Volt Drop 12V Rail under load Dual 6800U

S

starfury6

Limp Gawd
Joined
Feb 8, 2005
Messages
401
I have 2 XFX 6800 Ultra's in an SLI setup (Asus A8N-SLI Deluxe) with an OCZ 520W Powerstream PSU. The rails can handle as follows: +3.3V(28A), +5V(40A), +12V(33A) so the Amps are fine. However it would appear that the voltage on the 12v rail is dropping to aroun 10.8v under load (3dmark05). I can bump it up using the adjustable pots on the rear ofthe PSU but obviously that will overvolt it at default since it rises to about 11.85v when idle.

I have the primary card plugged into the PCI-e connector and the other via PCI-e/double molex addapter with the 2 sheilded molex lines. I have one SATA and one PATA drive, a, NEC DVDRW and a Sony DVDROM. No USB devices yet, and the SIL Raid, Marvell LAN, Serial and parallel ports are diabled. EZ-Plug is connected fine and I have had NO stability problems at all.

Is this drop normal? If it was that bad wouldn't I have stability problems? Some comments would be appreciated.

Thanks in advance

http://service.futuremark.com/compare?3dm05=590789

I'm pretty sure I should be getting more 3dmarks too with SLI...
 
starfury6 said:
I have 2 XFX 6800 Ultra's in an SLI setup (Asus A8N-SLI Deluxe) with an OCZ 520W Powerstream PSU. The rails can handle as follows: +3.3V(28A), +5V(40A), +12V(33A) so the Amps are fine. However it would appear that the voltage on the 12v rail is dropping to aroun 10.8v under load (3dmark05). I can bump it up using the adjustable pots on the rear ofthe PSU but obviously that will overvolt it at default since it rises to about 11.85v when idle.

I have the primary card plugged into the PCI-e connector and the other via PCI-e/double molex addapter with the 2 sheilded molex lines. I have one SATA and one PATA drive, a, NEC DVDRW and a Sony DVDROM. No USB devices yet, and the SIL Raid, Marvell LAN, Serial and parallel ports are diabled. EZ-Plug is connected fine and I have had NO stability problems at all.

Is this drop normal? If it was that bad wouldn't I have stability problems? Some comments would be appreciated.

Thanks in advance

http://service.futuremark.com/compare?3dm05=590789

I'm pretty sure I should be getting more 3dmarks too with SLI...
Click to expand...

The OCZ 520W doesn't seem to be a very strong PSU if it is only 33A on 12V... I smell powmax.

However, if you are having no instability issues, why worry about it?
 
I kind of thought it's not too much of a prob since I don't have stability issues, and this board is notoriously power hungry. I can push the voltage up on the 12v rail a little so it's 12.05-12.1 at idle, that should hlep.

Just a little worrying though...

AND the low 3dmark05 score. Could be the drivers I suppose.....
 
starfury6 said:
I kind of thought it's not too much of a prob since I don't have stability issues, and this board is notoriously power hungry. I can push the voltage up on the 12v rail a little so it's 12.05-12.1 at idle, that should hlep.

Just a little worrying though...

AND the low 3dmark05 score. Could be the drivers I suppose.....
Click to expand...

It is not the drivers. (As long as the drivers you are using are so old they do not support SLI)
Use ForceWare 66.93 from Nvidia.com or a beta like, 71.21, 71.24 or 71.81.

There is no way that SLI is enabled properly, if it was your score would be over 9,000.
 
Starfury: What are you taking this voltage measurement with? I wouldn't go by Software...

I have two 6800GT's running over Ultra speeds on My 18n-sli and I only have a 400w Zippy PSU. It has 30Amps on the 12v and normally runs at 12.01 but under load will dip to 11.95 (measured with multi meter)...

I would bust out A MultiMeter and check for sure, cause the onboard software solutions dont report accurate results.
 
Just software and bios readings.

I found that I was getting bad 3dmark scores because using the Auto setting on the motherboard for HTT it was setting itself to 4x, I manually set it to 5X and the speed is right, but I'm getting lots of artifacts and it wont make it through 3dmark05.

Could this be power related? I have plenty of cooling although this is what I'd expect from overheating....
 
I have herd that boar di power hungry also (not sure how one determins that) but still? I dont think its hungry for 12v...

The 5v and 3.3v are msot importiant for you board....i didnt even bother moding my 12v line lol... i wouldnt worry abot it untill you stability issuse...
 
10.8v is a lil.. computer hardware is designed with ~10% fluctuations of voltage. But unless you have stability issues, I wouldn't worry about it. And someone mentioned it before, 12 volt line is not really what runs your mobo (12 volts will fry everything on there), but more importantly is the 3.3 and 5.0v line. 12v is really for fans and hard drives.
 
DaLurker said:
10.8v is a lil.. computer hardware is designed with ~10% fluctuations of voltage. But unless you have stability issues, I wouldn't worry about it. And someone mentioned it before, 12 volt line is not really what runs your mobo (12 volts will fry everything on there), but more importantly is the 3.3 and 5.0v line. 12v is really for fans and hard drives.
Click to expand...

The MB converts the +12v rail down to whatever it needs to power at lower voltages such as 1.5v and 3.3v. Proof of this is the requirement of the 4pin +12v "p4" power connector in p4's and most AMD systems.
 
Viperoni said:
The MB converts the +12v rail down to whatever it needs to power at lower voltages such as 1.5v and 3.3v. Proof of this is the requirement of the 4pin +12v "p4" power connector in p4's and most AMD systems.
Click to expand...

very true, but its not as importiant to have a strong 12v rail, as nothing comes close to 12v usage...So if a 12v rail is being droped to 1.5v, then its ok to have a 11v rail, as it wont matter...

Unlke when a board uses the 3.3v line to make memory voltage, less head room there
 
Well one of the OCZ guys posts over at DriverHeaven.net so I PM'ed him and asked if I had connected up the PSU in the best way and told him about the drop, but since I measured it in software he said it's never right and could I provide him with some multimeter readings. I'll do that when I get home from work this evening.

Getting major texture problems in 3dmark05. Seems to start about the same time each run, just as the CPU test kicks in, but I see it start to wobble during the end of the last 3d game test.
 
Killa, you list your voltages as follows: 3.4v-32a, 12.2v-24a, 5.3v-40a

Are they adjusted by you to those values or just what your PSU runs at?
 
I(illa Bee said:
very true, but its not as importiant to have a strong 12v rail, as nothing comes close to 12v usage...So if a 12v rail is being droped to 1.5v, then its ok to have a 11v rail, as it wont matter...

Unlke when a board uses the 3.3v line to make memory voltage, less head room there
Click to expand...

Are you ABSOLUTELY certain on this?

http://www.xtremesystems.org/forums/showthread.php?t=53472

this guy had probs with his vid cards when the 12v rail was low... Then he boosted it up and everything worked fine...
 
starfury6 said:
Killa, you list your voltages as follows: 3.4v-32a, 12.2v-24a, 5.3v-40a

Are they adjusted by you to those values or just what your PSU runs at?
Click to expand...


i moded the 3.3v, and 5v lines on this PSU the 12v runs like that under load so i havent touched it. My older Entermax 431watt i moded all 3 rails...
 
I know you were talking about motherboards...

I was under the assumption that Vid Cards also do the same thing and take the 12v line and reduce it to something else... Are there any components on the vid card that really use the 12v?
 
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