Shared Knowledge
“Computer
Systems - Battery Backup (Part 1) UPS Selection"
30 January 2007
Modified 12 March 2007
I have 3 tower computers
running 24/7 on a 4 port wireless router local area network. I also have 3
laptop computers wirelessly linked to the 3 tower computers and the Internet.
I use a cable modem for
Internet access.
In the last 2 years, local
power has become very unreliable as it will drop out for a second or 2 or 3, at
least once a week and sometimes goes out for an hour or more, without any
obvious cause at all like an ice storm or high winds. Obviously, given my
current computing configuration and now my desire to convert from my local
phone company to Vontage, the voice-over-Internet protocol telephone services
provider, it was time for me to look seriously at acquiring an uninterruptible
power supply (UPS).
Why is everything so
difficult? Upon investigating available UPS devices, I found there are about 1000 different models (well, perhaps
not 1000, but a lot) in various volt\amp, physical configuration and
operational combinations and although I went to UPS manufacturer’s websites and tried looking for tutorials on the
subject, I only found bits and pieces from which I could figure out what I
wanted to do and which model or unit, I should buy.
So, what follows is what I
have learned in hopes it helps you make an informed decision:
There are 3 basic types of UPS devices: backup, line-interactive and dual-conversion. How these 3 types
respond to a main power outage is the main and most significant difference
between them.
A backup UPS waits until main power drops and then it switches
over to producing AC power via a battery and a DC to AC inverter. The backup UPS is the cheapest of the 3
types. The disadvantage of the backup UPS is that there is some inherent switching time from when the unit
detects main power going down until the battery\inverter combination kicks in
to restore power to attached computers. Now supposedly, the power supply in most modern computers can sustain a short
drop out in main power and keep right on ticking but in my case, I am dealing
with a cable modem, a router and eventually Vontage. With a backup UPS, I could not be sure that all devices, other than the computers, would
survive the switching time inherent in the device without me manually resetting
them.
A line-interactive UPS does not have the time delay in switching from main power to the
battery\converter when main power goes down as the battery\inverter is always
operational, just sitting on the side of main power. A line-interactive UPS is more expensive than a backup type UPS but not excessively so. It is also a lot cheaper than a dual
conversion UPS in that the battery charger and inverter are not
working under full load all the time, like they are in a dual-converter UPS
A dual-conversion UPS is at the top of the pile as main power never directly connects to the
devices attached to the UPS, rather main power feeds a battery charger, which
charges the battery (ac to dc) (conversion 1), which then feeds a dc to ac inverter
(conversion 2) to which all devices are then connected. Of all types of UPS, the dual conversion is the best in that there is not delay time in
switching from main power to battery backup as attached devices are always
running off battery power and this type UPS provides the very best filtering of power to attached devices, as the
battery services as a huge capacitor limiting changes in main power frequency
and voltage. The problem with a dual conversion UPS is that they are significantly
more expensive than a line-interactive UPS because all components must function all the time and thus be of
studier stuff than the simpler models. And then there is the potential problem
of all the heat a constantly functioning dual-conversion UPS can give off. As both the battery charger and the inverter are always
running and only at an efficiency of same 80 or 90 percent, the other 20 or 10%
is being given off as heat. On a medium size or volt amp (VA) unit, this could be a lot of
heat.
So which one to choose? For
me, the line-interactive seemed like the best bet: (1) it provides power
without any delay time in switching between main power and battery\inverter
power, (2) although more expensive than a backup UPS, it is considerably cheaper than a dual-conversion UPS.
Ok, so a line-interactive. What size?
Go to a computer store and
you can buy a UPS for $60 or one for $1000. The $60 is going to be a
backup type and be of very limited volt\amps or watts, meaning that it is not
going to supply power to attached devices very long before the internal or
externally connected battery(s) are going to drain and power is going to be
lost again to your computers or whatever. The $1000 unit is probably going to
be a moderate size dual-conversion unit.
In my case, I wanted to UPS 3 tower computers, my LCD screen, the cable modem, the router, Vontage
adapter unit as well as a telephone answering system. Using a power estimator
on the APC UPS manufacturer’s website, I determined that I would
need about 800VA’s as a minimum and if I wanted any significant run time
through power outages, I would need to double the VA’s of my UPS. Thus, I settled on a 1500VA, line-interactive UPS. In my case, I acquired an APC unit off the Internet for about $300.
Costs of UPS units. If it is hard to find decent information to make an
informed decision as to UPS type to buy and size of UPS needed, I was amazed as to price variation on the net and local
stores. The very same model number APC UPS ranges from $300 to almost $1000! Surprisingly, my
local computer store’s price was in about the middle of the range of prices but
being cheap, I still went with an Internet supplier.
Drawbacks to buying used
or via eBay. In any of the defined UPS types there is a battery
and this battery has a finite life. In the case of my APC UPS, it turns out that
APC recommends the battery be replaced every 3 years. So, if you do like I did
and buy a "new" unit over the Internet at the cheapest price I could find, you
could get one where the unit is "new" but the battery is one or more years old.
Now I may be wrong, but I think APC is saying replace after 3 years whether or
not the battery is in use, meaning I only have 2 years left on my "new" APC
Smart UPS battery. So, however you buy your UPS, try to check out the
manufacturing date and keep it as close to your buy date as possible to ensure
you get your 3 years of battery life.
Buying used and user name and password.
In my case, I bought my APC Smart UPS from a dealer on the Internet and as it
was "new", the default user name and passwords to log onto the UPS were still
set to defaults. However as I learned when I added a smart card to my UPS, if
you buy used, make sure the seller gives you the current user name and password
if not the defaults.
Signaling Software. Although I am
going to move into the territory covered more deeply in part 2 of computer
systems battery backup, when I went to the local computer store to do some
research on what UPS I should buy, most of the units for sale listed "signaling
software" included, which I took to mean that the UPS could command an attached
PC to shutdown gracefully and it does probably mean that but it only means 1
attached computer. Although I might be wrong having not actually had my hands on
devices and software from other manufacturers, I suspect that if you want to
command multiple PC's to shutdown at either a power or environmental event, a
UPS that has only "signaling software" is not going to do it. If you are only
going to shutdown one PC, then one of many units on the market may serve you
well.
Finally, although letting the cat out of the bag
some as more on this in another section on UPS, but once I was configured
my (3) tower computers running 600watt power
supplies each, (8) hard disk, (6) CD-Roms, (3) Ethernet boards and various other
devices like sound cards and large ADP video cards, the 1500 indicates that my
configuration is consuming about 29% of the available 1500VA with an estimated
run time on batteries of 29 minutes or more than enough time for all systems to
shut down gracefully. I am happy.