Two 6-Pin cables instead of Two 8-pin cables on a HD 7950

Dethan1999 · Nov 3, 2016

Hi there, I recently got a HD 7950 for free from a friend. It requires 2 8-pin PCIe connectors, but my motherboard only has 2 6-Pin PCIe cables. Would it work if I were to put 1 6-Pin cable in each 8-pin port?

I don't plan on doing too much heavy gaming. I plan on using it on my 2nd rig to run miners (don't tell me how inefficient it is... I know...). Anyways, I tested it using a combination of Molex-to-6-pin adapters and got a 6-pin-to-8-pin. With only 1 x 8-Pin cable, the PC didn't recognize the card. So would using 2 6-Pin cables (one per 8-pin slot) work?

Even if it's considered "risky", would it still work? I got it for free and I have a better card for my personal rig so I wouldn't be too upset if something happened.

Thanks for the help!

rgd1101 · Nov 3, 2016

what is the psu make and model?

13thmonkey · Nov 3, 2016

I don't think that 2x6 pins into 2x8 pin slots will even allow it to start up, 2 6 to 8 adaptors would BUT that's a fairly hungry card, so what PSU do you have and therefore why does it only have 2x6 pins.

Dethan1999 · Nov 3, 2016

Well, i hate to say this.... But the PSU I have is pretty crappy. It's a Logisys 480w PSU... I know, bad brand... Its for my 2nd rig.

It says 500w PSU recommended for the card, but I've read that its hard to get it to reach that unless under extreme load on all other components. My 2nd rig has an energy-efficient I5-3450s @2.8 GHz, and a crappy dell motherboard. I don't plan on doing much with it, just basic fiddling around.

The PSU itself has ZERE 6-pin connectors, but I used some Molex to 6-Pin connectors.

13thmonkey · Nov 3, 2016

in that case DO NOT use it. You know this already. It's not the wattage it's the 12V current that's the problem.

Dethan1999 · Nov 3, 2016

13thmonkey :

I'm a bit confused here... 12v current problem? I know Molex to 6-Pin is far more risky than a 6-pin straight from the PSU. Is it a heat issue? Thanks for the advice.

reedo_43 · Nov 3, 2016

No the issue is a very poor quality psu without the correct connectors in the first place.

13thmonkey · Nov 3, 2016

can your PSU supply enough current on the 12V rail, the lack of PCI-E connectors suggests not.

If it is this one http://www.newegg.com/Product/Product.aspx?Item=N82E16817170014 then the answer is no, it has 16A at 12V, that's 192W, really that's a 200W PSU and not a 480W PSU. Your GPU needs probably 150W (I disagree with their method although they get 138W http://www.guru3d.com/articles-pages/radeon-hd-7950-overclock-guide,3.html
So that leaves 40W for everything else that uses 12V. It's not enough, and thats why your PSU has no PCI-E cables.

Here they say 180W https://www.techpowerup.com/reviews/AMD/HD_7950/25.html so i might even be being too optimistic.

Dethan1999 · Nov 3, 2016

reedo_43 :

Yeah, I figured the PSU would be the real issue. Darn, I was hoping to be able to use it. I'm not really in the market for a better PSU for a 2nd rig. Oh well... I have a 750w EVGA PSU on my personal rig, but I don't plan on changing that to my 2nd rig. Thanks for the help!

Dethan1999 · Nov 3, 2016

Just out of stupid-curiosity... If I had another PSU, that had a 6+2 pin connector... Is there a way to... combine PSUs? Like, have a 6+2 Pin connector running from a separate PSU but use the main one for the other 8-pin and to power everything else?

If it doesn't work, that doesn't surprise me lol. At this point I'm desperate haha

Thanks for the help everybody!

13thmonkey · Nov 3, 2016

yes, something like this http://www.frozencpu.com/products/11742/cpa-167a/ModRight_CableRight_Dual_Power_Supply_Adapter_Cable.html
It provides the signal to the second PSU to start up.

Dethan1999 · Nov 3, 2016

13thmonkey :

I think it's this one: http://

Its probably the same one you mentioned, but black. They have a lot of Logisys 480w PSUs out there for some reason but I think that's it. I'll confirm when I get home.

13thmonkey · Nov 3, 2016

it's also 16A @ 12V

bloodroses · Nov 3, 2016

Do not, and I repeat, do not try to use that power supply with that video card. It will kill the PSU, possibly taking out the computer as well.

http://www.overclockers.com/logisys-ps480x2-review/

Dethan1999 · Nov 3, 2016

bloodroses :

....good to know... oh boy glad I came here before testing anything haha

Dethan1999 · Nov 3, 2016

13thmonkey :

Oh cool! That's perfect. Do you think it's even worth using the Logisys one AND the other one with that adapter? Or is the Logisys PSU an extreme risk? I've been told NOT to use it. I'm aware of how bad it is, I'm just trying to get it to work on a 2nd rig, because I havent been able to test it. If it works, Ill consider getting a much better PSU

13thmonkey · Nov 3, 2016

I wouldn't even keep it as a spare, you could power up a CPU (not AMD Fx8xxx/9xxx) and not much else extra.

Dethan1999 · Nov 4, 2016

13thmonkey :

Yeah, I just plan to use it for my simple computer that doesn't draw much power. I5-3450s and a micro ATX Dell Motherboard. Very light stuff. Other than that, Ill get a better quality PSU later this year. Thanks for the help!

Two 6-Pin cables instead of Two 8-pin cables on a HD 7950

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