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Author Topic: GUIDE - How to make your own PCIe extender with molex.  (Read 47774 times)
mistfpga
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May 29, 2013, 11:00:51 AM
 #41

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.



I was thinking of this too, use the cpu connector on the psu powering the gpu 6 pin connectors, but I think that is its own circuit. my other idea was to use the 20 pins of the 250 seasonic to power the atx and use the cpu 4pin, then use the 4pin extra atx (the bit that actually powers the pci-e) off the big psu (I have not checked what the other pins are and if this is plausible)...

However, I plugged a 6950 in to a 1x riser with the back drilled off, this was not attached to the motherboard. I then confirmed that B1, B2, B3, A2 and A3 are all on the same circuit (using a voltmeter set to ohms) then verified all the ground are connected.  I then striped these wires and soldered onto a 20awg.  I took only the three grounds in front of the slot (B4, B7 and A4) and soldered these to a 20awg wire.  put a molex connector on the end (female plastic, male pins).

Now, no matter which psu I attach it to, it only grounds through that psu, as far as i can tell. (I am now using a 430 antec neo as the mb psu because it is more likley to be able to handle the overcurrent/wattage)  The 430 antec (powering 24pin atx, 3 pci slots and 4pin cpu) did not pull more any more watts than if the 4th card was not connected.  Also the volts stayed ~240v - so it would appear to work. And if I did add it to a molex on the 430 antec psu the psu would auto shutdown after 3-4 mins when the fans started to make proper noise.  All hashrates were rock solid though.

NOTE: the antec is only rated for 384 watts on the 12v it auto shutsdown around 405 watts. (it was hitting this)

I would not advocate anyone try this, I still have a lot more experimentation to do, but I need to wait until I can get access to better testing equipment and mike (who actually knows real things about proper electronics - I just guess Wink ) and to be completely honest I am not that sure I am interpreting the results correctly.  I will find out tomorrow...
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mistfpga
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May 29, 2013, 11:18:27 AM
 #42

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?

How about with two psu's? one low powered controlling the motherboard, 24pin + 4pin cpu (psu 1). then using a different psu to power the gpus 6pin power sockets and "pcie plugin power thing" (psu 2).

it is 1x so you can pump ~ 6 amps into the slot, I can see one of 3 things happening;

1 - the ground on the "pcie plugin power thing" just grounds the 12v you are pumping in (from psu 2), so the psu is just powering that one slot, effectively doing nothing, and potentially burning the socket and/or psu.

2 - The big psu (2) is now dumping 6 amps into the low powered psu, whilst sucking 6 amps of the socket, effectively doing nothing but stressing both psus and the socket (potentially burning all three out)

3 - By some magic the switching supplies cope and everything works how it is supposed to.

it is a shame that XFX have blurred the backside of their connector.  if anyone can post images of both sides and what pins are attached, I will make one, try out the above, and see what happens Smiley
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May 29, 2013, 11:54:16 AM
 #43

electricity moves from high voltage to low voltage. it doesnt move 12v -> 12v. It moves 12v -> 0v (ground)

mistfpga
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May 29, 2013, 07:39:27 PM
 #44

electricity moves from high voltage to low voltage. it doesnt move 12v -> 12v. It moves 12v -> 0v (ground)

yes, but which ground? it always takes the path of least resistance... hence in my example 1 - grounds back to the supplying psu, 2- grounds into psu 1, which inturn would dump back into psu 2, or psu 1 will continually draw current from psu 2, getting greater and greater until something goes pop and the magic smoke escapes.

also it doesnt have to ground 0v (7volting fans is an example of 12v -> 5v) the thing is, without better knowledge of switching power supplies, or how pci-e connectors are attached to the motherboard I am just guessing.

remember I am not talking about powered risers in this example, but the things that connect a molex directly to the pci slot... like the EVGA powerboost (i mistakenly referred to is as an XFX product) There is an image of it installed halfway down along with some evidence it stabilises and boosts the 12v rail.  I can see how this would work if you use just one psu.  My question is what happens if one psu is powering this and another the rest of the motherboard.

unless I am overthinking it... I have some spare mb's and psus so i guess I will find out soon Smiley
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May 31, 2013, 06:50:47 AM
 #45

electricity moves from high voltage to low voltage. it doesnt move 12v -> 12v. It moves 12v -> 0v (ground)
This caught my attention, though I know what you are trying to convey, the actual statement is so wrong.

