Hello!

I am currently running 2x GTX 570 GPU's and a 8core AMD CPU for SETI. I have thought about getting 3x GTX 750Ti to bring the power use down. My question is since the GTX 750Ti cards dont have an external power supply connector, will 180watts be supported by the PCI-E bus on the motherboard without frying something up. Each 750Ti card is 60watts is how I came up with the 180watt.

All the best,
Aaron Lephart

www.smartcar451.com

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Each PCIe x16 slot is rated up to 75w. If the MB manufacture fully followed the specs it should be fine.

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Great to know HAL, thank you!

All the best,
Aaron Lephart

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There where a big discussion about that before in the forums, the problem is not in the PCI-e slots, each one of them can theoricaly handle up to 75W by specs IIRC, the problem is with the 12V lines from the 24 pin power connector who carries the sum of all current used by any 12V devices atached to the MB (plus the MB 12V devices itself). Most of them can´t handle the current used by 3x60W GPU´s plus the rest of the devices. Before the pros vs cons start again, yes initialy the 12V connectors can handle the current, but it´s at the edge of their capacity, and when you crunch (diferent from gamming) you use them at that capacity for a long time, so they will not last for long. An a melted 24 connector normaly destroy your MB. So if you want a long lasting cruncher with 3x60W GPU´s go for the external (6 pin VGA connector) models. From other side, some MB has separate power connectors for the 12V lines exactly to avoid that and there are some manufacters with better quality connectors rated for bigger current who could drive the current safely, but that is not common, you need to be sure if your MB specifications allow that.

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I second the suggestion made by juan BFB.

One of my builds has four of them installed http://setiathome.berkeley.edu/show_host_detail.php?hostid=7265951 and each has the 6-pin connector.

If your PSU doesn't have enough 6-pin connectors but has enough total power, I know there are adaptors that use two molex 4-pin connectors into a 6-pin connector to help power the cards.

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My question is since the GTX 750Ti cards dont have an external power supply connector, will 180watts be supported by the PCI-E bus on the motherboard without frying something up. Each 750Ti card is 60watts is how I came up with the 180watt.

My Asus GTX 750 Ti's have the six-pin PCIe external connector, and they are not the overclock version either. I have heard that some cards use it only for the fans, but I don't necessarily believe that applies in all cases.

At any rate, running GPUGrid they use only about 54 watts each, get almost as much output as GTX 660s (10-15% less) that pull around 140 watts each, and are great cards. Maxwell is the wave of the future, it is just the question of when will more appear.

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Those are GTS 250s, 7 of them. The standard GTS 250 is rated at 150 watts with one 75 watt power adapter. That means each one wants to draw 75 watts from the PCIe slot. Some of the PCIe extenders have a single 4 pin molex connector good for around 37 watts, the rest comes from the PCIe slot. You can see the bottom cards using 2 molex connectors to supply 75 watts. Add it up. As far as I know, nothing fried on that board, It Lives, It Lives !!

I personally have an Intel board with 4 full sized PCIe slots advertized to run four GPUs totaling 300 watts. As far as I know, none of those boards have been returned with damaged power plugs. I also have an HP xw4600 board and according to the specs, the PCIe/PCI slots can pull 275 watts by themselves. I think they know what they are talking about.

Still giggling at that one!

Hope the "Peter Jackson" spacers didn't go up in smoke!! :-P


(Far better to go 'electronic'. Better yet, go for no smoke?... That should convert nicely into more GPUs!! :-) Sorry, couldn't resist...)


Happy fast cruinchin',
Martin

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Something not fit, the standard GTS250 uses allmos all of it´s power from the 6 pin VGA connector ( i have few of them years ago) only as most of the bigger NVidias does, so in this case there is no problem with the 24 pin 12V connector, since the power used by the GPU´s comes directly from the PSU to the GPU´s and not pass on the MB, the PCIe slot is used only for transfer data so actualy very few power is draw from it. That´s is the big diference. And of course INTEL´s MB ate top of the class, with high quality components but normaly expensive.

But something you clearely show, the GPU´s on the multi GPU hosts must de powered my the external connector as your picture shows by ussing the molex to 6 pin adaptor.

BTW did you use this 7 x 250 for crunching? sure it´s works fine for gaming or other jobs but for continuous crunching for years?... sure mr. ohm is shaking in his graveyard.

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I have a 250 running right now, http://setiathome.berkeley.edu/show_host_detail.php?hostid=6796475
It's a 150 watt card with One 75 watt plug, http://en.wikipedia.org/wiki/Comparison_of_Nvidia_graphics_processing_units#GeForce_200_Series
That leaves 75 watts coming from the PCIe slot. Even if TA used the single Molex connector on all the cards, that still leaves 7x~40 watts coming from the PCIe slots. That's 280 watts, which is very close to HP's 275 and Intel's 300. That's probably why those fa..err, cigarettes didn't go up in flames.

