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When outages, spikes or surges hit, a desktop UPS gives you the time and power to protect your system

An uninterruptible power supply is often associated with preventing system damage and data loss during blackouts. It stands between a power source such as a wall outlet and a device such as a computer. It provides power for a limited time in case of an outage.

But it has other jobs, too. Not all power problems potentially affecting your computer result from power outages. They might seem less dramatic than blackouts, but they can wreak havoc with your computer and your data.

A brownout, for example, could be caused by extreme power demands on an outlying electric grid that feeds into your area and surreptitiously affects your computer's performance.

A surge, an extremely short burst of power, occurs when a nearby device such as an air conditioner shuts down. Surges often last only a fraction of a second but can erase all unsaved data in open applications.

A spike is like a surge, but many times more powerful. Spikes are usually caused by lightning strikes, though a jackhammer hitting an underground electrical line can have the same effects. They can burn out the circuit boards of anything connected to the power source, including your computer.

Last but not least, there's electronic noise caused by electromagnetic or radio frequency interference by anything from old or bad wiring to nearby radio transmitters. Ever have an Internet download stop dead in its tracks? The culprit very often is electronic noise on your incoming power source.

Many computer users try to avoid these problems by buying $20 or $30 surge protectors. They're better than nothing because they deal somewhat successfully with surges and spikes. But because they lack internal batteries, they can't handle full-fledged power outages or brownouts. A UPS is far more reliable.

There are several types of UPSes from which to choose; the best one for you depends on your equipment and requirements.

Offline. Also called standby UPSes, offline devices use a battery with an inverter'that is, a power conversion unit'and a switch that senses irregularities in the power source. Your system runs directly off the main power source until the switch senses something wrong. In a brownout or blackout, the unit switches to battery backup.

An offline or standby UPS is appropriate for home and small office systems.

Line-interactive. These devices enhance power protection with automatic voltage regulation.

AVR lets the UPS manage a wide range of power disturbances, such as regulating incoming voltage to 110 or 120 volts. If the power supply goes beneath a safe voltage level, as in a brownout, or if it exceeds a safe level, as in a surge or spike, AVR maintains a safe voltage range without using battery power.

In a power outage, AVR will automatically switch to battery backup, giving you time for an orderly shutdown routine.

Line-interactive UPSes are the appropriate choice for mission-critical PCs and workstations.

Online. These systems provide the best protection against the various power problems because they constantly monitor and clean up incoming power. Also called true UPSes, online devices provide continuous AC power from their inverters. And because the inverter is constantly running, there is no switch-over time when an outage occurs.

Online UPSes are among the most sophisticated and most expensive available. They are best suited for indispensable hardware, such as network servers. They are too complex and costly for most home and small offices.

UPS devices have several features that you should consider before buying.

Capacity. Most UPS vendors include a fairly wide range of capacities among their product lines. Capacity is measured in VA rating, which is the total load power a UPS can support.

The VA rating is the maximum number of volts times the amperes it can deliver. For example, if your PC or Mac requires at least 100 volts and 3 amps to run, it will require a UPS with a minimum capacity of 300VA (100 times 3). Add 20 percent to be on the safe side, and your UPS should have a minimum capacity of 360VA.

Add together the VA ratings of your monitor, printer and other peripherals you want to protect.

The chart below features fairly low-end desktop UPSes to protect basic systems. You can probably get by with an offline UPS with a rating of 350VA, 500VA or 650VA, costing between $50 and $200. If your requirements are higher, you'll pay more for an 800VA or 1,000VA line-interactive device. You'll get more, too.

Run time. The higher the VA rating, the longer the run time. A 650VA standby UPS would provide five to 10 minutes of run time in a blackout, whereas a unit with a rating of 1,000VA or higher would provide 15 minutes or more to effect an orderly shutdown.

Joule rating. A joule is the amount of energy delivered by one watt of power per second. The joule rating is used to measure the amount of surge a UPS can handle, but many industry insiders claim it is inexact and overrated as a measurement tool.

Surge protection. As with run time, the higher the surge rating, the better the protection. Prevention of surges up to about 7,000 amps is considered adequate for most PCs and workstations.

Connectivity. Depending on their prices and levels of sophistication, UPSes have connectivity options that make them flexible enough to meet almost anybody's needs. For example, Oneac Corp.'s Desk Power Series UPS has two battery backup and surge-protected outlets and two surge-only outlets; a data port to protect fax, modem and LAN transmissions; an RS-232 connection; and optional USB ports.

Other systems provide similar connectivity, including at least one DB9 or DB25 port for RS-232 connections, and an emergency-power-off port.

You can also buy units with 15-, 20- and 30-amp receptacles for either 120V or 230V power.

Connected-equipment insurance. Partly to illustrate the dependability of their products, many UPS vendors offer insurance to buyers that covers the cost of damage to equipment caused by a power surge, if the gear is connected to one of their devices.

For example, Belkin Corp. gives a $50,000 connected-equipment and data recovery warranty with its Home Office Series of UPSes.

Computer Engineering & Solutions and Tripp Lite Inc. each offer $25,000 lifetime equipment protection with their Back-UPS Pro Series and InternetOffice700 products, respectively.

Software. Monitoring and shutdown software is a critical but often overlooked component of UPS devices, particularly those with high-end features.

Most UPS manufacturers offer software for a safe shutdown even when nobody's around. IBM Corp.'s UPS 500 and UPS 675 both have power management shutdown software, and even APC Corp.'s relatively low-priced Back-UPS ES 350 and ES500 can conduct unattended shutdown.

Once main power has been restored, the software reboots your computer and you're off and running once again.

More advanced monitoring software, such as Falcon Electric Inc.'s UPSilon Monitoring & Shutdown software, uses Simple Network Management Protocol for monitoring and communicating with other network devices.

J.B. Miles of Pahoa, Hawaii, writes about communications and computers. E-mail him at jbmiles@hawaii.rr.com.

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