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Author Topic: GUIDE - Make your own open frame rig.  (Read 137007 times)
DeathAndTaxes
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February 07, 2012, 05:13:50 PM
Last edit: February 07, 2012, 05:43:06 PM by DeathAndTaxes
 #61

The very thin wires in the extenders do cause a bit more current to flow because of their added resistance. Rule of thumb is any and all dual-gpu cards with extenders should have molexes as well, and single gpu cards should be OK without them. However, the 7970 is a beast that needs more power, so it might be a good idea to have molexes, especially if you plan on overclocking.

Actually the exact opposite is true.  The PCIe spec limits current on the slot to 75W but most high end cards (those with 8pin PCIe power connectors) draw much less.  I measured wattage at ~30W for a 5970 across the extender.  A 5870 draws ~30W too.

A 26 gauge wire can safely handle 2.2 amps of current.
A 30 gauge wire can safely handle 0.8 amps of current.

75W / 4 wires / 12V = 1.56A per wire.
30W / 4 wires / 12V = 0.625A per wire.

@ 30 gauge, 1 foot, 0.625A the voltage drop is 0.132V which is within ATX spec.

Personally I would stick w/ 26 gauge wiring and max length of 0.5 feet but even longer thinner wires should be fine.


So why is a single card worse?
          5970          5870
4 GPU  60W total   120W total
6 GPU  90W total   180W total
8 GPU 120W total   240W total

The issue isn't the extender but the aggregate draw on the MB.  To be compliant a PCIe 1x device must draw <25W and a PCIe 16x device which identifies it self as high current drawless than 75W.  All devices must draw less than 10W until interrogated by PCIe controller (at boot).

It really comes down to how aggressive MB designer was in power distribution.  Take a board with 4 PCIe x16 slots & 1 PCIe x1 slot.  By the spec the MB should be able to have 325W worth of compliant devices however to save money the design may assume that only 200W or 150W or only 100W will be drawn from the PCIe bus.  The higher the load the higher the risk you bump into the corners cut by MB supplier.

Granted the shouldn't cut corners but the number of users who pull 300W+ across the PCIe bus are in a rounding error and beefy power distribution is expensive for a low margin product.

It gets worse when using a board with lots of PCIe 1x slots.  The more PCIe 1x slots less power the designer may anticipate as a realistic scenario as PCIe 1x slots can only draw <25W and many (SATA controllers, USB3.0, sound cards, etc) draw <10W.  (This is why the presence detect pin needs to be shorted on some boards for stability).

Sadly a lot of boards are non-compliant and available power across PCIe bus isn't a stat provided.  This makes it hard to predict how much of a load the board can handle safely and efficiently. 

As a rule of thumb I would be more concerned about overloading the board when:
1) Using more than 4 SLOTS (# of GPUs doesn't matter).
2) The board has less PCIe 16x slots and more PCIe 1x slots.
3) The board only has a 4 pin 12V connector not the higher current 8 pin 12V connector indicating a possible design choice in power handling.
4) The board is more of a budget model (not crossfire certified, etc).
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February 07, 2012, 05:22:23 PM
 #62

do they diminish the power to the card?  i see that some come with molex connectors.

Not the card, but they protect the mother board from "blowing a fuse" because of too much power draw.  For instance if you have 4+ 7970s on one mobo you are drawing a great deal of power directly from the mother board.  The molex connector can give you power directly from the power supply; then only a little power actually comes from the mobo, only the data.
The very thin wires in the extenders do cause a bit more current to flow because of their added resistance. Rule of thumb is any and all dual-gpu cards with extenders should have molexes as well, and single gpu cards should be OK without them. However, the 7970 is a beast that needs more power, so it might be a good idea to have molexes, especially if you plan on overclocking.

is a 6970 a "dual gpu" card?  how do i tell?
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February 07, 2012, 05:29:32 PM
 #63

is a 6970 a "dual gpu" card?  how do i tell?

No.  You can tell by checking it in the OS (aticonfig, catalyst control center, device manager).  Dual GPU cards show up as 2 independent GPUs.

The 5970, 6990, and 7990 are dual GPUs.  So is the 4870x2 but nobody mines with that.

And yes AMD changing the naming scheme makes things confusing. Smiley
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February 07, 2012, 05:31:16 PM
 #64

The very thin wires in the extenders do cause a bit more current to flow because of their added resistance. Rule of thumb is any and all dual-gpu cards with extenders should have molexes as well, and single gpu cards should be OK without them. However, the 7970 is a beast that needs more power, so it might be a good idea to have molexes, especially if you plan on overclocking.

