Can I draw power from the 4+4 CPU socket to power a second GPU (6+2 PCI-E)?

Kaboose22

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Very silly question probably but I just want a clarification about this. I have 2 GtX 980s both of which take 2 (6pin) cables to power. The first card is powered by connecting one of the (6+2) cables via the appropriate socket from the PSU (as in, the PSU has a clearly labeled socket called 6+2 PCIe). Below it is another socket marked 4+4 CPU. Here is a pic.

My question is can I power the second GPU via a 6+2 cable from the 4+4 socket on the PSU. Will there be a voltage difference?
 

Pinhedd

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Ah I see. As long as you're using the 8 pin EPS connector to provide auxiliary power to the CPU you should have no problems.

That bottom socket can be used for either a 4+4 pin CPU connector (for older motherboards that have only a 4 pin ATX connector, or dual-socket motherboards that require two 8 pin EPS connectors) or a 6+2 connector. You should have a cable for it.

EDIT: I see, there are two identical sockets stacked on top of eachother. Either one of these can be used for either PCIe or CPU power.
 

Pinhedd

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No. They are both 12 volt supplies but the pinout is different as is the key. It's not possible to convert them.

EDIT: It looks to me like your PSU is capable of supplying both from that socket, you will need to use the correct cable though.
 

Kaboose22

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Thanks for the speedy reply. According to my tinkering the 6+2 cables fit perfectly into the 4+4 CPU slot as you can see here and I am using the standard 2x 6+2-pin connectors that came with the PSU. Is this wrong? I am not sure I follow what you mean when you day the pinout is different

EDIT: Alternatively, the only thing I can think of is using the cables in this pic. The pair on the left were from the GPU and seem to convert the 2, 6-pin sockets into 4, 4 pin ones and I guess I could use the cable type (on the right of the pic) to connect them up with the 'peripheral' socket of the PSU.
 

Pinhedd

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There's three different keyings here

Key 1: the PSU cables have a PSU-specific keying on the PSU side of each cable. This is the same on the PSU end of both a 6+2 pin PCIe cable and a 4+4 CPU cable.

Key 2: the 6+2 pin PCIe cable has an industry standard keying for either a 6 pin PCIe connector or an 8 pin PCIe connector on the PCIe side of the cable

Key 3: the 4+4 pin CPU cable has an industry standard keying for either a 4 pin ATX auxiliary connector or 8 pin EPS auxilary connector

The ATX/EPS auxiliary power and PCIe power are nothing more than 12 volt supplies with some ground returns. Your PSU seems to be designed to provide both from the same receptacle on the PSU provided that the correct cable is used. If your PSU came bundled with only one cable that exposes both a 6+2 and a 4+4 that plugs into that slot then you're SOL. Either way, you will still need to provide auxiliary power to your CPU.

Out of curiosity, what PSU is this? If it has only one 6+2 cable it may simply not be up to the task of powering a pair of GTX 980s
 

Kaboose22

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Its a Cosair CS850M. It has the standard 24pin ATX cable (which is plugged to the mobo) and a 8pin eATX cable marked CPU which I connected to the CPU image, it also came with 2 (6+2 cables), one of which is already connected to the primary GPU. The only things not wired up in the case are the HDDs, optical drive and of course the last GPU. I don't believe my Rampage V mobo has a need for a 4+4 cpu power connector given the CPU is already powered and so was wondering if I could just use its socket in the PSU to connect the second 6+2 cable into and power the GPU. I feel like that is the only viable place to stick the cable into anyway as the other sockets on the PSU are 6 pins. Image here

If this is not the case due to differnt pin configs...then I am slightly at a loss as to how to power the second card
 

Pinhedd

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Ah I see. As long as you're using the 8 pin EPS connector to provide auxiliary power to the CPU you should have no problems.

That bottom socket can be used for either a 4+4 pin CPU connector (for older motherboards that have only a 4 pin ATX connector, or dual-socket motherboards that require two 8 pin EPS connectors) or a 6+2 connector. You should have a cable for it.

EDIT: I see, there are two identical sockets stacked on top of eachother. Either one of these can be used for either PCIe or CPU power.
 

Kaboose22

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Ah thanks so much, I was slightly perplexed as to why I had two of these cables but only (what appeared to be) 1 out for it. So, to be absolutely clear, I am all good to use the 6+2 connector to draw power from the 4+4 CPU out for the GPU?
 

Pinhedd

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it's a shared output, just a bunch of +12v and REF. The cables themselves marshal the outputs from the PSU to the form expected by the component. The specifications for that PSU list 4 PCIe connectors, probably in the form of two 6 pins and two 6+2 pins which would make it SLI capable.
 

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