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GTX 470 Tri-SLI and Power Supply  

post #1 of 37
Thread Starter 
Please see my sig rig. My psu doesn't have two additional pcie connectors to power another 470 but I do know the psu can handle three 470s. I know molex to pcie adaptors are not ideal so would a pcie splitter connector (1 to 2) be a better option or is there a better way I don't know of? I really do not want to buy a new psu with 6 pcie connectors.
Advice will be appreciated!
Edited by Zmanster - 5/10/11 at 6:51pm
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post #2 of 37
i'd do the molex to pci'e probably your best bet.
post #3 of 37
There's np.
    
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post #4 of 37
I will point out one thing.

You plan to put a GPU, with all your water-cooling system and HDDs and everything else on a 18A single rail, aka 216 watt of power (All the HDDs and molex are on that single rail).

Since you are OCing your GPU, which is a 215w TDP card (140w from PCIE connectors. 150w max when OCed), you are leaving about 66w for everything else in your system, including pump, fans and what every else you have in your system.

This is of course theoretical, since as you push the rail, it starts to voltage drift, so its not pure 18Ax12V, but more likely 18Ax11.6v, which is 208w (give or take), and you are looking at about 58 watt left.

In other words, I think its a bad idea really.
Over time PSUs starts to give way to "old age", and those 216w theoretical watts will start to become 200w or less over time.
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post #5 of 37
Quote:
Originally Posted by Defoler View Post

Since you are OCing your GPU, which is a 215w TDP card (140w from PCIE connectors. 150w max when OCed), you are leaving about 66w for everything else in your system, including pump, fans and what every else you have in your system.

This is of course theoretical, since as you push the rail, it starts to voltage drift, so its not pure 18Ax12V, but more likely 18Ax11.6v, which is 208w (give or take), and you are looking at about 58 watt left.

In other words, I think its a bad idea really.
Over time PSUs starts to give way to "old age", and those 216w theoretical watts will start to become 200w or less over time.
One thing you're forgetting DF is that most 'rails' are not very stringent, i.e. they have a pretty decent-sized cushion. The OCP on your average 18A rails won't actually kick in until probably around 25A.

Also, not sure what you mean by 'voltage drift' but your power won't start degrading until you actually start pushing the entire unit to it's capacity. A high draw on any single 'rail' won't cause that effect, because all the 12V 'rails' are is an OCP circuit on a given collection of wires.

BELATED EDIT:
I'd say it's worth trying with the molex adapters, and if the unit shuts off when you put it under load, try using the PCI-Ex splitters. Or you may even need to use a combination of both methods to make up the two plugs.

However, because you only have 1 molex cable, you actually wouldn't be able to use an adapter unless you acquire two more modular molex strands, as a 6-pin adapter should be made from two dedicated strands. You would probably also need some molex-SATA adapters, because you'll end up having to run 3 molex strands in order to power your pump.

Ergo the logical way to do this may well be through acquiring two 8-pin -> 2x6-pin adapters.

Situations like this is where a single-rail PSU comes in handy ... on a single rail unit, it wouldn't matter which way you wired it
Edited by brettjv - 5/12/11 at 3:46pm
    
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post #6 of 37
Quote:
Originally Posted by brettjv View Post
One thing you're forgetting DF is that most 'rails' are not very stringent, i.e. they have a pretty decent-sized cushion. The OCP on your average 18A rails won't actually kick in until probably around 25A.

Also, not sure what you mean by 'voltage drift' but your power won't start degrading until you actually start pushing the entire unit to it's capacity. A high draw on any single 'rail' won't cause that effect, because all the 12V 'rails' are is an OCP circuit on a given collection of wires.

BELATED EDIT:
I'd say it's worth trying with the molex adapters, and if the unit shuts off when you put it under load, try using the PCI-Ex splitters. Or you may even need to use a combination of both methods to make up the two plugs.

