Hardware Reference
In-Depth Information
•Adequatepowerconnectors(24-pinmain,4/8-pin+12VCPU,6/8-pinPCIeGraphics,
SATA, and so on) for the intended system
• Adequate power output (watts) for the intended system
• 80-plus certification
• Active Power Factor Correction (required with 80 PLUS)
• SLI and/or Crossfire certification
• Single +12V rail design
There are other variables to consider, depending on your specific needs or desires. One
feature that many people like is modular cables, which minimize the clutter in a system.
Another feature to consider is noise, which is mostly related to cooling. The type and ar-
rangementofcoolingfanshasagreateffectonhowquiet(ornoisy)theunitwillbe.There
are even some fanless units that are completely silent, but these usually come at a premi-
um price and with a lower overall power output capability.
When building systems with case windows, some people also like to look for PSUs with
appearance-related features like colored cases.
Modular Cables
One feature often discussed in relation to PSUs is the use of
modular cables
. This means
cables with connectors at both ends that are detachable from the power supply. Modular
cables allow you to attach only the cables you need—in some cases greatly reducing the
congestion inside the system.
The main argument against modular cables is that additional resistance is introduced via
another set of connector contacts. This is true, but how much resistance exactly, and is it
enough that it really matters? Fortunately, this can easily be calculated.
TheconnectorsusedinmodernpowersuppliesaremostlyMolexMini-FitJr.types,which
have a contact resistance of 10 milli-ohms (0.01 ohms). Most power supply cables use 18
AWG (American Wire Gauge) copper wire, which has a resistance of about 0.0064 ohms
per foot. This means that adding an extra connector at the PSU end is equal to about 1.5
feet of wire in additional resistance.
Toputitanotherway,inamaximumloadsituation,eachterminalnormallycarriesamax-
imum of about 4 amps, at which point the additional resistance equals about 0.16 watts
of power loss. In an 8-pin power connector, this only adds up to around a watt, a loss I
consider negligible.
Finally, when you consider that a typical PSU cable already consists of 1.5 feet of wire
with a connector on the end, adding another connector to make the cable modular only
