Custom design and manufacture of state-of-the-art battery chargers,
UPS, and power supplies
||More Engineering Resources
||Batteries and Packs
A1: What is this document all about?
is this document?
02: How is this document made available?
03: Who maintains this?
04: Where did this information come from?
05: How can I contribute?
06: How may this
document be distributed?
07: Got anything else you'd like to add?
What is a UPS and how does is work?
01: What is a UPS?
02: How do you pronounce " UPS"
03: Vendor X says that (description) is a UPS, is it?
04: Describe the types of
05: How can a UPS help me?
06: What sort of stuff does a UPS do?
long can equipment on a UPS keep running?
08: What is a " good" UPS?
contracts on UPS's.
10: Self maintenance tips.
11: Is a UPS a glorified power
12: How important is the UPS output waveform?
03: UPS monitoring/shutdown
01: Can a UPS shut the computer down when power is low?
02: Can I write my
own shutdown routines?
03: What freely distributable solutions are there?
04: No UPS
software works on my machines, what to do?
05: What other software is out there.
How big a UPS do I need?
01: How are UPS sizes determined?
02: What VA rating do I
03: How do I determine this?
04: What else should I consider?
05: Can I use
an UPS with a laser printer?
06: What UPS sizes do you use on what equipment?
Specific manufacturer's info.
01: What vendors are there?
02: UPS Hardware.
04: Other companies.
TOPIC: What is this document all about?
Q: What is this document?
A: This is a FAQ document on Uninterruptable Power
Sources. It is
intended to provide a starting point for those people that want
find out what they are, what they do, and what's available.
Note that most of this
document is very US-centric. The power
numbers, companies and services all emphasize US
needs. Sorry, but that's what I have to work with. All the
discussed here should be applicable just about
Q: How is
this document made available?
A: Currently, its " home" is comp.misc. It is also cross
comp.unix.admin, comp.sys.sun.hardware, comp.sys.hp.hardware,
news.answers. This posting is automated and will occur on or
the 10th of each month. If there are other groups to
which this document should be posted,
please let me know, but
if I post it to every group where UPS questions get asked, that
would be a lot of groups. I'm open to suggestions.
This document is also available
via anonymous FTP. The master
sits on navigator.jpl.nasa.gov (22.214.171.124) in
as the file UPS.faq. It is also available via anonymous FTP
Q: Who maintains this?
A: Right now, this document is maintained by Nick
preferred email address is email@example.com, and I
it very much if questions regarding this document
could have the word " UPS or UPS FAQ" or
some such in the Subject
line. Note: I am maintaining this on my own time, so please
don't be upset if it takes a while for me to respond to your
queries. Also none of the
information in here represents the
views or has the blessing of any organization
maintainer of the FAQ is to be held solely responsible for its
Q: Where did this information come from?
A: Thankfully, many
people have rallied to my cry to fill in
the many gaps in my original draft. This is now a
although I claim full responsibility for misstatements and
Q: How can I contribute?
A: You should mail new information,
corrections, suggestions, etc.
to the current maintainer of this FAQ. If you provide a
make sure you reference where the information is located in the
guarantee that suggestions of the form " Change the
word 'always' to 'almost always' in the
part about surge suppression."
will be ignored.
Q: Are there any
restrictions on distribution of this document?
A: This document is copyright by the author.
You are encouraged
to distribute this document for any non-commercial purpose
as the contents remain unchanged and a pointer to
an up-to-date version is included.
Q: Got anything else you'd like to add?
A: Yes, now that you mention
it. The people who contribute to this
document can speak only about equipment they have
This may reflect a bias toward or against certain brands, features,
functions, etc.. Please keep in mind that the suggestions, brand
names and functions here
are by no means exhaustive, or even
necessarily applicable to your situation. Also, if you
information that is not in this document, please submit it to
listed above. If you submit information, please
say whether you'd like it to be attributed
to you or not. I am
more than glad to give credit to the fine people who helped with
this document, but I want to respect the anonymity of those
people who would prefer
One more caveat: While the principles of UPS design and
likely to be fairly universal, the power
figures in this FAQ are *very* US-centric. Sorry,
they're the only numbers I have.