Actually the exact opposite is true.  The PCIe spec limits current on the slot to 75W but most high end cards (those with 8pin PCIe power connectors) draw much less.  I measured wattage at ~30W for a 5970 across the extender.  A 5870 draws ~30W too.

So why is a single card worse?
          5970          5870
4 GPU  60W total   120W total
6 GPU  90W total   180W total
8 GPU 120W total   240W total


To be compliant a PCIe 1x device must draw <25W and a PCIe 16x device which identifies it self as high current drawless than 75W.  All devices must draw less than 10W until interrogated by PCIe controller (at boot).

It really comes down to how aggressive MB designer was in power distribution.  Take a board with 4 PCIe x16 slots & 1 PCIe x1 slot.  By the spec that could draw 325W however to save money the design may assume that only 200W will be drawn from the PCIe bus.  If designed for 200W then either configuration would be fine up to 6 GPU but the 8 GPU 5970 setup is 20% overspec.  If they cut corners and design the power distribution to handle 150W safely well you likely are going to cause damage to the board if using more than 5 cards.

Granted the shouldn't cut corners but the number of users who pull 300W+ across the PCIe bus are in a rounding error and beefy power distribution is expensive.

It gets worse when using PCIe 1x slots.  The more PCIe 1x slots less power the designer may anticipate as a realistic scenario as PCIe 1x slots should draw <25W and many (SATA controllers, USB3.0, sound cards, etc) draw <10W.

Sadly lots of boards are non-compliant and available power across PCIe bus isn't a stat provided to it is hard to predict but as a rule of thumb I would be more cocerned about overloading the board when:
1) Using more than 4 SLOTS (# of GPUs doesn't matter).
2) The board has less PCIe 16x slots and more PCIe 1x slots.
3) The board only has a 4 pin 12V connector not the higher current 8 pin 12V connector.
4) The board is more of a budget model (not crossfire certified, etc).
Oho, interesting. So do 16x slots have additional power available? I thought all the power was in the 1x section, or at least that is how all the extenders that I have seen have ever been soldered. 5870s drawing more than 5970s? WTF. Maybe I need more powered molexes, or maybe I should just switch to 5970s Wink

Mining Rig Extraordinaire - the Trenton BPX6806 18-slot PCIe backplane [PICS] Dead project is dead, all hail the coming of the mighty ASIC!
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February 07, 2012, 05:56:49 PM
Last edit: February 07, 2012, 06:11:03 PM by DeathAndTaxes
 #65

Oho, interesting. So do 16x slots have additional power available? I thought all the power was in the 1x section, or at least that is how all the extenders that I have seen have ever been soldered.

All the power is actually is not in the  1x lane section.  There is a common section which handles various low level functions including power.

http://en.wikipedia.org/wiki/PCIe#Pinout

Pins 1-11 <- system interface (includes all power)
- notch -
Pins 12 - 18  <- Clock & Data Lane 0
- notch -
Pins 19 - 22  <- Data Lane 1
Pins 23 - 28  <- Data Lane 2
...
Pins 85 - 88  <- Data Lane 15

PCIe x1 slot - data lane #0 used.
PCIe x4 slot - data lane #0 to #3 used.
PCIe x8 slot - data lane #0 to #7 used.
PCIe x16 slot - data lane #0 to #15 used.

If you cover pins 19 to 88 on a Graphics card with electrical tape and insert it into a 16x slot the computer will see it as a 1x device.

The PCIe spec works like this (simplified):
At boot device must draw less than 10W from the bus.
Once interrogated by the controller any low-current device can draw up to 25W.
If the device identifies itself as high current it can draw up to 75W once interrogated by the controller (only PCIe 16x device are authorized).

On supplemental power connectors.  Device can draw 75W from a 6 pin or 8 pin connector.  Device must gound-sense pin #8 on 8 pin and detect a ground before drawing 150W.  If the device doesn't detect ground on pin 8 it must limit current to 75W. Yes this means if you connect pin #8 to the ground you could pull 150W from a 6 pin connector but if PSU can't handle it (in terms of amps on the rail) bad things will happen.  The PCIe 6pin connector can handle 150W just fine.  Technically it can handle 300W.  The extra pins on 8 pin connector aren't used for current.  They are just used for backwards compatibility.