I guess you missed the Link, It Lives, It Lives !!

That leaves 75 watts coming from the PCIe slot. Even if TA used the single Molex connector on all the cards, that still leaves 7x~40 watts coming from the PCIe slots.

That's not the way it works.
Cards that have the auxiliary power connector get most of their power from that, not the motherboard. They only draw power heavily from the motherboard if the auxiliary connector isn't supplying it.

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Grant
Darwin NT

How much does one molex connector supply? Obviously the 6 pin 75 watt connection Requires Two. Therefore, it is Obvious that One Molex Will Not Supply the 75 watts required from the board. One 6 pin connection is rated for 75 watts, the GTS 250 is rated at 150. Are you suggesting the 250 is pulling close to 150 watts from a 75 watt cable? People have tried that with splitter cables, it usually Fries the 75 watt cable. If you look around, you will see that the ATI 6970 had a habit of peaking the PCIe slot at Over 75 watts, even though it has aux connections. Let's not forget about HP saying their PCI system can supply 275 watts and Intel 300 watts...

Take a power supply apart, and you will see that the molex connector is just a direct connection from the 12V rail to the connector. Nothing in there that actually regulates how much power it provides. It will at least try and supply as much power as the load is trying to draw. Of course there is a limit where the connector starts to overheat, and could fail in quite a spectacular way (smoke and flames)

There is nothing that stops a molex connector supplying 150w, It's way over it's design spec, it may not last very long, but it will try and do it.

I'm sure that Intel and HP have boards that will supply 250 or 300w to the various PCI-E slots. Just a matter of heavy enough connectors and board traces to get the power from the PSU to the individual slots. No magic needed, just good engineering.

But that doesn't mean that any random budget 3 slot system board can do the same thing (reliably). The Intel and HP boards will be some of their higher end commercial stuff. Designed to run multiple high spec cards, so it's built to handle the worst case.

Ian

The accusation was made that 180 watts drawn from the PCI system would fry the 24 pin power connection. It is an ATX power connection. As far as I know, all 24 pin ATX power connections are the same...aren't they? So, how does 180 watts on one board spell disaster where 300 watts on another board doesn't? Think about that one.

BTW, it's already been established that all PCIe slots can deliver 75 watts to a video card. It's in the PCIe Specs. Even the lowly 1x slot has provisions to supply 75 watts to a video card. I ran my 150 watt GTS 250 in a 1x slot for months without any trouble. That's the GTS 250 with the single 75 watt aux cable. Are you saying there are 'budget boards' that don't follow the PCIe standard? I would think those companies wouldn't last very long if someone found they were not following the Standards.

As i say in the beginning of my previous post, we have this discusion before, don´t loose your time to try to explain something to someone who don´t want to hear, the fact is, 3x60W GPUs could work in some high quality MB like some HP or Intel MBs, but not work for a long time on normal MB with low cost components. I´m sure anyone who works in PC repair have experiences with melted 24pin connectors and knows what i talk about. It´s hard to see a melted 12V line pins destroying your expensive MB.

The 24pin connector could look similar, but there are big diferences in component quality that translate in more or less capacity of current, normaly cheaper MB uses cheaper components thats the industry roule.

By specs you could draw from the PCIe up to 75W IIRC but the specs say nothing about the sum of the PCIe capacity on the MB, so for example even on a high quality EVGA classified MB with 8 PCIe you can´t use all the PCIe at the same time, if each one uses even 60W (far from the 75W individual limit), it´s simply 480W@12V...40A >2x more current than the best 24 pins 12V connectors can handle. You can even build one ussing 8 GPU´s and make it work for a small amount of time in controled enviroment for demo but for 24/7 crunching... We can´t break the ohm laws.

Simply facts in the real world. Melting does not happening in seconds, sometimes takes months, even years depens on your enviroment, humidity temps, etc, each case is unique is not an exact science, but when happening you will know it happened in the worst case cenario.

So be safe, use external powered GPU´s (6/8 pin powered) if you wish to build a long lasting 24/7 multiple with 3 or more midrange GPUs cruncher. Obviusly you don´t need to worry about this on a 2xGPU host or if you use low power (like 25W) GPUs or high end GPU´s who allready draw most of it´s power from the 6/8 pin connectors (at least most of NV models) easely to imagine why.

I´m out of further discusions about.

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el-cheapo molex connections

LOL - Hey Guy, i realy like that, you explain all perfect in few words.

