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Author Topic: Using unpowered PCI-E 1x extender for 5970 possible?  (Read 3719 times)
chungenhung
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February 06, 2012, 08:49:36 PM
 #1

Is it possible to power a 5970 via just the 8+6PIN and not from the PCI-E slot? Such as using a un-powered PCI-E 1x extender. Would the 8+6PIN from the power supply provide enough power? I know it does for 5870, but not sure about 5970.
If it is possible for 5870, I am also assuming it would be possible with 7970.
Did some research, the 6pin can carry 75W, and the 8pin can carry 150W.
However, gauge 18 wire can handle way higher wattage than the specification of 150W.
So if one were to have a 5970 300W TDP card, it is theoretically possible to pull all 300 watt from the 6+8pin cables only.

Anyone have any experience?

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ummas
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February 06, 2012, 09:29:10 PM
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I was running it so.
But i would not recomend that for a long period of time.
Beter safe than sorry
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February 06, 2012, 09:47:19 PM
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You can't control where the card pulls power.  Technically the spec allows up to 75W from the PCIe slot however I have found the 5970 only pulls about 30W from the slot under full load.  I measured 260W at an aggressive overclock. 

It was:
PCIe slot: 30W
6 pin connector: 80W (yeah technically overspec)
8 pin connector: 150W

Even if you don't use a powered extender it still draws power from the slot.  If you use 1 to 3 5970 then you are drawing <90W from all PCIe slots.  Most boards can handle that fine. 4 is probably pushing it.  It may depend on the board.
malevolent
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February 06, 2012, 09:54:47 PM
 #4

PCIe slot: 30W


Was that max. you got for PCI-E? I can't really measure it myself but someone on the forum mentioned it only pulls up to 75W for a few seconds after pressing power_sw (to start the GPU) and I'm not sure to what extent it's true.
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Gerald Davis


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February 06, 2012, 09:58:14 PM
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I never detected a 75W surge but that doesn't mean it can never happen.   I think the "it pulls 75W" nonsense comes from the fact that the spec allows UP TO 75W. Some cards might pull 75W (probably ones which lack supplemental power connectors) but the 5970 doesn't.  The max I got was ~30W and that didn't occur until after mining has started.  I measured it for about a minute or so and it remained in the 27W-30W range.

Actually at startup it only pulled about 12W from the slot.  By the PCIe spec only PCIe 16x devices can pull >25W only once they have been identified (via bus interrogation) as high current device.  No device is allowed to pull >10W until identified.  I guess the card with 12W @ the slot on startup was slightly over spec.
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Gerald Davis


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February 06, 2012, 10:10:30 PM
 #6

Quote
Did some research, the 6pin can carry 75W, and the 8pin can carry 150W.
However, gauge 18 wire can handle way higher wattage than the specification of 150W.
So if one were to have a 5970 300W TDP card, it is theoretically possible to pull all 300 watt from the 6+8pin cables only.

I missed this the first time around.  While the PHYSICAL connector can support >300W just with a single PCIe connector the SPEC doesn't.

A little bit of history on how AMD/NVidia totally fucked everything up.

So first video cards were powered only by the bus.  Obviously not enough power so in the early days prior to ATX V2.1 (June 2005) both companies used Molex connectors or other propreitary connectors to supplement the bus.

They (AMD/Intel/NVidia/PSU suppliers) agreed to update the standard.  They came up w/ PCIe 6 pin connector.  Physically it can provide about 350W safely.  However AMD/NVidia said.  Wow.  No way we need 350W+75W for a card.  Lets make it 75W.  So the spec was ratified and power supply suppliers built PSU based on that assumption.  There are PSU designed under the assumption that no device will EVER pull more than 75W from a PCIE 6 pin connector.  Once the first PSU was built based on that inadequate spec we were forever fucked because of backwards compatibility.

Well it took about 9 months and AMD/NVidia needed more power.  The 8 pin connector has the same number of 12V wires as 6 pin connector.  This tends to confuse people.  The spec has an "interrogate" ground check in it now.  A card attempts to check for ground (ground-sense) on pin #8.  If it finds a ground it assumes it can use 150W.  If it doesn't then it must accept it can only pull 75W from that connector.  Both connector are capable of 300W+ so the 75W or 150W limit is just based on the spec.

AMD will never release a card which pulls 300W from a connector because if they did and it was hooked up so an older "compliant PSU" it would be a lawsuit waiting to happen.

Sadly the spec could have been a lot better had AMD/NVidia been forward looking.  
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February 07, 2012, 01:02:15 AM
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I never detected a 75W surge.   I think the "it pulls 75W nonsense" comes from the fact that the spec allows UP TO 75W. Some cards might pull 75W (probably ones with either supplemental power connector) but the 5970 doesn't.  The max I got was ~30W and that only occured a few seconds after mining started.  I measured it for about a minute or so and it remained in the 27W-30W range.

Actually at startup it only pulled about 12W from the slot.  By the PCIe spec only PCIe 16x devices can pull >25W only once they have been identified (via bus interrogation) as high current device.  No device is allowed to pull >10W until identified.  I guess the card with 12W @ the slot @ startup was slightly over spec.
True for mining. Now measure slot 12V current while actually doing something that gives the memory a workout, you'll be surprised Wink

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February 07, 2012, 06:18:59 AM
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I never detected a 75W surge.   I think the "it pulls 75W nonsense" comes from the fact that the spec allows UP TO 75W. Some cards might pull 75W (probably ones with either supplemental power connector) but the 5970 doesn't.  The max I got was ~30W and that only occured a few seconds after mining started.  I measured it for about a minute or so and it remained in the 27W-30W range.

Actually at startup it only pulled about 12W from the slot.  By the PCIe spec only PCIe 16x devices can pull >25W only once they have been identified (via bus interrogation) as high current device.  No device is allowed to pull >10W until identified.  I guess the card with 12W @ the slot @ startup was slightly over spec.
True for mining. Now measure slot 12V current while actually doing something that gives the memory a workout, you'll be surprised Wink
Nice reading! Thanks.

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