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Author Topic: powered pci-e extenders are largely unnecessary  (Read 10262 times)
eroxors
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May 09, 2013, 02:43:54 AM
 #1

I see so many topics regarding powered extenders and their importance, but from my experience, they are a waste of time/money.

I only have anecdotal evidence, but I have used dozens of cheap, unpowered extenders with a multitude of platforms/gpus and have never had any issues, even when doubled up (2 extenders chained) or used with a pci to pci-e adapter card (only 35 watts of power.)

Maybe I'm just lucky? Maybe component quality matters? (ps/mobo)

Maybe a smart person can explain why my 30+ card setup has no issues with unpowered risers but others do?

Just my 2 cents.


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May 09, 2013, 03:25:57 AM
 #2

How many cards per rig ?

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May 09, 2013, 03:30:10 AM
 #3

Yeah, what is your setup, and brand/model of mobo, video card, power supplies?
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May 09, 2013, 03:53:01 AM
 #4

I have multiple rigs with 4 x 6870 and know I don't need powered extenders.  Having said that you're a fool if you're trying to run 5970, 6990 or 7970s in a 4+ configuration off a board without additional power.  You might be able to get away with it in a cold climate but in anyplace warm you'll be drawing more power off each card.

There are numerous posts from 2011/2012 showing dead or damaged boards/connectors.
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May 09, 2013, 03:59:44 AM
 #5

I see so many topics regarding powered extenders and their importance, but from my experience, they are a waste of time/money.
^This.  I've thought a time or two about creating this very topic.  I run 258 GPUs.  These range from 2 cards per board all of the way up to 6 cards per board.  I also have some machines with 8 GPUs (4 dual GPU cards).  NONE of these machines have powered risers and I've been mining for almost two years.

I think the people who are burning out their boards are either running many cards with *significant* overclocks/overvoltage, or these people didn't have good connections to their card(s) (which drives up resistance, thus driving up the current needed).

I have 7 different models of motherboards being used, also...

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eroxors
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May 09, 2013, 03:59:57 AM
 #6

How many cards per rig ?

4/5 cards mixed
5770
5850
5870
6750
6850
6950
6970
7950

boards
Foxconn Destroyer
Asus P5GD1
Intel DG33FB

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May 09, 2013, 04:01:53 AM
 #7

Having said that you're a fool if you're trying to run 5970, 6990 or 7970s in a 4+ configuration off a board without additional power.

Wrong.  In fact, both of the dual GPU cards you mentioned draw *less* current through the PCI-E slot than their single GPU counterparts.  The 7970s don't draw much from the PCI-E connector either.

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eroxors
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May 09, 2013, 04:02:12 AM
 #8


I think the people who are burning out their boards are either running many cards with *significant* overclocks/overvoltage, or these people didn't have good connections to their card(s) (which drives up resistance, thus driving up the current needed).


None of my cards are overvolted, all are either undervolted or stock. All are overclocked.

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May 09, 2013, 04:03:32 AM
 #9

None of my cards are overvolted, all are either undervolted or stock. All are overclocked.

Same.

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May 09, 2013, 04:20:44 AM
 #10

How many PCIe 1x do you use per board? Do you use scrypt based coins ? Do you have 5870 ?

PCIe 1x doesn't support as much power as PCIe 16x, 5870 draw power from the PCIe connector for the RAM and scrypt-based coins are RAM intensive. I have a board that ran for more than a year mining bitcoins with 5x 5870, 4 of them connected to PCIe 1x connectors. It died in two weeks mining litecoins (the 12V power lines burnt through the PCB).

I can feel the difference between sha256d and scrypt just by touching the PCB on another board of the same model. Replacing extenders with powered ones gradually decreases the temperature.

I have the same experience with 5970s: they don't seem to require as much power from the PCIe connector than the 5870s.

So powered pci-e extenders aren't largely unnecessary: the combination of motherboard model, actual cards used, opencl kernel used, ram and gpu settings makes it impossible to predict what will happen without powered extenders unless you already tried the same combination. If it worked for you without them, consider yourself lucky.

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eroxors
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May 09, 2013, 04:46:35 AM
 #11

How many PCIe 1x do you use per board? Do you use scrypt based coins ? Do you have 5870 ?

