Hardware Reference
In-Depth Information
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.
The connectors used in modern power supplies are mostly Molex Mini-Fit Jr. 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.
To put it another way, in a maximum load situation, each terminal normally carries a maximum 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 adds about one-third
more overall resistance to what is already there, which was negligible to begin with.
If modular cables aren't much of a problem technically, why don't more PSU manufacturers include
them? Well, besides the (negligible in my opinion) extra resistance, they do add to the cost of making
a power supply, and that is reflected in a higher final price. They can also create clearance issues
with other components in the system, depending on exactly where the connectors attach to the PSU. In
addition, modular cables can easily become lost or misplaced. Think of opening a system to add
another internal drive or upgraded video card several years after it was initially built, finding that the
PSU uses modular cables, and discovering the extra cables needed are nowhere to be found. One
solution to this problem is to place any unused cables inside the case when building a system. For
example, you could place them in a small plastic bag and tape them inside, so that if or when you
need them in the future, they are easy to find. Besides these issues, perhaps the biggest drawback to
modular cables is that modular PSU cables using standard connectors are patented
(
www.google.com/patents/about?id=w0ehAAAAEBAJ
)
, and the patent is owned by Systemax (aka
TigerDirect and Ultra Products). There is another patent on modular PSUs that use nonstandard
connectors at the PSU end (
www.google.com/patents/about?id=iOGqAAAAEBAJ
). If there was no
legal “baggage” against using them, I suspect we would see more modular cable-equipped PSUs on
the market today.
Sources for Replacement Power Supplies
Literally hundreds of companies manufacture PC power supplies, and I certainly have not tested them
all. I can, however, recommend some companies whose products I have come to know and trust.
Although other high-quality manufacturers exist, for industry-standard ATX12V and EPS12V units I
currently recommend power supplies from PC Power & Cooling (
www.pcpower.com
), Corsair
(
www.corsair.com
), and SeaSonic (
www.seasonic.com
). These companies offer PSUs that meet all
the criteria I listed, and they are of excellent quality.
I also recommend ATXPowerSupplies.com as a source for hard-to-find power supplies, including
those using proprietary form factors as well as some of the less popular industry-standard designs.
