PSU Myths Busted by Antec

unknownsock · 19 Apr 2010 at 14:25

Some forums users and even some major companies are spreading the idea that single +12V rail power supplies power up the latest graphics cards in a better way, in order to market their products or to scare other users. This is of course total nonsense. To understand this matter better, let’s examine some different scenarios and how the actual power is being distributed to the graphics cards.

There are different kinds of graphics cards in the market today, and depending on the performance of the chip they come with, they have different levels of power consumption as well. The total amount of power that a graphics card consumes is called its thermal design power, or TDP. Graphics cards are usually connected to power supplies by PCI-Express connectors. The number and type of connectors that a card has, howe- ver, can vary wildly. Some cards have one 6-pin PCI-E connector, some have two; some others come with one 6-pin and one 8-pin PCI-E conne- ctor (sometimes referred to as a 6+2-pin PCI-E connector) and again others have none at all. In general you can say that the higher the perform- ance of the graphics card, the more power the graphics card will consume and the higher its TDP will be. All of today’s high-end cards come with a 6-pin and an 8-pin PCI-E jack (sometimes referred to as a 6+2-pin PCI-E jack).

NOTE: Not many people know that some power is also delivered through the PCI-E slot itself – that is, the slot on the motherboard right where you plug the card in. The PCI-E slot is powered by the 24-pin ATX connector attached to the motherboard.

The maximum power distribution for all of the connectors and slots that are able to connect to a graphics card is as follows:

PCI-E slot on the motherboard
(powered by the 24-pin ATX Connector)

6-pin PCI-E (PEG) Connector
Up to 200 Watts (~17A) Up to 75 Watts (6.25A) x2 with SLI
and x3 with Triple-SLI

6+2-pin PCI-E (PEG) Connector
Up to 200 Watts (~17A)

NOTE: The additional pins of the 6+2-pin PCI-E connector are both ground, and not additional +12V cables as is commonly thought.

All together, a graphics card could theoretically have a power consumption of up to 300 Watts. And, as you can see, regardless of which graphics card you use, there is more than one way for power to be distributed to it: 75W at 6.25A, just from the PCI-E slot, and up to another 200W (at around 17A) from each PCI-E Graphics (PEG) connector. As we’ll see, because of the way this power is being distributed, there is no way that you could possibly overload one of the different +12V rails on an Antec power supply (provided it has the right maximum output wattage).

Source:
http://www.antec.com/Believe_it/PSU/

I understand thats its written by a PSU company itself but its an interesting read, especially when its a dark area for myself.

skippy2421 · 19 Apr 2010 at 14:44

git i was just going to post this!

unknownsock · 19 Apr 2010 at 14:50

skippy2421 said:
git i was just going to post this!

bJN · 19 Apr 2010 at 15:33

It was an interesting read right up until

on an Antec power supply

At which point I decided I'm not going to click it, it's just another marketing ploy...

unknownsock · 19 Apr 2010 at 16:07

bJN said:
It was an interesting read right up until

At which point I decided I'm not going to click it, it's just another marketing ploy...

Hmmm like i said above its still an interesting read, maybe take some things lightly but theres a lot of facts in their that im sure a lot of people are unaware off.

EsaT · 19 Apr 2010 at 19:37

Only myth is that marketroids have moral and/or spine.

First lie in there: total amount of power that a graphics card consumes is called its thermal design power, or TDP
TDP is supposed to be maximum heat output cooling must be capable to handling... and when manufacturers have non performing product they lie in it to make product look better. Like hottest Intel's Pentium 4s or AMD's Phenoms, or Nvidia GTX480 which actually consumes clearly more power than HD5970 whose TDP is 45W higher.

6-pin PCIe connector is specified for 75W and 8-pin connector for 150W.

Jokester · 19 Apr 2010 at 19:48

Problem with split rails is that for Joe Public they just see the total figure of the PSU (and not even the total 12V power).

I've had issues where split rails has caused me issues with SLI even though the total 12V power was adequate, just the split meant there was wasted power that wasn't available to the GPUs.

The main reason for split rails is cost and size.

Jokester · 19 Apr 2010 at 19:48

Problem with split rails is that for Joe Public they just see the total figure of the PSU (and not even the total 12V power).

I've had issues where split rails has caused me issues with SLI even though the total 12V power was adequate, just the split meant there was wasted power that wasn't available to the GPUs.

The main reason for split rails is cost and size.

thingemajib · 19 Apr 2010 at 19:48

yeah, a couple of things dont quite add up here ... literally.

eg "All together, a graphics card could theoretically have a power consumption of up to 300 Watts. And, as you can see, regardless of which graphics card you use, there is more than one way for power to be distributed to it: 75W at 6.25A, just from the PCI-E slot, and up to another 200W (at around 17A) from each PCI-E Graphics (PEG) connector."

200+75 = 275, not 300.

i thought it was 75w from pcie slot + 75w from 6pin + 150w from 8pin = 300w.
also, how does having two extra ground pins magically conjure up an extra 75w on the 8pin?
(i thought it would be an extra +12v pin and a ground pin)

like i said, doesnt quite add up.