A: This was
contributed almost entirely by some kind soul. I just
cleaned it up a bit.
Blackout: Complete loss of power. Some literature considers a voltage
drop below about 80V
to be a blackout as well since most
equipment will not operate below these levels.
Sag or Brownout: Decrease in voltage levels which can last for
periods ranging from
fractions of a second to hours. Can be
caused by heavy equipment coming on line such as
elevators, compressors etc. Also occurs when utility companies
do this to cope with peak load times.
Spike: An instantaneous and tremendous increase
in voltage often
caused by a direct lightning strike on a power line or when
returns after a blackout.
Surge: An substantial increase in voltage lasting a small
of a second, often caused when high powered appliances such as
conditioners are switched off.
EMI/RFI Noise: Electromagnetic Interference and Radio
Interference. Caused by, inter alia, lightning, generators,
transmitters, industrial equipment.
MOV: Metal Oxide Varistors used to control spikes.
common in Power Strips. If you see more than two, you likely
have a fairly
decent Power Strip. They look like largish disk
Inverter: Circuitry that
converts DC battery power
to AC power required by most computer equipment.
Protector: Circuitry consisting of MOVs, capacitors, rod-core
inductors etc. for
suppressing surges and spikes usually embedded
in a power strip.
A transformer that attempts to smooth out
fluctuations in input voltage to provide near
voltage or voltage waveform.
TOPIC: What is a UPS and
how does is work?
Q: What is a UPS?
A: An Uninterruptable Power Source
is a device that sits between
a power supply (e.g. a wall outlet) and a device (e.g. a
to prevent undesired features of the power source (outages, sags,
harmonics, etc.) from the supply from adversely
affecting the performance of the device.
Q: How do you pronounce " UPS" ?
A: I pronounce it " ups" , but most of
the literature seems to favor
" you pee ess" , since they use " a UPS" instead of " an UPS"
document will try to follow the literature.
Q: Vendor X says that
(fill in description) is a UPS, but it's
different that what you describe above. Who's
A: There really is no standard definition of what a UPS is.
from a 9 volt battery backup in a clock radio
to a building/compound wide backup generator
has been called
a UPS by someone. The majority of this document refers to
larger than a beer can and smaller than a desk that
help devices remain temporarily
operational when changes to the
power they receive would otherwise interrupt their
Maintaining power to a minicomputer (like a VAX 11) is beyond
of this document. This FAQ deals with UPS equipment
that can be installed by a computer
owner/administrator. If you
have requirements that large, you need to talk to a
Q: Can you give me some more information on
A: (Kindly provided by Don Deal, my additions
are in [square brackets] )
The UPS industry is made up of many manufacturers, and there is
a lack of standard terms
within the industry. I think this
sometimes borders on deliberate misdirection. (It's a
There are basically three different types of devices, all of
which are occasionally passed off as UPSs.
1. Standby power supply (SPS). In this
type of supply, power is
usually derived directly from the power line, until power fails.
After power failure, a battery powered inverter turns on to
continue supplying power.
Batteries are charged, as necessary,
when line power is available. This type of supply is
called an " off-line" UPS.
The quality and effectiveness of this class
of devices varies
considerably however, they are generally quite a bit cheaper than
true" UPSs. The time required for the inverter to come online,
typically called the
switchover time, varies by unit. While some
computers may be able to tolerate long
switchover times, your
mileage may vary. [ Some articles in the trade press have
that their testing shows that modern PCs can withstand transfer
times of 100ms
or more. Most UPS units claim a transfer time to
battery of about 4ms. Note that even if a
computer can stay up
for 100ms, it doesn't mean that 100ms switchover is okay. Damage
can still be done to a computer or data on it even if it stays
features to look for in this class of supplies is line
filtering and/or other line
conditioners. Since appliances
connected to the supply are basically connected directly
the power line, SPSs provide relatively poor protection from
frequency variations, line spikes, and brownouts.
[Some SPS's claim to have
surge/spike suppression circuitry as
well as transformers to " boost" voltage without
the battery if a modest voltage drop occurs. An example is the
Smart UPS" which claims it will switch to this boosting mode
if voltage drops below 103V
(from the normal expected 120V) and
switches to battery only at 90V and below. This, it is
allows operation of the equipment indefinitely under brownout
long as voltage does not drop below 90V. I have
not tested this, and would be interested in
There are other vendors products that make similar claims.]
