PSU and Crossfire

[GregI]

Hey guys, just finalising my build after countless rethinks. I have settled on a 3870 for graphics with a corsair 520w PSU. If i wanted to go crossfire later in 2008, would i have to upgrade PSU to a higher wattage?(OC UK says min of 550w)

My build will consist of rather a core 2 duo(65w) or a quad core which will take 95.
One hard drive and a dvd burner running from the PSU.

This is where i get confused, and i know PSU's dont output 520w due to efficiency or whatnot but will my system even need 400W?

If im not mistaken, the 3870 takes 105w at max load. So well say 210w for crossfire. Add a 95w processor to give 305W. Not sure how much a DVD writer takes or a hard drive but i think it will still keep system load to under 400W. So why is 550w recommended/needed?

 

[jak731]

to give you the option of upgrading and to give some overhead for the psu, it doesnt help to run a psu at its peak capactity all the time.

 

[Ben M]

it should be fine

but it's only 20 quid more for a 620W model

PSUs run more quietly and efficiently when they aren't as near to their maximum output.

 

[Duke]

i think it will still keep system load to under 400W. So why is 550w recommended/needed?

Two reasons - one is that the PSU wattage is at peak and does not include any loss through inefficiency, second you need to look at the output on +12v on the PSU, as that is the 'true' wattage.

E.g. on the Corsair HX 520w, it is 480W. That PSU will be fine - got one myself & recommend it