PSU Required for two GPUs

[sssimon]

Hey guys,
I recently ordered a bunch of new parts for my rig and since I'm still kind of new to this, I'd like to know how powerful of a PSU I'll be needing.

The new motherboard I ordered is a ASRock Z75 Pro 3 and it supports two GPU's over a PCI Express 2 and 3 slot. Right now I'm running an AMD Radeon HD 7970 GPU which is recommended to have 500W of power available. If I wanted to install a second 7970, would I need 1000W?
I currently have a 650W seasonic PSU.

Thanks

 

[tweakboy]

Your 650watts will handle another video card easy.

 

[AntonioHG]

http://www.hardocp.com/article/2012/03/28/nvidia_kepler_geforce_gtx_680_sli_video_card_review/8

Seems like you'd be cutting it a little close with 650W, but you don't need a 1000W PSU to run two 7970s.

 

[guskline]

Read the power recommendations of either Nvidia or AMD for SLI or CF respectively.

You won't need a 1000W psu unless you are doing crazy overclocking and have a ton of fans or peripherals. That being said, I think a 650W PSU, even a Seasonic might be cutting it a bit close. Look for a quality 800 to 850 PSU and be done with it. Upping from your 650 to only a 750 doesn't seem to make sense or cents.

 

[Termie]

Just a heads up, I wouldn't Crossfire on that board Z75 board. It has a very slow PCIe 2.0 x4 slot as its second slot. While boards like this are advertised as Crossfire compatible, they really are very sub-optimal. Nvidia won't even let these configurations be used for SLI.

You'd probably only get about 75% of the capacity of the second card, which will lead to huge stuttering and overall poor performance, despite very high power use.

To answer your question, 750W is the minimum you need for 7970CFX.

 

[sssimon]

Just a heads up, I wouldn't Crossfire on that board Z75 board. It has a very slow PCIe 2.0 x4 slot as its second slot

That makes sense. Is there any way around this, or should I just overclock my 7970?
Would buying a lower end card for the 2.0 slot be a better idea?

Thanks for helping with my first question :thumbsup:

 

[Termie]

That makes sense. Is there any way around this, or should I just overclock my 7970?
Would buying a lower end card for the 2.0 slot be a better idea?

Thanks for helping with my first question :thumbsup:

Given your current setup, overclocking the 7970 is a much better idea. You should be able to get at least a 20% overclock out of it. You PSU is plenty strong to support it (in fact it's excellent, and it would be a shame to replace it for a sub-optimal Crossfire setup).

What CPU do you have? That is also relevant to overall performance.

 

[sssimon]

My CPU is laughable right now, it's an intel core 2 duo e8400. I'm aware that it's bottlenecking my setup, but I haven't found anything good enough in my price range to replace it.

If I can find a decent lga1155 cpu between $90-150 on NCIX or newegg, I'll order it as soon as possible

 

[Termie]

I would get the CPU before even bothering with an overclock on the 7970. You are probably running the video card at 50% load right now.

It sounds like you have a Z75 board without a CPU. That is a bit of a problem. Have you thought of just getting a B85 board plus a Core i3-4160 for $200? It's very unlikely you'll find a sale price on an 1155 chip anywhere, and they're a terrible value at retail prices. Maybe pick up a used 2500K?

 

[sssimon]

Yeah, I have all the parts I need shipping to me minus a CPU. That's why I've been looking into it. If I have to wait a few more weeks with my current setup before I can afford a great CPU for my newer setup, I guess I'll just have to do that.

Thanks a lot man.

 

[Termie]

Yeah, I have all the parts I need shipping to me minus a CPU. That's why I've been looking into it. If I have to wait a few more weeks with my current setup before I can afford a great CPU for my newer setup, I guess I'll just have to do that.

Thanks a lot man.

Can I ask why you ordered a Z75 board? There are a lot of very cheap Z87 boards that would have been a much better bet for you. The Z87 Gryphon, for example, is going for $90AR right now.

Unless you got that board for under $50, I'd return it if that's possible. It's really not a great board, and it's totally obsolete. My main system uses a Z77 board, and there's nothing wrong with it at all, but I'd never buy one today, even at a huge discount.

 

[sarfraz khan]

Hey guys,
I recently ordered a bunch of new parts for my rig and since I'm still kind of new to this, I'd like to know how powerful of a PSU I'll be needing.

The new motherboard I ordered is a ASRock Z75 Pro 3 and it supports two GPU's over a PCI Express 2 and 3 slot. Right now I'm running an AMD Radeon HD 7970 GPU which is recommended to have 500W of power available. If I wanted to install a second 7970, would I need 1000W?
I currently have a 650W seasonic PSU.

Thanks

You should go for a corsair or cooler master 750Watts psu . It will surely run both of your cards

 

[VirtualLarry]

Is a 500W PSU good enough for a single 7950 (OCed to 900 / 1250), and a G3258 @ 3.6?

The reason I asked is, I installed some EVGA 500 B PSUs into my PCs, and my computer on the right is OCed 100Mhz on the GPU core, and it rebooted some time today, and the computer on the left did not. They are both basically identical builds, and both are running DC on GPU and CPU.

 

[lehtv]

Should be... but you never know with HEC units. Although the unit tested by JonnyGuru fared quite well, HEC isn't exactly the most reputable PSU manufacturer, and I wouldn't be surprised if their output quality was inconsistent. Maybe your other unit just isnt as good as it should be

 

[kasakka]

Depends on the GPU. Don't know about the 7970 but I used to run two GTX 770s with a 525W PSU. I think it was cutting it close. Now running two GTX 970s with a 750W PSU.

But you definitely don't need those 1000W+ behemoths. Just a quality unit at about 750-850W should be more than sufficient.

 

[TurtleCrusher]

E8400/7970? Upgrade that CPU before ANYTHING.