Newsgroups: comp.periphs
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!quimby
From: quimby@madoka.its.rpi.edu (Tom Stewart)
Subject: Re: UPSes
Message-ID: <+94f.da@rpi.edu>
Nntp-Posting-Host: madoka.its.rpi.edu
References: <98590@tut.cis.ohio-state.edu> <1226@dms.UUCP>
Date: 24 Mar 91 16:01:46 GMT
Lines: 42

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)