How to calculate the
wattages of power supplies.....
Here some useful PSU-related things just for our members at the Rebels Haven Computer Forum. As
we are in the gigahertz- era
for some time
now ( AMD as well as Intel ), PSU is getting extremely
important. MSI, Epox, Abit etc. are making some of the fastest mainboards on the market and with
the speed, the “need for more current” is getting the major factor for
stability of such systems.
Avarage AMD CPU's (XP) systems need about 180W on the combined 3.3V + 5V power
lines. You should check the label of your PSU for the combined power output. A
lot of FAQs on the web give wrong information on how to estimate the combined
power output, forgetting abou the
efficiency
of a PSU, which is
not 100%
-
So If the label doesn't list the
combined wattage, you may try to calculate this way:
((5V x AMP's+3.3V x AMP's) / 3) x 2 = approx the wattage for most
powersupplies.....
From the above you can see, that the PSU-efficiency is between 60% and 70%.
Example:
If you have a PSU that does:
5V < >
20A
3.3V < >
15A
It will do about:
5x20=
100W
3.3x15=
49.5
W
100+49.5
=
149.5
W
149.5x2/3 =
99.8 Watts combined >
and this is way to low for most current
systems!
So 180W combined is suitable for a XP-1700+ under normal conditions.....
Using a GeForce 4 Ti4xxx card in this system is pumping up the need for
wattage: 200+W combined.
And:
Harddisks, Cdroms, DVD, CDRW and fans are really not using that much
power:
They take most from the 12V line....and that one has plenty power on most
PSU's-
So on the 12V-line if you only
have 10A this makes already ~80W ( 12 x 10 x 2 /3 )
The components which are stressing on
the 3.3V + 5V lines are:
·
CPU
·
Motherboard (depends on the board and
features)
·
Ram (estimated at 10W per 256MB no matter the
load)
·
Videocard (especially at full load, if GeForce
4 Ti for example)
You see, a high end system really would
need more than 180W combined -
often a reason, why games are crashing on such systems, while in IDLE everything
runs perfect – and even under full load it’s perfect, if the graphics card is
not stressed – that makes people often search for other reasons of their
problem, they forget, how much power current
VGA-cards are
taking.
And here some information out from an article, of how much
some
components are using:
|
Component |
|
|
|
|
|
High-wattage AGP card |
|
20 - 70W |
|
+3.3V |
|
Average PCI card |
|
5W |
|
+5V |
|
Cached SCSI controller PCI card |
|
20-25W |
|
+3.3V and +5V |
|
Floppy drive |
|
5W |
|
+5V |
|
10/100 NIC |
|
4W |
|
+3.3V |
|
50x Atapi CD-ROM |
|
10 - 25W |
|
+5V and +12V |
|
12x Atapi DVD-ROM |
|
10 - 25W |
|
+5V and +12V |
|
12x / 10x / 40x SCSI CD-R/RW |
|
20W |
|
+5V and +12V |
|
SCSI CD-ROM |
|
12W |
|
+5V and +12V |
|
RAM |
|
8W per 128MB |
|
+3.3V |
|
Ultra2 SCSI PCI card |
|
5W |
|
+3.3V and +5V |
|
7200rpm IDE hard drive |
|
5 - 15W |
|
+5V and +12V |
|
7200rpm Ultra2 SCSI hard drive |
|
24W |
|
+5V and +12V |
|
10,000rpm SCSI drive |
|
10 - 40W |
|
+5V and +12V |
|
Motherboard (without CPU or RAM) |
|
20 - 30W |
|
+3.3V and +5V |
Hope, this will be a little
help
J
By
ToXicbluE, 12/02