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Author Topic: How many 6970's per 1500W PS  (Read 1923 times)
MadHacker
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September 28, 2011, 11:16:11 PM
 #1

I currently have 4 6970 cards to 1500w Strider power supply...
and was wondering if i could add a 5'th one.
or will it pull to much power?

MB:P8P67 WS
CPU:i3-2100
and 1 harddrive.

thoughts?
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cicada
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September 29, 2011, 03:46:35 AM
 #2

Ah, multi-rail fail.  Appears that PSU has 8 12V rails, each capable of ~300W.  So 1 card per rail (~190W each).

I'd wager you've got 1 rail dedicated to the CPU 4/8pin, 1 to the 24pin ATX, and the other 6 divvied up between peripheral connectors.

As long as you can balance the rails properly, yes.  5 6970s is going to be ~1000W.

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Gerald Davis


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September 29, 2011, 03:59:54 AM
 #3

Buy a kill-a-watt.  Every miner should have one.

I don't think you will get another 5970 though.

A 3x 5970 system draws 945W @ the wall.  Overclocked they draw 1020.

I would guess 4x 5970 are drawing.  ~1100W maybe 1200W overclocked.  Unless you want efficiency to fall off a cliff (waste money, and more heat) you don't want to load powersupply more than 80%.  1500W @ 80% = 1200W.  You likely could squeeze one more in but the PS will be running very hot and inefficient.
cicada
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September 29, 2011, 04:14:07 AM
 #4

I currently have 4 6970 cards to 1500w Strider power supply...
and was wondering if i could add a 5'th one.

I don't think you will get another 5970 though.

I'd wager you're right Tongue

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MadHacker
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September 29, 2011, 05:16:45 AM
 #5

Buy a kill-a-watt.  Every miner should have one.

I don't think you will get another 5970 though.

A 3x 5970 system draws 945W @ the wall.  Overclocked they draw 1020.

I would guess 4x 5970 are drawing.  ~1100W maybe 1200W overclocked.  Unless you want efficiency to fall off a cliff (waste money, and more heat) you don't want to load powersupply more than 80%.  1500W @ 80% = 1200W.  You likely could squeeze one more in but the PS will be running very hot and inefficient.
ya i'm pulling between 1100 to 1200w
i have a kill-a-watt... clone
just hopefull i guess..

i have a spare 720w powersupply....
but only has 6 pin PCIe connectors.
guess I can hook them up to the 6 Pin connectors on 2 video cards and use the 8 pin connectors from the 1500W PS in the 8 pin connectors...


thanks for the replies
cicada
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September 29, 2011, 05:20:37 AM
 #6

I'm a little confused..  if you really meant 5970 you might want to edit the topic and OP Wink

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MadHacker
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September 29, 2011, 05:25:42 AM
 #7

I'm a little confused..  if you really meant 5970 you might want to edit the topic and OP Wink
myself i never said i had a 5970... nope don't have any
i have 8 6970's total...
just trying to cram more onto a single motherboard...
saves on power in the long run... i think
worldinacoin
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September 29, 2011, 05:27:18 AM
 #8

I put in 3, as much as I am tempted to add in another, I find it hard to dissipate the heat and also worry that any sudden spike will kill the PSU.  Better be safe than sorry.
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September 29, 2011, 05:42:35 AM
 #9

I recommend you get a PSU with a single 12V rail.
MadHacker
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September 29, 2011, 02:59:52 PM
 #10

I put in 3, as much as I am tempted to add in another, I find it hard to dissipate the heat and also worry that any sudden spike will kill the PSU.  Better be safe than sorry.

I have all my video cards in a mining rack.
heat isn't a problem. also this weekend i plan to watercool all my 6970 video cards and dump the heat into my cold air vent... warm the house.

I recommend you get a PSU with a single 12V rail.
I don't realy want to shell out more money for another powersupply.
can't justify the extra cost.
what i have works... i just want it to work better, more effeciently.
cicada
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September 29, 2011, 03:07:51 PM
 #11

ya i'm pulling between 1100 to 1200w

That seems like a lot for 4 6970s.. I've got a rig with 4 6950s that only pulls about 800W, and they're basically the same chipset.  The 6970 has a slightly higher stock voltage (1.175V), but it doesn't seem like enough to account for a 300W difference..

Have you over-volted these cards further?  Any other high-power components in the rig?

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MadHacker
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September 29, 2011, 03:14:43 PM
 #12

ya i'm pulling between 1100 to 1200w

That seems like a lot for 4 6970s.. I've got a rig with 4 6950s that only pulls about 800W, and they're basically the same chipset.  The 6970 has a slightly higher stock voltage (1.175V), but it doesn't seem like enough to account for a 300W difference..

Have you over-volted these cards further?  Any other high-power components in the rig?
I don't over volt them
and other then MB, CPU ram and harddrive.
no extra components.

