|
|
|
Pentium
Group: Forum Members
Last Login: Today @ 00:18:24
Posts: 2,175,
Visits: 5,048
|
|
I have often thought that PSU's are specified far above what a PC actually uses and this article seems to prove it although it doesn't mention it in it's conclusion.
The quad core machine with an 800W PSU doesn't seem to every use more than 210W. I also believe that the 800W is what the PSU can output whereas the 210W is what it draws and assuming 85% effiency (I'll come back to that) the components are really only using a maximum of 179W or 25% of the PSU.
No, the PSU is rated at 85% effieicny but that is at it's optimal power drain. It could well be running at 70% efficiency with such a low load.
I am aware that you need consider different power requirements at differrent voltagees on different rails but still, a modern PSU should be able to supply a minimum of what it quotes and peaks above that and should have it's outputs evenly balanced for a modern PC.
Perhaps there is another article in there about the PSU's being fashionable and not being matched for purrpose but looking at the table, the Miser PC would do fine with a 100W output PSU and it would run at it's quoted efficency. Can you buy a 100W PSU ... I think not!
gaming: E4400@2.66GHz / P5K-E / 2x1GB PC8000@533MHz / 2x80GB D'Max 9-RAID0 + 320GB / 8800GTS 512MB / ViewSonic VX2835wm
server+media: P4 2.8GHz @ 2.4GHz / 775Dual-VSTA / 2x512MB PC3200 / 1000GB+500GB+250GB / HD2400pro
also: P3 for the mrs and a linux box and probably enough bits to build another one
|
|
|
|
|
Rudolph @ 299,792,458 m/sec
Group: Moderators
Last Login: Yesterday @ 21:32:49
Posts: 3,919,
Visits: 5,997
|
|
I am far from an expert on the subject of PSU's, (I'll leave that to Oldphart, who spent much of his working life designing and building them) but I think that there may be a couple of errors in the assumptions.
Firstly, whilst a PSU may be capable of supplying up to a particular wattage, it does not do this constantly, but continually varies its output according to the demand put on it by the components.
The efficiency of a power supply is determined by taking the DC output and dividing it by the AC input. If a power supply draws less AC to produce more DC, then that power supply is more efficient then one that draws more AC to produce the same amount of DC.
(DC Output) / (AC Input) = Efficiency
To simplify the calculations, if you have have a power supply that is putting out 250W, and it's drawing 300W from the mains docket, it's efficiency is:
250 / 300 = 83%.
Conversely, it the demand is for 300W, at 83% efficiency the draw from the mains would be 360W (rounded off)
The "surplus" 17% in the above is given off as wasted heat.
So, the PSU only draws what is required, and the efficiency remains the same.
Secondly, whilst in steady state usage, idling, or carrying out a constant task like video encoding the PC / PSU may draw a particular wattage, there are times when this can be dramatically increased, in particular during boot-up when every device in the PC is operating at peak demand, (more or less) simultaneously.
Having said that, in general I agree that all too often PSU's are regularly recommended that are massively overspecified in terms of output. There are very very few rigs out there that will ever require a 850W PSU.
(I'm ignoring build quality, stability of rails etc.)
|
|
|
|
|
Pentium
Group: Forum Members
Last Login: Today @ 00:18:24
Posts: 2,175,
Visits: 5,048
|
|
Here is an example efficiency vs draw graph.
Taking the 520W Corsair you can see it has a maximum efficieny at ~340W and appears to go on to supply power upto 650W (probably drasticly shortening it's life). at 25% power output (130W) it is only about 77% efficient. All in all, a very nice PSU which is most efficient where it's mostly needed.
The NeoPower 480W seems to have a peak efficiency at 380W of only 80% and at 25% load it drops to below 60%.
A graph taken from here http://www.codinghorror.com/blog/archives/000868.html.
gaming: E4400@2.66GHz / P5K-E / 2x1GB PC8000@533MHz / 2x80GB D'Max 9-RAID0 + 320GB / 8800GTS 512MB / ViewSonic VX2835wm
server+media: P4 2.8GHz @ 2.4GHz / 775Dual-VSTA / 2x512MB PC3200 / 1000GB+500GB+250GB / HD2400pro
also: P3 for the mrs and a linux box and probably enough bits to build another one
|
|
|
|
|
Pentium
Group: Forum Members
Last Login: Yesterday @ 09:15:37
Posts: 1,799,
Visits: 4,022
|
|
Hi Folks
Interesting discussion, but it's about 'steady state' power consumption
and excludes transient needs.
