How to know is PCIe x16 capable of delivering enough power?

[SamathaV]

Assume I have a GTX 750 Ti, which is stated require max 20A from the 12v rail. When maxing out GPU usage the draw on the +12V rail is around 14A, how do I know it is all that the GPU needs, not all that the slot could deliver?

Reason I ask is that I have a system where the motherboard apparently sets a wattage limitation of 35 for the PCIe x16 slot. It either does or it in reality does not, it is hard to figure out from the specification. It either is set by the motherboard or it could be result of the small PSU.

 

[maxalge]

Assume I have a GTX 750 Ti, which is stated require max 20A from the 12v rail. When maxing out GPU usage the draw on the +12V rail is around 14A, how do I know it is all that the GPU needs, not all that the slot could deliver?

Reason I ask is that I have a system where the motherboard apparently sets a wattage limitation of 35 for the PCIe x16 slot. It either does or it in reality does not, it is hard to figure out from the specification. It either is set by the motherboard or it could be result of the small PSU.

the limitation is the crappy power supply


https://www.youtube.com/watch?v=HKq9rcLzJMw#t=31

 

[getochkn]

Ya, that board does say 35w. Normal PCIe specs should be 75w for the PCIe, but manufactures for small PC's do their own thing sometimes. Any card that needs external power, that external power is always taken after the 75w from the slot, so a card that needs 150w power, really is 75w from the slot and 75w from the 6 or 8 pin connectors.

In this case, I think maxalge is wrong, it's not the PSU. It's the MB. Either it can deliver the base 75w it should or not, and from the spec, it can't. It's a hard limit due to circuitry and adding a 10,000w PSU is not going to make the MB give anymore power to the PCIe slot.

 

[SamathaV]

Assume I have a GTX 750 Ti, which is stated require max 20A from the 12v rail. When maxing out GPU usage the draw on the +12V rail is around 14A, how do I know it is all that the GPU needs, not all that the slot could deliver?

Reason I ask is that I have a system where the motherboard apparently sets a wattage limitation of 35 for the PCIe x16 slot. It either does or it in reality does not, it is hard to figure out from the specification. It either is set by the motherboard or it could be result of the small PSU.

the limitation is the crappy power supply


https://www.youtube.com/watch?v=HKq9rcLzJMw#t=31

Thanks for the answer. I have seen this video, but I don't think it address the issue as the GPU in the video is directly powered from PSU. So, in scenario like this, it really does not matter is there a limitation on the PCI x16 slot as it gets the power from elsewhere, right? GTX 750 Ti does not have these external power connectors.

 

[SamathaV]

Ya, that board does say 35w. Normal PCIe specs should be 75w for the PCIe, but manufactures for small PC's do their own thing sometimes. Any card that needs external power, that external power is always taken after the 75w from the slot, so a card that needs 150w power, really is 75w from the slot and 75w from the 6 or 8 pin connectors.

In this case, I think maxalge is wrong, it's not the PSU. It's the MB. Either it can deliver the base 75w it should or not, and from the spec, it can't. It's a hard limit due to circuitry and adding a 10,000w PSU is not going to make the MB give anymore power to the PCIe slot.

Yes, that is the other possibility. Yet, what exactly is the circuitry that sets the limit? How one can be sure there is one? There could be, but that does not make it real either. There has been people being able to run these GPU's that require more what the PCIe x16 should be able to give out, like the GPU in the example, thus the original question.

 

[kancaras]

750ti doesnt use more than 6amps on 12v rail. I dont know where you get that 14a number since you say there is no external power connector except 35W PCIe.
http://www.tomshardware.com/reviews/geforce-gtx-750-ti-review,3750-21.html

BTW 6a x 12v = 70watts, 14amps x 12v = 168watts , 168w is way too much.

 

[maxalge]

Assume I have a GTX 750 Ti, which is stated require max 20A from the 12v rail. When maxing out GPU usage the draw on the +12V rail is around 14A, how do I know it is all that the GPU needs, not all that the slot could deliver?

