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crossfire questions

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xitsej

n00b
Joined
Jul 10, 2008
Messages
34
I just bought and installed a second ATI 4870 512MB graphics card and am setting up crossfire however I have a couple questions about setup.

At 1920x1200, will I need 2 crossfire bridges installed or just 1 (as of right now I only have 1, but I can buy another). I've seen people recommend either.

I was also wondering how I should go about connecting the cards to the power supply. The card requires two 6 pin connectors. The card came with a couple 1-to-1 6pin to molex connectors.
These connecters are 1-molex to 1-6pin connectors; however most connectors I've seen require 2-molex to 1-6pin.
Is it okay to use the 1-to-1 connectors provided by the manufacturer or should I use the 2 to 1 connectors (1-to-1 is obviously preferable from a cabling standpoint)?

I was also wondering if I could get away with connecting both 6 pins to their respective 1-to-1 converters, and then connect both of those to a Y molex connector which would only take up 1 power supply molex output?

AKA is this possible:

6pin-on-GPU--->6pin-to-molex-converter--\\
__________________________________y-connector-->PSU
6pin-on-GPU--->6pin-to-molex-converter--//

I understand if this is not a good idea, i just hope that i can at least use the included 1-to-1 6pins to molex converters even if I have to connect them to different PSU outputs.
 
1 bridge should be fine, but I'd get 2 just because. They aren't really pricey or anything.

1 to 1 should be fine so long as the PSU and adapters themselves are of good quality. 2 6 pins on a single molex from the PSU via a Y cable like you're suggesting is pushing it though. I would not do that, the possibility for over-current is pretty high.
 
the PSU is a corsair HX620W and the connectors are the ones provided with the PSU. I assume that is high enough quality?
 
Crossfire only needs 1 bridge, the only reason you have 2 bridge slots is to chain more than 2 cards together. In this pic you can clearly see what's happening.

amdcrossfirex.jpg


I actually connect both, I dont know why :)

As for power I certainly would not put both cards powered from one cable on the PSU you want to balance molex connectors across as many cables coming out of the PSU as possible, especially since whatever PSU you have might have several seperate 12v rails. The molex to 6 pin im not so sure about, I don't know why we'd have 6 pin PCIe if it supplied no more power than a molex connector, although I have definately seen both. I think what is happening here is that they're expecting you to use a proper 6 pin for one and the 2nd doesn't draw full power so you can get away with just 1 molex, I strongly suspect that 2 6pins both powered by only 1 molex wouldn't be enough juice.

I'm not even so sure 620W is enough for that rig, depends what else you run, but I have the same GPU set up right now and picked an Antec Quattro 850W for it back when I put the rig together, I was probably just being careful at the time but it's still a large difference.
 
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A HX620w should have 4 native PCIe cables... you shouldn't need to use any molex to PCIe adapters at all.
 
I'm currently running the card on both 1-to-1 converters and it seems to be running fine (a part of MW2 that was previously causing the frame rate to drop is running smoothly now). As for the power supply - it only has 2 outputs that are 6 pin, which are taken by the first card; however it seems to be running well as of right now with just the 2 molex pins.
 
As for the power supply being enough, i tried corsairs power supply calculator and it recommended the HX650W. Do you think the HX620W should be enough then (corsair does have incentive to recommend a higher end PSU)?
 
xitsej said:
As for the power supply being enough, i tried corsairs power supply calculator and it recommended the HX650W. Do you think the HX620W should be enough then (corsair does have incentive to recommend a higher end PSU)?
Click to expand...

650W is fine. great even. dont worry about it. :)
 
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