Difference between using PCI/E power cable to connect to GPU v/s peripheral power cables

[Dus]

I was replacing my old PSU with a new Seasonic when I noticed that the manual recommended using the specially marked PCI/E power cables for the GPU.

I'm done installing it and everything works perfectly, but I noticed that my old PSU (which was installed by a custom PC dealer) had instead used 4pin peripheral power cables forked into two 6pin adapters connected to the GPU and these pins weren't specifically marked PCI/E.

Can someone explain the difference between using these adapters v/s an explicitly PCI/E cable? My old setup worked without issues for over 3 years so I'm assuming the dealer's technicians knew what they were doing when they setup the PSU in the older rig.

Thanks in advance!

 

[junkeymonkey]

cards require power in a way so look at it like this

pci-e slot = 75w 6-pin pci-e =75w 8 pin pci-e = 150

now that's controlled and rated just to supply the cards

using an adaptor like molex to 6- pin and then find the lead is only putting out 60w to the card it would be under powering it by 10 w

 

[13thmonkey]

I wouldn't assume anything...

depending on what your card is it may not need all of the extra power provided by the pci-e ports, hence why it worked ok. The molex standard wasn't built to supply that much power. PCI-E is purposely designed for this purpose.

 

[Dus]

Thanks both of you, I get it now.

My UPS tells me that after installing the new PSU my power consumption has come down by almost 50 watts at peak usage. I'm chalking this down to the Seasonic S12 bronze being more efficient than my old PSU, although I"m not sure if the act of using wrong cables was also adding to any inefficiency.

 

[13thmonkey]

It will be the bronzyness of the PSU.

 

[Dus]

I'm afraid I have one more doubt on this topic.

I just got a new Zotac GTX card (970) and for some reason they've included the same 4 pin->6pin cables in the box that my dealer had used to connect my old card as described in the OP! That explains my previous setup - the dealer had simply wired up whatever they found out of the box. The Zotac manual offers only generic suggestions on the subject of power cables and there's no mention of PCIE cables at all.

Is it possible that they've included these cables for the sake of PSUs that don't have an explicit PCIE cable? I'm tempted to just plug the Seasonic PCIE cables into the 2 6pin slots on the GPU but I'd like to know what you folks think about this first!

 

[junkeymonkey]

what psu [brand and watt] do you got

if yopu got that seasonic unit as said above it should have the correct leads for your card

 

[junkeymonkey]

they've included these cables for the sake of PSUs that don't have an explicit PCIE cable?

yes and as stated above theres no guarantee the adaptor thing like molex to pci-e will supply the correct power as needed as will using the correct pci-e leads from the psu that's just meant for the cards


use the correct leads from the psu to the card

 

[Dus]

Thanks, I installed it using the PCIE cables and tested, all's good!

 

[junkeymonkey]

good deal