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
Best Power
P.O Box 280
Necedah
WI 54646
608-565-7200
800-356-7200
608-565-2221 fax
http://www.bestpower.com

Summary: Shortest battery life of the test units. The software is fine under Windows, but no GUI under Linux is a disappointment.

MGE
Pulsar EX20
$1545
1660 Scenic Avenie
Cost Mesa
CA 92626
714-557-1636
714-557-3256 fax
http://www.mgeups.com

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
$1,599
8609 Six Forks Road
Raleigh
NC 27615
919-872-3030
800-554-3448
919-870-3411 fax
http://www.powerware.com

Summary: Good battery times, pretty good software, with supposedly extended battery life due to charging time.

Tripp-Lite 2200RT
$1599
111 W 35th Street
Chicago
IL 60609
773-869-1234
http://www.tripplite.com

Summary: Good battery times, excellent software, OK design. An excellent choice all-round.