I have them overclocked to 950-960 and ram set at 240
fans running at 100%

one of the reasons i want to watercool them is to get them quiet.
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Gerald Davis


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September 29, 2011, 09:56:12 PM
 #13

ya i'm pulling between 1100 to 1200w

That seems like a lot for 4 6970s.. I've got a rig with 4 6950s that only pulls about 800W, and they're basically the same chipset.  The 6970 has a slightly higher stock voltage (1.175V), but it doesn't seem like enough to account for a 300W difference..

Three potential sources of higher load.

Power supply.  One that is 75% efficient vs 90% efficient will add 100W to 150W additional AC on the same 800W DC load.

Memory Clock.  At full clock these memory on these cards suck down some juice.  In my experience downclocking from 1375MHz to 300MHz saves 30W a card. 

On a quad core if you have the 100% CPU bug you will be burning 10W-30W extra.  Setting affinity to a single core can reduce that 70%.
MadHacker
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September 29, 2011, 10:44:57 PM
 #14

ya i'm pulling between 1100 to 1200w

That seems like a lot for 4 6970s.. I've got a rig with 4 6950s that only pulls about 800W, and they're basically the same chipset.  The 6970 has a slightly higher stock voltage (1.175V), but it doesn't seem like enough to account for a 300W difference..

Three potential sources of higher load.

Power supply.  One that is 75% efficient vs 90% efficient will add 100W to 150W additional AC on the same 800W DC load.

Memory Clock.  At full clock these memory on these cards suck down some juice.  In my experience downclocking from 1375MHz to 300MHz saves 30W a card. 

On a quad core if you have the 100% CPU bug you will be burning 10W-30W extra.  Setting affinity to a single core can reduce that 70%.


PowerSupply is a silverstone strider 1500W 80 plus silver.
all GPUs have memory clocked down to 250 mhz
affinity is set to first core, done in batch file
DeathAndTaxes
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Gerald Davis


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September 29, 2011, 10:48:39 PM
 #15

PowerSupply is a silverstone strider 1500W 80 plus silver.
all GPUs have memory clocked down to 250 mhz
affinity is set to first core, done in batch file

Well that is just WEIRD!  Widely divergent power draws with roughly the same settings and equipment.
RandyFolds
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September 29, 2011, 11:27:55 PM
 #16


I have them overclocked to 950-960 and ram set at 240
fans running at 100%

one of the reasons i want to watercool them is to get them quiet.

Are you sure everyone is talking about the same thing here?

My MSI Reference 6970s can NOT hit 950mhz stable without overvolting, and their stock clock is like, 880 IIRC. They can't even hit 920mhz at stock voltage. I get a solid 400mh/s at 910mhz.

Also, downclocking the memory below 300mhz usually always causes hard-lock. How in the hell did you manage to get it down to 240?

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cicada
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September 29, 2011, 11:28:57 PM
 #17

Weird indeed. Mad, if you have a voltmeter handy I would check that you're not getting bad voltage sag on any of your rails.  Also if your kill-a-watt lookalike shows volt readings on your mains, make sure that hasn't dipped significantly.  Anything < 110VAC is bad news for your PSU.

It really sounds like you've got some phantom draw or ineffeciency somewhere.. a whole 6970 could fit in the difference between our rigs.

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MadHacker
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September 29, 2011, 11:45:41 PM
 #18


I have them overclocked to 950-960 and ram set at 240
fans running at 100%

one of the reasons i want to watercool them is to get them quiet.

Are you sure everyone is talking about the same thing here?

My MSI Reference 6970s can NOT hit 950mhz stable without overvolting, and their stock clock is like, 880 IIRC. They can't even hit 920mhz at stock voltage. I get a solid 400mh/s at 910mhz.

Also, downclocking the memory below 300mhz usually always causes hard-lock. How in the hell did you manage to get it down to 240?

I'm using Clocktweak to set my Core to 960, Mem to 250 and Power to +20
i guess setting power to +20 is over volting... but i'm not manualy setting the voltage.
I get steady 429-430 Mh/s

Weird indeed. Mad, if you have a voltmeter handy I would check that you're not getting bad voltage sag on any of your rails.  Also if your kill-a-watt lookalike shows volt readings on your mains, make sure that hasn't dipped significantly.  Anything < 110VAC is bad news for your PSU.

It really sounds like you've got some phantom draw or ineffeciency somewhere.. a whole 6970 could fit in the difference between our rigs.

from what i understand setting fans to 100% pulls a lot of power... read somewhere 20W? not sure.
also from my comments above setting Power to +20 may be pulling more power then expected. not sure there either.
as for line power... my UPS (in adjacent room) sais i'm getting 121v
I do have a volt meter and i will check voltages later. i suppose connecting it to any molex connector will tell me what the volts are.
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September 30, 2011, 01:06:57 AM
 #19

Mine is running at 400mhash/s with a temperature of 80 degree celsius, I fix the fan at 85%, seems to be running well all along.
MadHacker
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September 30, 2011, 01:20:09 AM
 #20

Mine is running at 400mhash/s with a temperature of 80 degree celsius, I fix the fan at 85%, seems to be running well all along.
what are your clock rates/power settings/voltage? as well as ambient temperature?
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