weinri@athena.cs.uga.edu (Kevin Weinrich) (03/20/91)
Has anyone read any good articles about UPSes in any of the journals? I'm considering putting a SPARCstation 1+ and/or a 4/330 on a UPS, and I'm confused by all the electrical terms. One unit is called a "BEST MD500 vA" -- does this mean it handles 500 volt-Amperes? Is that the same as .5 kvA? On the back it says 4.1 amps. What should this mean to me? My monitor says 2.5A. Thanks in advance for steering me in the right direction.
kaufman@neon.Stanford.EDU (Marc T. Kaufman) (03/20/91)
In article <1991Mar19.200553.13176@athena.cs.uga.edu> weinri@athena.cs.uga.edu (Kevin Weinrich) writes: >Has anyone read any good articles about UPSes in any of the journals? >I'm considering putting a SPARCstation 1+ and/or a 4/330 on a UPS, and >I'm confused by all the electrical terms. One unit is called a >"BEST MD500 vA" -- does this mean it handles 500 volt-Amperes? Is >that the same as .5 kvA? On the back it says 4.1 amps. What should this >mean to me? My monitor says 2.5A. Thanks in advance for steering me >in the right direction. I use a BEST MD500 for my Mac. It is not only a UPS, but is a full-time line conditioner, as it uses a ferro-resonant transformer to isolate the computer from the line. Because the inverter is on the INPUT to the transformer, the output never sees even as much as 1/2 cycle dropout. The parameters to control the BEST are set and read out via an RS232 port. It isn't cheap, though. The 500 is about $900. The fuse ratings on your monitor and computer represent about 150% of the maximum load, with all memory and peripherals running, etc. My Mac + monitor + 2 disks represents about 250 watts. Marc Kaufman (kaufman@Neon.stanford.edu)
quimby@madoka.its.rpi.edu (Tom Stewart) (03/20/91)
Here's the wonderfull electrical stuff:
UPS's are, or should be, rated in VA. A VA is a VoltAmpere, and is
simply the AC RMS voltage multiplied by the AC RMS current. You
probably have been led to believe that a Watt is a VoltAmpere, and
this is mostly, but not quite, true. A Watt is only a VA into a
resistive load -- this is because with a complex load the voltage
and current aren't in phase, so multiplying the scaler quantities
doesn't represent the actual power at all. The electrical term for
this difference is called _power factor_, and in a purely resistive
load the power factor is 1, and W=VA. For a complex load, the power
factor is always less than 1, and W=VA(power_factor). The purpose of
power factor is to reduce the need for electricians to do vector math.
Here's what it means to you:
A UPS is limited by VA, not Watts, so if a UPS manufactor gives Watts you
should assume worst case, which is that they really mean VA. Computer
equipment is either rated in VA, A, or Watts. Use the VA rating if
possible. If they give A multiply by 120 to get VA. If they give Watts
divide by .7 or .8 to get an estimated VA. (This is ballpark for a
typical switching power supply. Note that the VA value is higher than
the Watts value.) Add up all of the VA's, multiply by your favorite
safety margin, and pick yourself a UPS.
Unless you've got either a very screwy power system, or a screwy
computer, you really don't need full time power conditioning. The
protection you want is from brownouts, blackouts/dropouts, and spikes,
which any good switching UPS will do. If your power is bad enough
that you need something else -- say you're running from a diesel
generator and power is very random -- you want a true on-line UPS.
Following the "fewer parts is better" rule suggests a switch mode
UPS with surge suppression for every "normal" installation.
My vote for a UPS would be an American Power, maybe a 450 or 520. They're
small, light, and very well built, have excellent surge supression, and
have the fastest switch times I've seen. They're also reasonably
inexpensive.
Hope this helps
Quimby
(mailer disfunctional, replies to: quimby@mts.rpi.edu, quimby@rpitsmts.bitnet)
disclaimer: I have no connection with American Power, any UPS/SPS
manufactor, or Hallmark greeting cards.
butzer@rugby.cis.ohio-state.edu (Dan Butzer) (03/21/91)
To cast my vote on the UPS's -- I must strongly endorse BEST. I have
a 3.1KVA unit protecting our console server and network racks. It is an
outstanding unit. Very well built, very solid, very nice instrumentation
including logging of power events as well as storing and displaying
input and recerence waveforms at the time of a power event. I have also
been very pleased with their sales staff.
