Your power source is safe, right? You have a blackout once in a blue moon, but that’s all you need to worry about, correct? Why bother with an Uninterruptible Power Supply (UPS) when you’re wall electrical supply is just fine. Don’t be fooled! Electrical problems are the leading cause of data loss, accounting for 45.3% of all losses, according to a Contingency Planning Study.

Several studies by the National Power Laboratory, who watch a few hundred sites in the U.S. and Canada and monitor power fluctuations, show the both systems have problems. NPL considers any fluctuation outside of the range of 104 Volts to 127 Volts as an “event”. Similarly, a power outage of longer than one quarter of a second is an event, as is a transient impulse between 100 and 6000 volts peak. These limits were established by the Computer Business Equipment Manufacturer’s Association (CBEMA) as the outer tolerances of computer equipment. Any power fluctuation within the limits should not cause a computer or peripheral a problem, but an event can exceed computer ratings. The US has over 350 events a year (Canada has around 170 a year). That’s 350 events that can cause catastrophic problems to computer equipment: that’s one every day.

An Information Week survey showed that home and office users have at least fifty percent of their critical information on a computer with no backup method of retrieval. According to the survey, only thirty percent of businesses and less than ten percent of home users have UPSs to protect their machines and data. Considering the price of a UPS, there’s no reason not to protect your equipment!

UPS types

The most common type of UPS is called a “standby” UPS, and is usually a low power unit used at home. A standby UPS uses a transfer switch that chooses between filtered AC power or the battery. It switches quickly to the battery when the AC power fails. The unit is called a standby UPS because the battery works only when the power has failed. Standby UPSs are inexpensive, primarily because they are easy to manufacture. However, they seldom have enough power to maintain a PC and monitor for more than a few minutes when the power fails.

Line Interactive UPSs use a battery that is always active. The battery feeds the AC outlets of the UPS. Because the system is always running from battery, the battery can supplement the incoming power to boost voltage in case of a brown-out, or regulate it whenever it peaks. Line Interactive UPSs are reliable and are available up to about 5kVA ratings, enough for several servers and their equipment.

Larger UPS units employ quite different designs than the smaller UPSs. Their designs are intended to provide fast switch-over from incoming electrical supply to battery backup, and regulate the outgoing voltage to be within a very narrow range. There are a number of ways this is achieved, each with its advantages and disadvantages, but we’ll leave a discussion of the larger units to another article.

You can often find white papers discussing UPS design on manufacturer’s Web sites. Be careful not to take everything in these papers as gospel, as most manufacturers are trying to push their technology over the competitor’s, and hence tend to emphasize only certain aspects of their designs.

Sizing your UPS

In order to buy a UPS for your system you need to know how much power you need. Underpowered UPSs can be more dangerous to your machines than no UPS at all. UPSs are rated by their power factor which is not the same as rated power. The difference between apparent power (V * A) and actual power from a UPS leads to the power factor. Apparent power is given as a VA rating, which must be multiplied by the power factor to get the actual power. The power factor can be quite different from a manufacturer’s VA rating. A recent PC magazine test found apparent power 50% higher than actual power on some units, so purchasing a 600VA unit could result in only 300VA of actual, usable protection.

Don’t confuse Watts and VA, or forget to take the power factor into account. A simple example shows why. Suppose your Linux server is rated at 400W and 400VA. You would think a 600VA UPS could handle the 400VA rating. However, with a typical power factor of .6 that UPS is only good for 360VA, and cannot power the server. Either the server, the UPS, or both will fail.

Determine the size of UPS you need is a matter of adding up the draw of the equipment that will be powered by the UPS. Use the VA rating or each device, not the number of Watts it draws. The VA rating of the UPS must be higher than the VA you calculated. Don’t work on the assumption that everything won’t be powered up at the same time. Instead, work on a worst case basis and assume everything is running full blast. The only device you shouldn’t protect with UPSs are laser printers, as these have a huge current draw when they power up that they can cause damage to even highly rated UPSs.

UPSs from different manufacturers tend to come in competing ranges. You’ll find 300VA UPSs, 600VA, 1kVA, and so on. When you’ve found the number of VAs you need for your system, move up one level in power at least to provide a safety cushion and allow for your future expansion.

The higher the rating of a UPS, the more features you tend to get, too. The number of output jacks on the rear of a UPS tends to increase as capacity increases: a 200VA unit may have four sockets while a 600VA UPS offers six, for example. You can use power bars in these sockets but this practice can lead to unintentional overloading of the UPS.

