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Silly power requirements, an over hyped myth?

Dureth said:
To factor in efficieny yiou need at least a 500w supply then for that power consumption. Maybe a bit more.
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No, its goes the other way.



Total power used at socket x Efficiency = Power used by components

e.g. 400W x 80/100 = 320W

Tbh is the rail current that's the real issue.
 
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fornowagain said:
No, its goes the other way.
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Actually it doesn't go either way. If power used at the socket is x Watts, then you need a PSU (of comparable efficiency) slightly more powerful than that.

However as mentioned it's more about the rail ampage. It's a shame more information isn't readily available, as there are probably some cheapish PSUs out there with reasonable 12v rails, just it's not advertised.
 
HangTime said:
Actually it doesn't go either way. If power used at the socket is x Watts, then you need a PSU (of comparable efficiency) slightly more powerful than that.
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Rubbish, the power specified at the rails is the supply DC wattage of the PSU. The consumed wattage measured by these meters, is "after" losses defined as the efficiency (DC-Output/AC-Input and excluding pf) and is due to heat.

e.g. 500W consumed by components at a stated efficiency of 80% will use 625W at unity.

(The only thing to watch for is that the 500W PSU is actually specified as a sustained load and not instantaneous, some of them cheat.)

You could also view it as a sum of the energy used.

500W consumed by components + 125W as radiant PSU heat = Total wattage consumed. This assumes real power unity, i.e.watts and not VA. Which is a whole other issue, doesn't effect domestic users.

http://www.silentpcreview.com/article28-page1.html
http://www.jonnyguru.com/forums/showthread.php?t=1036
 
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HangTime said:
Actually it doesn't go either way. If power used at the socket is x Watts, then you need a PSU (of comparable efficiency) slightly more powerful than that.

However as mentioned it's more about the rail ampage. It's a shame more information isn't readily available, as there are probably some cheapish PSUs out there with reasonable 12v rails, just it's not advertised.
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No, no, I'm pretty sure fornowagain is right. The PSUs are rated by output power, not input. So if they output 300W, then it is implied that whatever power they need to input from the wall, they are rated for that. So a 300W PSU should output 300W to the components regardless of how much power is needed from the wall.

Unless of course you have a £15 PSU, in which case once you reach 50% of the rated output it will either melt or blow up.
 
Guess its safe to assume that unless you have 1000's of extras (10 Hdrives, tones of LED's, pci cards etc) and there-for require national grid; 600W and over monsters are just overpriced pointless exercise if you just buy one of the top quality 500w PSU's...
 
Corsair have been trumpeting their 620w as handling 2 gtx's in sli and a quad for a while now.

The problem I see is what happens when DX10 games come out. Will we start seeing what these cards can do then, and will they start pulling more watts ? The owner over on Jonnyguru.com certainly thinks so and that site is pretty much recognised as an authority on psu's.

And if you buy a psu that just about handles your overclocked quad, sli, 8 hard drives, isn't it going to be noisy as it tries to stay cool as opposed to a decent 600-750w psu.
 
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Sean_UK said:
Guess its safe to assume that unless you have 1000's of extras (10 Hdrives, tones of LED's, pci cards etc) and there-for require national grid; 600W and over monsters are just overpriced pointless exercise if you just buy one of the top quality 500w PSU's...
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500W is plenty for most of us, even when overclocking. The thing is, hard drives don't use that much even. I think a 320gb sammy will use 5w each when seeking, and around 3w idle... so if you had 10 of them in RAID for example, that would be an extra 50w which isn't exactly gonna cause blackouts. ;) My fileserver has 5 x 320gb drives in raid 5, and the whole rig pulls less than 60W thru the plug.

