reel taperecorders. Although the operation of some appliances is affected by line frequency, they may still work satisfactorily (at somewhat lower or higher speeds): barbecue rotors electric fans portable heaters with fans
phd@SPEECH1.CS.CMU.EDU (Paul Dietz) (02/19/88)
In article <701@uthub.toronto.edu> koko@uthub.toronto.edu (M. Kokodyniak) writes: >Appliances that do care about line frequency (since some have >induction or synchronous motors): > some digital clocks (except those with battery backup) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ I can't speak in general, but my digital clock sync.s to the 60Hz (or cps, if you insist...) when it's available, and reverts to a very crummy battery powered RC osc. otherwise. (Also, trying to run at ~60 Hz, but not doing a very good job. Gains about 15 - 20 minutes per hour when runing on backup.) Paul H. Dietz ____ ____ Dept. of Electrical and Computer Engineering / oo \ <_<\\\ Carnegie Mellon University /| \/ |\ \\ \\ -------------------------------------------- | | ( ) | | | ||\\ "If God had meant for penguins to fly, -->--<-- / / |\\\ / he would have given them wings." _________^__^_________/ / / \\\\-
henry@utzoo.uucp (Henry Spencer) (02/21/88)
@#%$%@#! You're right, Wolfgang, just a rectifier wouldn't do it. I was
probably half-remembering an SCR-based circuit. Apologies to all. In any
case it doesn't alter the conclusion: the non-transformer converters work
only for things that don't care about waveform.
--
Those who do not understand Unix are | Henry Spencer @ U of Toronto Zoology
condemned to reinvent it, poorly. | {allegra,ihnp4,decvax,utai}!utzoo!henryalex@tiger.Princeton.EDU (Alexander Zaslavsky) (02/27/88)
I am sorry to crowd the net with trivia, but I am a novice in electronics and need some help. I bought a computer (Mac SE) + printer (Imagewriter II) for my father to use in Italy (220 V, 50 Hz). Now it turns out that the computer runs fine on European standard, but the printer needs a transformer rated at 200 W. If I were to get such a beast, would the frequency cause any problems (Apple has no suggestions in the manual)? If not, where can I get such a beast (J&R Electronics in New York wanted to sell me a 1000 W transformer that weighed at least 15 pounds and cost $60)? Please reply to tiger!alex, all advice greatly appreciated alex
dave@onfcanim.UUCP (Dave Martindale) (03/04/88)
>There is likely to be a little label on the back of your equipment giving >things like voltage and power requirements. If it says something like >"47-63 Hz", as many of them do now, you're in the clear. If it says >"60 Hz", then you are gambling if you hook up to 50-Hz power: it might >work, it might overheat, it might fail completely. And then there are the wonderful devices labelled "90-250 VAC 48-440 Hz". For these, you just need the right power cord or adapter (such devices usually have the "international" power input connector so the power cord is changeable). My Tektronix oscilloscope is like this - it accomplishes this by full-wave rectifying the line voltage, then feeding the pulsating DC to a switching regulator that provides 43 VDC out, which drives an inverter that generates AC again at 20 KHz. This is then fed to the main power transformer, which produces both low and high voltages for the instrument. Thanks and a hat tip to manufacturers who do something like this.