PCI-E Power Y-Splitter?

[jandlecack]

So I personally haven't used SLI or CF before. My current PSU (see sig) provides plenty of power for any SLI or CF configuration (obviously not tri, but regular should be fine). 50A on 12V rail etc.

However, it only comes with two dedicated PCI-E power connectors (6+2pin). If I wanted to run e.g. GTX285 SLI, I'd need two Y-Splitters to get two more PCI-E connectors out of the native ones. Doesn't this mean that the power supplied to the cards is halved?

Any risks I'd be taking here?

 

[theAnimal]

Drawing 1/2 the power from 2 sources is the same as full power from one source.

There shouldn't be any risks.

 

[WaitingForNehalem]

I wouldn't SLI on that.

 

[jandlecack]

Why not?

 

[Modelworks]

The 12V @ 50A would be across all the devices connected. So two connectors could pull 25A each ,or 10A on one and 40A on the other. The one thing to watch for is splitting off too many times on one connector. If the supply has 50A capacity and you try to use that full 50A over one connector coming from the supply you are going to melt some wiring. The wires on a PSU are not sized so that each wire can provide the total current of the supply. They intend for it to be spread among all the wires coming from the supply .

If they sold the supply with 2 connectors that provide 50A total , they designed it with 25A per connector in mind so the wiring is sized accordingly. So as long as each connector isn't required to supply more than 25A you should be okay.

 

[jandlecack]

I see. So would the current drawn from one of the PSU's PCI-E connectors be 25A / 2 if I used a Y-Splitter on it to connect to the two ports on a more power hungry graphics card? If so is that still according to spec requirements?

 

[HOOfan 1]

The cards will pull the power they need. the GTX 285 has two 6-pin PCI-E connectors. Each of these is allowed to pull 75W by PCI-E specification. I am pretty sure this is controlled by the graphics card itself, not what the PSU is willing to output on those connectors. So theoretically if you use a Y Splitter, each GTX 285 can pull 150W from a single PCI-E connector on your PSU. You said this was going to be a 6 pin to dual 6 pin splitter right? Do they make a 8 pin to dual 6 pin splitter? The 8 pin is allowed to deliver up to 150W. The 6 pin is actually capable of that though, the 8 pin only adds a couple of grounds. The Corsair 6 pin connectors have 3 18AWG 12V wires I believe. 4A a piece for those wire should be nothing

 

[jandlecack]

Originally posted by: HOOfan 1
The cards will pull the power they need. the GTX 285 has two 6-pin PCI-E connectors. Each of these is allowed to pull 75W by PCI-E specification. I am pretty sure this is controlled by the graphics card itself, not what the PSU is willing to output on those connectors. So theoretically if you use a Y Splitter, each GTX 285 can pull 150W from a single PCI-E connector on your PSU. You said this was going to be a 6 pin to dual 6 pin splitter right? Do they make a 8 pin to dual 6 pin splitter? The 8 pin is allowed to deliver up to 150W. The 6 pin is actually capable of that though, the 8 pin only adds a couple of grounds. The Corsair 6 pin connectors have 3 18AWG 12V wires I believe. 4A a piece for those wire should be nothing

Ah, I get it now. Thanks a bunch. Yeah I'll keep an eye out for 8-pin to 6-pin splitters, that actually makes more sense too since I got 8-pin connectors. Better be on the safe side.

 

[Lunyone]

I think your looking for something like this:
1ST PC CORP. 8" black sleeved splitter cable Model CB-PCIE8-Y - Retail

 

[HOOfan 1]

Originally posted by: Lunyone
I think your looking for something like this:
[L=1ST PC CORP. 8" black sleeved splitter cable Model CB-PCIE8-Y - Retail]http://www.newegg.com/Product/Product.aspx?Item=N82E16812706022

won't work on GTX285...they use 6-pin connectors only. It would work, if that company had made them split apart. as a 6+2 pin.

 

[daw123]

Double post

 

[daw123]

Originally posted by: HOOfan 1

won't work on GTX285...they use 6-pin connectors only. It would work, if that company had made them split apart. as a 6+2 pin.

You mean a splitter like this?
1ST PC CORP. 8" black sleeved splitter cable Model CB-PCIE8-Y - Retail

I want to Xfire two HD4870 X2s.

The X2 has a 6pin PCI-E power socket and a 8pin PCI-E power socket and I figure I can split the single 8-pin and 6-pin connectors from the PSU by:
Connecting this to the single 6-pin PCI-E connector from the PSU and plug both ends into the 6pin PCI-E power sockets on each graphics card;
Connecting this to the single 8-pin PCI-E connector from the PSU and plug both ends into the 8pin PCI-E power sockets on each graphics card.

