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Convert PCIe to 8-pin EPS (CPU)

post #1 of 9
Thread Starter 
I'll try to keep this as brief and to the point as possible; I've got a quad CPU workstation mobo that requires power from 3(!) 8-pin EPS power cables, and I forgot to order the adapter (Akasa AK-CB051) I initially thought would allow me to run the third one from PCIe. I'm pressed for time to get this thing up and running (professionally - no "second PSU" options are viable, TIA, also: no 4-pin Molex, either) and really would rather not wait a week to order an adapter that on second thought might not be the right answer.

As I understand it, a typical 8-pin PCIe has three 12v wires with five ground wires, and an 8-pin EPS connector has four 12V with four grounds. My first thought is to just "double tap" one of the 12V wires and "cap off" the remaining ground, but I've got some reservations, primarily stemming from the fact that the internet can't seem to conclusively decide what the wattage is for any of these standards - I've read 6-pin PCIe rated at 75W even though it uses the same three 12V connections as 8-pin PCIe which "magically" jumps to 150W with the addition of two ground wires, to say nothing of trying to get a concrete spec on either 4-pin or 8-pin EPS standards, the latter being rated up to 288W in some places.

So, erring on the side of caution I figure I should be able to cannibalize two PCIe cables, running two 12V and two ground from each to the 8-pin EPS - yes? No? All constructive and competent feedback is both welcome and greatly appreciated - I'd hate to trash an $800 board, but then again, this is overclock.net, where parts are broken and warranties voided with glee all in the name of science/cake/funsies...
post #2 of 9
What PSU are you using?
 
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post #3 of 9
Thread Starter 
Cooler Master Silent Pro Gold 1200W (single rail, 98A)
post #4 of 9
Then yeah, I'd just take two PCIs and make a single EPS...

Just make sure you have the correct pins.

I made a 4 pin a while back doing something similar: (4-pin)

So just figure out what your pinout is and go for it.
 
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post #5 of 9
Thread Starter 
Quote:
Originally Posted by deafboy View Post

Just make sure you have the correct pins.

I made a 4 pin a while back doing something similar: (4-pin)

So just figure out what your pinout is and go for it.
Dude, no offense but what the hell is going on with that Corsair PSU - mystery 10-pin connector above the 24-pin ATX, 12-pin "Current 4-pin EPS"...just...wow. I don't envy you having to deal with that abomination.

Pin-out should not be a problem - it's all 12V and ground as far as I know (unless I'm missing something, which is totally possible) - I'm really more concerned with output. I appreciate you trying to help, though thumb.gif

Solid information on this stuff is very hard to come by, probably because only EEs truly understand all the dynamics, variables and magika at play when it comes to streaming electrons. Still, my thin-air hypothesis leads me to believe that even if my worst case scenario is 200W (50 from each 12V PCIe wire), well, that's going to have to be close enough. We'll see what happens...
post #6 of 9
Quote:
Originally Posted by toolio20 View Post

Dude, no offense but what the hell is going on with that Corsair PSU - mystery 10-pin connector above the 24-pin ATX, 12-pin "Current 4-pin EPS"...just...wow. I don't envy you having to deal with that abomination.

Pin-out should not be a problem - it's all 12V and ground as far as I know (unless I'm missing something, which is totally possible) - I'm really more concerned with output. I appreciate you trying to help, though thumb.gif

Solid information on this stuff is very hard to come by, probably because only EEs truly understand all the dynamics, variables and magika at play when it comes to streaming electrons. Still, my thin-air hypothesis leads me to believe that even if my worst case scenario is 200W (50 from each 12V PCIe wire), well, that's going to have to be close enough. We'll see what happens...

Yeah, the AX750 had a lot of split lines, 18+10 for the 24 pin. 12 pin for 2 8 pins. Yeah, blah. lol.

The PCI slots are all 12v and ground, so it should be easy for you to covert it, not really anything complex about it. As long as you have a spare 8-pin EPS female connector it should only take you a minute to depin and put them in the correct orientation into the EPS connector.






What are you concerned about with the output? yellow -> yellow, black -> black.
 
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post #7 of 9
Thread Starter 
Quote:
Originally Posted by deafboy View Post

What are you concerned about with the output? yellow -> yellow, black -> black.
Heh no, not the wiring itself but rather if I'm going to run into any issues with power delivery - again, I've scoured through a LOT of threads, posts, "guides" and assorted dross that are all contradictory and probably mostly wrong, as a result I'm somewhat apprehensive. That, and this isn't some rinky-dink x-tr3m Asus-based "enthusaist" rig with a bazillion amazing 120mm LED fans but an enterprise-grade bespoke workstation, so there's a bit of pressure associated with taking an outside-of-box risk.

Still, I'm going for it, thanks for encouraging me to dare to reach for the stars and make my dreams come true...

edit: just payed attention to the indicia in your sig, the Asus comment was not a dig, promise - it's just...well, it is what it is, you surely get the point, simply wanted to clarify biggrin.gif
Edited by toolio20 - 5/24/13 at 1:42am
post #8 of 9
Haha, no worries, you won't have any issues with power delivery. A 12v is a 12v and a ground is a ground, the PSU doesn't care what its powering.
The rating for PCI is just to satisfy the spec.
 
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CoolingCoolingCoolingOS
Copper Tubing w/ push fittings 3x EK-FC R9-290X Lamptron FC-5V2 Windows 10 Pro 
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CPUMotherboardGraphicsRAM
Intel i7 3930k @4.8-5.2 Asus Rampage IV Black Edition 3x R9-290 Corsair Dominator Platinum 16GB @1866C9 
Hard DriveHard DriveHard DriveCooling
Intel 750 400GB 2x Samsung 840 EVO 500GB (1TB) SanDisk Ultra II 960GB EK Rampage IV BE Water Block 
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2x Swiftech D5 w/ EK Dual Pump Top XSPC EX480, EX360 & 2x Phobya 1080 EK Supremacy EVO CPU Block EK Advanced 250mL Res 
CoolingCoolingCoolingOS
Copper Tubing w/ push fittings 3x EK-FC R9-290X Lamptron FC-5V2 Windows 10 Pro 
MonitorKeyboardPowerCase
Samsung U28D590D 4K Leopold Otaku Corsair AX1200i Silverstone TJ07, heavily modified 
MouseMouse PadAudioAudio
Corsair M65 Corsair MM600 Sennheiser HD595 / HD428 / HD280 Corsair SP2500 
CPUCPUMotherboardRAM
Intel Xeon E5620 Intel Xeon E5620 Dell R710 Mobo Hynix 144GB DDR3 ECC PC3L-10600R 
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Intel X25-M G2 80GB Dell 710 2.5" - Google Search Appliance Dell Perc H700 Raid Controller 
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post #9 of 9
Thread Starter 
Quote:
Originally Posted by deafboy View Post

Haha, no worries, you won't have any issues with power delivery. A 12v is a 12v and a ground is a ground, the PSU doesn't care what its powering.
The rating for PCI is just to satisfy the spec.
Don't mean to semi-necro this thread but wanted to say thanks to Deafboy and also report, for prosperity, that this is indeed a workable solution - running the 8 pin EPS CPU connector via 2 PCIe cables with no issues (may have been able to get away with just one but I'll let someone more adventurous try that out).
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