Voltage does not move.  You cannot have a 12vdc line connected to a 5vdc line and have the voltage "move".  Nor can you have a 12vdc line connected straight to ground without burning the line, this is called a "short circuit".

Current flows.  If flows from negative to positive.

The voltage is the pressure for the current.  

To get current to flow, you need circuit.  A circuit is a complete "loop" or "circle" that includes an energy source, a load, and ground.  
Lets use a fan in our circuit as the load device. When we turn the fan on, energy or "power" is expended as heat. This is measured in watts.

So we have:

current which is amps using the symbol "I"
voltage using the symbol "E"
watts using the symbol "P"

If you remember "PIE", you can figure the number for current, voltage, or watts with this formula:

P over I times E  

  P  
 I * E

P=I * E
I= P / E
E= P / I

To the posts leading up to the above statement, someone already said what was needed for multi-psu systems, and that is a "common ground".

The PSU's, MB, GPU's all need to be grounded to the same source.  That is normally accomplished when everything is screwed into a case.  The metal tabs that hold the GPU's to the case are grounded on the PCB of the GPU card.  The PSU is screwed down to the case and the MB is properly grounded when screwed onto the backing plate through the brass/steel risers.

The same "common grounding" needs to be accomplished with our open-air builds especially with multi-PSU's builds.  The current in the circuit flows "everywhere" but will take the path of least resistance so having a common ground is important.  

For those using the squared aluminum pieces to make your open-aired frames, if you are using plastic connectors in the tubes, you will need to ground each segment.

For the wood based frames, using strips of metal connected with 12-gauge wire to connect all grounds together will work.

For milk carton cases, build a common ground to all components with 12-gauge wire.

By creating the common ground, you will prevent most of the problems with wires burning up or getting to hot that some have already experienced.
Mikeologist
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June 02, 2013, 03:05:44 AM
 #46

Thx for this guide.  I could have used this a week ago before I hacked up two of my connectors!   Tongue  Fortunately I got one of them to work.

I was not sure at first if I could just sever the connection the to the mother board or if I should tap into and preserve the connection.  I ended up not connecting the power to the motherboard, as I see you did not. 

I also tried desoldering the joint at the connector too.  That was pretty easy.

One issue I had was stripping the thin wires.  My autostrippers didnt work on that thin gauge.  I used a razor, but would like to look for a proper stripper.  Would the cheaper plastic autostrippers work on a ribbon?  Any idea what gauge the ribbon is exactly?

(Also, I did mine on PCIe x1 - PCIe x16 adapters, seemed to work just fine. )

Try this on a spare wire first, and always take all appropriate precautions.
Wear leather work gloves.
Separate you individual conductors from the bundle, and cut to desired length.
Using a bic lighter, quickly pass the strip point of your wire back and forth through the flame several times.
Just as it starts to deform, remove it from the flame and immediatly grasp the insulation at the strip point and tug gently but quickly.
Presto.

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June 02, 2013, 02:44:46 PM
 #47

I wouldn't bother with this. There is no tangible benefit to making your own unless you just happen to have non-molex cables lying around. Plus a certain number of people will half-ass the procedure and end up damaging their equipment. Why bother with this at all when, you can buy pre-made cables directly from Meitk in China. They don't cost $20 either. I think I last paid $3.70 each for 20 1x->16x and $1.50 each for 20 1x->1x.

http://meitk.en.alibaba.com/productgrouplist-218437331/Riser_cable_with_Molex.html

Hell, they even take paypal. It couldn't be easier.

