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Wiring Power for SLI with 4 PCI-E holes but only 2 plugs

Last response: in Components
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December 27, 2010 5:25:24 AM

I would like to get another GTX 460 for SLI. Each GTX 460 has two PCI-E power inputs, but my power supply only has a total of 2 PCI-E connectors. Of course I'll just have to use the molex converters, but how should I use them? Should I use one converter and one regular PCI-E connector for each card, or use both PCI-E for one, and both molex to PCI-E converters for the other? Does it even matter that I have more than one PCI-E connector per card??--because both of my power supply's PCI-E connectors share the same wires anyway. Does any of this matter?

My power supply is this one--hope it works:
Raidmax RX630Z 630 Watt
http://www.frys.com/product/6030458

Here is the rest of my computer if that matters at all:
GPU: EVGA GeForce GTX 460 Superclocked 1GB (01G-P3-1372-TR)
CPU: Intel Core i5-760 Lynnfield 2.8GHz Quad-Core running at 4.1Ghz
Mobo: MSI P55-GD65 LGA 1156 SLI
Memory: G.SKILL ECO Series 4GB (2 x 2GB) DDR3 1600 (PC3 12800) Model F3-12800CL7D-4GBECO
Cooler: Scythe SCMG-2100 MUGEN-2 Rev.B 5 Heat Pipes CPU Cooler
Soundcard: Creative Sound Blaster Audigy2 ZS PCI
Case: Antec NSK6580B Black 0.8mm cold-rolled steel ATX Mid Tower

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a b ) Power supply
December 27, 2010 10:20:22 AM

Your psu isn't the best and I don't think it has enough wattage or power on the 12v to run your system and sli 460's.

I am also running 2x460's off my psu with only 2 pci-e cables.

If you want to try it you need to put one pci-e cable and one adapter on each card.

I'd recommend a psu upgrade something like these, they are in order of preferance and all have 4xpci-e-

http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
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a c 144 ) Power supply
December 27, 2010 2:13:14 PM

A pair of GTX460's needs about 20 amps from the 12 volt rails.

My experience with Raidmax is that they are not too bad - if you derate them about 20%, in other words treat your 600 watt PSU as a 500 watt PSU. I think that you will have enough power. You won't have much left over, though.
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a b ) Power supply
December 27, 2010 2:26:26 PM

If you take the 3.3v and 5v from the 614w its even less than 500w available.

I read is was around 12a per card but even still with the OC'd cpu and the superclocked 1gb cards its tight.

Whats the worst that could happen. :cry: 
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December 29, 2010 2:42:37 AM

That's a bummer, but I thought that might be the case--stupid misleading SLI logo on the box... What is the worst that could happen BTW? Would I most likely just kill the PSU? At least then I could justify quickly buying a new one.

Maybe I'll just buy a SSD instead of another GTX460--how boring. Too bad two crappy PSUs can't be combined to power one good computer. Someone invent an external PCI-E power supply for cheap people like me in this situation :kaola: 
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December 29, 2010 2:43:00 AM

Best answer selected by cRACKmONKEY421.
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December 29, 2010 2:45:45 AM

I would not be surprised if you did kill off your psu if it does not have enough voltage. The concern then would be that the psu would also not be giving the cards proper power, even before it "dies". You could potentially shorten the life of other components in your computer. Drops can be damaging just like spikes when it comes to electricity through electronics.
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a b ) Power supply
December 29, 2010 6:47:42 AM

Best case it just wouldn't boot or would crash or artifacts, probably wouldn't cause serious damage.

You can use another psu to power your other card if you want but you'll have to run it with the side off.

The most important part of your PC is your psu so its worth spending a bit of money on.
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