Something About UPS

A UPS generally protects a computer against four different power problems like:

Voltage surges and spikes - Times when the voltage on the line is greater than it should be.

Voltage sags - Times when the voltage on the line is less than it should be.

Total power failure - Times when a line goes down or a fuse blows somewhere on the grid or in the building.

Frequency differences - Times when the power is oscillating at something other than 60 Hertz

There are two common systems in use today: standby UPS and continuous UPS. A standby UPS runs the computer off of the normal utility power until it detects a problem. At that point, it very quickly (in five milliseconds or less) turns on a power inverter and runs the computer off of the UPS's battery. A power inverter simply turns the DC power delivered by the battery into 120/240-volt, 60-Hertz AC power.

In a continuous UPS, the computer is always running off of battery power and the battery is continuously being recharged. You could fairly easily build a continuous UPS yourself with a largish battery charger, a battery and a power inverter. The battery charger continuously produces DC power, which the inverter continuously turns back into 120/240-volt AC power. If the power fails, the battery provides power to the inverter. There is no switch-over time in a continuous UPS. This setup provides a very stable source of power.

Standby UPS systems are far more common for home or small-business use because they tend to cost about half as much as a continuous system. Continuous systems provide extremely clean, stable power, so they tend to be used in server rooms and mission critical applications.

What Not to Connect to a UPS

Never connect a laser printer to a small UPS. When the fuser element heats up, a printer draws a large amount of current, more than a small or even medium UPS can provide. If this happens, you will trip the circuit breaker in the UPS. If you would like your new laser printer to be protected, only the larger UPS models will be able to provide the power required.

A UPS beeps to warn the user of a power problem or dead battery. Occasional random beeping typically indicates a temporary over- or under-voltage condition. If this happens often have your power checked out.

Update: UPS batteries typically last three to five years, depending in part on how often the battery is used.