Hardware Reference
In-Depth Information
tems. Unfortunately, the ratings on cheap or poorly made power supplies cannot always
betrusted.Forexample,I'veseen650W-ratedunitsthathadlessactualpoweroutputthan
honestlyrated200Wunits.Anotherissueisthatfewcompaniesactuallymakepowersup-
plies. Most of the units you see for sale are made under contract by a few manufacturers
and sold under a variety of brands, makes, and models. Because few people have the time
or equipment to actually test or verify output, it is better to stick to brands that are known
for selling quality units.
Most power supplies are considered to be universal, or worldwide. That is, they also can
runonthe240V,50-cyclecurrentusedinEuropeandmanyotherpartsoftheworld.Many
powersuppliesthatcanswitchfrom120Vto240Vinputdosoautomatically,butafewre-
quire you to set a switch on the back of the power supply to indicate which type of power
you will access.
Note
In North America, power companies are required to supply split-phase 240V (plus or minus
5%) AC, which equals two 120V legs. Resistive voltage drops in the building wiring can
cause the 240V to drop to 220V or the 120V to drop to 110V by the time the power reaches
anoutletattheendofalongcircuitrun.Forthisreason,theinputvoltageforanAC-powered
devicemightbelistedasanythingbetween220Vand240V,or110Vand120V.Iusethe240/
120V numbers throughout this chapter because those are the intended standard figures.
Caution
If your supply does not switch input voltages automatically, make sure the voltage setting is
correct. If you plug the power supply into a 120V outlet while it's set in the 240V setting, no
damagewillresult,butthesupplywon'toperateproperlyuntilyoucorrectthesetting.Onthe
other hand, if you plug into a 240V outlet and have the switch set for 120V, you can cause
damage.
Other Power Supply Specifications
Inadditiontopoweroutput,manyotherspecificationsandfeaturesgointomakingahigh-
quality power supply. I have had many systems over the years. My experience has been
thatifabrownoutoccursinaroomwithseveralsystemsrunning,thesystemswithhigher-
qualitypowersuppliesandhigheroutputratingsarefarmorelikelytomakeitthroughthe
power disturbances unscathed, whereas others choke.
High-quality power supplies also help protect your systems. A high-quality power supply
from a vendor such as PC Power and Cooling will not be damaged if any of the following
conditions occur:
• A 100% power outage of any duration