--Dan
(I'm only a very very happy customer)
--
Dan Butzer || butzer@cis.ohio-state.edu
IICF/CIS Hardware Support || voice: 614-292-7350 fax: 614-292-9021
"Fire in the hole..." || 2036 Neil Ave, Columbus OH 43210shepperd@dms.UUCP (Dave Shepperd) (03/21/91)
From article <98590@tut.cis.ohio-state.edu>, by butzer@rugby.cis.ohio-state.edu (Dan Butzer): > > To cast my vote on the UPS's -- I must strongly endorse BEST. I have > a 3.1KVA unit protecting our console server and network racks. I'd vote with Best also, at least for the bigger units. I have two 3Kva's here running all sorts of things (I just kept plugging things into it until the display read ~2800Va). We've run through one set of batteries already on one of them (took about 4 years). They have worked perfectly through the various power problems that we've had from time to time. I also have a Best 850Va unit at home. It runs all my computer stuff as well as the TV/Stereo/VCRs/Cable_decoder. I'm not quite as impressed with it because it: 1) is noisy. It has a fan that runs all the time; 2) doesn't do quite as good a job of handling input line drops as I think it should; 3) The output signal is not as clean a sine wave as I'd like; 4) is big; 5) is quite heavy. I have a desk lamp plugged in to it along with all the computer stuff and I can see the lamp flicker if the main AC drops out. Best goes to great lengths to suggest that the unit has a 0 cutover time, but if this were true, I believe one would not be able to see an incandescent lamp flicker. (It'll flicker the lamp even if the lamp is the only thing plugged in). I compare this little Best unit against two 1200VA units I got from American Power. The American Power units were cheaper, lighter, quieter (no fan runs while running off mains). One of the American Power units powers 2 PC/AT's, a whole bunch of ethernet stuff (bridges/repeaters/etc) and two terminal servers. The other one runs a uVax II/GPX and some external labratory hardware. These guys have also performed flawlessly over the years. They are not true UPS's being that they route the mains through to the output as long as the mains has AC on it therfore they don't correct brownouts (we don't have brown outs in this area, at least not yet). While the inverter is producing power, it makes a rather loud buzzing noise and an internal fan runs. Its (inverter) output is a mildly distorted sine wave which causes some of the driven equipment's power transformer to buzz a little, but so far, none of the eqipment has complained. We've been using them now for about 4 years. I think that if an SPS will do and you need something <1200VA, I'd recommend the American Power series. If you want a true UPS or something >1200VA, I'd recommend you get one from Best. -- Dave Shepperd. shepperd@dms.UUCP or motcsd!dms!shepperd Atari Games Corporation, 675 Sycamore Drive, Milpitas CA 95035. Nobody knows what I'm saying. I don't even know what I'm saying.
quimby@madoka.its.rpi.edu (Tom Stewart) (03/25/91)
shepperd@dms.UUCP (Dave Shepperd) writes: >I also have a Best 850Va unit at home. It runs all my computer stuff as well ... >I have a desk lamp plugged in to it along with all the computer stuff and I >can see the lamp flicker if the main AC drops out. Best goes to great lengths to >suggest that the unit has a 0 cutover time, but if this were true, I believe one >would not be able to see an incandescent lamp flicker. (It'll flicker the lamp >even if the lamp is the only thing plugged in). This fits in with a failure mode of ferro-res units that I've heard about. If the unit switched in half a cycle or less (~8ms), you'd never see that lamp flicker. This puts ferro-res at the slow end of the standby UPS's switch time. It seems that a typical type of power line fault is a shorted line, not just a voltage drop. This short seems to defeat or even reverse the advantage of the ferro-res transformer, possibly by causing it to "discharge" through the shorted line, possibly just by causing a large current spike that slows down the switching mechanism. In any event, the switch time of a ferro-res UPS is often much greater in a real world fault, or a simulated fault, than in a "pull the plug" test. I would suspect that some computers don't like half cycle dropouts, although some machines don't seem to mind a cycle or two missing. >I think that if an SPS will do and you need something <1200VA, I'd recommend >the American Power series. If you want a true UPS or something >1200VA, I'd >recommend you get one from Best. >-- >Dave Shepperd. shepperd@dms.UUCP or motcsd!dms!shepperd >Atari Games Corporation, 675 Sycamore Drive, Milpitas CA 95035. >Nobody knows what I'm saying. I don't even know what I'm saying. re: VA, good point. I tend to think in a tunnel-vision desktop machine mode most of the time, and as such many of my comments only apply to such systems. Quimby (mailer disfunctional, replies to: quimby@mts.rpi.edu, quimby@rpitsmts.bitnet)