Estimating System wattage

Rich Emberson emberson.rich at gmail.com
Thu Aug 21 23:17:49 UTC 2008


So, I recently built a new system. I figured out what
motherboard I wanted, what cpu, how much memory and
disk and then I when and used a couple of the online
system wattage calculators and got somewhere between
500 to 650 watts. I could not get (find) a PSU
with the right connectors for the motherboard so
I ended up getting Silverstone Zeus 750 watt supply
(yea, overkill). I then got a UPS from a local store.
They had a sale and a higher end UPS turned out to
be cheaper than a 600 watt unit, so I got a
APC UPS BX1500LCD (865 watt) (again, overkill but nice).
What is interesting about this UPS is that it can
show the current wattage used by your system on its
LED (along with other stuff).
Now, my strategy for constructing the new system was to pick
a motherboard that was build for high-end power and then
pick cool components; I am a developer, not a game player
and this system will house MythTV and Asterisk someday,
well as serve as a development box.
So, what I ended up with was:

    ASUS P5Q Deluxe
    Intel quad core QX9550
        95 watts max for $550
        (the QX9650 is 130 watts at $1000)
    8GB CORSAIR (DOMINATOR) TWIN2X4096-8500C5DF
    Asus EN7300GT silent graphics board
        idle: 8.7 Watts
        max: 16.1 Watts
    2 WD VelociRaptor Model: WD3000GLFS 300
        Read/Write  6.08 Watts
        Idle        4.53 Watts
        Standby     0.42 Watts
        Sleep       0.42 Watts
    2 WD Caviar GP Model: WD10EACS 1 TB
        Read/Write  7.50 Watts
        Idle        4.0 Watts
        Standby     0.97 Watts
        Sleep       0.97 Watts
    ASUS V60 cpu cooler (overkill)
    SAMSUNG  SH-S203N DVD/CD RW
    Logitech SBF-90 Black 3 Buttons 1 x Wheel
    Logitech 967738-0403 Black 104 Normal Keys
    SST-ST75ZF Zeus power supply (overkill)
    APC UPS BX1500LCD (overkill, but very nice)
    Lian Li PC-A71 Black (overkill, but very, very nice)
    BIOS 0803
    Fedora 9 64

Now, with no applications running, idle, according to the UPS
the system uses 70 watts.
The highest wattage I can get it to use running bunches of
parallel compiles is about 125 watts.

My question is: whats with the online wattage estimators?
Are they all implemented by folks selling power supplies
who want to sell users bigger ones than are needed?

In terms of power needs, I ended up way over-specing $$ the system.
Basically, I ended up with a system that
uses as much power as a 120 watt light bulb.

Richard
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