Question regarding 6+2 pin extension

[phtotrope]

First off, I have GTX 680 which requires 6pin/8pin. My PSU has 2 x 6+2 PCI-E cables. Now, I have a 6 to 6 pin extension for the 6 pin port of my GPU, but my question is in regards to the 8 pin. I'm having trouble finding a straight 8 to 8 pin VGA extension from NZXT, but they do offer a 6 pin to 6+2 pin. If I plug just 6 pins from a 6+2 PSU cable into the 6 to 6+2 extension cable and then have the 6+2 end go to my 8 pin port on my GPU, will it be fine?

 

[inzone]

Is NZXT the only place that you can buy from? There are other places to get cables frm.

1ST PC CORP. Model CB-8M-68F 8" 8-pin PCI-Express to PCIE 6+2pin - Sleeved (Extension/Adapter)
$7.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16812706024

OKGEAR Model FC88-12BKS 12" 8 pin PCI EXPRESS extension cable w/ black sleeved
$4.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16812123343

If your looking for upgraded sleeved cables then I can link some sites for those also.

 

[inzone]

The 6 pin to 6+2 pin cable will work also.

 

[phtotrope]

Well, I ordered the other cables I intend to use from NZXT and they're all the same style, so I'm trying to stick to the same company. But if you're saying the 6 pin to 6+2 pin will work then that'd be the easiest for me. I was just wondering if there was anything to worry about.

 

[blakwidowrsa]

My 4890 has 2x extra power connectors. 1x 6 pin and 1x 8 pin. I only have 2x 6 pins and its working fine.

I'll suggest checking with the gfx install manual for Required power plugs.

 

[InvalidError]

My 4890 has 2x extra power connectors. 1x 6 pin and 1x 8 pin. I only have 2x 6 pins and its working fine.

In principle, cards featuring 6+8 connectors that work fine with 6+6 should also work fine with 8+0 since both configurations yield 225W total available power. Giving the card the full 6+8 treatment is only necessary if you want to improve overclock stability and/or efficiency assuming you have a real 8-pin PCIe power connector from your PSU.

 

[blakwidowrsa]

In principle, cards featuring 6+8 connectors that work fine with 6+6 should also work fine with 8+0 since both configurations yield 225W total available power. Giving the card the full 6+8 treatment is only necessary if you want to improve overclock stability and/or efficiency assuming you have a real 8-pin PCIe power connector from your PSU.

Good to know thx.
It is the Sapphire HD4890 O.C. edition and it eats about 190W.
Just FYI there are 8 LED's behind the 2 connectors on the backside of this card. The corresponding pins led lights up red when there is a pin not powered. While I'm using the the 2x 6 pin plugs it lights up all of them on cold boot for 1-2 seconds. If I remove 1 plug it does not light any led's up and I dont notice a performance difference in games.

Theory?

 

[InvalidError]

Theory?

Either the game you are running does not stress the GPU hard enough for you to notice the reduced performance or the GPU is letting its VRM exceed the spec's power draw limit from the PCIe slot and/or remaining PCIe power connector.

190W - 75W from PCIe = 115W from 6-pin PCIe power connector(s) = ~10A @ 12V = ~3.3A per PCIe 12V/GND pin, no problem for #18 gauge wiring.

My guess: the VRM's current limit is set based on the 150W 8-pin power connector rating which has only three 12V pins. 150W / 12V / 3 pins = 4.17A/pin.

 

[blakwidowrsa]

Yes makes sense. I do see combined 29A(15A and 14A) on the PSU's 2x 12v Rails so it is enough if 3.3A x 6 = 19.3A .

I play Starcraft 2 , NFS Hot pursuit(2011), Homefront, Crysis 2, Diablo 3 all at 1080p High/Ultra no probs.