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Raidmax RX-520XP PSU
Author: jonnyguru
Date Posted:17/03/2005 10:07.18
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Bottom Line:
There's more to picking a PSU than the wattage, as explained in the first of a series of forthcoming PSU reviews.
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Wattage
So why be concerned
with what a power supply can do?
The first thing I need
to tell you is: Quit looking at wattage!! Wattage doesn't mean squat! All
wattage is is the total capability of all of a power supply's rails. The
5V, 12V, 3.3V, -12V, -5V and 5VSB capability all added up. That total number
really tells you nothing about the power supply's actual capability. And
then, is that wattage continuous power or maximum peak power? There's also
variables that come into play like, what was the temperature at which the
testing was performed? For what period of time was the testing performed
at the specified wattage? Basically, you should look at the amperage each
rail is capable of and then just consider that the power supply's BEST CASE
SCENARIO capability.
Now you need to figure
out your computer's WORST CASE SCENARIO load. There are several calculators
on-line that allow you to "add up" your computer's power. My favorite
is this one. There's also a very
simple one here.
Once you do this, you'll
really find out how unimportant maximum wattage is, and how important the
way the manufacturer distributes power across the rails is. If you have a
500W power supply with 40A available on the 5V line and you're using a Prescott
with SLI video cards, you might be in trouble because the 5V line alone is
using up 200W of that power supply's total power not leaving much else for
other rails! Given that most power supplies give you 20 to 30A on the 3.3V
(which is way high by today's standards, but even 30A on the 3.3V is only
100W) and split up about 20W for negative voltage and stand by, you're only
left with 180W for the 12V rail. That's only 15A! Mind you, we're talking
maximum combined peak power, but better safe than sorry, right?
If you don't have the time
or resources to do this, then just do this instead: Try to figure out if
your PC is going to be 5V heavy or 12V heavy, and then buy the biggest, best
quality power supply you can afford with the load balanced most appropriately
for your PC. For example: If you have a Pentium III or an Athlon XP board
without an ATX12V connector (like Biostar Socket A motherboards never have
the 2x2 connector) then something like an Antec or Raid Max with an insanely
high 5V is most suitable for you. If you have a Prescott or an AMD64, consider
something with a high 12V like an Ultra or an OCZ. If you have PCI Express
video card or cards, consider something with a really, really high 12V rail.
All that said, fact of
the matter is, if you have a power supply that has a load capability properly
balance for your PC, you could actually run your machine with a quite a bit
of stability with a mere 300W power supply. If you don't believe me, you
might want to consider picking up a Kill
A Watt. You might find that you're currently pulling about 200W from
the outlet. Given that PC power supplies typically only have an efficiency
of 75%, that's only 150W!! The problem here is that load balances vary greatly
from PC to PC, so you might have a 500W power supply with barely enough 12V
available for your CPU, drives, fans, lights and video cards because the
power supply puts out most of it's power on the 5V rail!
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