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Author Topic: GUIDE - How to make your own PCIe extender with molex.  (Read 47777 times)
kqpahv
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May 04, 2013, 12:18:29 AM
 #21

Made a few of those... My 7950 pulled enough power to burn through the molex 12v wire ! Tried to use two wires and now the cards crash if I try to overclock them so I guess there must be too much resistance......
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May 06, 2013, 04:49:01 AM
 #22

If you look at the pics of the powered riser cables that are sold online they look like they only splice into 1 of the 12V wires.


Is there a reason the have to splice into all 5 wires?  Or is 1 12V wire enough?


All of the ones I have saw look just like this.


http://www.hashratestore.com/shop/cables/powered-pci-e-16x-16x-riser-cable-with-molex/
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May 07, 2013, 12:23:14 AM
 #23

Anyone know about this?  I need to modify mine ASAP.
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May 07, 2013, 01:01:32 PM
 #24

Have a 3x PCI-E slots, needed to move the middle GPU out for airflow. Tried using an unpowered riser cable at first, and would have voltage drops that led to hard reboots while mining.

Tried modding a molex to the riser, works fine for a few hours, then the card goes SICK/DEAD. Rebooting doesn't help much, it goes sick/dead faster. Removing and adding back the riser-cable to the card seems to get it going again, but then the same problem comes back after a few hours.
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May 08, 2013, 12:38:51 AM
 #25

How about the 3.3 volt rails?

do they also need to be modified?

how much is the power draw on the 3.3volt rail?

what is 3.3 volt used for anyway?
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May 09, 2013, 07:13:41 PM
 #26

What I find a little odd about this is you need to complete a circuit to have current flow. The risers here only have the 12V connection. That means the current for the circuit is still flowing through the motherboard; although, only in one direction. Why not make the 0V connection? It's almost as if the jobs only half done. Although I suppose it reduces motherboard problems by 1/2.
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May 12, 2013, 10:14:26 AM
 #27

bookmarking
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May 14, 2013, 04:09:50 AM
 #28

What I find a little odd about this is you need to complete a circuit to have current flow. The risers here only have the 12V connection. That means the current for the circuit is still flowing through the motherboard; although, only in one direction. Why not make the 0V connection? It's almost as if the jobs only half done. Although I suppose it reduces motherboard problems by 1/2.

Anyone have an idea about why 1 wire is enough?  Where is the current from the one 12V wire being pulled down to?  Is it just being distributed across a bunch of data lines and that's why it's ok?
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May 14, 2013, 04:30:30 AM
 #29

The "ground" is all the same, for everything. You are getting ground from the PCIe pins, and also from the 6-8pins above. (Thus the two extra ground wires in the 8-pin, which are just the two from the 6-pin, shared.)

That is the "common" = "-12,-5,-3,-1.5" all in one. Also the "Frame" and anything-else metal in the computer.

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May 18, 2013, 03:20:50 AM
 #30

Made a few of those... My 7950 pulled enough power to burn through the molex 12v wire ! Tried to use two wires and now the cards crash if I try to overclock them so I guess there must be too much resistance......

Unfortunately, not all cables are created equal. In fact, some unscrupulous manufacturers will mark cables incorrectly. Copper is expensive, so bad cable manufacturers will use less than they should in an effort to make more money. Be aware of this when you're harvesting cables from fans or SATA power adapters.

In front of me I have two cables. One is marked '18AWG' and the other is '20AWG'. The 18 gauge is from a 4-pin molex -> SATA power adapter that I bought on eBay. The 20 gauge is from a PSU.

The 20AWG cable has 21 strands, each with a radius of 0.085mm, yielding a total cross-sectional area of about 0.48mm2. Ideally it should be 0.518mm2, but this is pretty close.

If you're not familiar with wire gauges, it's important to note that wires are larger at smaller gauges (so 18AWG should be a thicker cable than 20AWG). The cable marked 18AWG has 13 strands, and each is approximately 0.1mm in diameter. This gives us a total cross-sectional area of about 0.10mm2. 18AWG cable is supposed to be around 0.823mm2.