Hybrid UPS systems. I only know one vendor who sells them -
Best Power, Inc. The theory
behind these devices is fairly simple.
When normal operating line power is present, the
power using a ferroresonant transformer. This transformer maintains
a constant output voltage even with a varying input voltage and
provides good protection
against line noise. The transformer also
maintains output on its secondary briefly when a
Best claims that their inverter then goes online so quickly that
it is operating without any interruption in power. Other UPS
vendors maintain that
the transition is less than seamless, but
then again it's not in their best interest to
Best has a sizable part of the UPS market.
According to some sources, ferroresonant transformers in an
UPS system can interact with
ferroresonant transformers in your
equipment and produce unexpected results. The Moral:
before you buy. -npc ]
3. What I call " true" UPS systems, those
continuously operate from an inverter. Obviously, there is no
switchover time, and these supplies generally provide the best
isolation from power line
problems. The disadvantages to these
devices are increased cost, increased power
consumption, and increased
heat generation. Despite the fact that the inverter in a "
is always on, the reliability of such units does not seem to be
In fact, we have seen more failures in cheaper SPS units.
[ Note, though, that given the
same quality inverter, you'd expect the
one that runs least to last longest. ]
Q: How can it help me?
A: A UPS has internal batteries to guarantee that
is provided to the equipment even if the power supply stops
power. Of course the UPS can provide power for a while,
typically a few minutes, but that
is often enough to ride out
power company glitches or short outages.
1) Computer jobs don't stop because the power fails.
2) Users not inconvenienced by
computer shutting down.
3) Equipment does not incur the stress of another (hard)
4) Data isn't lost because a machine shut down without
doing a " sync" or
equivalent to flush cached or
real time data.
Q: What sort of stuff
does a UPS do?
A: A UPS traditionally can perform the following functions:
relatively small power surges.
2) Smooth out noisy power sources.
3) Continue to
provide power to equipment during line sags.
4) Provide power for some time after a
blackout has occurred.
In addition, some UPS or UPS/software combinations provide the
1) Automatic shutdown of equipment during long power
2) Monitoring and logging of the status of the power supply.
3) Display the
Voltage/Current draw of the equipment.
4) Restart equipment after a long power outage.
5) Display the voltage currently on the line.
6) Provide alarms on certain error
7) Provide short circuit protection.
Q: How long can
equipment on a UPS keep running after the power
A: How big a UPS do you have and
what kind of equipment does it
protect? For most typical computer workstations, one might
have a UPS that was rated to keep the machine alive through
a 15 minute power loss.
If you need a machine to survive
hours without power should probably look at a more robust
power backup solution. Even if a UPS has a very small load,
it must still operate it's
DC (battery) to AC converter,
which costs power. A rough extrapolation from APC's
documentation, leads me to guess that a 2000 VA UPS can
operate it's own converter (with no
extra load) for just
over 8 hours. A 1250 VA UPS could run its converter for
These are *very* rough guesses based on information
provided by one vendor for one
Q: Given the same vendor claims, how can I tell a " good"
UPS from a " poor" quality UPS?
A: Testing, testing, testing. I can't emphasize
this enough. There
are many good and bad units out there that call themselves UPS's.
There are many good units that are wrong for your situation.
properties you might look for are:
1) Sinusoidal power output. In general, the closer the
of the UPS is to a sine wave, the better it is for your
Many UPS units, especially the cheaper ones, deviate a great
deal from a sinusoidal output.
Some of them generate
square waves. Waveform effects are dealt with in section 2.12.
2) Does the UPS have a manual bypass switch? If the UPS is
broken or is being serviced,
can you pass power through it to
your equipment? The last thing you want is for a broken
be the cause of extra downtime.
3) The more information about a UPS's operation
you can get from
watching the unit itself, the better. How much power (or
load) the equipment is drawing, how much battery
life is left and indications of the input
power quality are
all very useful.