I think each PCI-E connector from the PSU comes from a separate rail and each rail (four in total) provides 25A (or half this per connector if the connection is split in two)

So from HOOfan 1's post above the PCI-E power standard says that it can draw up to 150W from each connector.

So from my calculations:
Each connector will have P = I*V = 25A * 12V / 2 = 150W maximum to draw from.

Bang on what is needed.

Please point out if I have got any of this wrong.

 

[HOOfan 1]

What Power Supply have you got Daw?

PCI-E specification says the 6pin connector should draw no more than 75W
8 pin connector should draw no more than 150W.

If your PSU only has a 6pin and an 8 pin PCI-E connector, it is more than likely not capable of, or at least not wise to try and run 2 HD4870X2s on it.

 

[daw123]

Originally posted by: HOOfan 1
What Power Supply have you got Daw?

PCI-E specification says the 6pin connector should draw no more than 75W
8 pin connector should draw no more than 150W.

If your PSU only has a 6pin and an 8 pin PCI-E connector, it is more than likely not capable of, or at least not wise to try and run 2 HD4870X2s on it.

I've got the True Power Quattro 1000W.

I've already got one X2, hoping to add another next month (provided my car doesn't bankrupt me when I have it repaired this Friday ) and I have a feeling that I'm going to be running out of PCI-E connectors if I add a third X2 in the future. My previous post was me working out how to power a third card (would that be hex-fire?).

P.S. It took me multiple edits to sort out the links and quotes in my previous post - something went screwy with the post editing function.

 

[HOOfan 1]

I wouldn't try running 3 HD4870X2s on a TPQ 1000W.

 

[daw123]

Originally posted by: HOOfan 1
I wouldn't try running 3 HD4870X2s on a TPQ 1000W.

What PSU would you recommend for this?

 

[HOOfan 1]

Does ATi even allow for a 6 way GPU setup?

Anyway Xbit labs found that the HD4870X2 can consume up to 260W of 12V power. Multiply that by 3 and you have 780W of 12V. The TPQ is supposed to be good for 840W 12V. That only leaves you 60W for the CPU, fans, harddrives etc.

Furthermore as you can see, they showed it pulling up to 213W from the PCI-E power connectors the way the TPQ 850W is set up 12V3 has the ATX connector and 2 PCI-E connectors and 12V4 has 2 PCI-E connectors. I am sure that the TPQ 1000W is set up the same way. Assuming that you are going to have to run 2 of your HD4870X2s off of 12V4...that is 426W. At that type of power draw you can be sure that the 12V rail is going to be dipping below 12V so you can assume at least 35A being pulled from that single rail...even accounting for the fact that the rail can probably handle more than 25A before shutting down...I am sure it won't allow 35A.

If you truely can run 3 HD4870X2s...then you will surely want something more than the TPQ 1000W. You could probably get by with some of the more powerfull 1000W units like the Corsair HX1000, or the Enermax Revolution 85+ 1050W...but I would go for something around 1200W instead, like the Enermax Galaxy Evo 1250W, or Silverstone Olympia 1200W, maybe the BFG EX-1200.

 

[daw123]

Originally posted by: HOOfan 1
Does ATi even allow for a 6 way GPU setup?

Anyway Xbit labs found that the HD4870X2 can consume up to 260W of 12V power. Multiply that by 3 and you have 780W of 12V. The TPQ is supposed to be good for 840W 12V. That only leaves you 60W for the CPU, fans, harddrives etc.

Furthermore as you can see, they showed it pulling up to 213W from the PCI-E power connectors the way the TPQ 850W is set up 12V3 has the ATX connector and 2 PCI-E connectors and 12V4 has 2 PCI-E connectors. I am sure that the TPQ 1000W is set up the same way. Assuming that you are going to have to run 2 of your HD4870X2s off of 12V4...that is 426W. At that type of power draw you can be sure that the 12V rail is going to be dipping below 12V so you can assume at least 35A being pulled from that single rail...even accounting for the fact that the rail can probably handle more than 25A before shutting down...I am sure it won't allow 35A.

If you truely can run 3 HD4870X2s...then you will surely want something more than the TPQ 1000W. You could probably get by with some of the more powerfull 1000W units like the Corsair HX1000, or the Enermax Revolution 85+ 1050W...but I would go for something around 1200W instead, like the Enermax Galaxy Evo 1250W, or Silverstone Olympia 1200W, maybe the BFG EX-1200.

Thanks for the reply HOOfan 1.

I've had a look on the ATI website and it looks as if you can crossfire three X2s.

With regard to doing this I'll stick with the quadfire, since I know the TPQ 1000W can defintely handle this (and it is confirmed by ATI). If I add the third card, then I'll have to invest in a better PSU.

 

[MagickMan]

Originally posted by: WaitingForNehalem
I wouldn't SLI on that.

It's more than capable of doing SLI, and still has ~100 watts to spare. That Corsair wouldn't even blink.