In general the amount of capacity of a UPS dictates the length of time it can be run off battery power. A typical system is designed to provide ten to twenty minutes of battery power when a power failure occurs. After that, the system must be powered off. Extra-long battery support is available either by purchasing higher capacity rating than you need, or by adding external batteries. Many high-end UPSs are expandable with external batteries or ganging UPSs together, but this is seldom possible with lower power (1kVA or less) units.

UPS software is an important point for many units today and practically every manufacturer has their own monitoring software. The software provides the ability to shut the computer down properly when power problems become serious. This is especially important with operating systems like Linux which can experience data loss if the system is not shut down properly. In most cases, the UPS software sends a signal to a driver on the computer when power failures occur. Eventually, the software starts a complete shutdown of the computer which then stay offs until started by the administrator. (A few software packages allow unattended restarts although this is rare.) Several years ago this type of monitoring software was restricted to Unix and Windows operating systems, but now most UPS manufacturers offer drivers for many operating systems, including Linux.

Sizing up the server UPSs

For this review we obtained UPSs in the 1kVA range (varying from 1kVA to 1.5kVA) from five manufacturers. The 1kVA UPS is a good size for a server because it gives lots of headroom for the server itself, and allows external peripherals (tape drives, external hard drives, modems, and so on) to be protected as well. With 1kVA units, you can cover all your equipment on a typical server and provide battery backup supply for about twenty to thirty minutes.

To test the UPSs we used them in routine daily use for a couple of weeks. We can vary incoming voltage and current on these machines through a complex device originally designed for testing telephone switches. Throughout the testing cycle we would vary the voltage and current a little, recording the output from the UPS’s rear sockets with a data recorder. We would also fail each UPS several times during the testing period and monitor the amount of time it provided battery backup power, and how well the UPS software reported problems and shut the systems down. Finally, we fed a series of spikes of varying intensity and duration to each UPS to monitor their filtering abilities while recording the output during each test.

The good news is that all the UPSs tested performed superbly in the lab. Each could handle all the routine variations in the incoming voltage, providing output of near-perfect 120V, 60Hz signals. Each also handled spikes easily, although in some cases a circuit breaker would trip and require manual resetting. The monitoring software for each of the UPSs tends to ship with the UPS itself and mostly consists of Windows NT drivers with the occasional Unix and NetWare driver thrown in. Some vendors do provide Linux drivers on their distribution CD-ROMs, while some we had to download from the vendor’s Web sites.

Two companies, APC and Tripp-Lite dominate the UPS market both in terms of units sold and profile among vendors. We’ll start with their units for this simple reason.


APC outsells all other UPSs by at least a two to one margin, primarily because of their broad product range and also their placement in many mass-market chains. APC’s UPSs, called SmartUPS in this power range, are attractive units. The SmartUPS has the traditional UPS long, low, thin shape although the edges are rounded and there’s a good front panel. The front panel shows battery capacity and current draw at all times, while , six status lights indicate the current condition of the UPS. Six sockets are on the back panel and they are too close for wall-wart power supplies. The back panel has a “smartslot” which allows add-in peripherals such as SNMP units and multiple serial port expanders. The SmartUPS can connect to external battery units through a rear connector.

The APC software is PowerChute and a Linux version is available for many implementations (with special versions for RedHat RPM and generic versions for other releases). The software installs easily and a serial cable connects to the UPS for monitoring purposes. The PowerChute software allows you to see all the UPS conditions on a GUI interface, as well as view a log of conditions and shutdowns. You can schedule unattended shutdowns and reboots if you want.

The 1.4kVA SmartUPS we tested lasted thirty-five minutes with a half load, and well over an hour when we switched off unneeded peripherals. The software worked well under Linux and the UPS is as solid as they come.

TrippLite SmartPro 1000

The TrippLite SmartPro 1000 is a thin, black design that can be rack mounted or stand vertically like a small tower in an included base. In the latter configuration it fits neatly against a desk or wall. The back panel has seven sockets tightly spaced leaving little room for wall-wart power supplies. The front panel has vertical scales to show load and battery capacity and a series of status lights for UPS condition. There is an expansion socket on the back for additional battery units.

The PowerAlert software included with the SmartPro has drivers and software for most operating systems, including generic Linux and RedHat. We downloaded a more recent release from the Web site for this review. One feature of the PowerAlert package is that is can manage and monitor practically every UPS currently on the market, including competitors’ units. Essentially, if the UPS is connected by serial cable or is networked, PowerAlert can mange it.

