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 down.  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,

Peter Shenkin, Department of Chemistry, Barnard College, New York, NY  10027
(212)854-1418  shenkin at cunixc.cc.columbia.edu(Internet) shenkin at cunixc(Bitnet