ABN.ISCAMS%usc-isid@sri-unix.UUCP (11/21/83)
Netland: My organization has been using some big heavy lunkers of Solas "constant voltage" transformers for years now to stabilize some of the horrible AC current we get under field conditions (Army generators, long cables running through mud, strangers hanging coffee pots and arc welders off the line, etc.) They've worked just fine with the usual 110V AC (+/- 20 volts), and also worked fine when I grabbed some three-phase 220. (Had to jumper them up internally for the 220-110 conversion, but they're designed for that.) Problem: Went to Germany. Took the good old Solas's along (they convert 220 to 110, don't they?). Plugged in (appropriately jumpered to 220>110 conversion). Got a beautiful, steady spikeless 96 volts! Huh! Found an already-transformered 110 wall plug. Rejumpered friend Solas, now 110>110 range. Plugged in. Got a beautiful, steady spikeless 96 volts! Reinvented the theory of AC transformers, and I need some feedback from you real electrical/electronics types out there (I'm a mere SF weapons man). I propose the core of a transformer vibrates from the AC cycles, or in some way creates a cyclic magnetic field. This magnetic field is cut by the windings, thus creating the output AC voltage. (Kind of like an alternator does, but the field moves instead of the windings.) The 50 cycle current available in Europe cycles the magnetic field slower, thus resulting in a reduced output AC voltage. (The 110/96 ratio is suspiciously close to the 60/50 cycle ratio, prompting me to this hypothesis.) Could this be right, wizards? Any way to cobble my trusty old Solas's up to kick that output voltage up (and no, I ain't gonna rewind that sucker either!)? Or just buy European 220/110 transformers with the cycle difference already accounted for? Anyway, lesson learned for you guys planning to go to Europe: don't depend on any Stateside 220/110 transformers working correctly. (Incidentally, the Apples I was using ran just fine on 96V. Two of three Corvus 20Meg hard disks ran fine (last one wouldn't run there; ran just fine back Stateside). Sanyo color monitors - just fine on 96V. Sanyo green screen monitors: yuck! Extremely blurry characters top and bottom of screen; totally unsatisfactory. Took a chance, grabbed the available 110 volt wall current, ran it through an isolator (really had dirty current at that location); green screen ran fine. Oh, yeah, blew up three (count 'em, 3) Global OOPSes (Uninterruptable Power Supplies) trying to run them on the available 110V wall plugs. Capacitors catastrophically destructed (really neat, lots of smoke and expensive smells). Lost two solid and one wet capacitors -- the wet one on the electronics board blew like a minigrenade, plastering bits of foil and gunk all over the board and actually blowing several traces off the board! Suspect the 110V in that building was obtained by "cycle clipping" (donno the real word for it, but you clip off one side of the 220V cycle, getting 110V all right, but a strange 110V that maybe electronics don't like so very much). One of the OOPSes ran OK for a couple of hours on Solas-transformed 220>96V, and then started complaining; so we never did get any use of our OOPSes. 'Nuff said on my experiences. Would appreciate some hints/suggestions/ background knowledge on European power and my hardware. Thanks in advance, David Kirschbaum SGM, USA Corps Automation Management Office HQ XVIII Abn Corps, Ft Bragg
w8sdz%brl@sri-unix.UUCP (11/22/83)
From: Keith Petersen <w8sdz@brl> Dave, the UPS and Sola units are "tuned" to 60hz, should NEVER be plugged into anything else. The capacitor/inductance combination is actually carefully peaked at 60hz to provide the desired core saturation to create the voltage regulation effect. Generally speaking 60hz equipment (such as monitors and computers) should not be run on 50hz because the transformers run hotter and may eventually fail from the heat (or the heat may cause something else inside to fail). If you intend your equipment to operate on both 50 and 60hz, it should be ordered for 50hz originally. The transformers have more iron in them and run just fine on 60hz (actually cooler). This of course cannot be done with "tuned" systems such as Sola CVTs.
Nail.wbst@PARC-MAXC.ARPA (11/23/83)
Dave, First, I would like to say that I am glad to see someone using the net in a way that is very effective and suit the medium very well. Kudos. Second. Sola transformers are resonant transformers with energy alternatingly stored in the magnetic field (L) and then in a capacitor(C). The this is a LC tuned circuit intended to run at the 60 cycles designed for your equipment. Running such a tuned circuit at any other frequency will not effectively exchange the stored energy between L and C in the circuit. Conceivably, the circuit can be retuned by changing the components (probably C would be easiest to change). You may be able to successfully retune the circuit, but you can expect the power handling characterists of the transformer to differ. My take on this is that you might find it to be better to get a transformer tuned for the 50Hz application. Good luck. Charlie
towson%amsaa@sri-unix.UUCP (11/23/83)
From: David Towson (CSD) <towson@amsaa> David - The answer to your constant-voltage transformer question becomes self-evident as soon as you hear the other name for them: They are also known as "ferro-resonant transformers". Their operation depends on a tuned circuit whose resonant frequency is slightly off the operating frequency. As the line voltage input changes, the amount of core flux changes, and since the relationship of core flux to exciting current (which results from the applied voltage) is non-linear for iron-core inductors, the inductance of a choke (inductor) in series with the transformer part itself (it's all inside the box) changes and this changes the voltage actually applied to the trans- former. The thing is set up so that the change is in the right direction to adjust the voltage to near what it should be coming out of the unit. When you run it on 50 HZ, you totally mess up the resonant action, which is tuned for 60 HZ. And that's the rest of the story. Dave
cdl@mplvax.UUCP (11/28/83)
A Sola Transformer is a tuned resonant-circuit device. As such, it
is designed to work over a small range of frequencies, typically
+/- 5% (57-63 Hz). Over this range, the output voltage will vary
1.5 times as much as the input frequency varies, all other things
being constant.
Running your Solas on nominal 50 Hz, all bets are off. You are lucky
that they didn't just burn up in a large puff of bad-smelling smoke.
Seriously, Sola does make 50Hz transformers, and possibly you could
re-tune yours by adding capacitance in the appropriate places.
I have used Sola transformers for many years in seagoing applications,
and have muttered about the poor frequency control of the shipboard
power, but at least they try to keep it at 60Hz.
For a concise explanation of the working of these transformers, see
"Electronic Transformers and Circuits," Ruben Lee, Wiley 1955,
pp. 252-3.
Carl Lowenstein
Marine Physical Lab., U.C. San Diego
{ucbvax,philabs}!sdcsvax!mplvax!cdl
mplvax!cdl@nosc