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tincanalley

AUX Power to GPUs

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Posted · Original PosterOP

I have a question about the additional power required by most of the GPUs.  For instance, my older GTX 760 has one 8 port and one 6 port.  Both of those are required to power the card (or so the manual and specs claim), obviously, but here's what I don't truly understand.  Take the PSU connection, most have a single cable with two connectors on it.  Usually two 6 pins and two 2 pins so you can use either 6 or 8 or a combination of the two.  So this cable is splitting the same power lines coming from the PSU to supply those two ports.  Since this is happening, why bother having 2 connectors on the card?  Why not just have one 8 since there is no difference in what you're getting from the supply side?  Even if you used two cables, if you have a single rail PSU, you would still be pulling from the same rail.

I'm hoping I'm missing something no too simple, but it is quite possible I am.


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Each pair of plugs supplies power at the rail's voltage but can only handle a certain amount of current without overheating. So you don't end up with thick, stiff cables, they use multiple, smaller ones in a comb or bundle.

The card needs a certain amount of power to operate, but that is more than 4 wires can handle (an 8 pin). Since the industry has standardized on 6 and 8, that is what the card manufacture had to work with. I'm sure they would have gone with a single 14 pin connector if it existed, but it doesn't.

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1 hour ago, tincanalley said:

Since this is happening, why bother having 2 connectors on the card?  Why not just have one 8 since there is no difference in what you're getting from the supply side?

PCIe connectors are rated for a certain amount of wattage. 6-pin is rated for 75W, 8-pin for 150W. The only reason why a card needs both is because it takes up more power than what a single connector can provide plus the PCIe slot (about 67W, because that's how much the 12V lines provides). Though it's not a good idea to meet just the requirement or even shy of the requirement. The more current you pull, the more voltage drops and/or everything heats up. Not to mention graphics cards can have spikes of power consumption.

 

Though I have no idea why that particular GTX 760 has both since a single 8-pin should be sufficient. It may be a higher-end model that was expected to be pushed.

 

1 hour ago, tincanalley said:

Even if you used two cables, if you have a single rail PSU, you would still be pulling from the same rail.

It may be advantageous in the most extreme of corner cases to use two cables but use the closer connector. A single cable will deliver slightly lower voltage because the cable still has resistance which drops voltage going into the card. Lower voltage means lower power assuming the same current, so the card draws more current from the same cable. More current means more heat. This heat can factor into one of the boost clock walls.

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Nvidia lists the 760 as requiring 170 watts so a single150 watt 8-pin would be insufficient if no power was drawn from the motherboard. 

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Posted · Original PosterOP

I don't think anyone is understanding.  The cable comes off the PSU from an 8 pin port and divides it up into an 8 and a 6 at the other end, so in reality, the card is getting both power ports supplied by a single 8 port from the PSU.


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Posted · Original PosterOP

I'm attaching a couple of pics.  This is a Corsair RM1000i and if you look at the PSU pic, you will see a single 6+2 cable in the upper left.  That is the GPU power.  Now the second is the GPU.  See how the single cable splits into 2 for powering both ports.  So power limitations set for an 8 pin are being ignored?

PSU GPU.jpg

GPU PSU.jpg


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@tincanalley

 

The PSU side can handle the amount of current of 2x 6+2 pin PCI-E connections without a doubt.

It would also depend on how the 6-pin and 8-pin connections ON THE CARD are routed.

The power coming from the 6-pin might be supplying power to the VRAM chips, VRM\s, fans, LEDs, and the 8-pin to  supplying power to the GPU core.

 

As others mentioned, there is a STANDARD / REGULATION that must be followed with PCI-E 6-pin and 8-pin connections.

It must be ATX ver. 2.4 compliant (the latest is 2.4 at least).

 

There is no standard on how the pin and wire configuration must be on the PSU end.

This is why you CAN'T mix-n-match modular 8-pin connection from an...EVGA PSU...onto a Corsair PSU.

You'll blow the damn PSU.

Pin #1 on the EVGA may be +12v 5A, and it could be GND pin on the Corsair... or +12v 3A or something.


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Posted · Original PosterOP
7 minutes ago, -rascal- said:

@tincanalley

 

The PSU side can handle the amount of current of 2x 6+2 pin PCI-E connections without a doubt.

It would also depend on how the 6-pin and 8-pin connections ON THE CARD are routed.

The power coming from the 6-pin might be supplying power to the VRAM chips, VRM\s, fans, LEDs, and the 8-pin to  supplying power to the GPU core.

 

As others mentioned, there is a STANDARD / REGULATION that must be followed with PCI-E 6-pin and 8-pin connections.

It must be ATX ver. 2.4 compliant (the latest is 2.4 at least).

 

There is no standard on how the pin and wire configuration must be on the PSU end.