Quote
5870s drawing more than 5970s? WTF. Maybe I need more powered molexes, or maybe I should just switch to 5970s
Remember that is just from the expansion slot.  Same number of slots ~= same power draw.  The 5970 simply uses half the number of slots putting less of a load on the PCIe bus (but more of a load on the PCIe 6/8 pin power connectors).
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February 07, 2012, 06:02:29 PM
 #66

do they diminish the power to the card?  i see that some come with molex connectors.

Not the card, but they protect the mother board from "blowing a fuse" because of too much power draw.  For instance if you have 4+ 7970s on one mobo you are drawing a great deal of power directly from the mother board.  The molex connector can give you power directly from the power supply; then only a little power actually comes from the mobo, only the data.
The very thin wires in the extenders do cause a bit more current to flow because of their added resistance. Rule of thumb is any and all dual-gpu cards with extenders should have molexes as well, and single gpu cards should be OK without them. However, the 7970 is a beast that needs more power, so it might be a good idea to have molexes, especially if you plan on overclocking.

is a 6970 a "dual gpu" card?  how do i tell?

6970 is a single GPU card.

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February 12, 2012, 08:28:08 PM
 #67

Started hastily with a lego rig that grew to this:



When I needed to cool the cards better (run the fans at a lower speed, spread out cards), I found some scrap wood and my trusty nail-gun and the result exceeded my usual "just enough" approach...



(the 5830 will be hooked up when the cablesaurus shipment arrives)
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February 20, 2012, 05:04:32 AM
 #68

nice work

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April 11, 2012, 12:04:11 PM
 #69

hmm, is that keyboard an IBM Model M 1391401?  or just a newer copy of one?

Back about 10 yrs ago, I bought half a dozen of 'em new in box off of eBay for ~$120 (all w/ 1989 manufacture date)

and I'm on my 2nd as of now...

Akakakakakak.
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April 18, 2012, 03:20:34 AM
 #70

hmm, is that keyboard an IBM Model M 1391401?  or just a newer copy of one?

Back about 10 yrs ago, I bought half a dozen of 'em new in box off of eBay for ~$120 (all w/ 1989 manufacture date)

and I'm on my 2nd as of now...

I have an old circa 94 IBM keyboard that I used to use for my mining rigs. I love it and it just won't die. This is an old picture, but I think this is the only one I have of it. http://i43.tinypic.com/4sl076.jpg

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April 26, 2012, 04:29:45 AM
 #71

I love the creativity of that lego setup. Although, one karate chop and the structure blows up haha.
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June 29, 2012, 06:51:50 AM
Last edit: June 29, 2012, 07:21:13 AM by Transisto
 #72

Funny how OP full size pictures make it's post 27mb.


Warning, building such GPU rigs at this time ? ; I suggest you consider their future profitability before investing time and $ into it.
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May 01, 2013, 06:09:52 PM
 #73

Here's mine:



Made from inch thick aluminium, with a removeable mobo tray and a PCI rack from an old server Smiley
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May 01, 2013, 06:53:57 PM
 #74

Started hastily with a lego rig that grew to this:



When I needed to cool the cards better (run the fans at a lower speed, spread out cards), I found some scrap wood and my trusty nail-gun and the result exceeded my usual "just enough" approach...



(the 5830 will be hooked up when the cablesaurus shipment arrives)

Does the wood work fine?
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May 24, 2013, 02:50:58 AM
 #75

Props to the OP!!  Grin Thanks so much my friend! Here's what I managed to put together.

http://i40.tinypic.com/308dusp.jpg

http://i40.tinypic.com/21otthl.jpg

http://i43.tinypic.com/258xc2p.jpg
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May 24, 2013, 05:34:18 AM
 #76

Looks very nice!


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May 24, 2013, 03:16:41 PM
 #77

 Cool

I should have got the grey connectors.


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December 05, 2013, 07:32:47 AM
 #78

Anyone know where I can find the 3-way connectors in Canada?
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December 25, 2013, 09:27:15 PM
 #79

http://www.ebay.co.uk/sch/zxcvbrna/m.html?item=201008369246&pt=US_World_Coins&hash=item2ecd084e5e&rt=nc&_trksid=p2047675.l2562

I hope the picture is used with permission ;-)
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December 25, 2013, 09:28:52 PM
 #80

by the way, what is the is minimum and what is the ideal distance between the GPUs for best cooling. I am thinking around 4 to 5cm..

And do I ONLY need to drill a hole and the screw should be able to screw itself in or should I buy a proper screw tapper ?
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