PC Power Consumption

[Chandler]

I recently purchased a low-cost plug-in power monitor and have been going around seeing what various appliances use.  I found out that our 32" LCD TV uses around 140W when running, and around 1W when in standby (presumably to keep the front panel powered).  An old 14" CRT TV uses 30W when running and a standalone DVD player, 20W.  A Topfield PVR uses 7W when in standby and 23W when in use.

The real interest to me though was in my PC power consumption.  First off I tried a Dell Inspiron 1501 laptop with Turion TL-52 CPU.  At idle it was around 25W and the highest I saw was around 50W, although I'll do some more extensive testing of that system later.

My main HTPC breaks down as follows:
Off/S5 = 6W
S3 Standby = 8W
Power On (Peak) = 102W
Idle = 74W
100% CPU Load = 95W
Watching DVD = 81W
Listening to iTunes = 74W (=idle)
Watching TV = 78W
Watching TV Recording = 77W

The 6W power consumption when in soft-off was a little disappointing, but I suspect it is due to the fact that things like PCI slots are kept powered when in this state, and there is no option to disable it.  I found that removing a USB TV tuner dropped the idle power from 74W to 71W, which when you consider USB is max 500mA@5V seems reasonable enough.  Turning off Cool'n'Quiet resulted in a 10W increase at idle, due to the CPU running at 2GHz rather than 1GHz.  Fully loaded power usage was the same regardless of CnQ on or off, which is to be expected.

Next up is the Dell Dimension E521:
Off/S5 = 2W
Power On (Peak) = 144W
Idle = 90W
100% CPU Load = 145W
Listening to iTunes = 92W
Watching TV = 102W

As you can see the ââ?¬Å?offââ?¬Â power consumption is far more reasonable, which may be attributed to the fact that there is a BIOS option to save additional energy by turning off devices when in soft-off states.  This is where things get interesting though.  The above was taken under Windows Vista (on the E521).  The power usage under XP was similar, except for the idle power, which never dropped below 97W.  That is a 7W difference between XP and Vista.  But if that wasnââ?¬â?¢t interesting enough, Vista was busy nearly all the time (hard drive access and 5-10% CPU load) whereas XP was apparently truly idle (no hard drive access and 0-1% CPU load).  I had to verify that Coolââ?¬â?¢nââ?¬â?¢Quiet was working, and it was, so Iââ?¬â?¢m not sure how to explain this.  Perhaps Vista is able to control the power management of certain devices more than XP is able to.  It is nice to know though that you can make use of all the 3D-niceness of Vista without increasing power consumption.

Finally, my good old Hi-Grade laptop:
Charger only = 1W
Off = 5W
Idle = 37W
100% CPU = 40W

The power consumption of this system is far lower than the desktops.  Setting the screen to minimum brightness dropped the idle power from 37W to 35W.  Removing the battery dropped idle power from 37W to 34W, which tallies with the charger only vs off power consumption.


As you can see from all this, computer power consumption is not nearly as high as some people would have you believe.  For the majority of systems out there, a 350W PSU will do the trick.  The power figures quoted here are from the AC wall socket ââ?¬â?? the actual usage of my HTPC is probably closer to 55-60W based upon the known efficiency of my PSU at sub-100W loads.

Has knowing this impacted my computer usage at all?  Yes.  I now use my HTPC for browsing the internet and checking e-mails.  It does the job just as well as the newer Dell (Athlon 64 3200+ vs Athlon 64 X2 3800+ - neither are slow processors) and consumes far less power in doing it.  The Dell is reserved for things that are out of my HTPCs reach, namely gaming (I wouldnââ?¬â?¢t be that cruel on the GeForce 6200 AGP).

[scuzzy]

Wow. Excellent information. I really appreciate that you shared that.

Scuzzy; I wonder how much power we could save at Poasters by banning Ace?

[Chandler]

What I find particularly interesting, is that a laptop with a couple of TV tuners attached to it can use a similar amount of power as a dedicated PVR (I expected this to hold a significant advantage).  But when you factor in the fact the laptop includes a screen in those figures and it in effect uses considerably less power.

The Dell Inspiron 1501 (say 35W) with a couple of Nova-t-Stick (3W each) gives a total of around 40W.  The PVR with a 14" CRT TV gives a combined total of 53W.  You could be doing other things while watching the TV too, such as browsing the Internet and as an added bonus the picture quality will be superior to the crappy CRT TV.

The PVRs standby power is also quite a disappointment.

[Whizbang]

That poses the question, "Is having a monstrous power supply really necessary, or is it just a bragging right necessity?"  I would be interested in the name of that power monitor, Chandler.

[Chandler]

The power figures quoted for power supplies are usually a total for all lines whereas the highest power draw is usually on the 12V and 5V rails, so you need to check the combined power for 12V+5V.

As for those stupid high powered no-name PSUs, I'd say "no" they are not needed.  A 300W Seasonic, Antec or Enermax would likely suffice for any reasonable system.  Of course if you're using a quad-core CPU and two high-end graphics cards in SLi with a RAID array of 10000RPM hard drives, you will need more than 300W.  But normal folk, not really.