CrossFireX Question

Page 2 - Seeking answers? Join the AnandTech community: where nearly half-a-million members share solutions and discuss the latest tech.

cusideabelincoln

Diamond Member
Aug 3, 2008
3,269
12
81
It's definitely the power supply. 24A on the +12V rail is not enough for two HD4850s (which need about 110W each under 3D load), although a single one should work perfectly fine.

Your cards have to share the same +12V rail (which probably also has your optical drives and hard drives and maybe even motherboard on it). 24A is the limit for one of the 12V rails. You are probably exceeding this limit, and thus the OCP built into the PSU is shutting down the computer to prevent it from frying. This is a good thing, as no components should be damaged by a failing PSU. Although a lot of PSUs usually allow for greater amperage than the stated limit.

You'll want to get a quality power supply, and make sure it can deliver at least 33A on the +12V rails combined. This should equate to about a 600W PSU, or as F1shF4t said 550-650W. If you want suggestions, look into the Antec Earthwatt series, any Corsair, any PC Power & Cooling, OCZ ModXStream Pro series, or any 80 Plus Seasonic.
 

Nik

Lifer
Jun 5, 2006
16,125
2
56
Originally posted by: F1shF4t
Originally posted by: Nik
After enabling crossfire again, it won't stay up. Crap.

Looks like I'm in the market for a new power supply. Again. :frown:

Thanks for the help, all.


For your machine a descent 550 - 650 watt psu would work fine. I'd recomend something like corsair units, I got 2 and no issues with them yet.

Also check out reviews before you buy. There are a lot of dodgy psus out there.

The one I have is a 680. Why would you suggest something less? :confused:
 

Viper GTS

Lifer
Oct 13, 1999
38,107
433
136
Originally posted by: Nik
Originally posted by: F1shF4t
Originally posted by: Nik
After enabling crossfire again, it won't stay up. Crap.

Looks like I'm in the market for a new power supply. Again. :frown:

Thanks for the help, all.


For your machine a descent 550 - 650 watt psu would work fine. I'd recomend something like corsair units, I got 2 and no issues with them yet.

Also check out reviews before you buy. There are a lot of dodgy psus out there.

The one I have is a 680. Why would you suggest something less? :confused:

Because the issue is not total power but how it is distributed. If you buy a single rail PSU a lower power unit would power your system with no issues. If you buy a multi-rail setup you need to be concerned with what each rail can do & how the connectors are assigned to the rails. In your case it looks like both video cards are off of one 12V rail that will only do 16 or 18A. If it was a single rail unit with 34A @ 12V it would probably do what you need.

Take this 650W Corsair for example:

http://www.newegg.com/Product/...x?Item=N82E16817139005

Single 12V rail with 52A. It has 50% more 12V current available even though it's rated 30W lower than the unit you have.

Viper GTS
 

F1shF4t

Golden Member
Oct 18, 2005
1,583
1
71
Originally posted by: Viper GTS
Originally posted by: Nik
Originally posted by: F1shF4t
Originally posted by: Nik
After enabling crossfire again, it won't stay up. Crap.

Looks like I'm in the market for a new power supply. Again. :frown:

Thanks for the help, all.


For your machine a descent 550 - 650 watt psu would work fine. I'd recomend something like corsair units, I got 2 and no issues with them yet.

Also check out reviews before you buy. There are a lot of dodgy psus out there.

The one I have is a 680. Why would you suggest something less? :confused:

Because the issue is not total power but how it is distributed. If you buy a single rail PSU a lower power unit would power your system with no issues. If you buy a multi-rail setup you need to be concerned with what each rail can do & how the connectors are assigned to the rails. In your case it looks like both video cards are off of one 12V rail that will only do 16 or 18A. If it was a single rail unit with 34A @ 12V it would probably do what you need.

Take this 650W Corsair for example:

http://www.newegg.com/Product/...x?Item=N82E16817139005

Single 12V rail with 52A. It has 50% more 12V current available even though it's rated 30W lower than the unit you have.

Viper GTS

QFT :thumbsup:

Op there are actually psus which can be rated up to 1000 watts or more, which you would not use on old P3/Athon/XP computers. This is due to them having low rated 3.3V and 5V rails, since there is no need for these rails to have high current capacity now days.