However, because you only have 1 molex cable, you actually wouldn't be able to use an adapter unless you acquire two more modular molex strands, as a 6-pin adapter should be made from two dedicated strands. You would probably also need some molex-SATA adapters, because you'll end up having to run 3 molex strands in order to power your pump.

Ergo the logical way to do this may well be through acquiring two 8-pin -> 2x6-pin adapters.

Situations like this is where a single-rail PSU comes in handy ... on a single rail unit, it wouldn't matter which way you wired it
I didn't "forget" anything.

I actually bothered to open another web page, google a few reviews which included an over-current run, and use my eyes to read them, and understand the PSU before I recommended something.

Also, I don't get you. Really I don't.

You are actually saying "hey, try it out, and if your PSU blows up after a few days because it couldn't hold to the OCP high usage over time, replace your PSU"?
Is that very smart to suggest?

Also are you serious? 25A?
Even the AX1200 doesn't have that big of a margine before OCP kicks in.
The X7 is a good PSU, but its not amazing one that can give you 38% extra on a rail. Don't be rediculous.

I actually prefer to say "don't risk it" instead of "try, if it blows, replace".
Edited by Defoler - 5/11/11 at 2:18am
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post #7 of 37
Thread Starter 
Well, now I'm confused. DeFoler, you think it's a bad idea because PSUs degrade over time (which makes alot of sense) and BrettJV thinks it'll be fine....basically give it a go. I don't know much about PSUs.....out of all the components in a PC, the PSU is the one I know the least about. I have searched reviews on PSUs and when I start to read them, I lose interest pretty fast

I guess I'll have to read up on PSUs and try to make a reasonable decision. Go for pci splitters or not.

DF, you're absolutely correct to assume that I have pushed my PSU by OCing my cpu and my two 470s. Furthermore, I have two pumps (XSPC and Koolance pmp-300) that power my WC setup and 10 + fans to cool my rads/rig.

If anyone else can chime in regarding this issue, I would like to hear your opinion.
Thanks again.
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post #8 of 37
Quote:
Originally Posted by Defoler View Post
I didn't "forget" anything.

I actually bothered to open another web page, google a few reviews which included an over-current run, and use my eyes to read them, and understand the PSU before I recommended something.

Also, I don't get you. Really I don't.

You are actually saying "hey, try it out, and if your PSU blows up after a few days because it couldn't hold to the OCP high usage over time, replace your PSU"?
Is that very smart to suggest?

Also are you serious? 25A?
Even the AX1200 doesn't have that big of a margine before OCP kicks in.
The X7 is a good PSU, but its not amazing one that can give you 38% extra on a rail. Don't be rediculous.

I actually prefer to say "don't risk it" instead of "try, if it blows, replace".
First off, to be clear, I didn't mean for it to sound like I'm criticizing your stance in telling the OP 'better safe than sorry'. I'm merely sharing my own perspective on the subject, and it appears that I believe that the 'risk involved' with trying the OP's prospective arrangement ... is significantly lower than you do. Everyone's entitled to their opinions

But, with all due respect, DF, I've 'bothered' to read hundreds of PSU reviews in the past

And that's how I know that it is highly unlikely that a '18A rail' on a 900W PSU is going to actually be locked down at 18A. There is definitely going to be leeway there, they are never locked down at the exact amperage specified on the box. Maybe it won't allow 25A, but it's going to be more than 18A, for sure. 25A is far from a 'rediculous' estimation. It may turn out to be slightly off, but it's perfectly 'realistic' to guess at this amount, absent the actual facts of the situation.

What the AX1200 does is fairly irrelevant to this equation. In fact, it's probably more likely that a very high-end unit like that would have more 'strict' OCP circuits defining it's rails.

Now, if you know for a fact from a review what the actual amperage is that can be pulled through that particular 'rail' on the OP's particular psu, please do share the review with us so we can see where we're at

Also, even if there was 'voltage drift', which, as I say, only applies if the entire PSU is being pushed to capacity (the concept does not apply to individual 'rails', save on an HX1000), that 18A rating is still based on amperage. I.E. even if your overall 12V circuit dipped to 11.5V due to the PSU being at capacity, you're still going to be able to pull the same total amount of amperage through that 'rail' before tripping it's OCP.