At PC start up all those little electro-mechanical fan and drive motors
need a lot of current, which is one reason why PCs can fail to start
properly, their power units need to meet that initial surge demand.
(Rule of thumb, about two and a half times steady state ?)
The other, sometimes continual need, is when running demanding
functions, like playing a video DVD, lengthy video transcoding or
video game playing (with powerful GPU demands kicking in.)
Using a little power consumption meter, you can measure those AC
power demands for your own real pattern of PC use, even enabling
a realistic calculation of utility bills.
I see that some forum members already have such meters.
By way of example a rig may need a 400watt PSU to start up,
consume 150watts 'doing nothing', draw 250watts when playing a
DVD movie, 300watts when transcoding video, but actually draw
400watts when playing C&C (a lot more for more demanding video
games). Lower power CPUs can help, but GPU motion video is the
big AC power user.
....................... Signature ......................
Still Learning and Trying to Keep It Simple in Sharing knowledge
[A] rig..ASUS-EN8500GT SATA-320+80GB G31MX-S2 2.6GHz E2160 2G
[B] rig..384M_XFX8800GS SATA-320+500GB G31MX-S2 2.9GHz E4600 2G
32-bit Mint4, Mint6rc1, WinXP & Vista Home Premium. http://tinyurl.com/MP3-Creation-with-the-Heron 
|
|
|
|
|
286
Group: Forum Members
Last Login: 01/11/2008 15:53:27
Posts: 465,
Visits: 2,448
|
|
Spedley (13/01/2008)
Perhaps there is another article in there about the PSU's being fashionable and not being matched for purrpose but looking at the table, the Miser PC would do fine with a 100W output PSU and it would run at it's quoted efficency. Can you buy a 100W PSU ... I think not!I think it's very common for people to buy PSUs that are far more powerful than they actually need. I'm always seeing people look at 600W+ PSUs for middle of the road C2D systems that would run very comfortably with a decent 400W supply. Maybe a few of them will look at the real world power consumption figures in that article and change their minds... As for 100W PSUs, you can get external 12V power bricks like those used in laptops, with a PicoPSU to use it with your desktop PC. As you'd expect they're very efficient at low output compared with typical PSUs. Great for a silent media centre PC, especially if you're using a slimline case that can't take a standard PSU.
|
|
|
|
|
486
Group: Forum Members
Last Login: Yesterday @ 20:06:27
Posts: 775,
Visits: 788
|
|
I use a Seasonic S-12 330w in my C2D E6300 PC and it's plenty.
The issue I had with the review was that the power draw of 32-bit Xp was compared to 64-bit 7.10 Ubuntu, on an ATI rig with a dodgy graphics driver.
A fairer comparison would have been 64-bit Vista Premium-vs-64-bit Ubuntu 7.10 on an Intel or NVidia graphics adapter, or 32-bit Xp-vs-32-bit Xubuntu.
ATI's Linux support is woeful.
|
|
|
|
|
Pentium
Group: Forum Members
Last Login: Today @ 01:04:17
Posts: 8,025,
Visits: 14,935
|
|
|
|
|
|
486
Group: Forum Members
Last Login: Yesterday @ 20:06:27
Posts: 775,
Visits: 788
|
|
Slipstreem (15/01/2008)
gn2 (14/01/2008)
Linux's ATI support is woeful.
Corrected. 
Cheers, Slipstreem.
Have to strongly disagree with you.
ATI has a long history of utterly dreadful driver problems in both Linux and Windows.
The difference between Nvidia and ATI's efforts at providing drivers for Linux is massive, ATI are simply dreadful in this area.
It is up to manufacturers to provide drivers, not Linux (or MS) developers.
You don't install drivers written by Microsoft for NVidia or ATI graphics cards do you.....?
|
|
|
|
| | |