Why is this important? It's important because the resistance of a cable (and thus the heat generated by it when a certain amount of current is flowing through it) is proportional to its cross-sectional area. Basically, thin cables get hotter than thick ones. If the cable is just slightly undersized, this will just mean warm cables. If the cable is seriously undersized, the insulation will melt, and the cable could cause a fire.

At most, a PCI-e video card should only be drawing 75W from the PCI-e slot. At 12V, this is about 6.25A.

tl;dr You should use at least 22 gauge cable (provided it hasn't been mislabeled).
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May 19, 2013, 06:36:48 AM
 #31

cool bro! card is now recognized , no need to buy powered riser lol

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May 21, 2013, 08:28:44 PM
 #32

Those instructions are valid for a x1 to x16 connector too?




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May 25, 2013, 01:43:33 AM
 #33

The "ground" is all the same, for everything. You are getting ground from the PCIe pins, and also from the 6-8pins above. (Thus the two extra ground wires in the 8-pin, which are just the two from the 6-pin, shared.)

That is the "common" = "-12,-5,-3,-1.5" all in one. Also the "Frame" and anything-else metal in the computer.
The "ground" is all the same, for everything. You are getting ground from the PCIe pins, and also from the 6-8pins above. (Thus the two extra ground wires in the 8-pin, which are just the two from the 6-pin, shared.)

That is the "common" = "-12,-5,-3,-1.5" all in one. Also the "Frame" and anything-else metal in the computer.

That is fine if you use a single psu. ground is ground is ground. makes no odds, and the slots are spec'd high enough on most mbs to happily allow 75 watts grounded into the socket without issues.

However, my situation is a little different:
I use a 250 watt seasonic to power the motherboard and pci-e slots. the psu has 22amps on the 12v.
I use a 750 watt seasonic psu to power the cards.
In my 4 slot motherboards (4 x 16)
Whith these motherboards I use a slightly higher spec psu (again a seasonic,14a and 15a over two rails)
I am using underclocked semperons
A very small ubuntu install (copied from bamt)


Now no matter what psu I use for the motherboard, slot 4 never gets enough juice if all 4 slots are full. (hashrate is normally rocksold 492.1) add a 4th card in slot 2 (0-3) this now hashes full speed and the 4th card jumps between 390 and 441.  So I need a powered riser.  But I need to connect the grounds up on the riser, I cannot risk the 750 watt psu grounding into the 250.

Do the 12v and 3v have different grounds? (there are 3 ground on the front notch) is each ground for something else?  I guess it wont take too long to workout, an inline multimeter should do the trick. I only have two old cards though, still hopefully it wont blow the card.

Does this sound reasonable? do you know anyone who has a schematic for a card with ground connected on the riser. in the pic on cablesaurus it looks like B4 and or B7 leaving out A4. although B4 and A4 makes slightly more sense, but this is just guesswork.  am I trying to fix an nonproblem (letting the card ground from teh 750 into the 250 - every fibre of my being says no)

cheers

steve
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May 27, 2013, 02:18:04 PM
 #34

The "ground" is all the same, for everything. You are getting ground from the PCIe pins, and also from the 6-8pins above. (Thus the two extra ground wires in the 8-pin, which are just the two from the 6-pin, shared.)

That is the "common" = "-12,-5,-3,-1.5" all in one. Also the "Frame" and anything-else metal in the computer.
The "ground" is all the same, for everything. You are getting ground from the PCIe pins, and also from the 6-8pins above. (Thus the two extra ground wires in the 8-pin, which are just the two from the 6-pin, shared.)

That is the "common" = "-12,-5,-3,-1.5" all in one. Also the "Frame" and anything-else metal in the computer.

That is fine if you use a single psu. ground is ground is ground. makes no odds, and the slots are spec'd high enough on most mbs to happily allow 75 watts grounded into the socket without issues.

