godling

This could go in either the Motherboard or Graphics Card section, so I chose the first one available.

There's a discussion at this thread here at PC Apex, http://www.forumapex.com/video_cards...d_install.html , regarding the power necessary for a particular graphics card. I posited that -- given the appropriate PSU is used -- the graphics card in question (an 8800GTX) would not require additional power from the PSU because the PCI-x 2.0 compliant mobo should provide 150w of power to the graphics card.

Dex informed me that a friend of his had tried just that -- bypassing the extra power cables -- and got "some lovely coil whine" from the PSU.

Hmmnn ... I did some research.

According to the standards for PCI-x, and as reiterated in this post at bit-tech,
bit-tech.net | PCIe 2.0 to arrive by Christmas , the 150w should be amply supplied through the mobo's PCI-x 2.0 slot.

However, according to this post over at Custom PC: Asus GeForce 8800 GT – first look | News | Custom PC , it appears that the graphics cards are still looking for something to be plugged into those extra power connectors, and complain mightily when something isn't.

What's the deal? Is PCI-x 2.0's power capability a fallacy, or are the graphics cards simply designed to not take the extra power through the slot interface, despite being labelled "2.0 compliant"??

I don't currently have a PCI-x 2.0 mobo or graphics card, so I can't test this. I hope someone here can.

-godling

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reflux

Well...I just switched my PC on without the PCI-E power connector plugged into my graphics card, and I got a lovely loud continuous beep. Running an X38 motherboard with a G92 GeForce card, so the 150w through the slot should be available. There is a molex input on the board, but the manual tells me that's only necessary for CrossFire.

Btw...coil whine does not necessarily mean something is wrong. My old PSU used to coil whine like mad all the time, but it was rock solid.

Is this not down to raw power, but rather amperage, which the slot cannot provide? I don't really understand the relationships between volts, amps, watts etc. (sleeping in high school physics ) so correct me if I'm wrong.

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TCG_Modder

i have always gone with the moto " where there is a hole, stick something in it!" doesnt matter if the box says it is 2.0 and should get the power from the PCI slot, chances are it will still require additional power.

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godling

Quote: Originally Posted by reflux Is this not down to raw power, but rather amperage, which the slot cannot provide?

An excellent question ... I don't have the answer.

-godling

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xgeko2

well ill be getting my board in a couple of days but im still atleast 2 weeks out from testing and trying that out maybe ill have better luck with the amd790fx chipset idk though my 2 12v rails only have 18amps so idk if my powersupply will even be able to handle it but i will try it out when i get the rest of my stuff.

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FeRaL

Ah... Amperage. How man 12 rails does your PSU have godling/refulx. How many amps per rail? How many Amps does the rail have that goes to the main power connector to the mobo?

That could be an issue right there if you don't have enough Amps.

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reflux

This is my PSU...

Products - Power - HPU-4M880

It has four 12v rails from what I can see, and the mobo one should be about 18A? I'm presuming that 12v 3 and 12v 4 are intended for graphics cards.

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FeRaL

Quote: Originally Posted by reflux This is my PSU... Products - Power - HPU-4M880 It has four 12v rails from what I can see, and the mobo one should be about 18A? I'm presuming that 12v 3 and 12v 4 are intended for graphics cards.

White Paper: Power Supplies - nedwards - Maximum PC

This was taken from th e above link....

The Power Supply Unit (PSU) converts AC electricity into regulated DC voltages, which it then delivers to the components inside your computer. Several different DC voltages are needed, the main ones being +12V, +5V, +3.3V, -12V, and 5V standby. Each voltage rail has a specific set of functions:

• +12V: In recent years, this has become the main rail to power most of the computer?s components. The motherboard uses DC-to-DC conversion of the 12V rail to provide the <1.5VDC needed for the CPU. It?s also used to provide additional juice directly to power-hungry videocards, with direct connection via 6-pin and 8-pin PCIe power connectors. +12V is also used to power hard drive motors and fans.
• +5V: The motherboard and many of its components use +5V.
• +3.3V: Used to run system memory, videocards, and other circuits.
• -12V: Provided for backward compatibility, mostly with some types of serial port circuits, typically with a current limit of <1A.
• +5V standby (SB): Always on as long as the power supply is plugged into AC and its main switch is left on, +5VSB is used to power the ?soft? turn on/off circuitry in the motherboard that tells the PSU to power up or power down. It is also used for ?self-powered? USB devices.

Well, I'm not sure how much your mobo and cpu require of your 12V rail, but you have a total of 216 Watts from the 12V to spread accross them and your graphics card.

Hope that helps!

FeRaL

P.S. One can infer from this that if you want to not have to use the power connectors on you PCI-E 2.0 video cards with your PCI-E 2.0 mobo that the best thing to do is get a PSU with one big 12V, i.e. e from PC Power and Cooling...

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