4) Some newer UPS's can communicate with their
via network connection and SNMP! This is wonderful *if* your
network is on a UPS! Also, beware, I have heard of dealers
advertising " Network UPS"
monitoring where the network is
the normal serial connection (no SLIP or PPP).
Does the UPS vendor offer support/maintenance contracts. If
they don't even offer them, I
would suspect the quality of the
If you do have a UPS that does not
output a sinusoidal waveform,
some manufacturers *strongly* urge you to not put a surge
between the UPS and the computer. The surge protector might mistake
non-sine waveform as a power surge and try to send it to ground.
This could be bad for your
UPS. I don't know if this has happened
or not, but I wouldn't chance it.
Q: Should I make sure I have a support/maintenance contract for my
Some people strongly recommend this, but to be honest, I don't
know how important it is. I
haven't had any UPS's long enough
to have enough of them fail to know what the failure
likely to be. Some people, with more experience than I in these
insist that a UPS support/maintenance contract is as
important as your computer
support/maintenance contract. I can't
argue with them. In any case, it's almost certainly
pricing at any rate.
Q: What sort of maintenance can I perform
A: One good thing you might want to do is periodically test the
their failure modes. A good time to do this might be
right after after a periodic level 0
backup. Nobody is logged
in and you've got full backups of the machines. Throw the
circuit breaker with the UPS on it to simulate and outage and
see how the transition goes.
Note that some UPS vendors suggest
that testing an UPS by pulling the plug from the wall is
a good idea (Tripp Lite is one of them). These UPS units like
to have a good idea
of what ground looks like. It is likely that
unplugging just about any UPS for a short
amount of time would
not be too dangerous (don't take my word for it, though!), but
all cases, throwing a circuit breaker would be a better thing
It might be
useful to install a GFI (Ground Fault Interrupter)
socket to facilitate this testing
without having to pull the plug,
especially if you don't have your UPS protected machines
an isolated circuit (which you probably should). These are the
sockets found in
most modern kitchens and bathrooms with a red
and a black button. You push the latter to
cut power and the
former to restore power.
Those UPS units that use lead-acid
batteries (that's most of
them, I'm told) do not have a battery memory and should be run
dry as few times as possible. It's probably not a bad investment
to do this once on
one UPS out of a largish batch to learn how
much UPS time you can expect in a real power
depending on the manufacturer, UPS batters can be expected to
between about 1 and 5 years before they ought to be replaced.
As a UPS gets older, its
battery life will become shorter. Of
course there's no way to reliably test how long it is
running the battery down and you don't want to do that because
they have lead
acid batteries. All of these are very
good reasons to get a support contract for them that
periodic battery replacement. At the very least, you can figure
batteries will still be good at the end of the UPS
warranty figure, so that's a good place
to start guesswork.
Q: Isn't a UPS just a glorified power strip/surge
some batteries and a little power conditioning thrown in?
It's also got a power inverter and some other circuitry.
It may also have a timer,
thermometer or other gadgets.
Q: How important is the UPS output
A: That's a good question, and one is worthy of some debate. One
thought holds that one should always run equipment on
the best approximation of sinusoidal
input that one can, and that
deviations produce harmonics which may either be interpreted
signal if they get through a power supply, or may actually damage
Another school holds that since almost all
computers use switching-type power supplies,
which only draw
power at or near the peaks of the waveforms, the shape of the
power waveform is not important. Who's right? I don't
know. My *opinion* is that
sinusoidal output is worth the
extra money, especially for on-line UPS systems that
provide their waveform to the computer. Also, if you don't *know*
equipment has a switching-type power supply, you might
want to think twice before buying a
low quality UPS.
[ Some of this information from a great article in the
issue of LAN Magazine, check it out. -npc ]
Q: If the power is out for a long time, I
would like to have my
computer automatically shut itself down gracefully before the
batteries die. Can I do this?
A: Yes. Most UPS manufacturers support software that will do
for some UPS's on at least some platforms. Ask your UPS vendor
Q: Okay, how about restarting the system for me once power returns?
A: Fewer software
products do this, but many do. Again, ask your
vendor. I do not know of any freely
distributable products that
will do this. It doesn't mean that they can't be built, but
vendor software is cheap enough (usually) that it's probably not
Q: How does it work? I'm a starving (fill in the blank) and I really
want to pay for software unless I absolutely have to.
