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Powering vid card with 1 power rail

Last response: in Graphics & Displays
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September 15, 2011 5:40:15 AM

got two gtx460s that ive been figuring out how to power with my psu that only has 2 pcie power rails. ive concluded that i should just use molex-pcie adapters. but anyone know what if i just power the cards with 1 rail each? i dont plan on overclocking or anything.
a b Î Nvidia
September 15, 2011 8:57:27 AM

Does your PSU have 2 or more +12V rails or just one? You can find that information on the sticker attached on the side of the PSU. You need to have two 6 pin power connectors connected to each card in order to run them. If you PSU doesn't have enough 6 pin PCI-E connectors you can use Molex adapters. However, your PSU may not be able to provide enough power for 2 GTX 460s. Most PSUs that can power SLI or Crossfire configurations come with at least 4 6 pin PCI-E connectors. Post how many amps you have on your +12V rail(s). If your PSU isn't up to the task, you'll have to upgrade that before going for an SLI setup.
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a b Î Nvidia
a b K Overclocking
September 15, 2011 9:14:20 AM

read the side of your PSU, this tells you how many 12v rails it has. The number of pcie power connectors does not = the number of power rails. For 2 x gtx 460's you probably want 40a or more on the 12v rail/combined rails. It has nothing to do with the number of pcie connectors.
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Related resources
a c 155 Î Nvidia
a c 152 K Overclocking
September 15, 2011 9:36:10 AM

Tell us what PSU you are using so we can better help you!
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September 21, 2011 11:59:55 PM

oops forgot about this thread. ive been learning alot about power from you guys.
have a CM RPP 650W
http://www.coolermaster.com/product.php?product_id=2551
didnt know power was this complicated! im not at my main comp with this psu right now but is this what im supposed to be looking at? so it has 3x 12V? dunno


gosh with these new video cards maybe i indeed have to get a new psu. hate wasting a perfectly good psu though. i may be heading the radeon 6970 route which means a single card (since i cant do crossfire on my sli board) so i may avoid all this hassle.
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a b Î Nvidia
September 22, 2011 12:07:55 AM

Assuming that power supply can actually deliver what it promises, that would be fine for two GTX 460s, you would just have to make sure that you connect each card to a different +12V rail so you don't wind up overloading one of the rails. I don't think CoolerMaster is known for making very good power supplies, though the one you linked to does at least look to be a modern design. I'd suggest looking for reviews of that PSU to see if it can deliver what is promises, the power supply market tends to be rife with false advertising ie. advertising the specs that a given unit can only maintain for about 2 seconds when placed in a refrigerator, rather than what it can do in real world conditions.
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a c 155 Î Nvidia
a c 152 K Overclocking
September 22, 2011 12:12:30 AM

Although CM PSU´s are hit and miss the specs on yours say it is good enough having 540watts available on the +12 volts gives 45amps combined all rails which is sufficient for your cards in SLI.
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September 22, 2011 12:19:07 AM

now how would i be able to know which rail each connector comes out of? there are two PCIE 6pin connectors, which i assume each are on their own 12V rail....whats that 3rd +12V rail? unless im misunderstanding the term "rail"

yea i bought this CM psu back when the first 80+ psu came out and didnt really check any reviews and such. honestly i bought it cuz it said 80+ and i thought that sounds cool LOL. :non:  i knew (and continue to know) few little about how power works in my computer. only now have i woken up and really want to learn as to not fry my expensive components.
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a b Î Nvidia
September 22, 2011 12:24:08 AM

The wires are usually colour coded. Yellow probably is +12V1, I'm not sure what the other colours might be, I haven't owned any PSUs with multiple +12V rails. You may have to look up the documentation to see which 4 pin molex connectors are attached to which rail. Your 6 pin PCI-E connectors will most liklely be on one rail. You'll have to use molex adapters to power your second card.
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September 22, 2011 12:25:45 AM

ok that gives me a lead to work with.

i was planning to power (if i get dual 460s) each card with their own PCIe 6pin and molex adaptered so not one card has all of the pcie 6pins
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a c 155 Î Nvidia
a c 152 K Overclocking
September 22, 2011 12:33:47 AM

Most likely the two PCIe connectors are on separate rails and the CPU/EPS connector on the third one. Using two different cables for the molex adapters you should be fine and not overloading any rail.
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