True power usage of a computer

[gf4200isdabest]

This question should have been simple; as it turns out, it's not. A certain engineering friend of mine laughed when I told him i had a 430W PSU on my computer. He pointed out that they use much smaller PSU's on things which probably require much more power.

We decided to put our words into action. We cut open the power cord, connected two different ampmeters and measured the alternating current. To my surprise and my friend's amusement, it showed about 1 amp of usage during idle and it never even got to 1.5 amps while playing Doom3. This means that my system, at no point, used anywhere close to 200W despite all the high power components being used.

Suffice it to say, the only valid conclusion I can seemingly draw from this is that all of these high end power supplies are marketing gimmicks. Based on this result, I can scarcely see a scenario where *any* PC would be using 300W+ of power, much less the average gamer. My system specs:

2.26GHZ
1.5GB Corsair XMS RAM
Geforce 4400 128MB
Expos 4g4a+ motherboard
Antec Truepower 430W PSU
2 WD special edition hard drives
DVD-ROM
DVD-RW

This isn't a brand spanking new system but, on the other hand, people were going saying "OMG OMG DON'T SKIMP ON THE PSU" back when it was brand new...

Has anyone conducted the same test? What results did you get? Also, is the PSU rating nominal power or theoretical peak? As in, for how long would the PSU last if it was producing near max power?

 

[oneshot47]

Some list the ratings as peak...some as sustained. you just gotta look close. As for it being a marketing gimmick, no, its not. Which rail did you measure the amperage of? Get down in there and measure the 12v going to the cpu while its crunching, or one of the hd rails while its spinning up. You have to remember too that the rails are seperate and measureing amps on a regular molex connector while youre playing a game doesnt really mean anything. Its the lines going to the motherboard that are being hit. Remember too, that the wattage spec is the wattage of each individual rail added up. A psu might say 400w but thats divided between a 12v, 5v, 3.3v, -12v, and -5v rail.

 

[3chordcharlie]

The PSU needs the flexibility to power systems with relatively large draws on any of the major power rails. So since configurations are not standard, the total available power needs to exceed the expected use. But that being said, quality 250W PSUs power top-end components in SFF machines, and yes, high Wattage numbers are something of a gimmick: a 250 watt supply that comes with an SFF is better than any generic 400 or 500 watt supply that comes with a cheap ATX case.

 

[oneshot47]

Originally posted by: 3chordcharlie
The PSU needs the flexibility to power systems with relatively large draws on any of the major power rails. So since configurations are not standard, the total available power needs to exceed the expected use. But that being said, quality 250W PSUs power top-end components in SFF machines, and yes, high Wattage numbers are something of a gimmick: a 250 watt supply that comes with an SFF is better than any generic 400 or 500 watt supply that comes with a cheap ATX case.

The reason its better is the quality of parts used, and the amperage availible on the rails. The cheapos have very low amp ratings and they make up for it by listing the peak watts instead of sustained.

 

[htmlmasterdave]

Cheap psu's are the bane of my existence

Originally posted by: oneshot47

Originally posted by: 3chordcharlie
The PSU needs the flexibility to power systems with relatively large draws on any of the major power rails. So since configurations are not standard, the total available power needs to exceed the expected use. But that being said, quality 250W PSUs power top-end components in SFF machines, and yes, high Wattage numbers are something of a gimmick: a 250 watt supply that comes with an SFF is better than any generic 400 or 500 watt supply that comes with a cheap ATX case.

The reason its better is the quality of parts used, and the amperage availible on the rails. The cheapos have very low amp ratings and they make up for it by listing the peak watts instead of sustained.

 

[bxp24]

I think I'm gonna jump in on this thread too, as power supplies are also a steady topic in car audio. I, too, heeded the warnings of "skimping on the power supply" and bought a hefty unit from a trusted brand. The way I figure it is that while it might be overkill, the PSU is one of the few components you won't have to worry about replacing if and when you decide to upgrade your system.

I'm gonna guess your friend is an electrical or mechanical engineer cause I've seen similar reactions regarding wire guage in car audio systems. Does even a 2000W car audio system need 0 AWG wire? I don't know... And is a 2000W system really putting out 2000W? Probably not, at least not during normal usage. But, like other people have already said, a lot the whole PSU situation is based on the quality of components and [in]accuracy of the ratings. With quality PSU, you're guaranteed the advertised power rating (which is probably underrated) and steady voltage. A cheap unit has misleading ratings and is more prone to voltage fluctuations. So, that's my take on it. I'd be curious to know the results though, if anyone measures the actual power a high-end computer typically uses.

--Brad

 

[oneshot47]

Originally posted by: bxp24
I think I'm gonna jump in on this thread too, as power supplies are also a steady topic in car audio. I, too, heeded the warnings of "skimping on the power supply" and bought a hefty unit from a trusted brand. The way I figure it is that while it might be overkill, the PSU is one of the few components you won't have to worry about replacing if and when you decide to upgrade your system.

I'm gonna guess your friend is an electrical or mechanical engineer cause I've seen similar reactions regarding wire guage in car audio systems. Does even a 2000W car audio system need 0 AWG wire? I don't know... And is a 2000W system really putting out 2000W? Probably not, at least not during normal usage. But, like other people have already said, a lot the whole PSU situation is based on the quality of components and [in]accuracy of the ratings. With quality PSU, you're guaranteed the advertised power rating (which is probably underrated) and steady voltage. A cheap unit has misleading ratings and is more prone to voltage fluctuations. So, that's my take on it. I'd be curious to know the results though, if anyone measures the actual power a high-end computer typically uses.

