How much power does a Xfire system require?

[Mech0z]

I am wondering if its possible to get a cheap PSU (Corsair 550/650w) and be able to run the given system 2x3870 + Core2Duo 2.66ghz? Because at first I do not want to buy Xfire, but I might do that later next year.

But is this power enough? Have not found any crossfire reviews showing power consumption while using crossfire. And I do not know how much power the rest of the system draws.

 

[MarcVenice]

You'll need a qaulity single 12v rail PSU, of 600w or more, with 45a or so on the 12v rail. Corsair 620hx jumps to mind for example.

 

[mpilchfamily]

I think the VX550 is adequate for that system. The 41A the unit offers on the single +12v rail is more then enough. Each 3870 can't pull more then 12A. Really it doesn't even have that much available too it. Each card uses a single 6 pin PCI-e connector. According to specs the 6 pin PCI-e connector can only provide a max of 75W or 6.2A @ 12VDC. The PCI-e card slots can only offer a max of 75W and that much be shared among both cards in the system. So we are talking 18A max for both cards. So the VX 550 would be the perfect choice.

 

[MarcVenice]

Even though the slots can only offer 75w, that doesn't mean videocards don't pull more then 75w from the PSU, or does it? How else could a GTX pull near 175w under full load ? Many videocards pull more then 75w from the PSU, so I'm a bit confused. I dunno, the 550vx will run those cards, I wonder how much headroom you'll have left though.

 

[Mech0z]

Well isnt that the reason they also have a power cable in them? Because the pcie slot cant provide enough themselfs.

 

[tomoyo]

Originally posted by: Mech0z
I am wondering if its possible to get a cheap PSU (Corsair 550/650w) and be able to run the given system 2x3870 + Core2Duo 2.66ghz? Because at first I do not want to buy Xfire, but I might do that later next year.

But is this power enough? Have not found any crossfire reviews showing power consumption while using crossfire. And I do not know how much power the rest of the system draws.

Just remember, 3870's only use 100 watts each at max load. So accounting for 150-200 watts of other components, you'd need around 350-400 watts of 12v power. Any good 500+ watt psu would likely be fine.

 

[Mech0z]

Ah ok that makes more sense Me reading reviews thinking that those numbers where from the card only, but being the whole system drawing that amount of power makes quite a difference ^^ Now get those cards to Denmark AMD!

 

[Lunyone]

Originally posted by: tomoyo

Originally posted by: Mech0z
I am wondering if its possible to get a cheap PSU (Corsair 550/650w) and be able to run the given system 2x3870 + Core2Duo 2.66ghz? Because at first I do not want to buy Xfire, but I might do that later next year.

But is this power enough? Have not found any crossfire reviews showing power consumption while using crossfire. And I do not know how much power the rest of the system draws.

Just remember, 3870's only use 100 watts each at max load. So accounting for 150-200 watts of other components, you'd need around 350-400 watts of 12v power. Any good 500+ watt psu would likely be fine.

If you go by what tomoyo says and look at this review that I found, you can see where Mpilchfamily is coming from.
http://techreport.com/articles.x/13603/9
192w underload (whole system) and then add the ~100w for the extra card = ~292w (300w) for the total computer. So the vx550w mentioned would be more than enough to power that system reliably.

Even though the slots can only offer 75w, that doesn't mean videocards don't pull more then 75w from the PSU, or does it? How else could a GTX pull near 175w under full load ? Many videocards pull more then 75w from the PSU, so I'm a bit confused.

Here is why:
http://www.newegg.com/Product/...C+OverClock+Video+Card
In the picture there is "2" 6 pin power connectors on the card. That is so they have enough power available to power up the card.

 

[Deleted member 4644]

Originally posted by: tomoyo

Originally posted by: Mech0z
I am wondering if its possible to get a cheap PSU (Corsair 550/650w) and be able to run the given system 2x3870 + Core2Duo 2.66ghz? Because at first I do not want to buy Xfire, but I might do that later next year.

But is this power enough? Have not found any crossfire reviews showing power consumption while using crossfire. And I do not know how much power the rest of the system draws.

Just remember, 3870's only use 100 watts each at max load. So accounting for 150-200 watts of other components, you'd need around 350-400 watts of 12v power. Any good 500+ watt psu would likely be fine.

This is wrong, wrong, wrong. 500W would BARELY hold.

I would go with the 550W as a MINIMUM, and really I think you are starting to look at the 650-700 W range with this set up. The ATI cards draw a LOT of power under load.

LOAD CONSUMPTION FOR *ONE* CARD IS 200W: http://www.anandtech.com/video/showdoc.aspx?i=3151&p=11

You need AT LEAST 450-500W of 12V to keep a dual set up going.

That means an overall power output of 650+

 

[Zap]

Originally posted by: MarcVenice
How else could a GTX pull near 175w under full load ?

The GTX uses TWO PCI-E 6 pin power connectors, which is how it can pull so much power.

Originally posted by: Deleted member 4644

Originally posted by: tomoyo
Just remember, 3870's only use 100 watts each at max load.

LOAD CONSUMPTION FOR *ONE* CARD IS 200W:

Those measurements are for the entire system, not just the video card.

A card with a single PCI-E power plug should be unable to use more than 150W total (75W PCI-E slot, 75W PCI-E 6 pin power connector).

 

[MarcVenice]

Ya I got it now, I was confused because of the pci-e slot part, not thinking the 6 pin power connector would also feed it with more power. Anyways, like Zap said, those power consumptions are the whole rig, not just the videocard. The charts show a single 3870 with x6800 cpu, 4x1gb of ram, 1 HD and other 'standard' components pulling 214w. If we assume another card pulls an extra 100w, and we add in another HD, dvd player, more casefans, we would probably end up at a total of 400-450w, where 450w is a somewhat HIGH estimate. If you know your rig can pull even 350w though, I would like to have a 600w PSU. That's roughly 60% of what your PSU can handle, that's more or less the norm, jonnyguru advocates not running your PSU over 50%, and other people say don't run it over 60-70%.

So I'm sticking with my 620hx recomnendation.

 

[Mech0z]

So if I want to overclock my X3870 and my Q6600 I ordered, is the Corsair HX620W then enough? Havent seen any bench for that loading

 

[MarcVenice]

A single 3870 and a q6600 will run on a corsair 450vx or a antec earthwatts 500w. If you plan on adding another 3870, then yes, the 620hx would be a good pick.

 

[Mech0z]

Well I think I will go Xfire next year when I get some more cash and it begins to run abit slow

 

[MarcVenice]

TBH, in a year or so, you're better of with a single new videocard, that will beat the living crap out of two crossfired 3870's. Especially since crossfire doesn't scale 100%, generates more heat, and requires a beefier PSU. If you save the money on the PSU right now, and buy a cheaper PSU, and just buy a single new videocard in a year, I bet you will be a happier gamer.

 

[Mech0z]

Well I was more thinking in a couple of month, but year it might be better to just keep a single card. Is the 450 gonna cut it if I overclock? Because thats a lot of money saved tbh :/