30 Amps on the +12v rail?

[hdtv guy]

I got a geforce 8800 gtx card and it says that it needs at least 30
amps on the +12v rail. I also got an OCZ 700W GameXStream power
supply. It says it has four +12v outputs and each one is 18 amps. Does
that mean that it has 72 amps on the +12v rail? What do they mean by
rail? I did a little googling and one web site said they used two 8800
GTX's in SLI mode with an OCZ 700W psu.

 

[Conor]

I got a geforce 8800 gtx card and it says that it needs at least 30
amps on the +12v rail. I also got an OCZ 700W GameXStream power
supply. It says it has four +12v outputs and each one is 18 amps. Does
that mean that it has 72 amps on the +12v rail? What do they mean by
rail? I did a little googling and one web site said they used two 8800
GTX's in SLI mode with an OCZ 700W psu.

Yes, you've got a total of 72 amps. By rail, they mean wire.

--
Conor

As a Brit I'd like to thank the Americans for their help in the war
against terror because if they'd not funded the IRA for 30 years, we
wouldn't know how to deal with terrorists.

 

[Dave]

I got a geforce 8800 gtx card and it says that it needs at least 30
amps on the +12v rail. I also got an OCZ 700W GameXStream power
supply. It says it has four +12v outputs and each one is 18 amps. Does
that mean that it has 72 amps on the +12v rail? What do they mean by
rail? I did a little googling and one web site said they used two 8800
GTX's in SLI mode with an OCZ 700W psu.

Rail is just that. What can the power supply put out, at +12V? The video
card makers have suggested hardware requirements for other components in the
system, based on some common assumptions. That is, your video card isn't
the only user of +12V, so the =recommendation= from the video card maker
will be more than the video card needs. If the video card really needs 15A
on the +12V rail, the recommendation might be for a power supply that can
output 30A on the +12V rail, for example.

According to the specs., the maximum power draw of that GPU is about 15A.
But I've read that the card has two PCI-Express power connectors. So most
likely, it will draw a maximum of about 4A from each of two (18A max each)
+12V rails, as it draws some power from the PCI-Express expansion slot
itself (doesn't get all the power from the PCI-Express connectors)

Total draw at +12V might reach maximum 15A, but even that maximum draw is
likely to be divided up between at least 2 or 3 of the +12V rails of the
power supply you chose. You have nothing to worry about. -Dave

 

[Paul]

I got a geforce 8800 gtx card and it says that it needs at least 30
amps on the +12v rail. I also got an OCZ 700W GameXStream power
supply. It says it has four +12v outputs and each one is 18 amps. Does
that mean that it has 72 amps on the +12v rail? What do they mean by
rail? I did a little googling and one web site said they used two 8800
GTX's in SLI mode with an OCZ 700W psu.

http://www.xbitlabs.com/articles/video/display/gf8800gtx-roundup_6.html
http://www.xbitlabs.com/images/video/gf8800gtx-roundup/8800gtx_full.gif

The card needs about 10.7 amps (128W/12V), and it is split among the PCI Express
slot, PCI Express #1 and PCI Express #2 connectors.

The quoted number of 30A, is probably intended to be a system number.

The wiring of the GameXStream is explained here. And it looks like
the label on the supply, also tells you how it is wired.

http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=24

Even if you had a 130W Pentium D processor (144W/12V=12A at 90% Vcore efficiency),
I don't think it would be a problem for that supply. That would be 23A so far,
leaving room for a 0.6A hard drive, a 1.5A CDROM, 0.5A for fans etc. That is
what it takes to get to the magic "30A" number, is some high estimates
for other components in the system.

Paul