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Question on Graphics Card and PSU

Last response: in Components
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so i read the sticky on powersupply already, but theres a few things that i still need clartification on.
my first time building a new computer, and as i was reading over the power reqs for the 8800GT card it says

8800 GTX:

This graphics card requires:

PCI Express®-compliant motherboard with one x16 graphics slot

2 6-pin supplementary power connectors

Minimum 450W or greater system power supply (with 12V current rating of 30A)*.

so anyways, i checked out some PSU on the web and i have never seen a 450W psu that has a 12v rail with 30A. can someone tell me how exactly does this work? so hypothetically if i have 2 12v rails at 15A each, and i plug both in my card, itll give 30A right? but then can i plug 2 rails into a video card? sorry this is a noob question, but someone plealse explain in a way that i can understand.

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Power supply Master
Graphics card Authority

bluesky- said:
so anyways, i checked out some PSU on the web and i have never seen a 450W psu that has a 12v rail with 30A. can someone tell me how exactly does this work? so hypothetically if i have 2 12v rails at 15A each, and i plug both in my card, itll give 30A right? but then can i plug 2 rails into a video card? sorry this is a noob question, but someone plealse explain in a way that i can understand.


The 8800GTX by itself does not need 30 amps, this is a system power recommendation. All you need to look for is a combined amperage output of 30a (360w on the +12v) or more.

1769117,2,296003 said:
You need 26-28 amps just to run an 8800 card. If I were you I would be looking for something with 40+ amps on the 12v rail.
said:



The 26-28a minimum 450w PSU is NOT just to run the card... its the average whole system. If an 8800 was to use 26amp on a 12v rail it would use a whopping 312W which is just not right.
http://www.atomicmpc.com.au/forums.asp?s=2&c=7&t=9354 for total power usage of just GPU.

Most PSU's now come with multiple 12v rails, this can in GENERAL be added together to give an overall amperage. Where this isnt the case its generally noted on the side of the PSU or on manufacturers website. something like
12v1 = 18a
12v2 = 18a
12v3 = 18a

*note total 12v1, 12v2 and 12v3 = 50amps combined.

In any case the Corsair 520W is an awesome PSU and would easily cover your system.
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okay thanks, 1 last thing, how does 3 rails of 18a combine for 50amps? i dont they arent stackable but what is the formula to calculate it?

also i used the eXtreme PSU calculator and it comes out at a 650Watts..

i play on buying:
- q6600, G0 if possible
- gigabyte ga p35 ds3
- 2x 1gb ddr800 4-4-4-12
- 8800GT
- zalman 9700
- 4 LED 120mm case fans
- 7500rpm hdd
and maybe a dvd combo drive + laser mouse/keyboard

does it really take that much power? if so, ill need an other psu suggestion thx.
Power supply Master
Graphics card Authority

bluesky- said:
also i used the eXtreme PSU calculator and it comes out at a 650Watts..


You probably made a mistake when entering your components, even with 100% system load and 20% capacitor aging I come up with only 416 watts.
The Q6600 is a single socket processor.

bluesky- said:
ohh my bad, i think i entered an additional pcie x16 card which added 80+watts to it. anyways, can someone explain how 3 12v rail 18a combine for 50amps? formula?


Sorry i think you have missed my point... that little table i did was an EXAMPLE of the info you would get from the PSU manufacturer, or indeed on the side of the PSU. Just because my example says 18x3 is 50 doesnt make it true for everything.

i understand what ur saying, but most psus have a table that says, for example, 12v1 12v2 12v3 12v4 and then 18v 18v 18v 18v for each of those rails. but how am i supposed to know the total current for the 12v if you cant simply do 18x4? most psus dont give you the total wattage for the 12v's neither do they give you a total current, just seperate 18v's for each rail. but apparently i need to know the combined figures and not the individuals.

bluesky- said:
i understand what ur saying, but most psus have a table that says, for example, 12v1 12v2 12v3 12v4 and then 18v 18v 18v 18v for each of those rails. but how am i supposed to know the total current for the 12v if you cant simply do 18x4? most psus dont give you the total wattage for the 12v's neither do they give you a total current, just seperate 18v's for each rail. but apparently i need to know the combined figures and not the individuals.


What PSU are you looking at? I could have a quick look if you wish, but in general if it aint on the Manufacturers website a quick google search will reveal some reviews that will more often than not have the answers.
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