UPS (Uninterruptable Power Supplies)... kinda long.

[Peter S. Shenkin]

I'm trying to sort through the maze of vendors' claims in order to pick
a UPS to protect a Silicon Graphics Personal Iris (PI).  I am hoping that 
someone out there more knowledgable than I can help me out.  I will summarize 
to the above newsgroups.

The following is in fact a summary of what I've learned about these
devices so far, but the purpose of this posting is to find out more.

The PI has a power rating of roughly 1kVA;  however, I am looking at units
in the 2-5kVA range for the sake of future expansion.  The 1990 Science
"Guide to Biotechnology Products and Instruments" (Science, vol 247, 
23 March 1990, Part II) lists 19 suppliers, though probably there are only
about 5 manufacturers and the others re-sell or OEM these units.

So far I've spoken to the following companies:
	Best:				(800) 356-5794
	Clary:				(818) 287-6111
	Personal Computer Tools	:	(800) 767-6728
	Shape Electronics:		(800) 367-5811
	Anixter Electronics:		(800) 323-8166
	Elgar Electronics:		(800) 733-5427
Lambda and Liebert are also listed, and I want to talk to them.

Now, I gather there are "on-line" units, and "standby" units;  standby units
are cheaper, and also seem to come in lower power ratings.  Elgar sells
a 1.5kVA standby unit for $1875, and then jumps to a 3kVA on-line unit
for $6145.  A standby unit kicks in only when the power goes down, which
has two implications:  (1) there is a time-lag during which you don't have
power.  Elgar quotes 4ms for their 1.5kVA unit.  (2) you get no (or little)
surge protection and power conditioning from the unit.  The on-line units
are, theoretically at least, supplying power all the time, and are said to
give good power conditioning.

So my FIRST QUESTION is:  for the intended use, is this a red herring?  I have
been assuming I need an on-line unit, but is a 4ms delay likely to give
problems?  (I note that using 60 Hz power, 4 ms is a bit less than 1/4 of
a cycle.)  In fact, I probably want a unit with larger capacity anyway, but
the answer to this question would still be good to know, and it comes up
again, just below.

Of the so-called on-line units, Best has the best list prices.  Examples:

*	Best:		2.1kVA, $2995;  3.1kVA, $3695.
*	Anixter:	2kVA, $4335.
	Elgar:		3kVA, $6145.
*	Clary:		2kVA, $5590;  3kVA, $6550.
  * = offer some academic discount;  range is 5-15%.

However, it seems that there are on-line units, then again there are on-line
units.  Best's inverter doesn't always run;  they've got a big ferroresonant
transformer that ballasts the load while the inverter kicks in.  Clary 
emphasizes that their inverter always runs, and therefore that their unit
is "really" on-line at all times.  On the other hand, Best's transformer
is bound to give excellent power-conditioning, or so it would seem to me,
as should Clary's unit.  Best presents their way of doing thing as a virtue:
since the inverter doesn't always run, the UPS is cheaper to operate, and 
will also last longer.  Clary also says that only their unit meets UL-544 
for low leakage current, which qualifies the unit for use in surgery.  I'm 
confused about this;  where is current going to leak to?  Is this a 
ground-leak, or what?  It seems to me that no matter what the power supply 
does, the load is only going to draw what it needs.  Clearly, I'm confused.

So my SECOND QUESTION is whether the ballast route to making a unit "on-line"
as "good" as the inverter-always-on route?  That is, perhaps instead of
a two way classification (standby and on-line), we should have a three-way
classification:
	standby (eg 4ms delay)
	ballasted standby (eg, Best)
	"true" on-line (eg, Clary).
So the question is:  which one should I get?  :-)   Is the ballasted unit
really more like a standby, or more like a true on-line? and where is the
critical breakpoint for my application?  Has anyone heard of a ballasted
unit (eg, Best) failing in a computational application?

My THIRD QUESTION is:  can you clarify my confusion about UL-544 and low
leakage current?  (a) What does it mean, and (b) Do I need it?

Now I simply comment about battery capacity.  All the units mentioned 
will run at full load for at least 10 minutes; some units run longer.  If 
instead you run at half load, you more than double your backup time.  My own
purpose is to protect my equipment, not to continue operations uninterrupted
for significant lengths of time;  therefore 10 minutes is fine;  it's plenty
of time for an orderly shutdown of a workstation.  Which brings us to our 
next topic:

Computer interface.  Just about all of these machines (exception: Elgar on-line
units) are equipped with RS-232 interfaces which signal the state of the UPS.  
For example, some line goes from low to high when the external power has failed,
and the machine is running on battery power.  A setuid root program that 
monitors the port can then bring the machine down if this happens, or if
the condition persists more than x minutes, or when the UPS signals only
five minutes backup power remaining, or whatever.  For some of these units
the RS-232 is bundled, and for some it is an extra-cost option (Clary: $200).
Some of the vendors supply software to monitor the port (Elgar: $250-300;
Best: $125) but others (Clary) don't have UNIX drivers.  Some of the vendors
actually issue unix-flavor-specific drivers (eg, SunOS), as well as generic
UNIX drivers.  The Elgar standby units have the following feature:  the
UPS can be set to turn itself off after it brings the computer.  Some users 
tout this feature.  

QUESTION FOUR:  why do you care whether or not the UPS turns itself off, once
it's safely brought the machine down?

I have heard that there is a company (maybe Apunix?) that OEMs some UPS,
and also supplies kernel mods, at least for SunOS, that allow the UPS to
reboot the machine when the power comes on again.  I don't feel I need
this feature, and am mentioning it for completeness.  But I do have a 
final question:

QUESTION FIVE:  Do you have personal experience with any of these power
supplies, or with their competitors?  If so, I'd appreciate it if you'd share
your experiences, likes, dislikes.

Thanks,

	-P.
************************f*u*cn*rd*ths*u*cn*gt*a*gd*jb**************************
Peter S. Shenkin, Department of Chemistry, Barnard College, New York, NY  10027
(212)854-1418  shenkin at cunixc.cc.columbia.edu(Internet)  shenkin at cunixc(Bitnet)
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