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Power Supply limiting CrossFire 7950 WF3’s + VRM Voltage & VRM amperage

post #1 of 8
Thread Starter 
I currently have my rig set up with 2 GV-R795WF3-3GD in CrossFire and have to say i am loving it. But it does crash after a while at a modest overclock. Max temp on the first card is about 71 c after running at full load for 2-3 hours. For example Metro 2033 crashed after about 2 hours last night with all settings maxed at 1920 x 1200 @ 1125/1575. I am not sure what is causing the problems, but i think i might be under powering my system. I have my system running on a Corsair CX600 and everything else seems to be working fine. My main concern is the GPU VRM's are putting out almost 120 amps each at full load then add the other VRM's and its 242 amps which seems like a lot for a 600 watt ps. But if you look at wattage for the cpu and gpu's it only looks like 289 watts so. . .

Here is HWinfo log showing the crash on line 77 @ 22:15:18.

hwinfo_1119.xlsx 78k .xlsx file
post #2 of 8
I would expect each GPU to pull in excess of 220 W just for safety.then add your CPU, fans, etc. and my guide is to add 25%

So I would use a 750 W PSU so that at stock values it's only at 50% load, maximising efficiency. But also leaving a bit of headroom under full OC'd madness.

All IMHO.

dunx

P.S. 242 Amps is at 1 V after the GPU VRM's have done their work.... that's only 20 Amps @ 12V + some allowance for the less than 100% efficiency of the process.
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post #3 of 8
What PSU are you running? If it's a good one it won't be causing the crashes and it should be sufficient for your feel uses, especially with a 3770k. Those things barely sip power! I'd say it's probably just an unstable overclock. I need 1.2v to get to those kind of clocks with stability on my 7950.
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post #4 of 8

He's using the CX600:

 

http://www.overclock.net/lists/display/view/id/4639045

 

If the 7950s were at stock, then I would be able to guarantee that the CX600 has enough:

 

http://www.guru3d.com/articles_pages/radeon_hd_7950_crossfire_review_2_and_3_way,5.html

 

The two 7950s alone pulled 279W from the PSU.  This review does not take into account the idle wattage, nor does it take into account the CPU (because the CPU was idling).  The idle wattage would be about 150W for this, and the CPU would pull up to 150W if it were under full load.  So, let's add 300W which would make the PSU pulling 579W from the wall outlet.  If the PSU is 85% efficient while pulling 579W from the wall, then the system would be pulling 492W from the PSU.  Of course, these are unrealistically high values, so I believe it's possible that 425-450W would be more realistic.

 

This calculation is assuming that the CPU is under full load at the same time as the two 7950s.

 

The CX600's +12V capacity is 522W, and so I guess it's possible that the limit is either being reached or exceeded a little.  Except, this is a continuous capacity, so I am a little bit more inclined to say that it's just instability.

 

However, the CX600 V2's +12V capacity is only 480W, so if the CX600 V2 is being used here, then perhaps it's more likely that maybe it doesn't have enough power.

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post #5 of 8

must take into account that voltage regulation starts losing efficiency the closer the load is to max rating typically... 

 

**Measure the +12v input on your GPU's at the PCI-E plugs.. under idle and load. If your PSU is to blame, you should see a low input value.. like 11.7v .. compared to a healthier 12.1 or 12.2v

post #6 of 8
I have read that Corsair outsources some of their psu series from Seasonic. Well, it so happens to be that Seasonic has a guideline which explains the viable performance of their psu's are 80% of total output at a temperature above 50c celcius.
As a result, I would advise for more airflow in your installation NO MATTER THE COST. (En taro Tassadar.)
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post #7 of 8
Quote:
Originally Posted by mtcn77 View Post

I have read that Corsair outsources some of their psu series from Seasonic. Well, it so happens to be that Seasonic has a guideline which explains the viable performance of their psu's are 80% of total output at a temperature above 50c celcius.
As a result, I would advise for more airflow in your installation NO MATTER THE COST. (En taro Tassadar.)

 

True, but the GS600 is a Channel Well Technology PSH-II, and the HX1000 is a Channel Well Technology PUC.

 

I'm cheating by using this:

 

http://www.overclock.net/t/654983/on-corsair-psus

 

:)

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Hard DriveHard DriveHard DriveOptical Drive
250 GB Samsung 840 EVO (C:\) 250 GB Samsung 840 EVO (D:\) 150 GB WD VelociRaptor Samsung SH-S243N 24x DVD Burner 
Optical DriveCoolingOSMonitor
Samsung SH-S203N 20X DVD Burner Thermaltake Frio Win 7 Home Premium x64 SP1 Retail AOC G2460PG (24" 1920 x 1080 144Hz G-SYNC) 
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Filco Majestouch 104-key Cherry MX Blues w/NKRO Corsair HX650 (Bronze, ordered on 12-12-2009) CM 690 Intellimouse Optical (1.1A) 1000Hz polling rate 
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post #8 of 8
Thread Starter 
I have definitely upgraded the airflow almost to the max to max sure that it is cooling properly. CM MegaFlow 200 front intake at full speed, a CM R4 rear exhaust at full speed, the two top exhaust fans and 2000 rpm side intake fan + the push pull on the hyper 220.

It seems to do just fine at 1000/1425 @ 1.15 with pretty good frame rates.
The two cards are different revisions even though they were purchased at the same time. One has the old bios on it and the other has the latest for that revision so that might also effect the stability.
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