Estimating System wattage

[Knute Johnson]

Rich Emberson wrote:
> 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
> 

Watts are simple, you just add them up.  When I add up yours, I get 
114.5 max load for the items you listed.  I would guess then that the 
125 watts you are seeing is probably pretty close.  The power supply you 
bought is probably bigger than you need but the UPS, if you want to run 
on the battery more than a couple of minutes, is probably undersized.

If I were going to build a computer, I would probably size my power 
supply for twice the expected load plus a little to account for things I 
don't think of.  Now it is possible to put a lot of load on USB ports 
with external drives or other equipment so you would want to allow some 
more for that.

-- 

Knute Johnson
linux at www.knutejohnson.com