However, my situation is a little different:
I use a 250 watt seasonic to power the motherboard and pci-e slots. the psu has 22amps on the 12v.
I use a 750 watt seasonic psu to power the cards.
In my 4 slot motherboards (4 x 16)
Whith these motherboards I use a slightly higher spec psu (again a seasonic,14a and 15a over two rails)
I am using underclocked semperons
A very small ubuntu install (copied from bamt)


Now no matter what psu I use for the motherboard, slot 4 never gets enough juice if all 4 slots are full. (hashrate is normally rocksold 492.1) add a 4th card in slot 2 (0-3) this now hashes full speed and the 4th card jumps between 390 and 441.  So I need a powered riser.  But I need to connect the grounds up on the riser, I cannot risk the 750 watt psu grounding into the 250.

Do the 12v and 3v have different grounds? (there are 3 ground on the front notch) is each ground for something else?  I guess it wont take too long to workout, an inline multimeter should do the trick. I only have two old cards though, still hopefully it wont blow the card.

Does this sound reasonable? do you know anyone who has a schematic for a card with ground connected on the riser. in the pic on cablesaurus it looks like B4 and or B7 leaving out A4. although B4 and A4 makes slightly more sense, but this is just guesswork.  am I trying to fix an nonproblem (letting the card ground from teh 750 into the 250 - every fibre of my being says no)

cheers

steve

IMHO if they are both connected to the same outlet / extension cord then it shouldn't be any problem but I would like somebody else to chime in here and confirm because I am no expert. Just what I have heard on the forum regarding multiple PSUs and one GPU being powered from 2 diff PSUs.
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May 27, 2013, 05:44:08 PM
 #35

The "ground" is all the same, for everything. You are getting ground from the PCIe pins, and also from the 6-8pins above. (Thus the two extra ground wires in the 8-pin, which are just the two from the 6-pin, shared.)

That is the "common" = "-12,-5,-3,-1.5" all in one. Also the "Frame" and anything-else metal in the computer.
The "ground" is all the same, for everything. You are getting ground from the PCIe pins, and also from the 6-8pins above. (Thus the two extra ground wires in the 8-pin, which are just the two from the 6-pin, shared.)

That is the "common" = "-12,-5,-3,-1.5" all in one. Also the "Frame" and anything-else metal in the computer.

That is fine if you use a single psu. ground is ground is ground. makes no odds, and the slots are spec'd high enough on most mbs to happily allow 75 watts grounded into the socket without issues.

However, my situation is a little different:
I use a 250 watt seasonic to power the motherboard and pci-e slots. the psu has 22amps on the 12v.
I use a 750 watt seasonic psu to power the cards.
In my 4 slot motherboards (4 x 16)
Whith these motherboards I use a slightly higher spec psu (again a seasonic,14a and 15a over two rails)
I am using underclocked semperons
A very small ubuntu install (copied from bamt)


Now no matter what psu I use for the motherboard, slot 4 never gets enough juice if all 4 slots are full. (hashrate is normally rocksold 492.1) add a 4th card in slot 2 (0-3) this now hashes full speed and the 4th card jumps between 390 and 441.  So I need a powered riser.  But I need to connect the grounds up on the riser, I cannot risk the 750 watt psu grounding into the 250.

Do the 12v and 3v have different grounds? (there are 3 ground on the front notch) is each ground for something else?  I guess it wont take too long to workout, an inline multimeter should do the trick. I only have two old cards though, still hopefully it wont blow the card.

Does this sound reasonable? do you know anyone who has a schematic for a card with ground connected on the riser. in the pic on cablesaurus it looks like B4 and or B7 leaving out A4. although B4 and A4 makes slightly more sense, but this is just guesswork.  am I trying to fix an nonproblem (letting the card ground from teh 750 into the 250 - every fibre of my being says no)

cheers

steve

i'm really gald i came across this - i'm in almost excatly the same situation - but i have two large PSU Maxrevo 1500w so i can just use one for the mobo and say 5 cards if i get them up - with un-powered on an z77a-gd65 only 4 cards would ever work. and i'm not even sure powered risers will help , but they are the best chance and it should be fun to try  {burning smell}

but its an important point for multi PSU - so if anyone knows that would be great - i was thinking about mixing actually the cables and being a little tricky .

what about this :

1. Running PSU one that is jumped to say 3 cards , PLUS the 4 or 6 pin on the Motherboard ?

2. Then with PSU 2 plug the 24 pin in to the motherboard - and two or 3 more cards.

each PSU is connected to a common ground then.


