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PSU Assistance required

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September 6, 2011 4:29:11 PM

Hello,

I'm getting completely confused when it comes to purchasing a new PSU to support new upgrades.

I'm running:

Win7 x64 w/ SP1
Intel i7 920 oc'd to 3.5Ghz per card
2x Gigabyte GTX560 Ti's
6GB of DDR3 RAM oc'd
Intel X58 mobo w/ water cooling
2x 500GB HDD's + 1x 320GB Velociraptor

My current PSU is a Dell 875EF w/ 875W and 18amps per 12v rail (it has 2 rails with 2 6-pin connectors per rail).



It's an Alienware ALX PC, btw.

I upgraded to the GTX560's from GTX260's and assumed 875W would be enough but, of course, I have now learned that the amps are vital too :(  and it eems the amps my current PSU supplies is insufficient?

I am looking for guidance on which PSU to buy.

My current PSU has no wires - all the wires from the mobo/sata card etc are in one bundle and combine into a single connector that plugs into the PSU.

My questions are:

Is my current PSU sufficient?

If not, should I opt for single-rail or multi-rail?

Will a modular unit be better for my pre-built system due to the wiring?

What amps do my cards need? I can onlt find the stock nVidia values


I have been looking at a Corsair HX850 but it is a single-rail unit and I can only find one is non-modular which may not be tidy eough in my current rig :( 
a c 105 ) Power supply
September 6, 2011 4:42:04 PM

Your current PSU should be sufficient (looks like it claims to have five rails, not just two), but if it doesn't have the right cables, well then you may still need to replace it.
In modern designs, single-rail vs. multi-rail has no bearing on effectiveness or capacity, despite some marketing claims. I personally believe a multi-rail design is safer, as a near short on a single-rail can appear to be just a heavy load, whereas on a mult-rail PSU with properly configured OCP, the PSU will shut down before something burns.
The PSU calculator at http://www.extreme.outervision.com/psucalculatorlite.js... can help you decide how big a PSU to get. Off the top of my head, you may want 750W because of your OC and the water cooling.

Edit: plugged in my own guesses and allowed for 10% capacitor aging and got 666W.
a c 126 ) Power supply
September 6, 2011 4:54:14 PM

1) Your current psu should be sufficient, assuming it is not defective.
It shows 825w max on the 12v rails total, which is 68amps. That is plenty. I estimate that 50amps should be sufficient for asli GTX560ti's.

2) single rail vs multi rail is a non issue.

3) Modular is usually a non issue, unless you have a very small case, and an oversized psu. For a properly sized psu, you will be using most of the leads anyway.

4) A GTX560 needs 450w with 24a on the 12v rails plus two 6-pin PCI-E power leads. That assumes a normal complement of dvd's, hard drives, fans, etc. Overclocking adds little. A second card can, at max, use 75w from each of the 6 pin connectors, plus 75w from the slot itself. That is about 19a maximum added to the base 24a.

5) Unless you have suspicions about your current psu, go ahead and try it.

6) If you want a modular 850w psu, look at the XFX 850w unit. Silver certified too:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Related resources
September 6, 2011 4:54:34 PM

Hello,

Well I've got good news and bad news.

The bad news is, you probably need a new power supply (at least I would get a new one in your situation). 36 Amps is more typical of a 500W PSU than an 875W (Cheap brands often overstate their wattage).

The good news is, you don't need 875W PSU. You probably need something in the 650-700W range. The cheapest I would reccomend is this: Antec Earthwatts 750W ($105 w/$25 MIR)

If you want something modular look at: Corsair 750W Modular ($130)

Don't get too hung up on how many rails there are. Total amps and total watts are what matters.

