Apparent Power is derived from multiplying Voltage by Ampere's, which equals Volt-Amp's. So for example if a 19" Samsung SyncMaster 900IFT monitor draws 120V, 1.2A, the apparent power load is 120 (x) 1.2 = 144VA. While a good rule of thumb for monitors, calculating apparent power by looking at the specs on the side of the PCs power supply isn't very helpful for a whole bunch of reasons which are beyond the scope of this review.

A 500W Vantec Ion power supply may be rated for a maximum load of 10A at 120V, but in real life it probably won't come anywhere near that 1200VA requirement. To accurately determine apparent power, P3 International sell a handy meter called the Kill-A-Watt which you can plug into the wall, and measure loads of up to 1875VA.

If this all seems a little confusing, don't fret. As an example, in this review we test the Powerware 5125 UPS with a 19" CRT monitor and pretty standard 2.0GHz Pentium4 computer whose combined power draw is about 300VA. In other words, the 1000VA Powerware 5125 UPS is easily adequate for a desktop PC or two and a large monitor. Although, now might be a good time to mention that you should never ever run a laser printer off a UPS, the heating elements inside simply draw too much current.

Controls and Indicators on the Powerware 5125

The control panel on the front of the Powerware 5125 has the standard set of power on/off keys, along with a few very useful icons which denote the status of several UPS power settings.

Looking at the picture just to the left, we find battery mode, service, ground fault, and AC power indicators, as well as a percent-load bar graph. The LED illuminated bar graph indicates at a glance, the percentage load on the UPS from all devices which are plugged into it. If you've overloaded the Powerware 5125 UPS by plugging in too many devices, the red overload LED will light up and an annoying alarm will sound. If that happens it's best to unplug something to decrease the load. If the power goes out and the UPS is overloaded, it will protect itself from damage by quickly shutting down.

The AC status indicator is another indicator worth taking notice of because it illustrates, roughly, what the quality of the AC power at any given moment is. For example, in the labs we routinely see the mains supply rise up past 126V at the end of the day. When that happens, the AC status LED will occasionally glow orange to indicate a slight over voltage. If there is a voltage spike, the Powerware 5125 can go into a "bucking mode," where it drops the voltage supplied to connected devices down to normal levels.

On the other hand, if the utility power drops down to low, for whatever reason, the Powerware 5125 will enter into a boost mode, where it compensates with battery power. The UPS is pretty versatile. Voltages as high as 20% over normal, or 30% under normal are automatically filtered and transformed for the devices plugged into one of the Powerware 5125's six plug sockets.

Features on the Powerware 5125

Behind the plastic cover on the front of the Powerware 5125 is where the battery is stored. The 26V DC sealed lead acid batter is hot swapable, which means if it has failed (as indicated on the control panel) it can be replaced with a new one without turning the UPS off. Because there is only one battery in the unit, it cannot be replaced while the UPS is running off battery power, obviously.

The battery is user replaceable, so all anyone needs to do is have a spare battery on hand (from the manufacturer), and consult the manual on the proper steps to follow.