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May 27, 2013, 08:17:00 PM
 #36

Quote
Correct, you don't want to push voltage to the mb v out, prob wouldn't end well.

Are you saying that pushing 12v power down into the motherboard from the pci-e slot is somehow bad? I don't think it works that way. If you think it would fry your computer, then why would a product like this be sold from a big name GPU brand?

http://www.evga.com/Products/Product.aspx?pn=100-MB-PB01-BR

IMO, I would prefer to buy something like that than mess with 6 individual risers and 6 individual molex. Powered risers are just a mcguyver solution. Having on-board supplemental GPU power is the best solution (MSI Big Bang XPOWER II has a PCI-E plug on the motherboard to supply dedicated 12v power to PCI-E slots, and some higher end Gigabyte boards have a SATA plug to achieve the same thing). Getting the EVGA Power Boost is a solution between the mcguyver and the built-in. It's professional, and neat/tidy.

edit: hashratestore's risers feeds 12v power back into the board, so other cards can draw off the molex too. Only 1 or 2 of his risers should sufficiently prevent ATX plug burnouts when a full complement of GPU's populates a motherboard.

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May 28, 2013, 06:11:05 AM
 #37

Quote
Correct, you don't want to push voltage to the mb v out, prob wouldn't end well.

Are you saying that pushing 12v power down into the motherboard from the pci-e slot is somehow bad? I don't think it works that way. If you think it would fry your computer, then why would a product like this be sold from a big name GPU brand?

http://www.evga.com/Products/Product.aspx?pn=100-MB-PB01-BR

IMO, I would prefer to buy something like that than mess with 6 individual risers and 6 individual molex. Powered risers are just a mcguyver solution. Having on-board supplemental GPU power is the best solution (MSI Big Bang XPOWER II has a PCI-E plug on the motherboard to supply dedicated 12v power to PCI-E slots, and some higher end Gigabyte boards have a SATA plug to achieve the same thing). Getting the EVGA Power Boost is a solution between the mcguyver and the built-in. It's professional, and neat/tidy.

edit: hashratestore's risers feeds 12v power back into the board, so other cards can draw off the molex too. Only 1 or 2 of his risers should sufficiently prevent ATX plug burnouts when a full complement of GPU's populates a motherboard.

Re - Big Bang XPOWER II

just a note there - be careful about buying an all 16x slot board, the 16x slots will use up all your availible lanes - = you will not run more than 4 cards.

the MSI guys are useless at understanding what we are doing here - they can't understand what or how we are doing things, so don't expect help from them .

i went on there , and they locked my topic becasue the mod said Cryptocurrency was "illegal becasue people buy drugs with it"  lol , aslo he thought we were "cracking passwords" : D lol.

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May 28, 2013, 08:21:55 AM
 #38

I never said I was using my xpower board for mining. Why would I spend $350 plus a required $200+ cpu for a 7 slot board when I can buy a z77a-gd65 and celeron for almost a third of the cost? (I can get a z77a-g45 for even less money for 6 useable slots)

Also, for what it's worth, all the slots on the xpower work. It's something like 16x > 1x > 16x > 1x > 16x > 1x > 16x. It is clearly documented in the manual.

PS: Way to not read any of my post except for the part where I used a motherboard as an example.

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May 28, 2013, 11:09:45 AM
 #39

I never said I was using my xpower board for mining. Why would I spend $350 plus a required $200+ cpu for a 7 slot board when I can buy a z77a-gd65 and celeron for almost a third of the cost? (I can get a z77a-g45 for even less money for 6 useable slots)

Also, for what it's worth, all the slots on the xpower work. It's something like 16x > 1x > 16x > 1x > 16x > 1x > 16x. It is clearly documented in the manual.

PS: Way to not read any of my post except for the part where I used a motherboard as an example.

hey slow down cowboy - i wasn't having a go,  the advice about the BigBang comes direct from the MSI noobs on thier own forum (but according to them "Cyrptocurrency is illegal" , and if you can get 6 slots working on a GD45 - i'll give you money to show me how :



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May 28, 2013, 03:42:09 PM
 #40

Excellent guide! THX  Wink
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