How much power PCI uses?

[ZUnit]

Well thats my question, how much maximum power from my PSU, one pci slot can use?

 

[imported_litesgod]

I believe traditional PCI bus can handle ~25watts, while PCI Express can handle ~75watts.

 

[Zero Plasma]

I think hes right about pci.Don't know about pci-e.

 

[ZUnit]

How much max it can handle on each rail (+3.3V, +5V, +12V)? Thats how i should ask this firstly.

 

[thermalpaste]

Here are the details:
Depending on the present signal, the slot determines whether the expansion board had been inserted or not. After the expansion board is inserted, 2 pins namely PRSNT1# and PRSNT#2 determine how much peak power the PCI card is going to need:
PRSNT1 | PRSNT2 | Power allocated |
-----------------------------------------------
open open> 0Watts
open g> 15 Watts
g open> 25 Watts (max)
g g> 7.5 watts

g = ground.

I dunno about PCi-X.

 

[imported_whatever]

iirc, pci cannot draw 3.3v as it was around before atx. i have no idea about 5v or 12v, but i would guess that it is 5v only, which would be 5 amps.

 

[ZUnit]

thermalpaste i kinda dont understand how u mean.

yep i forgot it dont use +12V are you sure about 5 amps whatever?

 

[TerryMathews]

Originally posted by: whatever
iirc, pci cannot draw 3.3v as it was around before atx. i have no idea about 5v or 12v, but i would guess that it is 5v only, which would be 5 amps.

Yes it can, PCI 2.2 spec added it on a pin that was N/C in previous specs.

 

[thermalpaste]

Originally posted by: ZUnit
thermalpaste i kinda dont understand how u mean.

yep i forgot it dont use +12V are you sure about 5 amps whatever?

A PCI card determines how much power the PCI bus is going to allocate to it. Here are the details:
There are 2 pins : PRSNT1# and PRSNT2# which determine the power allocated to per PCI bus.

When both PRSNT1# and PRSNT#2 are open, it is obvious that a PCI card had not been added, so the PCI bus allocates a maximum of 0Watt to that particular bus

When PRSNT#1 is open and the PRSNT#2is ground then the PCI bus knows that the expansion card will consume a maximum peak power of 15 Watts.

When PRSNT#1 is ground and PRSNT#2 is open then the card consumes 25 Watts which is maximum for any given PCI slot.


WHen both these pins are grounded, then the card consumes a peak 7.5 watts, and not more than that.

 

[thermalpaste]

Originally posted by: ZUnit
Well thats my question, how much maximum power from my PSU, one pci slot can use?

So, getting back to the point if you have 6 PCI slots, they can use a maximum of 6*25= 150 watts.
If you have a PSU of say 400 Watts, then they will consume approx. (150/400)*100 = 37.5% of the total power. As mentioned earlier if your PCI slots are empty, they do not comsume any power...

 

[thermalpaste]

Originally posted by: ZUnit
thermalpaste i kinda dont understand how u mean.

yep i forgot it dont use +12V are you sure about 5 amps whatever?

5 AMps is correct according to my calculations.

 

[ZUnit]

Man i am not technician and i dont need to know how pci works i just want to know what i ask and i dont get clear answer yet.
All i understand from your message is that PCI can use max 5W on +5V rail, and 20W on +3.3V rails is this correct?
And this is only info i need how much it can use on +5V max and how much it can use on +3.3V max.
Edit: Watts not Amps

 

[ZUnit]

Ops messed, i mean Watts not ampers.

 

[ZUnit]

I found info i need in PCI 2.2 specs. If someone else need here here they are.

Originally posted by: PCI 2.2 specs
4.3.4.1. Power Requirements
All PCI connectors require four power rails: +5V. +3.3V, +12V, and -12V. Systems that provide PCI connectors are required to provide all four rails in every system with the current budget specified in Table 4-10. Systems may optionally supply 3.3Vaux power, as specified in the Pi 7 Bus Power Management Interface Specification. Systems that do not support PCI bus power management must treat the 3.3Vaux pin as reserved.
Current requirements per connector for the two 12V rails are provided in Table 4-10. There are no specific system requirements for current per connector on the 5V and 3.3V rails; this is system dependent. Note that Section 4.4.2.2. requires that an expansion card must limit its total power consumption to 25 watts (from all power rails). The system provides a total power budget for PCI expansion boards that can be distributed between connectors in an arbitrary way. The PRSNTn# pins on the connector allow the system to optionally assess the power demand of each expansion board and determine if the installed configuration will run within the total power budget. Refer to Section 4.4.1. for further details.
Table 4-10 specifies the tolerances of supply rails. Note that these tolerances are to be guaranteed at the components not the supply.


Table 4-1U: Power Supply Rail Tolerances

Power Rail------Expansion Boards (Short and Long)
5 V ±5%--------5 A max. (system dependent)
3.3 V ±0.3 V---7.6 A max. (system dependent)
12 V ±5%------500 mA
-12 V±10%----100 mA

So there seems to be no max limit on +3.3V and +5V except that PCI expansion card cant consume more than 25W froma all rails.