Timothy
Parker Consulting Incorporated
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Double-conversion 2kVA UPS We’ve reviewed UPS systems many times before. Most of the
UPSs we’ve examined have been stand-by designs, whereby the battery is
switched into the circuit supplying current to the outlets when the power fails.
For this wrap-up we switched testing in two different ways: we tested
double conversion 2kVA units, and we tested primarily under Linux. The double conversion design for UPSs is also called an
on-line UPS. In double-conversion
units, the battery is used only when absolutely necessary, with regulation of
the incoming voltage supplied by circuitry inside the UPS.
When the voltage cannot be regulated properly, or incoming voltage fails,
then the battery kicks in. There
are two primary advantages to the double conversion design. The first is that
battery life is considerably extended compared to the stand-by design.
This is because the battery is not used for low voltage correction or as
a tap switch. Also, the battery
tends to be kept at a more constant operating temperature with double conversion
units because they all feature fans to keep the circuitry cool.
A cool battery, or at least one that doesn’t exhibit temperature
fluctuations, remains in a better condition than one exposed to wide temperature
swings. The other advantage to
double-conversion units is the switching time to the battery.
This is usually far faster than can be achieved in stand-by designs. The disadvantage to the double conversion UPS design is two-fold: size and money. The circuitry for double conversion designs is complex and costly, making the units more expensive than similar stand-by designs. Also, double conversion units tend to be bulkier and need fan cooling, which makes economy of scale for these units impractical for devices under a coupe of thousand VA. Most double conversion UPSs start at 2kVA, although there are some models designed for much lower capacities. A typical double-conversion unit massages incoming voltage
into a different form, then converts it back to sine wave.
Typically, incoming voltage will be filtered into straight DC power, and
then reconverted back to AC. By converting to DC, most events that would corrupt
the output waveform can be trapped and discarded.
Double conversion units provide much tighter control of output voltage
than many other designs used in less-expensive UPSs.
Typically, a double conversion unit can provide a two to three percent
voltage regulation across many voltage ranges without need to resort to a
battery power. Our tests on the
units we received indicate that the double conversion UPSs can typically operate
anywhere between 80 and 140V with full regulation.
Above or below this range, the batteries can be involved to provide extra
power to the sockets, or to control downward regulation of the output voltage. There are several double-conversion UPS vendors on the
market. We gathered four of the
better known companies and invited them to submit UPSs in the 2-2.2kVA range.
APC, the largest vendor of UPSs in the world, does not offer a
double-conversion design unit and hence was not included.
APC does offer devices with the same design goals of these double
conversion UPSs, but because the comparison between units would not have been
fair we excluded APC from this review. Cold start capabilities are provided with most
double-conversion UPSs of this size. Cold start refers to the ability to provide
electrical power to the external units even when the incoming power has failed,
running the UPS from battery power. Many
UPSs do not allow cold starts: when the power fails and you shut down the unit,
it is off until the power returns. Cold starting is an important ability for many servers and
workstations, allowing boots for a short time to perform routine tasks. We tested these four UPSs in a rack-mount server setup.
We configured four dual-CPU servers in a rack with four different
operating systems (SCO OpenServer, RedHat Linux 6.2, SuSe Linux 6.4, Mandrake
Linux 7.1, and Windows NT). Each UPS was installed at the base of the UPS and connected
in turn to each of the servers for monitoring and shut-down tests.
The software for each UPS was installed on the servers (which were
reloaded between each test to ensure no compatibility problems would arise) and
connected to the UPS first by serial cable (RS232) then through a subnet
Ethernet network connected to SNMP cards in the UPSs. We performed basic tests
by failing the incoming power several times, watching the software displays of
status and automated shutdown routines. We
measured battery lifetimes at full load, half load, and 500VA (equivalent to a
heavily configured server with external peripherals). After testing in a rack, each UPS was moved to the bench
where it was tested by protection engineers using a fully variable input
voltage. The equipment allows
incoming electrical supply to be varied over a very wide range, and we monitored
the output voltage at a 15A 120V sockets on the back of the UPS.
We also subjected each UPS to spikes and noise artificially introduced to
the input voltage. Since the primary focus of this wrap-up was Linux, we
focused on the UPS software in that environment, but all four were tested under
Windows and SCO OpenServer, all with excellent results.
Since Linux is still becoming a main-stream operating system we expected
a variation in Linux drivers and software support, and indeed we found quite a
range. Best Axxium The Best Axxium 2KVA UPS is the most industrial looking
unit of the lot, designed primarily for rack mounting and with esthetics to
match. The unit is rack width, three and a half inches tall, and nineteen inches
deep. It weighs 28 pounds. The
front panel has a perforated grill for cooling air, a set of status lights, and
a couple of buttons for power and testing.