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As i say in the beginning of my previous post, we have this discusion before, don´t loose your time to try to explain something to someone who don´t want to hear, the fact is, 3x60W GPUs could work in some high quality MB like some HP or Intel MBs, but not work for a long time on normal MB with low cost components. I´m sure anyone who works in PC repair have experiences with melted 24pin connectors and knows what i talk about. It´s hard to see a melted 12V line pins destroying your expensive MB.

The 24pin connector could look similar, but there are big diferences in component quality that translate in more or less capacity of current, normaly cheaper MB uses cheaper components thats the industry roule.

By specs you could draw from the PCIe up to 75W IIRC but the specs say nothing about the sum of the PCIe capacity on the MB, so for example even on a high quality EVGA classified MB with 8 PCIe you can´t use all the PCIe at the same time, if each one uses even 60W (far from the 75W individual limit), it´s simply 480W@12V...40A >2x more current than the best 24 pins 12V connectors can handle. You can even build one ussing 8 GPU´s and make it work for a small amount of time in controled enviroment for demo but for 24/7 crunching... We can´t break the ohm laws.

Simply facts in the real world. Melting does not happening in seconds, sometimes takes months, even years depens on your enviroment, humidity temps, etc, each case is unique is not an exact science, but when happening you will know it happened in the worst case cenario.

So be safe, use external powered GPU´s (6/8 pin powered) if you wish to build a long lasting 24/7 multiple with 3 or more midrange GPUs cruncher. Obviusly you don´t need to worry about this on a 2xGPU host or if you use low power (like 25W) GPUs or high end GPU´s who allready draw most of it´s power from the 6/8 pin connectors (at least most of NV models) easely to imagine why.

I´m out of further discusions about.

The problem is, they don't make low end cards with aux connections because they are not required. The PCIe group designed the standard with that in mind. Over six years ago companies were marketing computers with 4 x 75 watt configurations. I'm sure if you looked hard enough you could find the limit for the ATX power connector. Until then I would suggest going by what Intel/Apple/HP/etc market, around 300 watts for the PCI system. Melted connectors are usually from people not bothering to research, such as using a 6 pin splitter on a 75 watt cable assembly expecting it to carry 150 watts. I did learn something about 4 pin Molex connectors though. Since 2 are used to deliver 75 watts, you can expect one to start melting somewhere below 75 watts.

If you consider the above, and see that PCI Express logo on your GPU box, there isn't any problem running 3x60 of even 4x75 watt cards. Any company not capable of marketing a produce to standards would see that PCI Express logo disappear very quickly.

There where a big discussion about that before in the forums, the problem is not in the PCI-e slots, each one of them can theoretically handle up to 75W by specs IIRC, the problem is with the 12V lines from the 24 pin power connector who carries the sum of all current used by any 12V devices attached to the MB (plus the MB 12V devices itself). Most of them can´t handle the current used by 3x60W GPU´s plus the rest of the devices. Before the pros vs cons start again, yes initially the 12V connectors can handle the current, but it´s at the edge of their capacity, and when you crunch (different from gaming) you use them at that capacity for a long time, so they will not last for long. An a melted 24 connector normally destroy your MB. So if you want a long lasting cruncher with 3x60W GPU´s go for the external (6 pin VGA connector) models. From other side, some MB has separate power connectors for the 12V lines exactly to avoid that and there are some manufacturers with better quality connectors rated for bigger current who could drive the current safely, but that is not common, you need to be sure if your MB specifications allow that.

Juan BFB, I had that happen to Me, My present motherboard is dying slowly, I'd had an Antec adapter cable in place to power an Antec HTPC case that plugs in between the motherboard and the power supply(the psu is still damaged on the power connector), all cause I had 3 GTX295 cards, so now I've bought motherboards that have that extra connector for the pci-e slots, so the slots will have enough power, like an Asus Rampage III Extreme X58 and an EVGA X79 Classified, My next motherboard with this extra power socket will be to replace this motherboard so the cpu will have somewhere to run on, I'm hoping to get an Asus Maximus III Extreme, though an EVGA FTW or EVGA FTW-200 also has that socket onboard too, all three are LGA1156. On some motherboards Molex power connections are used, newer motherboards use the 6 pin pci-e(VGA) type.

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The T1 Trust, PRR T1 Class 4-4-4-4 #5550, 1 of America's First HST's

EVGA makes a small power card that will supply power to the pci-e slots and yes the card is so small that the card actually will fit under the heatsink shroud of most video cards and yes I use one, the card is called the EVGA pci-e Power Boost and the card uses a molex power cable to supply 12v to the pci-e bus. The card costs $14.99 plus shipping and is located Here.

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The T1 Trust, PRR T1 Class 4-4-4-4 #5550, 1 of America's First HST's