Gainward 7600GT AGP power adapter

They make noise, too.

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mits
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Gainward 7600GT AGP power adapter

Post by mits » Wed Nov 29, 2006 10:42 pm

Hi all,
a friend of mine just bought a Gainward 7600GT AGP.
http://img99.imageshack.us/img99/8466/8 ... 8m7rj7.jpg
For connecting the card to the PSU (which doesnot have a PCI-E coonector) the card comes with an adapter that has 2x4-pin male molex connectors and 1x6-pin PCI-E female connector that plugs in to the card.
A connecotr like this:
http://img177.imageshack.us/img177/1408/6pinjo2.jpg
My question is : Does he have to connect both molexes to the PSU or just one of the two is enough. Nothing is stated on the cards manual.

andyb
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Post by andyb » Thu Nov 30, 2006 2:59 am

You should connect 2 molex connectors to the adaptor cable not just 1.

And also you should connect the 2 molex connectors from 2 different strings of connectors. This will not overload your PSU in anyway, whereas it could if you connected both of the molex connectors from one string of power connectors.

I have just had to buy one of these (I got 2), the instructions explicitly state this.


Andy

mits
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Post by mits » Thu Nov 30, 2006 9:56 pm

Ok, thanks a lot.

Brian
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Post by Brian » Sat Dec 02, 2006 6:35 pm

Of course that's what the instructions say. And it's sound advice if it's not difficult for you to follow. But is two the minimum number of required molecies? I can tell you my GF7800GT runs fine, drawing its power from such an adaptor. I've plugged both of the molecies on the same string (the PSU only has a single 12V rail anyway), which demonstrates that my card would run fine if the plug were designed to sit on a single molex.

But I've blown enough hot air. I'm going to power down and unplug one of them, so I can tell you whether you need both.

Downside to unplugging one: you have a live 12V male swinging around in your case.

Brian
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Post by Brian » Sat Dec 02, 2006 6:39 pm

Yeah, it boots without a problem and RTHDRIBL (stressful 3D app) runs fine. And look, I can plug in two IDE devices now!

Conclusion: The PNY GeForce 7800 GT only needs one of the two molecies plugged in.

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Post by Vicotnik » Sat Dec 02, 2006 7:07 pm

The reason for not one but two molex connectors is safety only (as far as I know). Two paths for the power means half the resistance. You don't want that cable to get to hot. :) Not that it's likely to happen with a non overklocked 7800GT, but still.
That the PSU has one or two +12V rails has nothing to do with it.

andyb
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Post by andyb » Sat Dec 02, 2006 7:37 pm

You would have to be totally insane, or know exactly what you are doing with the equipment that you have not to follow the very simple instructions that EVERY manufactuer provides with every card that needs an adapter.

By default, all PCI-E cards with PCI-E power supplies are ruled out, the reason is simple, the 12v load is already distributed, thats the specification and no-one is allowed to advertise otherwise.

By not using the specified wiring you are risking hardware. Good Luck


Andy

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Post by cAPSLOCK » Sun Dec 03, 2006 4:19 am

The 6pin PCIe power plug has two pins for 12v, one coming from each molex connector, so if you plug in only one molex connector only one of these pins gets power, so you could be lucky and the two pins join together anyway on the graphics card PCB, or there could be something like one VRM for each input in which case you could end up damaging your graphics card by only giving it power on the one input.

The whole story of plugging the two molex connector to two different "strings" of connectors is more of a safety measure. All the 12v comes from the same part of the PSU, even different rails are just two different overcurrent protections and not different transformers. If you plug in both connectors on the same "string" the worst that can happen is you melt the wires, although I seriously doubt it.

Please note that I have nearly no knowledge in electronics, and many people on these forums are probably more qualified than me to answer this question, I just use common sense.

@Brian: I know a buddy that ran his 6800Ultra without plugging in the PCIe power, and it booted fine, just that it crashed after a couple of minutes of intensive use, in your case you should be ok since you tested with rthdrbl, and apparently your gfx card only needs one of the 12v pins to be powered, but this might not be the case for everyone!

mits
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Post by mits » Sun Dec 03, 2006 10:11 pm

Thank you all guys for your info. I also e-mailed Gainward and they suggested that i must connect both moleces to the psu. Card is connected now and is running fine.
Thanks again.

Brian
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Post by Brian » Mon Dec 04, 2006 6:11 am

I'm very much comfortable voiding my warranty and taking calculated risks with my hardware. Any time you run a fan at less than 12V, or undervolt a processor, you run hardware outside of its specifications.

It would be better to connect the three yellow wires on the PCIe-to-Molex adaptor, but in my case, it would appear unnecessary.

I guarantee your wires will not melt. The power supply is intended to be incapable of sending more than 20A down any 12V line. If your power supply's designers are competent, or at least smart enough to copy off of competent people, then they chose a wire size that's capable of carrying 20A without melting.

Your comments about how one ought to use two strings are valid, though. Based on the 75W my video card probably draws, and 18AWG wire, I'd save ~40mW by using a two-conductor cable instead of a single-conductor cable. Using a proper, three-conductor PCIe connector would bring an additional small savings.

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