PCIe 1x doesn't support as much power as PCIe 16x, 5870 draw power from the PCIe connector for the RAM and scrypt-based coins are RAM intensive. I have a board that ran for more than a year mining bitcoins with 5x 5870, 4 of them connected to PCIe 1x connectors. It died in two weeks mining litecoins (the 12V power lines burnt through the PCB).

I can feel the difference between sha256d and scrypt just by touching the PCB on another board of the same model. Replacing extenders with powered ones gradually decreases the temperature.

I have the same experience with 5970s: they don't seem to require as much power from the PCIe connector than the 5870s.

So powered pci-e extenders aren't largely unnecessary: the combination of motherboard model, actual cards used, opencl kernel used, ram and gpu settings makes it impossible to predict what will happen without powered extenders unless you already tried the same combination. If it worked for you without them, consider yourself lucky.

3x PCIe 1x per board, typically... yes, I use 5870s, litecoin on a few but not extensively tested

Good idea testing the PCBs, I'll try that out.

Prediction: you will not hurt anything using unpowered risers as long as you don't overvolt it or damage the slot in some way

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May 09, 2013, 04:48:15 AM
 #12

Having said that you're a fool if you're trying to run 5970, 6990 or 7970s in a 4+ configuration off a board without additional power.

Wrong.  In fact, both of the dual GPU cards you mentioned draw *less* current through the PCI-E slot than their single GPU counterparts.  The 7970s don't draw much from the PCI-E connector either.

I don't want to get into a shouting contest but I think it suffices to say YMMV.  If I have my 4x6870 rig running in 40F ambient I pull almost a whole 80w less from the wall than I do if I am running in an ambient of 95F.  After 2 years of mining I'm starting to see some extenders go bad as the temps are really heating up here in SoCal.

So a blanket statement of you DO/DON'T need powered extenders is silly. Some people are able to run their cards in a milk crate like TacoTime.  I tried that setup and most of the cards went to thermal throttle withing 3 minutes.

If you are running overclocks (and I don't know too many people not running OC) with powerful cards you could benefit from powered risers.  Are they necessary - well than depends on each individual application.  The thread title says they are largely unnecessary.  I don't use powered risers because I can't have a density of more than 600-700w on a rig without heat problems.  People who can pull 1100 watts off a PSU probably should consider using one - IMHO.
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May 09, 2013, 05:17:57 AM
 #13

I don't want to get into a shouting contest but I think it suffices to say YMMV.
Oh, agreed.  Again, one could come up with a configuration where they draw too much from the PCI-E bus.  You'd just really need to be pushing a bunch of single GPU cards very hard.  I just think that nearly everyone seems to tout powered risers as an absolute requirement to GPU mining for some reason.  I'd argue that unless you're basically trying to kill your cards, they aren't required.  I have hundreds of non-powered risers.  It's not just good luck.  It's something that can be measured and quantified.


If I have my 4x6870 rig running in 40F ambient I pull almost a whole 80w less from the wall than I do if I am running in an ambient of 95F.  After 2 years of mining I'm starting to see some extenders go bad as the temps are really heating up here in SoCal.
Correct.  GPUs will draw less power the cooler they run (less leakage).


So a blanket statement of you DO/DON'T need powered extenders is silly.
He said "largely".   Cheesy


People who can pull 1100 watts off a PSU probably should consider using one - IMHO.
I've got about 42 rigs that would fall into that category, so it's not quite that simple (again, many card designs draw almost all of their power from the 6/8 pin PCI-E connectors).

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May 09, 2013, 05:20:30 AM
 #14

I see so many topics regarding powered extenders and their importance, but from my experience, they are a waste of time/money.
^This.  I've thought a time or two about creating this very topic.  I run 258 GPUs.  These range from 2 cards per board all of the way up to 6 cards per board.  I also have some machines with 8 GPUs (4 dual GPU cards).  NONE of these machines have powered risers and I've been mining for almost two years.

I think the people who are burning out their boards are either running many cards with *significant* overclocks/overvoltage, or these people didn't have good connections to their card(s) (which drives up resistance, thus driving up the current needed).

I have 7 different models of motherboards being used, also...

