Hardware Reference
In-Depth Information
chase a UPS that provides enough power to run your system and peripherals and enough
time to close files and provide an orderly shutdown. Remember, however, to manually
perform a system shutdown procedure during a power outage. You will probably need
your monitor plugged into the UPS and the computer. Be sure the UPS you purchase can
provide sufficient power for all the devices you must connect to it.
Because of a true UPS's almost total isolation from the line current, it is unmatched as a
line conditioner and surge suppressor. The best UPS systems add a ferroresonant trans-
former for even greater power conditioning and protection capability. This type of UPS is
the best form of power protection available. The price, however, can be high. To find out
just how much power your computer system requires, look at the UL sticker on the back
oftheunit.Thisstickerliststhemaximumpowerdrawinwatts,orsometimesinjustvolts
andamperes.Ifonlyvoltageandamperagearelisted,multiplythetwofigurestocalculate
the wattage.
As an example, if the documentation for a system indicates that the computer can require
as much as 120V at a maximum current draw of 5 amps, the maximum power the system
can draw is about 550 watts. The system should never draw any more power than that; if
it does, a 5-amp fuse in the power supply will blow. This type of system usually draws
an average of 200 to 300 watts. However, to be safe when you make calculations for UPS
capacity, be conservative; use the 550-watt figure. Adding an LCD monitor that draws 50
wattsbringsthetotalto600wattsormore.Therefore,toruntwofullyloadedsystems(in-
cluding monitors), you'd need a 1,200-watt UPS. A UPS of that capacity or greater nor-
mallycostsseveralhundreddollars.Unfortunately,thatiswhatthebestlevelofprotection
costs. Most companies can justify this type of expense only for critical-use PCs, such as
network servers.
Note
The highest-capacity UPS sold for use with a conventional 15-amp outlet is about 1,400
watts.Ifit'sanyhigher,yourisktrippinga15-ampcircuit whenthebatteryischargingheav-
ily and the inverter is drawing maximum current.
In addition to the total available output power (wattage), several other factors can distin-
guishoneUPSfromanother.Theadditionofaferroresonanttransformerimprovesaunit's
power conditioning and buffering capabilities. Good units also have an inverter that pro-
duces a true sine wave output; the cheaper ones might generate a square wave. A square
wave is an approximation of a sine wave with abrupt up-and-down voltage transitions.
The abrupt transitions of a square wave are not compatible with some computer equip-
ment power supplies. Be sure that the UPS you purchase produces power that is compat-
ible with your computer equipment. Every unit has a specification for how long it can
