Modern PSUs and their power usage when idle?

Mangelwurzel · 27 Sep 2007 at 21:44

This is something that's been bugging me for ages, and has probably been the niggling doubt in my mind that has prevented the next PC upgrade.
My PC is switched on for most of the day, a lot of the time I'm just sending/receiving & waiting for emails, or surfing the web. Come the evening time I'm using it for gaming. I definitely haven't got the space for two PCs.

What I'd like to know is: Approximately what percentage of a modern PSU's capacity is used when the PC is running idle? I don't want the situation where my PC is switched on all day just waiting for the odd email, whilst it's using the best part of a kWh of power.

Owenb · 27 Sep 2007 at 21:56

A large PSU won't use any extra power. In fact if it is very efficient it might use less than a smaller one. However if you need a larger PSU it probably means that when the PC is "working hard" (gaming) it would probably draw more power.

Dave M · 27 Sep 2007 at 22:02

Ignore the wattage when looking - thats maximum.

If it was really drawing max all the time where would that power go, to heat? Thats far too many watts to dissipate, your CPU only hits out 40-80W, imagine what 400W or more of wasted heat would feel like :eek:

Most good PSU's now will be 85% efficient, older or cheaper low wattage models may not be as efficient, also it's usually assumed that PSU's are more efficient when working well within their limits than when on the edge but that may have no basis in fact.

JIM_BOB7813 · 27 Sep 2007 at 22:10

You can buy measuring devices that you plug into the mains which measure the amount of power you are drawing. I believe they are around £15.
From reading a few reviews and such it appears that GFX cards draw the most, especially 8800s which dont clock down for 2D.

If you make full use of power-saving functions like speedstep, 2d/3d clocks and
power-down of HDDs I don't think power consumption is much of a problem.

Mangelwurzel · 28 Sep 2007 at 09:34

That's good news. I feel a lot better about an upgrade now.

Thanks for the info.

Corasik · 28 Sep 2007 at 11:41

A typical PC while idle draws between 100 and 150 watts. Mostly depending on what cpu and graphics card are installed. The total size of the PSU makes virtually no difference to idle power consumption. (This is excluding any form of monitor.. as I assume when the system is idle, your screen goes to power save mode)

Even a PC speaker system can draw a fair amount of power when powered up but silent. Although that largely depends on the amplifier's design. Mine draws around 40W, so its best to turn them off to save power when they are not needed.

Power savings can be had by making the system drop down to sleep mode when idle for too long, or even hibinate. A ViiV platform can come out of hibernation within a couple of seconds, and be ready at the windows desktop. (Many non ViiV systems are just as good) Hibernate to Ram drops power requirements down to about 5-10 watts. Added up over the course of a year, that can be quite a considerable saving. (For a system left on idle 24/365 and assuming a 10p/unit bill, an Idle PC consumes around £100 per year of power, thats just the PC. Not including monitor/speakers/other accessories)