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*AMD R9 295x2 Power Requirements WARNING*

post #1 of 16
Thread Starter 
Before grabbing and putting one of those cards in your system it's very important to be aware of the following:

The R9 295x2 does not confront to the PCI Express 3.0 power delivery specifications.

According to the Peripheral Component Interconnect Special Interest Group the said specifications specify a power draw of 150 watts from each 8-pin PCIe power connector, 75 watts from each 6-pin PCIe power connector and 75 watts from the PCIe slot.

The R9 295x2 is powered from two 8-pin PCIe power connectors and the PCIe slot. The maximum specified power draw from these adds up to 375 watts. According to AMD, the R9 295x2 can draw up to 500 watts on some typical scenarios and can even peak to about 600 watts.

For validation and more information on the related specifications you can visit the PCI-SIG website (http://www.pcisig.com/).

-

What does this mean for me?

It means that the R9 295x2 can overload the cables on your power supply, resulting in cables melting and a possible fire hazard.

-

What can I do about this?

AMD is fully aware of this situation and plans to setup a list of compatible power supplies. Whenever the list becomes available AMD plans to put it on the following web address:

http://www.amd.com/r9

Some of the R9 295x2 reviewers were also informed about the situation with the following note:



The best things you can do are to consult the power supply compatibility list AMD has (whenever it becomes available) and to specifically ask your power supply maker to tell you if the power supply is compatible with the R9 295x2.

-

Spread the word and inform yourself and the ones affected. It's better to spend some time with customer support than to kill hardware that costs thousands!

Be reasonable people.
post #2 of 16
thanks for informative post thumb.gif

I'm surprised how amd was quick to put two chips on one pcb and did not execute a proper power design from PCI-e
  
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post #3 of 16
Thread Starter 
Well, the PCIe cables on most power supplies are over-speced so they can take it, just make sure that they actually can take it before risking it.
post #4 of 16
I'm pretty sure the cables are far beyond the specs of which the PSU can deliver in amperage. I wouldn't worry too much about it. The PSU will definitely shut off long before the cables will melt.

Also, the PCI-E port on the motherboard must be able to deliver 300 watts if it conforms to PCI-E 3.0 standards, not 75 watts. That's for the PCI-E 1.0 standard.

300 + 150 * 2 = 600W = the peak you posted (do you have a source for that?)

If you look HERE the 290x draws 390W peak, which is far beyond the suggested (and average on that site!) rating of 250W. The 295x is 2x 290x cards glued together basically, just on the same board. So the average power consumption should be around the double if not lower. Even with a peak of 780W, which indeed is a lot, it would still have to meet the requested standards of the card of 28A per PCI-E connector, which is the equivalent to (28A * 12V = 336W) per connector, which is still within the announced specs. 336 * 2 = 772, plus the 300W from the PCI-E 3.0 port, which results in 1072W of "requested" power use from the manual.

Here's the link for the PCI-E 3.0 specs. Look at page 17:
http://www.pcisig.com/specifications/pciexpress/PCIe_Base_r3_0_Errata_2013-06-20.pdf
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post #5 of 16
Thread Starter 
Quote:
Originally Posted by gonX View Post

I'm pretty sure the cables are far beyond the specs of which the PSU can deliver in amperage. I wouldn't worry too much about it. The PSU will definitely shut off long before the cables will melt.

Also, the PCI-E port on the motherboard must be able to deliver 300 watts if it conforms to PCI-E 3.0 standards, not 75 watts. That's for the PCI-E 1.0 standard.

300 + 150 * 2 = 600W = the peak you posted (do you have a source for that?)

If you look HERE the 290x draws 390W peak, which is far beyond the suggested (and average on that site!) rating of 250W. The 295x is 2x 290x cards glued together basically, just on the same board. So the average power consumption should be around the double if not lower. Even with a peak of 780W, which indeed is a lot, it would still have to meet the requested standards of the card of 28A per PCI-E connector, which is the equivalent to (28A * 12V = 336W) per connector, which is still within the announced specs. 336 * 2 = 772, plus the 300W from the PCI-E 3.0 port, which results in 1072W.

Here's the link for the PCI-E 3.0 specs. Look at page 17:
http://www.pcisig.com/specifications/pciexpress/PCIe_Base_r3_0_Errata_2013-06-20.pdf

Not all cables are so over-speced. There were even some issues with some power supplies and the R9 290x (which also goes off specs, although not as much).

The source of the power delivery comes from various place, but in order to avoid sending TMI, here's just a couple of examples:

http://www.tomshardware.com/reviews/radeon-r9-295x2-review-benchmark-performance,3799-16.html

http://www.techpowerup.com/reviews/AMD/R9_295_X2/22.html

Note that techpowerup uses more accurate measurement equipment, but doesn't seem to measure what the card draws from the slot (only total).


Edit: Also, I believe that the limit on the document you linked to refers to the combined load on all the PCIe slots, while I refer to power draw from a single slot.
Edited by PsyM4n - 4/9/14 at 3:07am
post #6 of 16
Quote:
Originally Posted by gonX View Post

I'm pretty sure the cables are far beyond the specs of which the PSU can deliver in amperage. I wouldn't worry too much about it. The PSU will definitely shut off long before the cables will melt.

