Corsair VX450 for XFire?

[Ha-Nocri]

I was looking around for some numbers and found out that a system with q6600 quad-core and one HD 4870 installed is spending 280W in load (200W idle). That is with only one HDD 250GB 7k and no DVD-ROM's. That makes sense since 4870's TDP is around 180W and 6600's 105W. That is 185W combined (what could spend 100W more beside HDD btw?). Now I am wondering if Corsair VX450 PSU with 33A on the singe +12V rail could be enough for this system:

CPU: Phenom II X3 720 -> 95W TDP => 8A
VGA: HD 4770 (80W TDP => 6.7A) X2 in CF => 13.3A
... 21.3A combined... 11.7 "free" amps left for the rest of the system.

And that is the case only if both cards and the CPU are extremely OC'ed as far as I understand. So I think that a good 450W PSU with 33A on +12V rail would be enough to run this CF configuration without much sweat. Am I right? If not why?

[RollingThunder]

I was looking around for some numbers and found out that a system with q6600 quad-core and one HD 4870 installed is spending 280W in load (200W idle). That is with only one HDD 250GB 7k and no DVD-ROM's. That makes sense since 4870's TDP is around 180W and 6600's 105W. That is 185W combined (what could spend 100W more beside HDD btw?). Now I am wondering if Corsair VX450 PSU with 33A on the singe +12V rail could be enough for this system:

CPU: Phenom II X3 720 -> 95W TDP => 8A
VGA: HD 4770 (80W TDP => 6.7A) X2 in CF => 13.3A
... 21.3A combined... 11.7 "free" amps left for the rest of the system.

And that is the case only if both cards and the CPU are extremely OC'ed as far as I understand. So I think that a good 450W PSU with 33A on +12V rail would be enough to run this CF configuration without much sweat. Am I right? If not why?

Ha,

The 450VX doesn't have the cabling for crossfire for a reason.

[Ha-Nocri]

I know. But I would use coverter I got with my 3870. 2 4-pin MOLEX connectors into one 6-pin PCIe connector... and I am sure each 4770 comes with one such converter...

[RollingThunder]

I know. But I would use coverter I got with my 3870. 2 4-pin MOLEX connectors into one 6-pin PCIe connector... and I am sure each 4770 comes with one such converter...

Ha,

Since you're going to do it anyhow, post back how it goes. If you are restricted to using that power supply if you already own it, then you have no choice. Personally with the choices of economical quality power supplies available today, it makes more sense to buy one that already has the connectors for lower end SLI or Crossfire setups like 4770's.

[CharlieCS]

When they were making those power supplies a 85 watt cards were not present on the market , id say it will work in worst conditions everything overclocked 4770 x2 200 watts , 720 another 180 watts ( i saw a review with those numbers , cant recall which site ) , by any means it shouldn't be the most stable system but it will work .

[Evilsizer]

people wonder why i didnt like the idea of the 4770 having a pcie 6pin plug
http://www.ocforums.com/showthread.php?t=604448
and
http://www.xbitlabs.com/articles/video/display/radeon-hd4770_5.html

in either case though PCIE 1.0=75watts,PCIE 2.0=150watts.at pcie 1.0 current supply to the card from the 12v rail, is 6.25 amps. if a single 4770 does need 6.7amp then it should be able to pull the rest of the power from a pcie 2.0 slot. even if you have to use a twin molex to single pcie 6 pin it isnt going to be pulling that much power thru the cables. though ati states a requirement of 550 for CF of two 4770's.
http://ati.amd.com/products/radeonhd4700/requirements.html

[Ha-Nocri]

@RollingThunder
I don't have that PSU. I just wanted to check if my calculations are correct b/c I indeed plan to CF 2 3870's or 4770's

@CharlieCS
damn, 180W is a really high value. Can it be that it was consumpion of the whole system?

@Evilsizer
and I thought PCIe 2.0 gives only double the bendwidth of PCIe 1.0...

[CharlieCS]

@CharlieCS
damn, 180W is a really high value. Can it be that it was consumpion of the whole system?


Just looked it up , i believe you are correct :) then it will definitely work :)