A: Usually, there is a serial
connection running from a UPS into
your computer. The UPS sends information along the
as it goes. If you can decode which pins contain which information,
information is formatted and figure out what it wants to
hear from the computer side,
you're all set. Make sure you have
the right serial cable and know how the pins map between
DB25 as both your computer and your UPS may take either.
Since UPS units
with network based monitoring capabilities are
appearing on the market, we can hopefully
get something that will
communicate with those units.
Here is a skeleton script
provided by Joe Moss, firstname.lastname@example.org.
Definitely check this out as a starting point,
but don't expect
it to do anything meaningful without some work.
# Shut down system in case of
extended power failure
# This should be the serial port to which the UPS is connected
# This port must be set to block on open until the DCD line
# is asserted - many UNIX
systems have this determined by
# the minor device number, if not, see if there is some
# to enable this behavior on your system
# Ok, this should
block until there is a power failure
: > $PORT
# If we reach this point,
we've lost power
wall < < EOF
The sky is falling!! The sky is falling!!
# call shutdown (or init or whatever)
Q: Hmmm... that sounds kinda
complicated. Has someone already done
A: Any solution would almost certainly be
vendor specific. However,
some brave souls have provided partial functionality for
vendors' UPS's. I don't know the original source, but I have a
for anonymous FTP at navigator.jpl.nasa.gov in
the pub/src/UPS directory as upsd.tar.Z. I
haven't tried it and
I don't honestly know if it even works.
UPS's produce different sorts of signals. Just
installing this already built package may
require a great deal of
work. The cabling can be complicated, etc.. I would be
interested in hearing where this software does/doesn't work.
Another good example,
that probably works straight away for
SunOS 4.1.X machines using APC Back-UPS devices, is
available on navigator for anonymous FTP in the pub/src/UPS
directory is pf.c.
It was written by Ronald Florence
(email@example.com). It looks like a nice framework for
to other OS platforms and UPS implementations. Give it a try.
Q: I can't find monitoring software that will work on my configuration.
What should I
A: Well, it seems you have a few choices:
1) Build your own. See item 03.02.
2) Use something freely distributable. See item 03.03.
3) Lean on your UPS vendor to port
to your platform.
4) Try a different vendor that supports your platform.
Q: What other software is out there?
A: Software packages for UPS
machines are getting more sophisticated.
Most provide some level of power and status
lately there are more GUI's, more interactive packages, SNMP
and even call-out paging. See the software section
05.03 for more info.
TOPIC: How big a UPS do I need?
Q: How are the " sizes" of UPS's
A: Typically, a UPS has a VA rating. The VA rating is the maximum
Volts * Amps it can deliver. The VA rating is not the
same as the power drain (in Watts)
of the equipment. Computers
are notoriously non-resistive. A typical PF (power factor:
Watts/VA) for workstations may be as low as 0.6, which means that
if you record a drain of
100 Watts, you need a UPS with a VA
rating of 167. Some literature suggests that 0.7 may be
good conversion factor, but this will depend heavily on the
machine. WARNING: Don't
take my word for it! Note: Some UPS's
can continue to deliver power if the VA rating is
merely can't provide above their VA rating if the power goes.
can't provide power above their VA rating at all. Some may
do something really nasty if
you try. In any case, I *strongly*
recommend not doing this under *any* circumstances.
Q: How can I tell what VA rating I need for my equipment?
A: First, when
possible, get VA rather than wattage ratings. See
There are a couple of
1) Direct measurement. You can get equipment to
measure the current draw of your
You may or may not have access to this. If you are part of
organization that has it's own facilities/electrical
type people, they're likely to be able
to do this. They
might help you out if you ask nice.
2) Compare notes. If you know
someone with the same setup
you're using, ask them what they use and how close they
to the maximum VA rating.
3) Use a chart. Most vendors can help you out for common
equipment. If you have an unusual setup, or mix
vendors a lot, you're probably out of luck
4) Use the equipment rating. Most pieces of computer
equipment have a power
rating on some back panel. This
number is usually high, as it is necessary for the
manufacturer to play it safe or they'll get sued.
