Watts in use?

Quick question. I was wondering if you put a big PSU (like 500W) in a machine, is the PSU going to eat up 500W regardless of what you installed in the box just because it is on...or does it only use the wattage up to what the machine needs?

For example:

4 hard drives spinning and a big power hungry video card vs.
1 hard drive and wimpy video card

Basically, I am thinking on how much it will cost per month to run the box all the time...

Thanks!

Power supply will only draw the amount of power it is actually using(load of the parts plus any loss). So when I upgraded from my Antec Smart blue 350 to the Enermax Noisetaker 420w, my power usage(assuming same loss, which believe those are both about 70% efficiency) the acutal power drawn from the power socket(or UPS in my case) is the same.

The bigger PSU just gives you more capacity for expansion, but it won't actually draw more power unless you put more devices. So in your example, the first thing is going to draw more power than the second configuration, no matter what size power supply you are using.

Note, a 550 watt PSU on a system drawing only 400 watts will run much cooler than that same system running on a 400 watt PSU.
So it is advisable to get more PSU than needed.

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And the sign says "You got to have a membership card to get inside" Huh
So I got me a pen and paper And I made up my own little sign</pre><p></font color=red>

A PC as a space heater! Inventive.

Pavelow

Dell 8250, mother board i850e chipset w/ 4xAGP slot, 2.4ghzCPU, 512 RDRAM, 120gbATA/100, GeForce4 MX 420, SBLive5.1, SamSung 48xCDRW, LiteOn 851S DVDRW