SmartPro is a clever and attractive piece of software, probably our favorite UPS monitoring package. The RedHat 6.2 system works well and provides easy at-a-glance summaries of the state of the UPS. When failed at half load, the SmartPro lasted twenty-three minutes (it’s only a 1kVA unit while many others in this test have more capacity). The TrippLite UPS itself is solidly built and came through our tests perfectly.

Best Fortress

Best Power’s Fortress UPS is designed like most other UPSs (in other words, beige, with a long body and square front end) and can sit under a desk out of the way. The front panel has two pushbuttons and a vertical stack of lights. The back of the Fortress has four outlets in a staggered arrangement, with one outlet able to handle wall-wart power supplies.

Best Power’s CheckUPS software is available for many operating systems including generic Linux. CheckUPS has excellent graphics and is pleasing to work with. We found that automating shutdowns was easier than with most of the other software packages we tested. If there’s a down side to the package, it’s that only a generic Linux version is available. No updates to the software were found on the Best Power web site.

The Best Fortress lasted the longest when we failed it at half load, managing forty minutes of runtime. While Best’s profile as a UPS vendor seems to have dimmed a little in the last few years because of the push by APC, many of us still remember Best UPSs fondly. The Fortress is a solid UPS worthy of consideration with any of the others in this review.

MGE Pulsar

MGE is a well-known name in Europe but a new name here. We tested a rack-mount Pulsar UPS with an attractive front panel curved in a wave shape. The unit is quite slim for a UPS of 1kVA. The front panel has six LEDs for status conditions. The back panel has four outlets all closely spaced and a connector for additional battery subsystems. An SNMP card can be plugged in for network monitoring.

The CD-ROM that came with the Pulsar didn’t include Linux drivers, so we downloaded them from the Web site. The Linux drivers, and MGE’s UPS software in general, are all workable but not as polished or attractive as the other software packages tested. It all works, but it has no flash to the package. Perhaps as the company adapts to the US market this will change.

The Pulsar UPS lasted thirty-six minutes in our half load failure test, which is especially respectable considering the small size of the UPS. The MGE unit sits very nicely in a rack and worked well, testing near the top of the pack in all our routines. With a little bit of market penetration, MGE will become a name to be reckoned with.

Powerware Prestige

Powerware used to be called Exide, a name long associated with batteries. The Powerware 9 Prestige UPS is a rectangular box much like the other UPSs we’ve tested but it looks quite attractive because of a well-designed case. Several cases can be stacked on top of each other to provide a UPS tower, each a separate UPS or battery extension for one unit. The unit we tested was rated at 1.4kVA.

The front panel has the usual stack of LEDs to show battery condition and status of the unit. The back of the unit has only four outlets all closely spaced. The back has a connector for attaching auxiliary battery packs nd a 25-pin RS232 cable. We would have preferred more sockets on the back panel, but power bars allow expansion.

The FailSafe III software CD-ROM includes drivers for many operating systems, including a ton of Linux implementations. The software is both character and graphical, allowing you to choose what suits your needs. FailSafe III is attractive and easy to work with and quickly became a favorite of the testing team. When failed with a half load we obtained twenty-one minutes from the battery, the lowest life of any of the UPSs we tested.

Choosing a UPS

As we said earlier, all these UPSs are excellent products. You can choose any of them and be sure your server or workstation is protected. The choice really comes down to software and price. You should check each vendor’s Web site for the Linux drivers you need before buying, as some do not include support for all variants of Linux. All offer generic Linux drivers, with character-based interfaces to the UPS. Most offer RedHat GUI clients as well. After that, price out each unit you are interested in, based on similar ratings, and go with the least expensive!

132 Fairgrounds Rd
West Kingston
R.I. 02892
401-789-3710 [fax]
Rating: 9/10

Summary: Expandable UPS with excellent Linux software support

PO Box 280
WI 54646
608-565-2221 fax
Rating: 8/10

Summary: Excellent UPS but Linux support is generic

MGE Pulsar
1660 Scenic Avenue
Costa Mesa
CA 92626
714-577-9788 [fax]
Rating 7/10

Summary: Attractive rackmount UPS but software a little weak

8609 Six Forks Road
NC 27615
919-870-3411 fax
Rating: 8/10

Summary: Excellent Linux support but the lowest battery backup life of tested units

SmartPro Net 1400
1111W 35th Street
IL 60609
773-869-1329 [fax]
Rating: 9/10

Summary: Solid UPS with useful Linux software drivers