Instead of rackmounting, the unit can be vertically stacked and brackets
are provided for this purpose. The
least attractive of the UPSs tested, the Best Axxium is best left out of
executive offices! The back panel of the Axxium has six outlets, all in a
single group. A socket allows plugging in external battery units for extended
life. A number of optional cards can be plugged into the back panel, including a
Web and SNMP card. As with one other unit in this test, the ability to use HTTP
for status updates is handy for those who do not have or don’t want to
configure SNMP networks. Best provides a $25,000 damage incurance policy in case
of failure of the UPS. All Best units are shipped with CheckUPS II, which has been
mentioned many times before in these pages. Although CheckUPS II works best with
Windows machines as the host, there are Linux drivers available, as well as many
UNIX versions as well. CheckUPS II
provides a cute dashboard view of UPS status, and allows programmed shutdowns
and other features. The
graphics are not supported by Linux, only Windows, which restricts CheckUPS’
appearance under Linux. You do have
character-based access to all features, though. Our runtime tests with the Best Axxium showed a full load
failure runtime of just over four minutes, the worst result of the group.
With half load, we managed eleven minutes, while a 500VA load lasted
twenty-four minutes. MGE Pulsar EX20 The Pulsar EX20 is similar in appearance to the rest of the
MGE product line, which is to say, attractive.
Even in the rack-mount industrial case, the sweeping curves of the front
panel design add a little class to a rack.
For the stand-alone units, the design is artistic and elegant.
The EX20 is a 2kVA unit weighing in at 32 pounds, rack width (19 inches),
5 and a half inches high, and 22 inches deep. The front panel has a set
of LEDs to show load and various status conditions as well as two buttons for
power and buzzer suppression. The back panel of the Pulsar EX20 has a single 120V 20A
socket (the large round sockets often associated with 220V equipment) and three
standard 120V sockets ganged for a maximum of 15V. The sockets are treated as a
single group with no ability to turn individual or groups on or off as with
other UPSs. The complement of
standard sockets is small, forcing use of power bars for even a single server
and associated external equipment. Alternatively,
an electrician could wire a breakout panel for the 20A circuit. An expansion
plug on the back allows additional battery units to be daisy chained. Two fans
on the back keep the unit cool, as well as surprisingly quiet. A socket on the
back is designed for the plug-in optional SNMP card. Our review unit was shipped with software, so we used a
copy of MGE’s Solution Pac from a previous review, loading updates from the
company Web site. The Solution Pac provides support for Windows and UNIX/Linux
platforms with an SNMP agent included with the software. Solution Pac provides
good management and diagnostics from the UPS (it didn’t control any of the
other UPSs in this test), either over a serial connection or through the SNMP
module and Ethernet, the method we mostly used. Our runtime tests with the Pulsar EX20 showed a full load
failure runtime of just over eight minutes.
With half load, we managed eighteen minutes, while a 500VA load lasted
forty minutes, the best results of the group. Powerware 9125 The Powerware 9125 2000 is a 2KVA unit.
Designed for rack mounting or standing on end next to a desk or shelf
unit, the Powerware 9125 is attractive enough.
The beige box is 3.5 inches high, standard rack width (rack mounts are
included), and 20 inches deep. The
front panel has a rectangular display area containing status lights and load
level (which also acts as a battery level when the unit runs from batteries).
Half the front panel has a grill design, presumably to allow cooling air to be
drawn through the unit. The back panel has six plug sockets arranged in a tight
pattern. The six sockets are set up in two banks of three, and the UPS allows
you to control each bank separately. This
is a neat feature as it allows less important devices to be placed in a second
bank and powered down when necessary to preserve battery power for the first
bank. The back panel also has an RS232 port which can be replaced by an optional
SNMP module or a six RS232 port multiport module. A USB module is also available
for the system to allow communications with Windows 98 and Windows 2000 units.
Finally, there are sockets for external battery modules, allowing extended
runtime from additional batteries. The extended batteries units match the original’s size and
design. One claim to fame of Powerware 9125 UPS units is the
battery charging method. Most UPSs
provide a continuous trickle charge to the batteries in the units.
With most lead-acid batteries this results in gradually depreciating
capacities. According to Powerware a typical battery will lose half its capacity
over three years, whereas batteries in their units will last double that time.
The trick, according to the design documents, is a three-stage charging
method. We could not test the
effectiveness of their design (or this review would be very long in testing) but
it is true that UPS batteries will lose effectiveness over time.
However, our tests on some five year old batteries in 2kVA units show
only a twenty percent capacity loss. The software that accompanies the Powerware 9125 is LanSafe
III. It is designed for a number of
operating systems, including Linux and SCO.