Also, the PCI-E port on the motherboard must be able to deliver 300 watts if it conforms to PCI-E 3.0 standards, not 75 watts. That's for the PCI-E 1.0 standard.

300 + 150 * 2 = 600W = the peak you posted (do you have a source for that?)

If you look HERE the 290x draws 390W peak, which is far beyond the suggested (and average on that site!) rating of 250W. The 295x is 2x 290x cards glued together basically, just on the same board. So the average power consumption should be around the double if not lower. Even with a peak of 780W, which indeed is a lot, it would still have to meet the requested standards of the card of 28A per PCI-E connector, which is the equivalent to (28A * 12V = 336W) per connector, which is still within the announced specs. 336 * 2 = 772, plus the 300W from the PCI-E 3.0 port, which results in 1072W of "requested" power use from the manual.

Here's the link for the PCI-E 3.0 specs. Look at page 17:
http://www.pcisig.com/specifications/pciexpress/PCIe_Base_r3_0_Errata_2013-06-20.pdf
I have first hand experience of Seasonic cables melting from a 290x. rolleyes.gif
I thought it killed my Sapphire card too
I made a thread, handful of people had same issue.
  
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post #7 of 16
Thread Starter 
OK, I looked into the power draw according to SIG because 300 watts from the slot sounded non-applicable (blatantly impossible actually) due to mechanical limitations. Well, it is really not applicable.

The draw limit from the slot is actually specified at just 75 watts and technically it could just go slightly up. The pins on the slot can't go above 1.5 amperes each without burning (normally that's even less at 1.25A). Never mind that, most vanilla ATX boards are not capable of giving that much to the slot either (all 3.3v and 12v output from the ATX plug will not be enough to power all pci slots and peripherals).

The previously mentioned document describes the operation of the Base Power register, which specifies the total consumption limit of the connected PCIe card at a given time, not just what it draws from the slot. The power draw on the said register can be specified to even higher values than 300 according to the implemented connectors on each card.

There. tongue.gif
post #8 of 16
Quote:
Originally Posted by PsyM4n View Post

OK, I looked into the power draw according to SIG because 300 watts from the slot sounded non-applicable (blatantly impossible actually) due to mechanical limitations. Well, it is really not applicable.

The draw limit from the slot is actually specified at just 75 watts and technically it could just go slightly up. The pins on the slot can't go above 1.5 amperes each without burning (normally that's even less at 1.25A). Never mind that, most vanilla ATX boards are not capable of giving that much to the slot either (all 3.3v and 12v output from the ATX plug will not be enough to power all pci slots and peripherals).

The previously mentioned document describes the operation of the Base Power register, which specifies the total consumption limit of the connected PCIe card at a given time, not just what it draws from the slot. The power draw on the said register can be specified to even higher values than 300 according to the implemented connectors on each card.

There. tongue.gif

Thanks for correcting. I do however believe that the point of PCI-E 2.0 was to provide 150w from the port alone. A lot of the budget cards can draw +75W at peak but do not have a PCI-E power connector IIRC.
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post #9 of 16
Thread Starter 
Quote:
Originally Posted by gonX View Post

Thanks for correcting. I do however believe that the point of PCI-E 2.0 was to provide 150w from the port alone. A lot of the budget cards can draw +75W at peak but do not have a PCI-E power connector IIRC.
NP

The 150w update is also a false misconception. I believe that it was conceived when leaked info that had to do with the specification of the 6+2 pin cable came out and people mistook what they read. The way technical docs are written also doesn't make it easy to understand partial information taken from them.

Because the said specs are not really freely available to the public, it's needlessly hard to find this information written somewhere reliable. Note that the doc you linked to just has some errata updates from some places of the actual spec, with jumps to random sections that are not placed in any sensical manner. The rest docs available to the public there are not all that different, but some training materials, errata and updates actually have the power limits of the spec listed at some point (the aforementioned doc didn't though).

You mentioned some cards getting more from the slot than 75 watts. This is possible but note here that continuous drain from all the 12v pins there can't be really higher than 90 watts max, with peak about 10-20 watts more but only for <1sec cases. Everything else is beyond the mechanical limits of the standard slot (someone could make the pins on the slots of his motherboard thicker or something thus over-specing them, but most don't, like with some psus having 16awg wires instead of 18awg).

Now, I didn't mention the 3.3v pins for a reason. They are not meant to supply the card with its main power and are left to power control ICs on it and the likes (the vrm modulator etc.). Essentially the same way the 5v and 3.3v lines are nowadays treated on most sata drives. This classification is according to the standard.
Of course the one making the card can selectively ignore the standard in this case without any real life side-effects and have the 3.3v pins supply additional "main" power. The extra power in that case wouldn't be more than ~20 watts without undesirable catastrophic side-effects.

All in all the 75 watts can add up to 110 watts safely. There are some slot-only powered GPUs with more theoretical tdp but you can safely tell that they either are using up to 110 watts or they didn't burn the slot and themselves cause the motherboard has over-speced pcie power pins and traces.
Edited by PsyM4n - 4/9/14 at 8:47am
post #10 of 16
We should have a list of compatible PSU in the OP, that'll help a lot of people.
    
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