Cheers
a c 243 ) Power supply
September 6, 2011 4:59:15 PM

2 x 18 amp rails and 6 amps per pcie slot = a total of 48 amps of power available to the video cards, more than enough power for a couple of cards that when stressed might use 26 amps combined.
Are you having issues ?
a c 243 ) Power supply
September 6, 2011 5:03:21 PM

subasteve5800 said:


The bad news is, you probably need a new power supply (at least I would get a new one in your situation). 36 Amps is more typical of a 500W PSU than an 875W (Cheap brands often overstate their wattage).
Ya gotta read the label
825 watts combined 12v output = roughly 69 amps
a c 126 ) Power supply
September 6, 2011 5:03:37 PM

For what it is worth, the psu label shows 5 12v rails with 18a each.
The maximum is not 5 x 18=90a, but the maximum of combined 825w, or 825/12 = 68.75a.
Surely more than enough.
September 6, 2011 5:10:49 PM

My bad. I'm at work and for some reason our internet filters out images. I was answering the question blind.
September 6, 2011 5:13:15 PM

delluser1 said:
2 x 18 amp rails and 6 amps per pcie slot = a total of 48 amps of power available to the video cards, more than enough power for a couple of cards that when stressed might use 26 amps combined.
Are you having issues ?


Well, it's just that someone on the Crysis 2 forums suggested that my constant crashing when using DX11 w/ max settings on Crysis 2 might be down to insufficient power.

I had my doubts because it didn't feel like a lack of power as the pc didn't BSOD or power off - the game just crashed to desktop but my curiosity was piqued and when I looked into it the more I got confused :pt1cable:  and I wasn't sure how the 18A figure worked when across multiple rails etc.

a c 126 ) Power supply
September 6, 2011 5:24:32 PM

WastedJoker said:
Well, it's just that someone on the Crysis 2 forums suggested that my constant crashing when using DX11 w/ max settings on Crysis 2 might be down to insufficient power.

I had my doubts because it didn't feel like a lack of power as the pc didn't BSOD or power off - the game just crashed to desktop but my curiosity was piqued and when I looked into it the more I got confused :pt1cable:  and I wasn't sure how the 18A figure worked when across multiple rails etc.


I doubt your problem is the psu.

Is your graphics driver up to date? Can you try cleaning out the driver and reinstalling?

Is there possibly a beta version you could try?

Is there a crysis2 patch available?

Are the GTX560's overclocked? Perhaps try downclocking them.

September 6, 2011 5:34:30 PM

geofelt said:
I doubt your problem is the psu.

Is your graphics driver up to date? Can you try cleaning out the driver and reinstalling?

Is there possibly a beta version you could try?

Is there a crysis2 patch available?

Are the GTX560's overclocked? Perhaps try downclocking them.


I've tried everything - underclocking, overclocking, reverting to older drivers, running with just one card etc. I've defragged, ran with minimal windows services and nothing stops the crashing.

I think I'm satisfied, thanks to the help of you guys, that my PSU is not the problem.
a c 105 ) Power supply
September 6, 2011 6:00:08 PM

Run memtest, and Prime95. RAM is the next suspect.
a c 126 ) Power supply
September 6, 2011 7:15:21 PM

WastedJoker said:
I've tried everything - underclocking, overclocking, reverting to older drivers, running with just one card etc. I've defragged, ran with minimal windows services and nothing stops the crashing.

I think I'm satisfied, thanks to the help of you guys, that my PSU is not the problem.


Since the GTX560's are new, perhaps one of them is bad, Try running with one card, to see if you can isolate the problem to one card.
a c 105 ) Power supply
September 6, 2011 8:11:09 PM

He has done that.
Test your RAM.
September 6, 2011 8:34:31 PM

I'll run a memtest. I remember they can take ages :( 
a c 126 ) Power supply
September 6, 2011 9:46:54 PM

Onus said:
He has done that.
Test your RAM.


Yep, I need to read.

Does the problem still happen with the old cards?
September 7, 2011 7:39:52 AM

Memtest completed - zero errors

It didn't happen with my old cards. The only difference is DX11.

Crysis 2 in DX9 mode runs perfectly.

It has to be the game :( 
September 7, 2011 4:13:26 PM

Well there is an easy way to test if its the GPU/PSU. Download Furmark and run it. Furmark is much more stressful on the GPU and the PSU than Criysis. If you can run Furmark without crashing then you are right, it has to be the game.
!