Reason I ask is that I have a system where the motherboard apparently sets a wattage limitation of 35 for the PCIe x16 slot. It either does or it in reality does not, it is hard to figure out from the specification. It either is set by the motherboard or it could be result of the small PSU.

the limitation is the crappy power supply


https://www.youtube.com/watch?v=HKq9rcLzJMw#t=31

Thanks for the answer. I have seen this video, but I don't think it address the issue as the GPU in the video is directly powered from PSU. So, in scenario like this, it really does not matter is there a limitation on the PCI x16 slot as it gets the power from elsewhere, right? GTX 750 Ti does not have these external power connectors.

i see, if you are buying a card that runs off the power of the pcie slot alone then yeah not a good idea

 

[SamathaV]

750ti doesnt use more than 6amps on 12v rail. I dont know where you get that 14a number since you say there is no external power connector except 35W PCIe.
http://www.tomshardware.com/reviews/geforce-gtx-750-ti-review,3750-21.html

BTW 6a x 12v = 70watts, 14amps x 12v = 168watts , 168w is way too much.

I got it from here: http://en.community.dell.com/support-forums/desktop/f/3515/p/19657233/20862488?rfsh=1452111213561 and as one can see, I presented the same kind of question about is not that too much in there. Also have been discussing about it here: http://en.community.dell.com/support-forums/desktop/f/3514/t/19667225

I know very little of these things. Finding one that could give an answer than is better than a sophisticated guess seems really hard. :/

 

[SamathaV]

Ya, that board does say 35w. Normal PCIe specs should be 75w for the PCIe, but manufactures for small PC's do their own thing sometimes. Any card that needs external power, that external power is always taken after the 75w from the slot, so a card that needs 150w power, really is 75w from the slot and 75w from the 6 or 8 pin connectors.

Started to think about this. From where one can read more about this? Why would card assume to take first 75W from PCIe, when it could take all directly from the source?

Edit: Similar thread around different hardware: http://www.tomshardware.co.uk/answers/id-1959070/pci-x16-watt-maximum.html Same problem here as everywhere, only sophisticated guesses. :/

 

[kancaras]

I got it from here: http://en.community.dell.com/support-forums/desktop/f/3515/p/19657233/20862488?rfsh=1452111213561 and as one can see, I presented the same kind of question about is not that too much in there. Also have been discussing about it here: http://en.community.dell.com/support-forums/desktop/f/3514/t/19667225

I know very little of these things. Finding one that could give an answer than is better than a sophisticated guess seems really hard. :/

He is basing his calculations on measurments from socket draw, thats not how it should be done at all. Your best option is to go for 750ti with external 6pin if youre thinking about buying one. Or do you have it right now and youre complaining about something?

 

[SamathaV]

I got it from here: http://en.community.dell.com/support-forums/desktop/f/3515/p/19657233/20862488?rfsh=1452111213561 and as one can see, I presented the same kind of question about is not that too much in there. Also have been discussing about it here: http://en.community.dell.com/support-forums/desktop/f/3514/t/19667225

I know very little of these things. Finding one that could give an answer than is better than a sophisticated guess seems really hard. :/

He is basing his calculations on measurments from socket draw, thats not how it should be done at all. Your best option is to go for 750ti with external 6pin if youre thinking about buying one. Or do you have it right now and youre complaining about something?

Yea, that is what I would do, if I would be buying a card for the system. But I don't have the system, I have the card.

From his latest post: "I ran the Firestrike benchmark and got a score of 3847 (I5-2400 and GTX 750 Ti)". It would probably show in this sort of test, if the GPU would not get enough power, right? Result seems to be in line for that setup.

 

[kancaras]

If you just want to make sure if a 750ti is working correctly then yeah, compare it to benchmarks.
http://www.tomshardware.com/reviews/geforce-gtx-750-ti-review,3750-9.html
for example BF4 on FHD ultra 2xMSAA should run 30fps+

 

[SamathaV]

If you just want to make sure if a 750ti is working correctly then yeah, compare it to benchmarks.
http://www.tomshardware.com/reviews/geforce-gtx-750-ti-review,3750-9.html
for example BF4 on FHD ultra 2xMSAA should run 30fps+

Does not the test he used take the maximum out from the GPU? (To my understanding it has separate GPU test and CPU test, and the final score is combination of those.) If it does and it performs as expected (as it supposedly did), then the wattage limitation in the specification is unlikely to be real, as the card should use more than it can provide, right? If it does not, what is the point of it then?

 

[kancaras]

Actualy best method would be to compare wattage at socket of two sets of benchmark: 1) only prime95 2) prime95 and furmark.

If the rig will be able to go more than +35W should be clear by then. Draw at socket should jump 90-100w considering PSU efficiency effect the final 70-75w at 12v end.