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5850 two molex vs 2x6 splittler

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April 25, 2010 4:23:25 PM

I just purchased Radeon 5850. The card has two 2x6 PCI-E outs on it. I'm looking for best power conservation and OCing capabilities. My PSU has a 2x8 and 2x6 PSU slot so my cord options are:


1. Two molex pheripheral to 2x6 PCI-E (this is what came with the card)

2. A single 2x6 PCI-E cord that splits into two PCI-E on opposite end. (will this limit the power my card gets?)

3. A 2x6 to 2x6 PCI-E and a 2x6+2 to 2x6 PCI-E.



My system specs:
Phenom x4 @ 2.5ghz
Radeon 5850
8GB ram
Raidmax Volcano 630w PSU
Antec 900 case


Side bar question: People talk about splitting the load on the PSU between the rails. How do you tell which rail a certain device is on?



Thank you!
April 25, 2010 4:37:23 PM

I have not much confidence in cable converters. But in your case, I suggest to just use the molex pheripheral to 2x6 PCI-E connector since that is what came with the card. Thus, the first card will draw power from the 6PIN PCIe that comes with your PSU while the 2nd card will therefore draw the power from the MOLEX to 6PIN converter that came with your card. Seems the safest bet for me.
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April 25, 2010 4:40:07 PM

The Dowlz said:
1. Two molex pheripheral to 2x6 PCI-E (this is what came with the card)
Best option

2. A single 2x6 PCI-E cord that splits into two PCI-E on opposite end. (will this limit the power my card gets?Probably)
Not a good option

3. A single 2x6 PCI-E cord and a single PCI-E 2x8 with a 2x6 adapter on it. (im guessing this is worst option)
Will work, but check you 2x8, it may be molded to allow you to remove 2-pins, making it a 2x6
..........................
Side bar question: People talk about splitting the load on the PSU between the rails. How do you tell which rail a certain device is on?
You would have to use a PSU tester, but most PSUs with multiple rails do not have more than one 2x6 or 2x8 plug on the same rail.

If you need more info, please post your PSU make and model number.
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April 25, 2010 4:47:17 PM

PSU is Raidmax Volcano 630w as listed above, it has two PCI-E, one 2x6 and one 2x8. Yes the 2x8 cord has an option to remove two pins, edited my first post for clearity.


@ Randomkid: No you're confused I have only have one graphics card and it requires two PCI-E 2x6 slots (lots of power)
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April 25, 2010 5:02:33 PM

Options 2 and 3 will draw from different rails correct? 12v and 3v rails. Which would be better for the GPU?
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April 25, 2010 7:34:57 PM

I downloaded your PSU manual. You have 2 12V rails: 1 is 16-18 amps and the other is 17-18 amps. The PSU has two PCI-e connectors on the same power cable, so it is likely to be on the same rail. Try those connectors first on your 5850. If it doesn't work, use 2 of the molex connectors to the 6-pin cable that came with the card and one of the 6-pins on your PSU's modular cable. Of the options you listed in the original post, try option:
-- 2 first, then
-- 1, then
-- 3
As long as you are not cross-firing 5850s, your PSU should work well with your rig.
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April 26, 2010 3:42:37 AM

I thought you said it was a bad idea to use the splitter?

I used the splitter and the card runs fine so far OC'd to max on CCC. I'm just thinking I could get more out of it if I had two moxel cords powering it off separate rails.
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April 26, 2010 3:48:53 AM

1.) Don't worry about which rail has what/etc., chances are that they are tied together inside.

2.) Also, don't worry about the wires. They are rated to carry much more current than they do. The weakest link is the GPU PCB connectors, but by then they are split again.
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April 26, 2010 4:05:00 AM

So back to my question. Which to use?


1. Two molex pheripheral to 2x6 PCI-E

2. A single 2x6 PCI-E cord that splits into two PCI-E on opposite end.

3. A 2x6 to 2x6 PCI-E and a 2x6+2 to 2x6 PCI-E.

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April 26, 2010 12:30:05 PM

The Dowlz said:
I thought you said it was a bad idea to use the splitter?

I used the splitter and the card runs fine so far OC'd to max on CCC. I'm just thinking I could get more out of it if I had two moxel cords powering it off separate rails.

That was before I read your PSU manual, saw the PSU power label, and saw the PCI-e cable configuration in the illustrations. Many PSUs are marginally OK, and it seems to me that most people end up buying a low-cost, poorly performing PSU after spending a lot on the other components. You did not do that. If you are OCing and its functioning well, be happy.
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