Another thing I'd point out is that if you believe, as you appear to state above, that 150W is the maximum that can be pulled out of two 6-pin PCI-Ex connectors, you are mistaken on this point. That is just the spec that the card makers are expected to adhere to. Once you start OC'ing, you certainly could pull more than 150W out of those connectors, because the card is no longer in 'spec'.

The actual maximum that can be pulled from every connector on your PSU is dictated by the amperage allowed by the OCP circuit on the 'rail' it's connected to (not applicable to single-rail PSU's), or the OCP on the entire unit, or, worst-case scenario, the gauge of the wiring itself.

Obviously, the OP doesn't want to spend money he doesn't have to, otherwise he wouldn't be on here asking if he can make do w/what he has. 900W is, in theory, enough power for this rig.

Ergo, it SHOULD be possible, through one wiring scheme or another, for it to be able to support the third card. Yes, it will be running close to spec if put under full load, and in fact it's possible that his OC'ing capability on the cards will be limited. But he should almost certainly be able to make it work with the cards at stock.

Lastly, it is extremely unlikely that PSU would 'blow up' due to what he's trying here. We're not talking about an Allied/Deer or Raidmax piece of crud PSU, and therefore, if you draw too much current, either through a particular 'rail', or on the unit as a whole, the PSU will shut down, not 'blow up'.

All PSU's have an OCP circuits at the level of the entire PSU, the reason it's there is EXACTLY to protect the PSU from 'blowing up' when too much current is drawn. And OCP circuits are like 100 year old technology, so I think they pretty much 'have it down' at this point Only the cheapest junk PSU makers flub this piece of the equation and fail to use adequate components to protect the unit and your system.

OP ... most likely the best thing to do here is going to be to fashion one 6-pin connector through the molex cables, and the other through splitting one of the PCI-Ex 8-pins (EDIT: Please see 'Belated Edit' in the above thread )

Hook up your other 3 PCI-Ex connectors, one per GPU. Then make use of your 3 'adapted' cables as the 2nd connectors on each of the three.

Like I say, it's possible your OC'ing capability may be limited somewhat using this PSU. It's also possible that you'll have to try various wiring schemes to get it working right. And it's also possible that over time the unit will degrade faster than it would if you weren't pushing it hard. But I'm talking it's like the difference between the PSU lasting 5 years instead of 10 years.

And let me just state for the record that I would NOT suggest something to someone if I thought they were putting their system at risk, esp. not w/o making significant disclaimers to that effect

If you don't have the money right now for a new PSU and want to get this going, and don't mind your OC'ing perhaps being limited for a time until you get a new PSU, you should be able to get this setup safely working on your current PSU. It may take some patience and trial/error but it is highly unlikely (note: not impossible) that you are risking damaging your system, 'blowing up' the PSU, etc.
Edited by brettjv - 5/12/11 at 3:47pm
    
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post #9 of 37
Its nice that you read "hundreds of PSU reviews" but it still doesn't matter, as you did not read this PSU review.
Not all PSUs are the same, and you should know that pretty well.

Also your asumption that you can pull 25A from a 18A rail, is pretty funny.
It could have been correct if the PSU was working on this rail alone, and nothing else.
But clearly, this is not the case. There are other 4 rails, and all of them are being pushed.

So all this theory of yours, goes out the window.

I'm disappointed with you really. The fact is that you did not bother to look up on this particular PSU, and you are talking a lot on something you don't understand.

Also I will say it again.
You can't pull 138% of the amp from a rail without causing damage to it. The cables, resistors and the connection board is not designed for this increase.
The sata cables and molex cables are designed for 75w. You are going to recommend him pushing 100w+ on these cables?
Unbelieveable.

900watt is irrelevent. You are telling him to push a 216w rail (and 75w calbes) to its limits. Awesome...
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post #10 of 37
Where's the PSU Guru when you need him?
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