question about high power PSUs

[Flancen]

Hi there, as topic says i got some questions:

If i were to buy a highpower PSU, say 850w, would it generate less noise at lower levels of loads than a 500w PSU?

and didnt SPCR have a review of 600w and 850w dark power pro PSUs?

EDIT: will the system be able to boot up with a 850w PSU? i got a AMD x2 5000+ 4gb DDR2 3 HDDS and a 8800GTS 320MB

[Elvellon]

Depends on the "smartness" of its fan control system. For example, the units reviewed by SPCR:
Enermax Galaxy 1000 W: 29 dBA at minimum load, 50 dBA at 500 W and upwards.
Zalman 1000 W (850W is the same): 20 dBA up to 400 W, 26 at 500 W, 40 at 1000 W.

If your system pulls 500 W while gaming (GTX280 SLI ), the Zalman PSU will be 24 dBA (!!) quieter! A difference between "SPCR quiet" and a lawnmower.

Or let's take less extreme PSUs at 300 W load (single 4870 ).
Enermax Pro or Modu82+, Corsair HX: 22 dBA
Antec Earthwatts 430: 37 dBA.
A difference between almost inaudible and not quiet.

[Flancen]

thanks for the answer, now if someone can answer the rest of my questions:)

[nafets]

..

[Flancen]

The system should boot up just fine, with an enormous amount of wattage to spare...

but that extra wattage wont be seen on the electric bill, right?:)

[Elvellon]

but that extra wattage wont be seen on the electric bill, right?:)

Nope . PSU watts rating is the maximum it can transform from AC to DC. How much is does actually transform depends on your hardware.
PSU efficiency may affect your electric bill. For example, if your hardware needs 160 W, a 80% efficient PSU will pull 200 W from the wall, 40 W wasted as heat.
The peak of the efficiency curve of a PSU is somewhere in the middle of its maximum power, so that's the way the wattage rating may affect your power bill. But IMHO the difference between a good brand PSU (more efficient overall) and a bad one is greater.

[SebRad]

but that extra wattage wont be seen on the electric bill, right?

Correct, your computer will draw the same amount of DC power (100 to 200w, yes really that little unless overclocking a lot!) regardless of 330w or 1000w PSU. The AC power drawn from the wall (and hence on your electric bill) will vary slightly according to PSU efficiency. Most PSUs are now 75-85% efficient; at 200w DC this equates to 235 to 267w from the wall. PSUs are usually most efficient around the middle of their output range so a 200w system may see optimal PSU efficiency with 380-430w PSUs. Except if your system is idle most of the time it maybe in the 80-100w range and a lower 300-350w PSU maybe more efficient at that low level while still being able to cope with full load. Have a look at the SPCR (and maybe Anandtech.com) reviews of PSUs to see how the efficiency varies with load.
Bottom line: look at the nice SPCR table of power vs noise and pick the PSU that is quietest at the load your system will produce that you can find and afford to buy.
(Corsair VX450 and Seasonic S12II look good to me)
Regards, Seb

[Flancen]

thank you for the answer now to find a proper review of the 850 PSU with noise measurements:)

[nafets]

..

[jaganath]

you don't need anywhere near an 850W PSU. your maximum draw is ~200W, at that DC output Corsair VX450W is still at lowest noise level.

[lm]

EDIT: will the system be able to boot up with a 850w PSU? i got a AMD x2 5000+ 4gb DDR2 3 HDDS and a 8800GTS 320MB

My system is Q9450, 8GB of DDR2, 8800GTS 512MB, Velociraptor, another hdd, and other stuff, with Gigabyte EX38-DS4 mobo. I run it just fine with a Corsair VX450.