This is why you CAN'T mix-n-match modular 8-pin connection from an...EVGA PSU...onto a Corsair PSU.

You'll blow the damn PSU.

Pin #1 on the EVGA may be +12v 5A, and it could be GND pin on the Corsair... or +12v 3A or something.

So the PSU makers can pump more than the standard amount of power through their connector and the cable, but the receiving end has to adhere to the standards?  Not really a huge deal, but the darn cable looks ugly.  I'm hoping the RTX 2080 Super will have a single 8 pin and then I'll get a custom cable for it.  Until then, I'm using this ugly one.

 

Thanks for the info


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1 minute ago, tincanalley said:

So the PSU makers can pump more than the standard amount of power through their connector and the cable, but the receiving end has to adhere to the standards?  Not really a huge deal, but the darn cable looks ugly.  I'm hoping the RTX 2080 Super will have a single 8 pin and then I'll get a custom cable for it.  Until then, I'm using this ugly one.

 

Thanks for the info

 

Correct, there is no official standard PSU manufactures needs to follow.

I even remember DeepCool (Or Apevia) KingWin used to sell PSUs with round cable ends.

They were 4-pin or 5-pin cables.

 

Image result for KingWin modular PSU

 

Image result for KingWin modular PSU

 

 

SeaSonic could make a PSU that uses two thicc wires...one wire that can supply... +12v 18A, and a GND wire...then split it into 2x 6+2 pin connections for PCI-E.


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11 minutes ago, tincanalley said:

So the PSU makers can pump more than the standard amount of power through their connector and the cable, but the receiving end has to adhere to the standards?  Not really a huge deal, but the darn cable looks ugly.  I'm hoping the RTX 2080 Super will have a single 8 pin and then I'll get a custom cable for it.  Until then, I'm using this ugly one.

 

Thanks for the info

There's no "standard" amount of power (or more technically amps). As long as the cable can handle the amount of amps going through it, it's fine.

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Posted · Original PosterOP
2 hours ago, Mira Yurizaki said:

There's no "standard" amount of power (or more technically amps). As long as the cable can handle the amount of amps going through it, it's fine.

So then if the PSU manufacturers can use an 8 pin that can go beyond what an 8 pin on the PCIe side can handle, then the PCIe side needs to use something similar to make things easier and more efficient.  Less cabling and cleaner look. 


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Posted · Original PosterOP
2 hours ago, -rascal- said:

 

Correct, there is no official standard PSU manufactures needs to follow.

I even remember DeepCool (Or Apevia) KingWin used to sell PSUs with round cable ends.

They were 4-pin or 5-pin cables.

 

 

 

 

 

 

SeaSonic could make a PSU that uses two thicc wires...one wire that can supply... +12v 18A, and a GND wire...then split it into 2x 6+2 pin connections for PCI-E.

That would be nice to have a twin wire to an 8 pin (for both PCIe and motherboard supply).


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37 minutes ago, tincanalley said:

So then if the PSU manufacturers can use an 8 pin that can go beyond what an 8 pin on the PCIe side can handle, then the PCIe side needs to use something similar to make things easier and more efficient.  Less cabling and cleaner look. 

The only thing that would make for a cleaner look is reducing the connectors, but they would probably have to be enlarged in some way to accommodate the increased current. Most recommended PSU sellers have PCIe cables that can carry enough power to supply two 6+2-pin connectors. This is the most any one graphics card needs anyway and at most all you're needing is two plugs.

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Posted · Original PosterOP
21 hours ago, Mira Yurizaki said:

The only thing that would make for a cleaner look is reducing the connectors, but they would probably have to be enlarged in some way to accommodate the increased current. Most recommended PSU sellers have PCIe cables that can carry enough power to supply two 6+2-pin connectors. This is the most any one graphics card needs anyway and at most all you're needing is two plugs.

Looks like the 2070 Super has two 8 pin connectors, so the 2080 Super that I am waiting for will also have two 8 pins.  Guess I know I can now order to custom 8 pins.


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13 minutes ago, tincanalley said:

Looks like the 2070 Super has two 8 pin connectors, so the 2080 Super that I am waiting for will also have two 8 pins.  Guess I know I can now order to custom 8 pins.

I only see a 6+8, but the 6 is using the same housing as the 8-pin.

 

Though the 2080 Super is supposed to have the same TDP rating as the 2080 Ti, which uses two 8 pins.

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Posted · Original PosterOP
23 minutes ago, Mira Yurizaki said:

I only see a 6+8, but the 6 is using the same housing as the 8-pin.

 

Though the 2080 Super is supposed to have the same TDP rating as the 2080 Ti, which uses two 8 pins.

Asus has their versions up on their site, less pricing, and they have the 2070 Super noted as having two 8 pins.  So I'm assuming the 2080 Super will have the same.


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