I have 4 card setups that have burned through pin 3 ATX connector on the mobo from the PSU

After 2 PSU's I use powered risers ...everything is LTC

Even when i started out i was buying old cards from forum members (noob mistake) ...they would mine BTC all day all night but would crash and burn even trying to mine scrypt

Even with 3 cards on risers and one on the board they will run for about 2-4 weeks and then cards start to disappear (i.e u will drop a card and suddenly its a 3 card rig ) you either have to bring another card back down to the board which starts to run into heat issues

So 250 GPU's is impressive ...but i think we can say we are talking about BTC only...either that or my 70 gpu farm is totally fucked in my approach

All new vtx 6970's (2 months old)
All New Sapphire 7950 vapor -x (2 weeks old)
All New MSI 990fxa gd 80 v2

I would love it if i was wrong but so far powered risers seem to be the solution ...I only got them 5 days ago and so far they have stopped cards falling off a rig and no more toasted PSU's

Intrested to hear any advice to the contrary

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May 09, 2013, 06:35:42 AM
 #15

I see so many topics regarding powered extenders and their importance, but from my experience, they are a waste of time/money.
^This.  I've thought a time or two about creating this very topic.  I run 258 GPUs.  These range from 2 cards per board all of the way up to 6 cards per board.  I also have some machines with 8 GPUs (4 dual GPU cards).  NONE of these machines have powered risers and I've been mining for almost two years.

I think the people who are burning out their boards are either running many cards with *significant* overclocks/overvoltage, or these people didn't have good connections to their card(s) (which drives up resistance, thus driving up the current needed).

I have 7 different models of motherboards being used, also...

I have 4 card setups that have burned through pin 3 ATX connector on the mobo from the PSU

After 2 PSU's I use powered risers ...everything is LTC

Even when i started out i was buying old cards from forum members (noob mistake) ...they would mine BTC all day all night but would crash and burn even trying to mine scrypt

Even with 3 cards on risers and one on the board they will run for about 2-4 weeks and then cards start to disappear (i.e u will drop a card and suddenly its a 3 card rig ) you either have to bring another card back down to the board which starts to run into heat issues

So 250 GPU's is impressive ...but i think we can say we are talking about BTC only...either that or my 70 gpu farm is totally fucked in my approach

All new vtx 6970's (2 months old)
All New Sapphire 7950 vapor -x (2 weeks old)
All New MSI 990fxa gd 80 v2

I would love it if i was wrong but so far powered risers seem to be the solution ...I only got them 5 days ago and so far they have stopped cards falling off a rig and no more toasted PSU's

Intrested to hear any advice to the contrary

Interesting... I wonder if the memory subsystem is powered by the PCIe bus on all AMD cards or just the midrange.

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May 09, 2013, 07:05:26 AM
Last edit: May 09, 2013, 09:24:45 AM by mrb
 #16

Time to clear up the many wrong statements that people are making in this thread. I am the person who made the first powered PCIe extender and who documented why this is necessary: http://blog.zorinaq.com/?e=44

Firstly, the current drawn through the PCIe slot vary a lot depending on the card. Dual-GPU cards usually draw more than single-GPU ones (contrary to what someone said). Here are some of my own measurements with a clamp meter around the 12V lines of a PCIe extender, while Bitcoin mining:

HD 6990: 4.2 A
HD 5970: 4.1 A
HD 5870: 3.2 A
HD 6950: 2.5 A
HD 7970: 0.9 A

So for example the 7970 (and probably most other 7xxx series cards, but I have not tested them) draws so little power that they pretty much don't need powered extenders.

Also, eroxors, most of your cards are pretty low-end/mid-end. They likely all draw less than 3 Amp or so because your most power-consuming one seems to be the HD 5870 (3.2 A through the slot). Even if you had 4 of these cards, that's only 12.8 Amp total, so only 6.4 Amp per 12V wire of your 24-pin ATX adapter.

But most importantly, whether the 24-pin ATX connector overheats or not depends a lot on whether the Molex Mini-Fit Jr. pins in the PSU 24-pin plug have a single or double spring. You can tell by removing the pin from the plastic housing and seeing if it has one or two pairs of "dots" at the end. This one has two: http://www.alliedelec.com/images/products/Small/70090646.jpg The single spring pins (typically used by inexpensive PSUs) have a higher (edit: electrical) resistance and are more prone to causing the connector to burn out over time.

For example, in my farm of 4x5970 and 3x6990 machines from the old days, I noticed that upgrading from single-spring pins to double-spring pins pretty much made powered extenders unnecessary.

