OK to use 2 Molex to PCIe adapters for an SLI set-up?

[smilingcrow]

I have an old Seasonic S12 430W which has no PCIe connectors. I want to build an SLI system using two 7900GS cards and a C2D; the maximum total power draw for the system will be in the range 200 – 250W AC. I notice that there are adapter cables that can turn two 4 pin Molex connectors into a single 6 pin PCIe connector; they are supposed to be used one per power supply cable set.
My Seasonic has 3 cable sets, one of which I need to power a hard drive and optical drive; will it be okay to use the other two to power a PCIe card, one per cable set?
The 7900GS consumes roughly 45-60W at full load.
Is this idea reasonable?

[wundi]

I certainly think it's reasonable.
I have two 7800GTs in SLI with an S12-430 and it works fine.

I wouldn't recommend it though, because tidying up the cables won't be much fun at all. Especially in a P180.

I'm actually on the lookout for an equally quiet SLI-ready modular PSU. The Be Quiet! Dark Power Pro series seems promising, but I'm not sure how its noise compares. Any suggestions?

[Tzupy]

In principle, to increase the efficiency of the PSU (when a lot of load is on the 12V line), one should add a 3.3V or 5V load on the same PSU connector.
There was an article some time ago about this. I did it for my 7900 GTX, the power is provided through an adapter and shared with the WD 3200 JD.

[smilingcrow]

I certainly think it's reasonable.
I have two 7800GTs in SLI with an S12-430 and it works fine.

I’m not clear, are you using 2 Molex to PCIe adapters?
The 7800GT is more power hungry than the 7900GS, so this is a good sign.

I'm actually on the lookout for an equally quiet SLI-ready modular PSU. The Be Quiet! Dark Power Pro series seems promising, but I'm not sure how its noise compares. Any suggestions?

The two that spring to mind are the Corsair CMPSU-520HX and the Antec NeoHE 500. The Corsair is supposedly made by Seasonic anyway, which is promising and
reviews that I‘ve seen are complimentary about it.

It’s not easy to determine what the best power supply is for a particular SLI system. They will typically push the power consumption into the range where the power
supply fan will ramp up in speed and noise quite noticeably. So a difference of 10-20W per VGA card might make all the difference in overall system noise; as much as 5dB in some cases.
This SPCR review shows a comparison of the Antec Neo HE 430 & two S12s across a range of DC outputs.
Since the power supply fan will ramp depending on temperature, the installation of the power supply is critical; that’s probably the main reasons that I chose the P180, for the isolation of the power supply.

One solution that I’d consider would be to use a passive power supply in a P180 and use a fan controller that has a temperature sensor to control a Nexus 120mm installed in the lower chamber. A fanned power supply will also likely benefit from a case fan in the P180, although the temp sensor fan controller is probably redundant here.

In principle, to increase the efficiency of the PSU (when a lot of load is on the 12V line), one should add a 3.3V or 5V load on the same PSU connector.
There was an article some time ago about this. I did it for my 7900 GTX, the power is provided through an adapter and shared with the WD 3200 JD.

Thanks for the info; was this an SPCR article or forum post, or was the article located somewhere else? This does contradict the other information that I’ve read, so I’ll need to do some research.
I could do this with my system, but the cabling would get a bit tricky in a P180, especially as the hard drive is in the lower chamber.

[wundi]

I have two 7800GTs in SLI with an S12-430 and it works fine.

I’m not clear, are you using 2 Molex to PCIe adapters?

Yes, exactly.

I'm actually on the lookout for an equally quiet SLI-ready modular PSU. The Be Quiet! Dark Power Pro series seems promising, but I'm not sure how its noise compares. Any suggestions?

The two that spring to mind are the Corsair CMPSU-520HX and the Antec NeoHE 500.

Thanks for the hint! Sadly I can't find Corsair PSUs available in Finland, but it seems I've overlooked the Antec NeoHE 500. It's also less expensive than the BeQuiet unit!

It’s not easy to determine what the best power supply is for a particular SLI system. They will typically push the power consumption into the range where the power supply fan will ramp up in speed and noise quite noticeably.

You're right -- still for me the idle noise is definitely most important. Which raises another question: will the NeoHE's slow-running 80mm fan be able to cool my two Samsung P120s in the lower chamber sufficiently? The S12-430 keeps them just below 40C, which I'm happy with, but I'm worried that my HDD temps might rise (even significantly?) if I move to NeoHE. Need I worry?

[smilingcrow]

Which raises another question: will the NeoHE's slow-running 80mm fan be able to cool my two Samsung P120s in the lower chamber sufficiently? The S12-430 keeps them just below 40C, which I'm happy with, but I'm worried that my HDD temps might rise (even significantly?) if I move to NeoHE. Need I worry?

Do you have a fan in the lower chamber? If not, then a fan at even 600 RPM will do wonders for your drive temps; at least it does for me, but I’m using a fanless P/S which might make a difference.
It’s hard to directly compare power supplies as the orientation of the fan and other issues mean that their performance in a given system is not always easy to pre-determine.