LED's are also very low power - 100 blue or white ones will use around 6 or 7 watts... weather you want your PC to look like a christmas tree tho is another matter. :D

CCFL's use a bit more, but not really enough to worry about... The only thing IMO that would require a quality PSU of more than 500W would be crossfire/SLI, or maybe people with crazy vmods to allow uber overclocks with water/phase/nitrogen. My trusty tagan 480w will be going in a c2d rig soon. :)
Flanno said:
And if you buy a psu that just about handles your overclocked quad, sli, 8 hard drives, isn't it going to be noisy as it tries to stay cool as opposed to a decent 600-750w psu.
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A more efficient PSU is the way to go here... With a high efficiency psu there is Less heat = less noise, especially with large loads. silentpcreview is a good site, as is compares PSU's noise, and often the higher power PSU's aren't really that quiet when driving large loads.
 
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MikeHunt79 said:
The thing is, hard drives don't use that much even. I think a 320gb sammy will use 5w each when seeking, and around 3w idle... so if you had 10 of them in RAID for example, that would be an extra 50w which isn't exactly gonna cause blackouts. ;) My fileserver has 5 x 320gb drives in raid 5, and the whole rig pulls less than 60W thru the plug.
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More like 9.5W during seek. Its not as simple as that, don't forget current draw is much higher during spin up, at least 2A. 10 in raid could pull a lot to start up. Its the same with any electrical system, initial surge current can trip limiters. Another is called diversity (factor), it just means that its very unlikely that every component will pull 100% of its maximum load all at the same time. A bit like everyone boiling a kettle at half time during the World Cup. Its one of the reasons why the online PSU calculators can be inaccurate. Other reasons can be derating from heat and age.
 
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fornowagain said:
Rubbish, the power specified at the rails is the supply DC wattage of the PSU. The consumed wattage measured by these meters, is "after" losses defined as the efficiency (DC-Output/AC-Input and excluding pf) and is due to heat.

e.g. 500W consumed by components at a stated efficiency of 80% will use 625W at unity.
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this guy speaks the truth, dunno what all this malarky is abut efficiency, don;t care even if its 70% efficient, the power stated on psus is the dc power as mentioned above and is not the amount of power the unit will pull from the wall.
 
Iirc, the SATA spec allows up to two drives at a time to spin up to keep the surge current down. must have come about, especially with redundant arrays due to the start up currents becoming a real problem for PSU's. A normal PC sees so much of its load from graphics cards and cpus, that a few hard drives aren't an issue.

Jonnyguru tested one of those meters, against a multimeter. He didn't find it that accurate after a certain point as I remember, good as a guide I guess. It always amazes me when someone buys a 1kW PSU or more. Seems like such a waste, don't people realise just how much power that is? Seems to be fashionable or maybe its an ego thing?

http://www.jonnyguru.com/forums/showthread.php?t=2284

Its the having tons to spare for later mentality. The thing to watch for is some of those PSU aren't very efficient with light loads, it could be chucking out more heat than than a smaller PSU loaded correctly. The trick is to balance that against running too near the upper limit as that's not good either.

 
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And the manufacturers don't put enough PCIe connectors on lighter PSU's. Its a conspiracy I tell ya. Does anyone know the lowest rated PSU with 4 x PCIe? In the 700W range I'd say (650W Etasis used to, don't know if thats still a current model).

Overclocked dual core C2D - 100W. SLi GTX - 260W. Motherboard, ram, a few drives and fans - 100W.

Maybe I don't want a 700W PSU just for the 4 PCIe connectors? A good solid single 40A 12v rail will do thanks.
 
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If i remember right My system reads 229watts idle and about 360watts load (3dmark06)

C2D 6600 running 3500mhz
8800gtx running 630/950
18watt waterpump
6x 120mm fans
1x 92mm fan
x3 harddrives
1x dvd writer

I check again this evening after work...

Idle wattage....i get a load wattage picture up later
DSC00127.jpg
 
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Just out of interest how much risk is there running a PSU close to its maximum output for long periods of time? I.e. is it safe to draw 420W from a 450 or 500W PSU for an extended amount of time?
 
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