How much of power PSU?

[jelibo]

Hello,

I am trying to figure out what kinfd of PSU I will need for this system spec:
Intel Core i5-3350P
3x GIGABYTE GV-R927OC-2GD
SSD
2x DD3 4GB

Will a 750W be sufficient? What if I only have 2 GPU's instead of 3?

Thanks

 

[clutchc]

A high quality 750W would be a bit on the low end for 3 x 150W cards. For 2 cards it would be fine. I would go 850W quality PSU or better. But the key word there is "quality".

 

[jelibo]

Hi, thanks for the reply.

I have picked a Corsair RM850. It should have 6x pcie, But somehow I cannot see it on the picture of the PSU. I see only 5 of them lol: http://www.corsair.com/us/media/catalog/product/cache/26/image/9df78eab33525d08d6e5fb8d27136e95/r/m/rm850_dc_side.png

Would this be ok for 3 cards that require 6+2?

 

[clutchc]

Hi, thanks for the reply.

I have picked a Corsair RM850. It should have 6x pcie, But somehow I cannot see it on the picture of the PSU. I see only 5 of them lol: http://www.corsair.com/us/media/catalog/product/cache/26/image/9df78eab33525d08d6e5fb8d27136e95/r/m/rm850_dc_side.png

Would this be ok for 3 cards that require 6+2?

I think each PCIe power cable is double ended with that PSU. So each cable will have 2 x 6/8 pin connectors.

Since that PSU has a +12V rail rated at 71 amps @ 850W, it should be OK. But I didn't realize that card was the factory overclocked version until just now. It may have a top end demand of more than the usual 150W. Maybe nearly as high as its big brother the R9-270X (180W). That would be 540W if all cards were maxed out. (I doubt that will happen tho)

I still think the PSU will handle 3 of them though. But if you are spending that kind of money for gfx cards, you may want to consider a 1000W unit to have more headroom. But if you already have the 850W Corsair, it should be sufficient.

 

[Rammy]

3 way Crossfire/SLI is really inefficient as it's quite a lot to spend without the performance to back it up, not to mention the reasonably high end PSU and motherboard you need just to get it to turn on.

A standard R9 270 only requires a single 6pin PCIe, but that card you mentioned uses two, which implies it uses more power. It has a tdp of nearer to the 270X, so that seems like a better card to base judgement from. 750W would be enough, but like you have discovered most 750W are wired for 4 8pin PCIe power (equivalent to 8 6pin) as running multiple low level cards is very uncommon.

The RM850 will do the job, as it does have 6, but I'd give some thought as to the viability of your overall solution.