[alejo]

Whoa. That's freaky. I hadn't logged onto SPCR forums in a long time but I retrieved my password in order to ask the same question with regards to the same cards and the same old version seasonic 430.

Anway, I found and adapter that actually split a single PCI-E power connector into two. Would it be OK to use a molex to pci-e and then chain it with the splitter?

[smilingcrow]

Whoa. That's freaky. I hadn't logged onto SPCR forums in a long time but I retrieved my password in order to ask the same question with regards to the same cards and the same old version seasonic 430.

I imagine that the 7900GS is going to be pretty popular around here; good value, good performance, dual dual-link DVI (an essential feature ), HDCP and low power enough to make cooling it quietly relatively trivial. It makes the passive 7600GT cards seems a bit redundant to me.

Anway, I found and adapter that actually split a single PCI-E power connector into two. Would it be OK to use a molex to pci-e and then chain it with the splitter?

I don’t think this is recommended and with the Molex to PCIe connectors costing as little as £1, I don’t intend to risk it.

[wundi]

Do you have a fan in the lower chamber? If not, then a fan at even 600 RPM will do wonders for your drive temps; at least it does for me, but I’m using a fanless P/S which might make a difference.

I don't have an extra fan in the PSU chamber and I'd rather not add one either, since the fan of a good, quiet-enough PSU (such as my S12-430) can move enough air on its own to keep my HDDs cool. I've considered the passive PSU & extra fan route too... But I have the feeling that my X2-4600+ 7800GT-SLI rig may be a bit too power-hungry for the current passive PSUs. There's also the hassle with a fan in the tight spot with a longer-than-standard PSU (the Phantom 500 is just obscenely long!).

So I guess I'll have to go back to the BeQuiet plan, hmh.. I don't like this.

Anway, I found and adapter that actually split a single PCI-E power connector into two. Would it be OK to use a molex to pci-e and then chain it with the splitter?

I'd also advise against it. It's safest to stick the adapters to separate molex "branches".

[Tephras]

The Be Quiet! Dark Power Pro series seems promising, but I'm not sure how its noise compares. Any suggestions?

The 600W model was included in this PSU roundup, not much focus on noise though, I assume you have to wait for the SPCR review to get some proper info (it is in the Upcoming Reviews & Articles-list).

[wundi]

The Be Quiet! Dark Power Pro series seems promising, but I'm not sure how its noise compares. Any suggestions?

The 600W model was included in this PSU roundup, not much focus on noise though, I assume you have to wait for the SPCR review to get some proper info (it is in the Upcoming Reviews & Articles-list).

Thanks for pointing that out. It's somewhat reassuring that the BeQuiet was complimented for its low noise more than the S12-500 in that roundup. It has received good reviews at other sites as well. But perhaps I'll wait for the SPCR review, though it might take some time..

I also had a look at the Gallery here and the NeoHE seems to fit quite well with an extra 120x25mm fan. Ah decisions, decisions.. I wish I was The Decider!
(And sorry for taking the thread off-course.)

[Tzupy]

@smilingcrow: The article was at Extremetech, here is the link:
http://www.extremetech.com/article2/0,1 ... 947,00.asp
The SPCR forum discussion is here:
http://forums.silentpcreview.com/viewto ... 605bd815c7

[smilingcrow]

I don't have an extra fan in the PSU chamber and I'd rather not add one either, since the fan of a good, quiet-enough PSU (such as my S12-430) can move enough air on its own to keep my HDDs cool. I've considered the passive PSU & extra fan route too... But I have the feeling that my X2-4600+ 7800GT-SLI rig may be a bit too power-hungry for the current passive PSUs. There's also the hassle with a fan in the tight spot with a longer-than-standard PSU (the Phantom 500 is just obscenely long!).

I’m also wary of running a 250W SLI system with a fanless power supply rated at 300W. The Phantom 500 is of no interest to me as it’s not fanless at 250W output and louder than a Seasonic I believe. I wouldn’t want something that long in a P120 as well; it would make cable management very awkward.

I mentioned the idea for a fan in the lower chamber as you were worried whether the Neo HE would keep your drives cool enough. The Neo HE isn’t that quiet at 250W, so I would rather wait for Seasonic to bring out a modular design or take a risk with the Corsair. The Be Quiet! Dark Power Pro is a new one on me; let’s hope they live up to the name; it would be embarrassing otherwise.

@Tzupy - Thanks for the links, they make very interesting reading. I’m not clear though on one issue:

It seems as if running two VGA cards that are powered from one ‘rail’ will sometimes fail; but if you power one of the cards using a Molex to PCIe adapter, that power is 'distributed more evenly' and the system runs okay. Since I’m considering running both VGA cards using Molex to PCIe adapters, does this still apply? They will be running from different 'cable runs' though. Anyone?

[nici]

The Be Quiet! Dark Power Pro is a new one on me; let’s hope they live up to the name; it would be embarrassing otherwise.

They have been very quiet in the past at least Not counting passive PSUs, BeQuiet! was pretty much the only truely quiet PSUs available here before antec released the NeoHE and someone started importing SeaSonic. I still have an old 350W BQ with a nexus fan swap running nice and cool