Note: Method 1 is by far the best,
method 2 and 3 are secondary,
method 4 is usually overkill, but pretty safe. There are
examples in section 4.6, but the information is probably worth
what you paid for
Q: Hmmm... seems like a tough thing to determine.
A: Yeah, it can
be. It's also very important. If you get a UPS
that's too big, then you've overpaid, but
your equipment can
survive a longer outage. If you get a UPS that's too small,
you could be in deep trouble. Therefore, I recommend that
you be conservative in buying
these things, unfortunately, this
Q: What else should I
A: It would be nice to know how long your site's typical power
In some places, with nice weather and a flaky
power grid, the power is almost never out for
more than 5
minutes, but this could happen quite frequently. In this case, you
well use a UPS with a VA rating close to your equipment
rating with no extra batteries. If
your area has longer outages,
in the half hour or hour range, as is often the case in
thunderstorm country, you can either buy UPS's with multiples
of the VA rating of the
equipment, since oversizing a VA rating
for a UPS has the effect of lengthening the amount
of time your
equipment can stay up in case of a power outage, or you can buy
additional battery units for a smaller UPS. You can probably
get away with doing simple
math to determine how much longer a
larger UPS will keep your equipment running, but I
running a few tests before committing to a large purchase
order. Also, your
UPS vendor will almost certainly be glad
to help you size the equipment you need. If all
and you guess wrong, or move equipment to a location with
status, you may be really, really glad if you
bought a UPS that can have additional
battery packs added.
Q: How about I use one of these UPS thingies for a
A: Don't *ever* do this. If you ever measured the current draw
laser printer during startup (and during printing) you'd
be stunned at what it pulls. All
UPS manufacturers I know of
tell you not to do this.
Okay, I have to back down
from this. I know APC, just as an
example, now does rate some of their UPS units for use
certain laser printers. Not that I think this is a good
idea, mind you. In
general, they are difficult to size and
rarely do they require the same level of uptime as
In any case, don't do this without specific approval of
Q: So, what sorts of UPS sizes do you use on your equipment?A:
BIG DISCLAIMER. I disclaim everything about these figures.
they are very, very rough. Heck, I may be lying.
Don't trust them. Here they are
Note also, this is what the equipment apparently PULLS, not
the UPS sizes
that are on them. Generally, I've been using
UPS's that are about 2X the VA ratings shown.
At the very
least, I would using UPS sized 1.5X the VA ratings here.
Sparc 2 with 3 600 MB disks, 1 200 MB disk, 1 exabyte 8200
tape drive, 19" color
HP 750 with 4 1.3 GB disks, internal 4mm tape drive and
CD-ROM drive, external disk cabinet and 19" color monitor.
SPARC 2GX clone. 1 1.2 GB disk, 4 2.0 GB disks, 2 tape drives,
1 CD-ROM drive, " big"
Sparc 2 clone with 100W power supply, internal 424 disk, 16"
color monitor, external 1 GB disk drive.
These are U.K. numbers, based on 240 V wall
current. Most of
these VA numbers are very close to " American" VA numbers, but
caveats weren't strong enough earlier... .
SGI Indigo R4400, 48 MB RAM, 1
GB int. disk, no graphics, no
SGI Indigo R4400 configured as
above with 17" Sony monitor plus
3 19" monochrome X terminals.
Another word of
warning, don't assume that power requirements
scale with compute power and number of
if they are different architectures. Older equipment, CPU's,
disks, monitors, whatever almost universally requires more
power than new equipment. For
example, it seems that an HP
9000/425e with 1 internal 420 MB disk and 19" color monitor
pulls a lot more power than a much more modern and much faster
HP 9000/715 with an
internal 1.3 GB disk, CD-ROM drive and
more modern 19" color monitor. Again, the moral is
TOPIC: Specific manufacturer's information.
Q: What vendors are there and what do they produce?
A: Here is a very incomplete list,
based only on what I know.
Please give me information to expand it. I make no claims
to the accuracy of this information. It is mostly based
on personal recommendations and
Note: The October 1994 issue of LAN Magazine has a great
list. I have used it to update many of the entries
here. However, there is a lot of
there that I don't have space to include here. This
an excellent starting point for comparative pricing
on UPS equipment.