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Author Topic: 3x6990 system powers off with 6 GPUs active  (Read 1442 times)
Tril
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July 14, 2011, 06:06:10 PM
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I can run 5 GPUs all day long, but if I try mining on 6 GPUs, the system turns off in half an hour. The power LED blinks and case fans keep spinning, and I need to flip the power switch off and back on to get it to boot.  According to multiple places AX1200 and 890FXA-GD70 can handle 3x6990.  The GPU temperatures are always very good (under 85C). I have underclocked video RAM to 350MHz. The machine has a Sempron 145 CPU and one IDE hard drive. USB instead of IDE doesn't help. Do I need a PCI-E extender or is there an easier solution?
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Tril
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July 14, 2011, 06:57:31 PM
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I just changed the OC switches on all 3 cards from "2" to "1" and it turned off even faster.
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July 14, 2011, 07:49:12 PM
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In my opinion 1200W is not enough for your purpose. probably the PSU gets too hot because it's running at maximum load, don't forget that 1200W with 90% efficiency results in 1080W real usable power. even if 1 6990 with 2 GPUs uses only 346W, you would reach 1038W with 6 GPUs not even counting in the mainboard and cpu (appox. 80W) + cooling you have and hdd (1100W+)
5 GPUs result in round about 1000W overall use, which seems to be the limit for your PSU with 24/7 usage.

so, either get a 1250W enermax revolution85+ or something bigger or keep it running with 5 gpus.


edit: turning the switches from 2 to 1 (into OC mode?) drains even more power(~210W per GPU), which results in faster shutdown of the psu to prevent your personal computer-meltdown ;-)

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July 14, 2011, 09:34:54 PM
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If 1200W is not enough, how come these guys sell a 3x6990 rig with 1200W:

http://www.bitcoinrigs.com/products/Professional-Rig-2000.html

and why does this page have a pre-built 3x6990 system with 1200w:

https://en.bitcoin.it/wiki/Mining_rig#Three_ATI_6990s,_Approximately_2.1_Ghash/s

and why does this guy say it works too?

https://forum.bitcoin.org/index.php?topic=27963.0
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July 14, 2011, 10:58:21 PM
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some brands may perform better than others.

It is pitch black. You are likely to be eaten by a grue.

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July 15, 2011, 12:12:25 AM
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the last link says the guy took off the side panel and directed a box fan at it.
you now, a 120v fan probably 12 or 14 inches.

cooling the cards down will effectively reduce the load on the power supply.

which allows the supply to "handle" the 3 cards.

just one possible solution/scenario.

the answer to the original question is most certainly insufficient power availability.

good luck!

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July 15, 2011, 04:58:19 AM
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I disconnected the 3 HAF-X case fans, and the system has remained stable with all 6 GPUs running for close to an hour so far.  Both sides of the case are off, with no external fans needed yet (it's pretty cool today).
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July 15, 2011, 05:34:38 AM
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if it's working with everyone else, you probably got a "monday PSU" Wink )

but it's the power, you proved it with the fans (also I would not recommend to disconnect cooling parts Smiley )

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July 15, 2011, 08:09:34 PM
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I can run 5 GPUs all day long, but if I try mining on 6 GPUs, the system turns off in half an hour. The power LED blinks and case fans keep spinning, and I need to flip the power switch off and back on to get it to boot.  According to multiple places AX1200 and 890FXA-GD70 can handle 3x6990.  The GPU temperatures are always very good (under 85C). I have underclocked video RAM to 350MHz. The machine has a Sempron 145 CPU and one IDE hard drive. USB instead of IDE doesn't help. Do I need a PCI-E extender or is there an easier solution?


Based on available data, a single 6990 draw close to 400W, mainly on the +12V at full load. With 3 cards, you're looking at 1200W which is the rated limit for the AX-1200. Add in the power required by the motherboard, CPU and such, not much compared to the GPU but as you discovered, just enough to tip the over-current protection. Downclocking the ram chips don't really help much as they generally consume about 1~2 watts per chip, halving that makes very little difference.

It's usually not a good idea to push a PSU at close to 100% for extended period of time, dies faster and therefore reduce your real income from mining. Getting a "cheap" auxilliary 450W PSU just to connect a couple of those +12V connectors may be a better long term solution.

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July 15, 2011, 08:13:27 PM
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In my opinion 1200W is not enough for your purpose. probably the PSU gets too hot because it's running at maximum load, don't forget that 1200W with 90% efficiency results in 1080W real usable power.

Hope you won't mind me correcting you on this. A 1200W PSU with 90% efficiency will (or should) provide 1200W of real usable power. It just takes about close to 1400W of AC power to provide that 1200W. So the difference between a 85% efficient 1200W PSU and a 90% efficient 1200W is really in the cost of running the same load, but they will both be able to (assuming real 1200W capable PSU) drive a 1200W load.

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July 15, 2011, 08:42:49 PM
 #11

In my opinion 1200W is not enough for your purpose. probably the PSU gets too hot because it's running at maximum load, don't forget that 1200W with 90% efficiency results in 1080W real usable power.

Hope you won't mind me correcting you on this. A 1200W PSU with 90% efficiency will (or should) provide 1200W of real usable power. It just takes about close to 1400W of AC power to provide that 1200W. So the difference between a 85% efficient 1200W PSU and a 90% efficient 1200W is really in the cost of running the same load, but they will both be able to (assuming real 1200W capable PSU) drive a 1200W load.


Sure not, thanks for that info! Was never sure if it means 1200w = 90% or 1200w = 100% Smiley

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July 15, 2011, 09:34:39 PM
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In my opinion 1200W is not enough for your purpose. probably the PSU gets too hot because it's running at maximum load, don't forget that 1200W with 90% efficiency results in 1080W real usable power.

Hope you won't mind me correcting you on this. A 1200W PSU with 90% efficiency will (or should) provide 1200W of real usable power. It just takes about close to 1400W of AC power to provide that 1200W. So the difference between a 85% efficient 1200W PSU and a 90% efficient 1200W is really in the cost of running the same load, but they will both be able to (assuming real 1200W capable PSU) drive a 1200W load.

nah, it's better marketing to say its power consumption, rather than its power output.

It is pitch black. You are likely to be eaten by a grue.

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