PowerGate: What are the PCI-E specs?

[evilsofa]

I am seeing a lot of assumptions being made that if a card is pulling more than 75W out of the slot, it is out of the PCI-E specs. Some are saying that if it ever goes above 75W, it's out of spec; others say if it averages above 75W, it's out of spec.

But what do the specs actually say? I don't know the answer, I'm asking the question. Here's a link to what are apparently the PCI-E specs:

PCI Express Base Specification Revision 3.0 (link goes to .pdf)

 

[DF-1]

theres like 4 threads about this gategategate thing, i think thats enough.

 

[Araxie]

just read this very detailed article, should be more than enough to understand everything,

Power Consumption Concerns on the Radeon RX 480 | PC Perspective

 

[NKD]

#RamGate #PowerGate both sides have a gate!

 

[Ieldra]

#RamGate #PowerGate both sides have a gate!

Now it's more like #DeadMoboGate

 

[Sycraft]

Power specs are done for long term power output, not instantaneous. The reason that you have to limit power over a given circuit is heat. More power at a given voltage requires more current and more current over a given size of wire equals more heat. So draw too much current and the wire will heat up and melt or cause a fire or the like. However a short term spike is fine. So long as it is very short, and not too extremely high, you won't see any issues. Simple example: Ever turn on a high drain device like an A/C or fridge or vacuum and see the lights dip in brightness for a second? What is happening is that device draws a ton of current to get started, so much it causes the voltage to sag. However it quickly gets down to normal levels and everything is fine. If you measure it you can see a momentary spike well above the 12 amps a single device is allowed, but it'll settle back in that range in a hurry. Breakers are designed to deal with this kind of thing explicitly. They don't trip the second something goes a bit above their limit, rather they have to have a sustained overdraw before they trip. How fast they trip depends on how much over current draw there is.

Basically with graphics cards, don't worry much about little spikes that you need a high frequency scope to see. That is normal, all kinds of devices do it. Worry about long term draw over the spec. Also, worry mostly about the motherboard, not the PCIe power connector.