4850s and PSU question...

[bosshoss]

Just a quick question, I just received another 4850 to put in xfire on my mobo. I have a thermaltake 550w psu which is modular and has one rail for pci-e, and one for everything else. My question is; the one rail for pci-e has two connectors on the same cable, the psu claims to be SLI compatible, would I be better off puttting the second card on the other rail with the included molex-pci-e adapter, or would both cards be fine on the single rail/dual plug?

 

[dagger]

Just a quick question, I just received another 4850 to put in xfire on my mobo. I have a thermaltake 550w psu which is modular and has one rail for pci-e, and one for everything else. My question is; the one rail for pci-e has two connectors on the same cable, the psu claims to be SLI compatible, would I be better off puttting the second card on the other rail with the included molex-pci-e adapter, or would both cards be fine on the single rail/dual plug?

The so called "rail" are internal channels, and has nothing to do the physical cables going out from your psu. They'll switch automatically as needed, so don't worry.

 

[sdrac]

Whats the exact model of the PSU?

 

[bosshoss]

http://www.newegg.com/Product/Product.aspx?Item=N82E16817153059 is my PSU.

 

[aevm]

Read this:
http://techreport.com/articles.x/14882

P45 chipsets have a total of 16 lanes. They can be distributed as 16x+0x (one card) or 8x+8x (two cards). You can divide 16 into 16+8. Gigabyte is saying 16 + 8 but it actually means 16 for the first one when the second one is not used, and 8 for the second one when the first one also drops to 8. Of course, it's simpler and shorter and advantageous for them to put it like they did ("one running at x16 model, another one running at x8 model") but it's misleading and they should be kicked somewhere for doing it.

 

[aevm]

LOL, I answered your question above but by the time I submitted you had edited and removed the question. Just to clarify, I was talking about GA-EP45-UD3P and their claim that the PCI-E slots run at 16x+8x. It's true, kind of, it's just that they can't do 16x+8x at the same time.

 

[bosshoss]

Ahhh, thanks, and yes that is VERY misleading.

 

[sdrac]

Let me see if I can answer your original question (hopefully I'm understanding it properly):

Two 4850s in crossfire:
HD4850 CF 78W-199W - 199W max 3d draw, no overclocking. Thats 16.5A.
From http://archive.atomicmpc.com.au/forums.asp?s=2&c=7&t=9354

Your PSU shows ATX12V 2.2 compliant, 70% efficiency (low by todays standards) and the following
(from http://www.thermaltakeusa.com/Product.aspx?S=1172&ID=1536#Tab1 )

12V1 14A, 12V2 15A, 3.3V 22A, 5V 32A

Just by the numbers above, with the split on the rails you won't be able to power two cards (this doesn't even account for the fact that the 3.3 and 5V lines will potentially reduce the power avialable to you on the 12V rails). Also, since its ATX12v 2.2 compliant, one of the rails is dedicated to the cpu - meaning the other is for powering the rest of the rig - so it doesn't matter which way you split up the connectors, their all on the same line and its under powered for the cards by themselves, let alone the entire machine.

Hope that helps.

 

[bosshoss]

^^ Dum dum dummmmmmmmmmmmmm, says the bearer of bad news!!!! Informative answer, but ultimately not what I wanted to hear. That SUX. Hopefully my PSU will stay intact long enough to run for a month until I can buy a better one. I have had a bad experience with a PSU literally EXPLODING on me, (sounded like an al-qaeda warcamp goin off in my room...BOOM). Just hoping it will hold out long enough to buy somethin better. The one I had a bad experience with was a very expensive antec, was 600w and cost around 150bux about a year ago, (cant remember the model). Is there anything in the $100 price range ya'll would recommend for me?
Thx fellas!

 

[aevm]

The Corsair 750TX is $100 at newegg. That should handle HD 4850 CF all right.

LOL, Corsair even has a video on their site showing a PSU exploding. of course, they say it from the competition, not a Corsair Sorry I don't remember the URL, I just got the link in another thread a few weeks ago.

 

[sdrac]

Personally, if I were you, I'd error on the side of caution and only run with a single
4850 until I got the new PSU (I'm assuming your a gamer and would be pushing the card(s)).
If your PSU goes it could take the mobo or your GPU(s) along with it.

As for the choice of PSU, the Corsair that aevm suggests is a good one - lots of people like it and it got a good write up at JonnyGuru. I myself am actually a Thermaltake user - but I have the Toughpower 750W modular - one of their better PSU's.

You might have seen this before: http://www.xtremesystems.org/forums/showthread.php?t=108088

Pick a PSU from the top 2 tiers and you really can't go wrong (your current PSU is a tier 4 - not so good).
Just make sure you have enough Amps on the 12V rail(s) - most folks favor a single large rail these days so that you don't end up having potential power trapped on a rail you don't make full use of.

 

[bosshoss]

yea I referred to that before choosing
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139006
but that specific model wasn't mentioned in that write-up, so I'm hoping that it's an upper tier PSU.
And I noticed that has one GIGANTIC rail instead of multiple smaller rails.

And thanx, I think I will wait till that gets here monday before I fire both cards up.