Finally, eroxors, you are right that the memory subsystem of Radeon cards (at least the 5xxx I tested years ago) is powered through the slot, not through the 6-pin or 8-pin power extenders. So Litecoin miners need powered extenders more than Bitcoin miners (at least for 5xxx and 6xxx cards, again the 7xxx series seems to draw so little from the slot, that powered extenders may not be necessary).
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May 09, 2013, 07:18:42 AM
 #17

Time to clear up the many wrong statements that people are making in this thread. I am the person who made the first powered PCIe extender and who documented why this is necessary: http://blog.zorinaq.com/?e=44

Firstly, the current drawn through the PCIe slot vary a lot depending on the card. Dual-GPU cards usually draw more than single-GPU ones (contrary to what someone said). Here are some of my own measurements with a clamp meter around the 12V lines of a PCIe extender, while Bitcoin mining:

HD 6990: 4.2 A
HD 5970: 4.1 A
HD 5870: 3.2 A
HD 6950: 2.5 A
HD 7970: 0.9 A

So for example the 7970 (and probably most other 7xxx series cards, but I have not tested them) draws so little power that they pretty much don't need powered extenders.

Also, eroxors, most of your cards are pretty low-end/mid-end. They likely all draw less than 3 Amp or so because your most power-consuming one seems to be the HD 5870 (3.2 A through the slot). Even if you had 4 of these cards, that's only 12.8 Amp total, so only 6.4 Amp per 12V wire of your 24-pin ATX adapter.

But most importantly, whether the 24-pin ATX connector overheats or not depends a lot on whether the Molex Mini-Fit Jr. pins in the PSU 24-pin plug have a single or double spring. You can tell by removing the pin from the plastic housing and seeing if it has one or two pairs of "dots" at the end. This one has two: http://www.alliedelec.com/images/products/Small/70090646.jpg The single spring pins (typically used by inexpensive PSUs) have a higher resistance and are more prone to causing the connector to burn out over time.

For example, in my farm of 4x5970 and 3x6990 machines from the old days, I noticed that upgrading from single-spring pins to double-spring pins pretty much made powered extenders unnecessary.

Finally, eroxors, you are right that the memory subsystem of Radeon cards (at least the 5xxx I tested years ago) is powered through the slot, not through the 6-pin or 8-pin power extenders. So Litecoin miners need powered extenders more than Bitcoin miners (at least for 5xxx and 6xxx cards, again the 7xxx series seems to draw so little from the slot, that powered extenders may not be necessary).


This makes sense as to why so many cards burnt up back in 2010/2011 and you see so few (so far none in 2013) now a days (on Bitcointalk). How many amps is safe to pull through the MOBO? Since you seem to be the only person able to acquire these numbers would be cool if there was a sticky with yearly updated information Cheesy.

Im wondering if its safe to have 6 7950's on 1 board no powered extender.
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May 09, 2013, 10:34:02 AM
 #18


3x PCIe 1x per board, typically... yes, I use 5870s, litecoin on a few but not extensively tested

Good idea testing the PCBs, I'll try that out.

Prediction: you will not hurt anything using unpowered risers as long as you don't overvolt it or damage the slot in some way

Prediction fail: all my cards are undervolted and underclocked and I still fried one board and could verify the problem on another like I explained above.

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May 09, 2013, 10:48:04 AM
 #19

Time to clear up the many wrong statements that people are making in this thread. I am the person who made the first powered PCIe extender and who documented why this is necessary: http://blog.zorinaq.com/?e=44

Firstly, the current drawn through the PCIe slot vary a lot depending on the card. Dual-GPU cards usually draw more than single-GPU ones (contrary to what someone said).

That was me.

The amps you gave are probably for reference cards. I owned 2x Sapphire 4GB with the Accelero ventirad which have a custom PCB design and I'm pretty sure that they drew less power than a 5870: I could use a 6 GPU setup without problem (2x 5970 + 2x 5870) on a motherboard model where cards started disappearing from the system at 5x 5870 and eventually fried one board.

So my conclusion remains: unless you use always the same motherboard and card model, there's no way to predict what will happen.

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May 09, 2013, 11:35:24 AM
 #20

well if i didnt use powered risers my board would smoke in 2 minutes

5x7950 draw 15 A from the board which is build for maybe 7A MAX

with 4 cards and no powered risers it got so hot i was unable to touch it within 10 sec
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