--Brad

The problem is, car audio manufacturers dont have to adhere to any standards when they report specs on their equipment. That 2000w amp for one is probably 2000w at 2 ohms, its probably peak rating, and its not always measured the same as other manufacurers. Most of those "2000w" amps can only manage 500 or so dirty watts in the real world. I have a friend who rep'ed for high end home and car audio companies for 30 years whos taught me a lot.

 

[bxp24]

Yeah, you're right. The lack of standards is an issue. Mind if I ask which company your friend worked for? I'm not an engineer, but I know a fair amount about car audio and am getting into home audio. Always looking to learn more though, so if you know any good resources (even for general electrical info) I'd greatly appreciate it.

--Brad

 

[oneshot47]

He was with blaupunkt for a long time, i think ads at one point, he does some stuff for subzone now....i cant really remember all the different ones. His experience really came from just being in the business and listening to a lot of different stuff. At one point he was invited out to the skywalker ranch to tour the theater set up there.

 

[Zepper]

My computer box runs about 130 true watts max from the wall (AC) so at 70% efficiency (which is pretty good for a typical switching PSU) that is about 91 total Watts DC being output from the PSU... The key is getting a high quality PSU - the good brands have been covered here endlessly. Also you want the total output weighted more heavily to the 12V rail these days as a good mobo will power the CPU from the 12V rail. I like to see 13-15A on the +12 rail as a minimum.
.bh.

 

[Sonic587]

Originally posted by: oneshot47
The problem is, car audio manufacturers dont have to adhere to any standards when they report specs on their equipment. That 2000w amp for one is probably 2000w at 2 ohms, its probably peak rating, and its not always measured the same as other manufacurers. Most of those "2000w" amps can only manage 500 or so dirty watts in the real world. I have a friend who rep'ed for high end home and car audio companies for 30 years whos taught me a lot.

This regulation problem is also rampent in the PSU market. Many shadey manufacturers will list completely unrealistic specs/watteges/ect or just flatout lie about their supplies. Anything to sell them to unsuspecting customers. It's not completely people's fault, either. Many times you have to dig into PDF files or have an indepth knowledge of PSUs to know what is right for your system.

The answer to this problem is also the same: Strict standards and regulations.

 

[0roo0roo]

eh we had a thread on power use a while back. you can buy this power measurement thing to see how much ur pc is drawing. about 25 bux i think, kill-a-watt.

cheap psu's measure their output at some absurdly low temp. efficiency goes down as temp rises.

 

[CraigRT]

of course it's marketing ... i still tell people to this day to just buy a quality 300W PS and they'll be fine!

i had my dual mp1800+ with 2 drives, 9800 pro, 2 opticals, 1gb RAM, running off an SPI (Sparkle) 300W PSU without issue.

 

[alb1221]

people are saying that 6800ultras require a 350+ psu or elese DANGER!!! is this true?? from what you say that is probably jack sh!t

 

[Sonic587]

Originally posted by: alb1221
people are saying that 6800ultras require a 350+ psu or elese DANGER!!! is this true?? from what you say that is probably jack sh!t

http://www.gamespot.com/news/2004/05/10/news_6096837.html

 

[alb1221]

Originally posted by: Sonic587

Originally posted by: alb1221
people are saying that 6800ultras require a 350+ psu or elese DANGER!!! is this true?? from what you say that is probably jack sh!t

http://www.gamespot.com/news/2004/05/10/news_6096837.html

thx that was a cool little article

 

[RalfHutter]

This article contains some excellent info about PSUs. In particlular, read the section on page 2 called "How Much Power is Enough?". Also looks at the links on the top of page 3, especially the one called "How much will a 300W PSU run?". Lots of real-world case studies in that thread.

 

[gf4200isdabest]

I certainly agree with everything that was said regarding using quality components but this still leaves me wondering whether there's anything besides marketing to everyone recommending all these massive power PSU's. It seems that now even Dell has jumped on the bandwagon and is offering a 470W PSU on its high end system; this is to say nothing of alienware who offers an upgrade to like a 600W PSU.

However, this seems to be an issue which I can't find discussed on any hardware review sites in specific. Everyone is quick to praise a good 400W+ PSU even though, by these tests, it is abundantly clear that, even if i were to put in a gf 6800 and the latest CPU/mobo, I would not get anywhere near that number.

So a better question would be, what are the specifications to look for in a PSU? I think this would be useful to a lot of Anandtech members who have always just heard "buy a quality PSU and don't skimp on it." Really, that doesn't tell me anything. Just because something is high priced doesn't mean it's good. What kind of specs does the average high end user need? What about an overclocker?

EDIT: To clarify oneshot47's question earlier in the thread: my measurements were done on the actual power strip; i measured the AC as a whole to get the total power the computer was using; not just the power on any individual rail.

 

[MercenaryForHire]

Originally posted by: RalfHutter
This article contains some excellent info about PSUs. In particlular, read the section on page 2 called "How Much Power is Enough?". Also looks at the links on the top of page 3, especially the one called "How much will a 300W PSU run?". Lots of real-world case studies in that thread.

/waves to RalfHutter

Haven't posted at SPCR myself for a looooong time. I've got a couple more machines doing a PSU Limbo now as well - maybe I should check in again.

- M4H

 

[dclive]

RAID0 set with 4 drives, plus 2 additional drives (total of 6 drives)
PCI MegaRAID IDE RAID card
PCI modem
2 512M chips
AMD 3000+
Asus KM400-based motherboard
all in a Compaq case (with the 4 drives loose)
all with Compaq's stock 250w power supply (it's a Presario S6000Z, a $350 Compaq....)

Never a problem, and the system is constantly under heavy load.