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June 07, 2013, 05:54:01 PM
 #48

Hey, so ive made my powered riser 1x16 and get about 13v between the pins. However my HX850 gold psu only has enough blue 8-pins for 3 gpu's. I feel i am stupidly missing something. if i use the powered riser do i have to use the 8 and 6 pin plugs from the psu or is the power going through the riser already? at the moment the fan doesnt turn on when i dont have the 8 and 6 pin connectors plugged in.
2 7950 gpus out of action at the mo...i really need them going asap..
 Huh

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June 08, 2013, 02:41:46 AM
 #49

Hey, so ive made my powered riser 1x16 and get about 13v between the pins. However my HX850 gold psu only has enough blue 8-pins for 3 gpu's. I feel i am stupidly missing something. if i use the powered riser do i have to use the 8 and 6 pin plugs from the psu or is the power going through the riser already? at the moment the fan doesnt turn on when i dont have the 8 and 6 pin connectors plugged in.
2 7950 gpus out of action at the mo...i really need them going asap..
 Huh



Regardless of the origin of the power along the pci-e connector, YOU MUST ALWAYS USE BOTH OF THE POWER PLUGS ON TOP OF YOUR CARD.

Following this rule should help.

The reason is simple; there is a specific amount of power, as defined by the industry standard, that will be available through the motherboard's interface. Modern high-end video cards exceed this specific amount by 1 to 5 times the max. To wit, all of these cards are made with additional, mandatory power connectors.

If your card has power connectors on the top, they must always be powered.
People here are making these powered connectors so the can use multiple power supplies, or use more than 3 or 4 cards without melting their motherboard.

Does this make sense?

If you have anymore specific questions to get your rig online, type the key terms in the search box as every question that a noob might have has likely been answered on this forum already. Ask though, if you can't find it after looking.

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June 09, 2013, 09:53:29 PM
 #50

Many thanks for this very useful guide!  I wouldn't have attempted it otherwise, but I ended up with two working (1x to 16x) cables on the first try.
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June 11, 2013, 10:23:40 PM
 #51

This is definitely worth doing you guys.  Or if you don't want to do it at least buy them.

Just as a test I did this to my 6 riser cables powering 7970s.  I then combined all the cables into a single 18AWG power cable. Within 10 minutes of mining the cable was VERY VERY Hot.  Those poor motherboards that are pushing all these cards without powered risers.

Anyway I separated them individually like one should and they are rocking away.

Thanks for this guide, I was unsure how to do this since looking at pictures online can be very misleading, if it wasn't for your guide I would have done it wrong, actually I wouldn't have done it at all.  Especially pin 1 on side A.  On my cables that line is red which many people would assume it's power, but it's not.  Ignore the colors on your cables and just follow this guide.

Cheesy
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June 12, 2013, 08:18:00 AM
 #52

electricity moves from high voltage to low voltage. it doesnt move 12v -> 12v. It moves 12v -> 0v (ground)

If the +12V at two PSU has slight difference, if you connect them together, there will be current moving between them.
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June 20, 2013, 12:23:13 AM
 #53

I just ran another quick test and found out my 6 7970s pull 230watts from the motherboard.  That's 38watts per card.  And actually now that I think about it that wasn't even full throttle, that was probably 80%+/-.  I feel much better using powered risers now.  Smiley
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June 23, 2013, 09:55:01 AM
 #54

Is there a guide to making 16x->1x powered risers?
BlazinBeaches
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June 23, 2013, 05:08:15 PM
 #55

It's the same
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June 23, 2013, 05:09:13 PM
 #56

Is there a guide to making 16x->1x powered risers?
you take your x1 riser, then you saw off the end.

It is pitch black. You are likely to be eaten by a grue.

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February 02, 2014, 01:17:23 AM
 #57

Reviving this very old thread...

What about if I just cut the B3 line? (without connecting them to power).

I seem to have powered-risers with the B3 line not connected to the molex so I may have to cut it (I have two psus) and it would remain not powered.

Best regards,
ilpirata79
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February 09, 2014, 05:02:58 PM
 #58

Hi.

3 GPU works fine without extra power for risers.
I have done one powered riser and fourth GPU is still not recognized.

If I got four GPU, do I need to have 4 powered risers?

BR.
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