Some questions regarding AGP power ...

[NoobyDoo]

1) Which rail/s does a AGP slot draw its power from ?

2) What is the max power that can be supplied by a AGP slot ? 45 W ?

Thanks.

 

[mpilchfamily]

The AGP card will pull what it needs. If additional power is required for the card then it will have molex connectors to draw additional power from the PSU. Here are the specs for the AGP slot.
http://pinouts.ru/Slots/agp_pinout.shtml

Doesn't specify the amount of power offered threw the slot. But its not a problem since video cards that use the AGP slot don't require allot of power to start with. Those that do will have additional connections for receiving power.

 

[NoobyDoo]

If someone can give me the info, I'd be grateful.

For PCI-E, this is what I found :

The PCI-E Version 1.0 slot provides two voltages from the motherboard, 3.3V and 12V.

You can have up to 3A on the 3.3V rail and up to 5.5A on the 12V rail. Combined thats 9.9W from the 3.3V and 66W from the 12V for a total of 75.9W.

 

[mpilchfamily]

What seams to be the problem.

Yes the PCI-e slot offers a max of 75W or 6.25A from the 12V rail. Are you looking to power some sort of card off the AGP slot?

I have found the full Intel spec for AGP.
http://members.datafast.net.au/dft0802/specs/agp30.pdf

Section 3.6 Page 77 covers the power distribution of the slot.

Browsing the spec reviles now power limits which suggest that all voltages supplied threw the slot are less then 1A. AGP cards where not demanding in power when AGP was first introduced. Those that needed more had additional power inputs as covered before. So if you plan to use the slot of anything other then a video card don't expect to pull more then a few milliamperes from it. If you trying to test a motherboard to see if the slot is supplying the proper amount of power your not going to get the slot to output any significant amount of current without a load. Chances are the current threw the AGP slot will be the same or similar to that of the PCI slots. basically AGP is a specialized PCI slot that has its own controller so it doesn't have to share the bridge the other slots are on offering fast data transfers.

 

[NoobyDoo]

The info I got at SPCR is :

Contrary to what I posted earlier, the AGP slot actually draws power from the 5V and 12V rails in addition to the 3.3V rail. The maximum power is listed by various sources as 3.3v 6A, 5v 2A and 12v 1A. Combined this gives around a 42 watt maximum.

I'm trying to replace a old ( really old ) PSU where most of the power is supplied by the 3.3 & 5V rails. The system has a AGP card, trying to find out if a 'modern' PSU will do. Trying to calc how many amps are reqd on the 3.3 & 5V rails.

Got all the info I need, thanks.

 

[mpilchfamily]

Well unless the system uses an abnormal amount of power from the 3.3V and 5V rails any PSU will support it. Modern PSUs still offer more then enough power threw the 3.3V and 5V rails. Though more and more power is being diverted from those rails to the 12V side.