The graphical interface is best used under Windows platforms, but all the
functionality of the Windows interface is available under other operating
systems, too. LanSafe III can
manage multiple UPSs and divide them into groups. With SNMP modules installed in
the UPSs, constant status messages can be received and displayed from all
monitored units. A couple of neat features of the software are voltage logging
(which provides a graphical viewof power fluctuations) and an internal block
diagram of a UPS showing active components as the conditions change.
Alert messages can be customized to some degree, a nice feature. Our runtime tests with the Powerware 9125 showed a full
load failure runtime of six minutes. With
half load, we managed fifteen minutes, while a 500VA load lasted thirty-two
minutes. The LanSafe II software reported all changes and charges properly. Tripp-Lite 2200RT The Tripp-Lite 2200RT is a 2.2kVA UPS that can be rack or
vertically mounted. The unit is a
little larger than most of the other UPSs we tested. It’s standard rack mount width and height are the same, but
the 2200RT is 26 inches deep, requiring a good rack location to avoid
unbalancing the setup. It’s also
heavier than most, at 66 pounds. The
front of the Tripp-Lite 2200RT has the same display as other models in the linup,
providing two LED arrays showing battery status and current load.
There’s also status lights for conditions, as well as two soft buttons
for power and testing. The back of the Tripp-Lite 2200RT has six sockets arranged
in two banks, one of two and one of four. The
loads on one bank can be shed to save battery power for the other bank.
The back panel also has an RS232 port and an optional module bay for SNMP
and HTTP management cards. A
cooling fan sits next to the battery expansion connector, which allows
daisy-chaining of external battery packs. The Web card is a neat feature we
didn’t get to play with, but allows access to the unit through HTTP instead of
SNMP. The possibilities for such a
setup would be attractive to many network and system administrators.
Tripp-Lite provides a lifetime insurance policy with their UPSs, offering
$100,000 damage reimbursement from surges passed through their unit. The software provided by Tripp-Lite is PowerAlert, which
we’ve mentioned many times before in First Looks and Roundups.
The latest release of PowerAlert provides a few new features, with
operating system support for practically every machine you can think of.
Linux support is very good. PowerAlert provides the ability to manage
almost every vendor’s UPSs (it handled all those units we tested without
problem). PowerAlert’s interface is clean, elegant and easy to use, and
reports status messages from the UPS perfectly. Our runtime tests with the Tripp-Lite 2200RT showed a full
load failure runtime of six minutes. With
half load, we managed seventeen minutes, while a 500VA load lasted thirty-eight
minutes. Summary All four tested UPS units performed perfectly on our lab
bench, handling the variations in voltage and surges with aplomb.
You won’t go wrong choosing any of these units from the UPS hardware
point of view. The ability to add
external battery packs to all four allow extension of runtimes from the battery
to practically any amount of time. The
output voltage from all four was stable and within two or three percent of the
ideal, all the time. Mechanically
all are excellent, albeit heavy, and ideally suited for rack mounting for
servers and workstations. The design of the double conversion units proved excellent
in our tests, especially compared to the stand-by designs we tested last year.
Double conversion costs more, but you get better power handling for the
price, as well as a more robust UPS. While
a double conversion UPS at $1,500 may seem silly for a single workstation, when
you consider that these UPSs easily handle four servers and their equipment, the
prices are validated compared to four stand-by UPS models. A few of the UPS units had idiosyncrasies that niggled us,
such as only three 15A ports on the MGE Pulsar EX20 and the lack of true GUI
support under Linux for most of the software packages. Still, for many users,
the idea of a UPS is to plug it in and ignore it, not bothering to watch the
fancy graphics provided by the management software. If the unit shuts down properly under trigger conditions,
that’s all that matters. All four
units managed the shutdown processes and alerts perfectly. Of the four units tested, we choose the TrippLite 2200RT as Top of the World. It didn’t get that accolade because of its battery life (the MGE beat it handily), its design (again, the MGE is more attractive), or any other single hardware factor. Instead it was the software, PowerAlert, that impressed us. All four vendors offer excellent software for managing their UPS under Windows, but support for Linux is still not complete with them all and this is, after all, a test under Linux. PowerAlert’s excellent Linux interface as well as support for all the vendor’s UPS units made it our clear choice. Software aside, though, it would be an honest toss-up for winner. Shop based on price if the Linux software support is a secondary issue for you. Best Axxium Summary: Shortest battery life of the test units. The
software is fine under Windows, but no GUI under Linux is a disappointment. MGE Summary: The longest battery life of the tested units, and
arguably the most attractive of the units. The software is OK but not
exceptional. Powerware 9125 Summary: Good battery times, pretty good software, with
supposedly extended battery life due to charging time. Tripp-Lite 2200RT Summary: Good battery times, excellent software, OK design. An excellent choice all-round. |
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