Confused about PCI-E Extenders with Molex Connectors - Help

[Benny1985]

I'm trying to figure this out, and help would be appreciated.

I'm in the process of fleshing out a rig that will use 5 or up to 6 GPUs (Radeon 7950s). Obviously, I need extenders for them, but I am totally confused as to if they need to be powered or not.

At first glance, the GPUs should be powered directly by the PSU. If so, do I still need the PCI-E with Molex connectors? Or can I just use PCI-E extenders without the Molex connectors (which are significantly cheaper and easier to obtain)?

I get conflicting information almost every time I ask.

And for reference, I am planning to use the folllowing parts:

http://cablesaurus.com/PCIe-x16-Extender-Cable-w-Molex-Connector

GPU:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814202030

Mobo:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813130645

PSU:
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&N=100006676&isNodeId=1&Description=1250+watt+seasonic&x=0&y=0


Thank you!

[A Meteorite]

You will want the PCI-E extenders with molex if you hook up a lot of GPUs to a motherboard (greater than 4 if a good motherboard, or less if a junk one). The reason is they can pull 75W from the slot by spec (although cards usually pull most of their power from the PCI-E aux, you never know). I've seen pictures of melted ATX plugs/motherboards from too much current going over a few wires and traces.

If you want to hook up 5 or 6 7950s, you would definitely want at least 2 or 3 of them hooked up with extenders that have a molex.

Also keep in mind you don't want to overload the molexes off your PSU. So try to use different chains...

EDIT: Here's one such story. https://bitcointalk.org/index.php?topic=102890.0 I have seen others but don't have examples handy.

[MaGNeT]

DIY powered PCIe extender cables:

http://blog.zorinaq.com/?e=44

[Benny1985]

You will want the PCI-E extenders with molex if you hook up a lot of GPUs to a motherboard (greater than 4 if a good motherboard, or less if a junk one). The reason is they can pull 75W from the slot by spec (although cards usually pull most of their power from the PCI-E aux, you never know). I've seen pictures of melted ATX plugs/motherboards from too much current going over a few wires and traces.

If you want to hook up 5 or 6 7950s, you would definitely want at least 2 or 3 of them hooked up with extenders that have a molex.

Also keep in mind you don't want to overload the molexes off your PSU. So try to use different chains...

EDIT: Here's one such story. https://bitcointalk.org/index.php?topic=102890.0 I have seen others but don't have examples handy.

Could you explain this further:

Also keep in mind you don't want to overload the molexes off your PSU. So try to use different chains...

How do I run them off different chains?

[A Meteorite]

Could you explain this further:

Also keep in mind you don't want to overload the molexes off your PSU. So try to use different chains...

How do I run them off different chains?

So you have a couple cables off the power supply providing a few molexes each. You shouldn't hook up every powered extender to the same cable coming out of the power supply. If I recall correctly, the max that you'd safely want to pull from a molex is 75W - exactly what the slot can provide by spec. So to be absolutely safe, try to use a different molex cable coming out of the PSU for each powered extender. However, if you must, I personally would feel safe with two on the same cable if it's a high quality PSU (but don't do it if you don't have to).