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Single rail dual rail question?

Last response: in Graphics & Displays
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November 11, 2012 8:12:00 AM

Okay I have a rather simple question to ask. Will a graphics card with two slots for the PCI-e 6 pin work if you connect it with just a single PCI-e 6 pin rather than occupying both the slots? For example this graphic card: GTX 560 SE; it has two slots for the PCI-e 6 pin, will it work if I connect only one PCI-e 6 pin, with enough amperes on the rail, onto the slot?
Secondly, I can't seem to find the power requirement for GTX 560 SE anywhere. How many amperes will it need on a 12V rail?

Thanks! :) 
November 11, 2012 9:03:59 AM

Anyone?
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a c 204 U Graphics card
November 11, 2012 9:14:06 AM

yes you need both 6 pins connected or the card wont run and you risk burning out your pci video slot drawing more power that the slot can supply. most video cards now come with a molex to pci power connector if your ps has none or one video power connector.
http://www.geforce.com/hardware/desktop-gpus/geforce-gt...

show the card max wattage is 150w. to get wattage is volts times amps. to fine the amps for 150w you divide 150w by 12v. or 12.5A.
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November 11, 2012 10:18:36 AM

I see... thanks for answering! :D 
Yeah I know how to get the amps being a physics student and all... :p  but that's besides the point. How much amps you recommend should be on the 12V rail(s)?
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a b U Graphics card
November 11, 2012 10:53:34 AM

Generally speaking you want the highest amount of amps available on any given psu. I personally like a single 12v rail PSU with the highest amount of amps for the wattage I need and I also recommend a modular psu. My reasoning is that I can connect any and all devices without having to worry about going over the amp rating found on multiple rail psu's and because it's modular, do not have extra cable that I have to tuck and hide away inside the case. Also, don't forget to tak into account the efficiency rating of the psu, if it's a 650 watt psu that is 80% efficient, the actual amount of watts is 520.

Which is something to keep in mind, some psu's have single 12v rails and some have dual or multiple (3+) 12v rails. Most psu makers that have multiple rails do not readily tell you that they put amp limiters on each rail, be sure to look at the label on the psu. Makers put limiters on to force you to use the multiple rails evenly (spread the load) rather than connecting all your devices to just one 12v rail and overloading it.

Most newer psu's have the 6-pin connector on it's own rather than connected to the same cable as the 4-pin molex used for hard drives. Having the 6-pin connector from the psu by itself would be the ideal.

If there is any on part on a build to not be cheap on, it's the psu!

I highly recommend Corsair psu's, but that's m y humble opinion.

Goo luck!
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November 11, 2012 11:46:50 AM

Wow thanks for the awesome reply! :D 
I'll definitely take your recommendation into consideration, in fact, I'm thinking of buying this power supply:

http://www.amazon.com/Corsair-Builder-Series-Watt-CX500...

It has 38A on a single +12V rail. Good enough?

My system is a budget based one:

Intel i3 2120 @ 3.30GHz
RAM: 4GB DDR3
Motherboard: ASUS P8H61 M-LE

And I'll be getting the EVGA GTX 560 SE soon.

Oh and I just want to understand something... if this graphics card is rated 150W maximum usage, that means it'll draw a maximum of 12.5A of current from the 12V rail?
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a b U Graphics card
November 11, 2012 2:03:57 PM

Only $52 after $10 MIR: http://www.newegg.com/Product/Product.aspx?Item=N82E168...

1) Yes the total Current would be as you indicated; However is shared between the PCI-e slot and the two PCIE-e 6 pin power connectors. SO Generally not a problem.

2) Correction, Quote: "if it's a 650 watt psu that is 80% efficient, the actual amount of watts is 520. " The Eff Rating is based on power at the wall verses power output. IE (for 80% Eff PSU) if the PSU is delievering 350 Watts to computer, then power at the wall (What you pay for) is 437.5 Watts. A 650 Watt PSU if at max load (for a quality PSU it should be 650 W) then the power PAID for would be 812.5 W - The Ouptut power is NOT reduced by the eff rating.

3) PSU you referenced is a OK PSU Much better than some of the Low end Junk PSUs floating arround. On the same token it is not considered a "High quality" PSU like the Corsair TX and HX models, But then you pay more for them.
ie: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
You Idle power should be around 130 Watts @ idle and around 310 when gaming - Note these are total system power, not just for the GPU. So 500 is agrat choice Unless planning on SLI with two cards, then Min PSU should be 650 to 750 range.


4) do Not get tied around the axle on single rail PSUs and Modular cables.
... Most "Quality PSUs"limit the current to a single rail at 20 Amps. This is more than enough on a per Rail in the VAST majority of Cases. You do NOT need to Balance the Power - just stay under the 20 amp limit per rail which is generally not a problem. Is a problem if the Multiple rails have different Values, ie one of mine has like 18 amps v1, 16 Amps v2 and only 4 Amps on V3. (A old PSU that i'm still using - may be slightly off on rails but you get the gist). ONly real Neg of single rail is that MUCH higher current can flow increasing the fire hazzard when a LOW resistance is present (Higher than a short which SHOULD trip the PSU to shut down).

...Modulars - Great Plus for cable management, But higher contact resistant. But this is normally only a problem down stream, ie 3->5 years.

Just a comment on Manufs ratings:
Your corsair CX500 will NOT really deliever 38 Amps on the +12 V. For Ex 38 X 12 = 456 Watts. That sounds OK sense it is rated at 500, BUT the +5 Volt and the +3.3 Volt rail would be limited to only 44 Watts. NOTE this is a common practice, Indivdual rails are rated as IF no power is provided by the other rails. Just add up the individual power for the Rails and you will find that in the majority (NOT all) cases they exceed the manuf total rating.
Corsair CX500 = 500 Watts, BUT not = 3.3V * 25A + 5V * 20A + 12V * 38A + 5V * 3A. Which works out to be 653 W, OPPS slightly more than 500 Watts.
AS STATED do not hold this against Corsair, Love ther quality PSUs, as other manuf do the same thing.
.... This is just part of PSU 101 - LOL, Enjoy
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November 11, 2012 3:06:58 PM

Hahaha, thanks a lot. I've learnt a lot about power supplies today! :D  Yeah I'll most probably be going with the corsair 500W I mentioned; it fits right in my budget. :) 
Once again thanks for your help!
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November 11, 2012 3:07:12 PM

Best answer selected by MoonShock.
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