Question about splitting PCIe power

[rcarlos243]

Lets say I want to split a 1x 8PIN PCIe power for a riser and a GPU, will it properly work?

 

If the riser is asking for 75W and the GPU is asking for 95W, would the power gets delivered asymmetrically?

 

If I get a 6PIN to dual 8PIN splitter, will the 3rd 12v rail work if the extra 2PIN (one has sense) is not populated? Will it simply overload the two 12v rail to get more than 75W?
https://2.bp.blogspot.com/-vJ2afsvYPkA/Vux5bOLpp6I/AAAAAAAAi4s/0Q9XN77kfE4yWS5aNigozkvsepwJ2tMKg/s1600/PCIe_pinout.png

 

[Eigenvektor]

1 hour ago, rcarlos243 said:

If the riser is asking for 75W and the GPU is asking for 95W, would the power gets delivered asymmetrically?

The riser itself doesn't need power, it's that a PCIe port can provide up to 75W. So any card connected to the port (through riser) needs to be able to pull up to 75 Watt from it. The card is going to pull however much power it currently needs from PCIe cable and port. As long as both of these can provide as much as is needed, it should work.

 

1 hour ago, rcarlos243 said:

If I get a 6PIN to dual 8PIN splitter, will the 3rd 12v rail work if the extra 2PIN (one has sense) is not populated? Will it simply overload the two 12v rail to get more than 75W?

Splitting a 6-pin to dual 8-pin sounds like a really bad idea. As I said, the card is going to pull as much as it needs. As long as the power supply is able to provide that, it will. However it could overload the cable, since you're operating outside its specifications.

 

A 6-pin is rated for 75W, while each 8-pin is rated for 150W. So theoretically the card could try to pull up to 300W through a connector rated for 75W. In your example the card might pull up to 75W through the PCIe port and 95W through the PCIe cable. If that comes from a single 6-pin you're still pulling more than twice what it is rated for.

[rcarlos243]

22 minutes ago, Eigenvektor said:

The riser itself doesn't need power, it's that a PCIe port can provide up to 75W. So any card connected to the port (through riser) needs to be able to pull up to 75 Watt from it. The card is going to pull however much power it currently needs from PCIe cable and port. As long as both of these can provide as much as is needed, it should work.

 

Splitting a 6-pin to dual 8-pin sounds like a really bad idea. As I said, the card is going to pull as much as it needs. As long as the power supply is able to provide that, it will. However it could overload the cable, since you're operating outside its specifications.

 

A 6-pin is rated for 75W, while each 8-pin is rated for 150W. So theoretically the card could try to pull up to 300W through a connector rated for 75W. In your example the card might pull up to 75W through the PCIe port and 95W through the PCIe cable. If that comes from a single 6-pin you're still pulling more than twice what it is rated for.

 

I don't think you understand what I am asking.

 

I am specifically asking about a riser that is connected via a USB cable to the motherboard so it does not carry enough power and needs an external power source like 6PIN PCIE

 

[Eigenvektor]

16 minutes ago, rcarlos243 said:

I don't think you understand what I am asking.

Well, maybe you should've mentioned this little detail in your original question? That's not what people typically mean by riser. This is an M.2 to PCIe converter, rather than a simple riser.

 

My point about splitting PCIe 6-pin into dual 8-pin remains, it's a bad idea. Or do you want to split one 8-pin into dual 6-pin for this contraption?

 

As far as I can see this converts an M.2 slot into PCIe x1 and then provides a physical PCIe x16 slot? Are you using a board without PCIe or why do you want to use such an unconventional method of connecting the GPU?

[rcarlos243]

42 minutes ago, Eigenvektor said:

That's not what people typically mean by riser. This is an M.2 to PCIe converter, rather than a simple riser.

 

Not typical? Almost every single GPU miner uses a riser and a large portion of GPUs bought are used for mining

 

The M.2 to PCIe is just a form factor, but most riser uses a PCIe 1x

[--SID--]

3 hours ago, rcarlos243 said:

the riser is asking for 75W and the GPU is asking for 95W

75w + 95w = 170w while a 8 pin is specified for 150w. You're taking a risk, also because most of the splitters are terrible quality.

 

What make and model PSU?

[rcarlos243]

10 minutes ago, --SID-- said:

75w + 95w = 170w while a 8 pin is specified for 150w. You're taking a risk, also because most of the splitters are terrible quality.

 

What make and model PSU?

 

The main question is being derailed.

 

I am specifically asking about the mechanism of a PSU

 

I am asking If the load can be asymmetrical if a single 8PIN PCIe is split towards a riser and a GPU.

 

The amount of load and PSU model is irrelevant, but since you are asking It would be an Antec ST1000 and the load depends on the GPU (e.g. 130W for RTX 3070)

[Eigenvektor]

3 hours ago, rcarlos243 said:

I am asking If the load can be asymmetrical if a single 8PIN PCIe is split towards a riser and a GPU.

That's not an asymmetrical load from the PSUs point of view. If you have a single cable going into the PSU, then the load it sees is the combined power draw of the devices attached to that cable. The PSU doesn't care or see how many devices there are, nor which devices contributes how much to the overall load.

[rcarlos243]

1 hour ago, Eigenvektor said:

That's not an asymmetrical load from the PSUs point of view. If you have a single cable going into the PSU, then the load it sees is the combined power draw of the devices attached to that cable. The PSU doesn't care or see how many devices there are, nor which devices contributes how much to the overall load.

 

Are you making an assumption or do you have any data?

[Eigenvektor]

18 hours ago, rcarlos243 said:

Are you making an assumption or do you have any data?

Not sure what kind of data you expect me to provide here. That's how electricity works. If you attach multiple consumers to the same socket on your PSU, that socket has to be able to provide their combined load.

 

A splitter is a parallel circuit, so devices attached to it will get the same voltage, with each device drawing as much power as it needs. Voltage will drop slightly under load, but that drop will be equal for all devices. You'd have to worry if you attached one device to two power sources, and those power sources had different voltages and internal resistance. But that shouldn't be the case here.