Cable question about my PSU and Vega

[SPG]

So I'm going to be buying two vega's and putting them under water, my psu is pretty kick ass and can handle it...but I remember reading in the manual that I shouldn't use the PCI-e cords with 2 plugs on them if the card consumes more than 250w and I should use two separate wires.

but two of my cords are normal, and the other two have 8 extra pins....is it still safe to just use the one wire to get rid of clutter? or should I just suck it up and stop bitching? Normally I would just use the one wire, but liquid vega consumes a lot of power.

PSU for reference https://seasonic.com/product/x-1250/

I guess a better question would be...how much power can a single cable have going through it without issues? I already know that 1 8 pin supports 150w and that my psu is sharing the same rail for almost everything....so I shouldn't be worrying about anything. is it ok to have 300w going through one cable? or should I divide it.

[bughtoo]

36 minutes ago, SPG said:

So I'm going to be buying two vega's and putting them under water, my psu is pretty kick ass and can handle it...but I remember reading in the manual that I shouldn't use the PCI-e cords with 2 plugs on them if the card consumes more than 250w and I should use two separate wires.

but two of my cords are normal, and the other two have 8 extra pins....is it still safe to just use the one wire to get rid of clutter? or should I just suck it up and stop bitching? Normally I would just use the one wire, but liquid vega consumes a lot of power.

PSU for reference https://seasonic.com/product/x-1250/

I guess a better question would be...how much power can a single cable have going through it without issues? I already know that 1 8 pin supports 150w and that my psu is sharing the same rail for almost everything....so I shouldn't be worrying about anything. is it ok to have 300w going through one cable? or should I divide it.

3 years ago when i made my PC, i bought 2x 290x watercooled it and oced them pretty hard, each of them consuming around 300-350W each of them going only through one cable. I had Evga Supernova P2 1000W PSU, run them like that for over 2 years then i sold them and upgraded them to WC 1070. 

I would say it is absolutely okay to run it through one cable, just make sure u are not overstressing your PSU(consuming more than it can produce)

 

EDIT: just checked the PSU, 1250w IS PLENTY ENOUGH maybe even for 3....

[orangecat]

I would recommend 1 8 pin cable for ever 8 pin on the GPU. So in your case you would need 4 8 pin cables coming from the PSU.

[STRMfrmXMN]

58 minutes ago, SPG said:

So I'm going to be buying two vega's and putting them under water, my psu is pretty kick ass and can handle it...but I remember reading in the manual that I shouldn't use the PCI-e cords with 2 plugs on them if the card consumes more than 250w and I should use two separate wires.

but two of my cords are normal, and the other two have 8 extra pins....is it still safe to just use the one wire to get rid of clutter? or should I just suck it up and stop bitching? Normally I would just use the one wire, but liquid vega consumes a lot of power.

PSU for reference https://seasonic.com/product/x-1250/

I guess a better question would be...how much power can a single cable have going through it without issues? I already know that 1 8 pin supports 150w and that my psu is sharing the same rail for almost everything....so I shouldn't be worrying about anything. is it ok to have 300w going through one cable? or should I divide it.

I promise whatever cable configuration you throw at that Seasonic it won't struggle with. Don't overthink it.

[SPG]

9 hours ago, STRMfrmXMN said:

I promise whatever cable configuration you throw at that Seasonic it won't struggle with. Don't overthink it.

oh I know, they have great stuff (I actually followed your guide when I bought it) I was more concerned about the cable itself, not really the PSU not supplying enough power.

[STRMfrmXMN]

7 minutes ago, SPG said:

oh I know, they have great stuff (I actually followed your guide when I bought it) I was more concerned about the cable itself, not really the PSU not supplying enough power.

I know but I'm saying that Seasonic isn't stupid and you'll be fine plugging in whatever cables into your GPU you'd like.

[SPG]

Just now, STRMfrmXMN said:

I know but I'm saying that Seasonic isn't stupid and you'll be fine plugging in whatever cables into your GPU you'd like.

Alright then, I'll just use the one cable with the spliter on the end.

[mariushm]

You can wire any way you want.

The ideal way would be to use the four strips of pci-e plugs, one strip for each pci-e 8pin connector on the video cards.  It's always better to have MORE wires between the power supply and a device (video card, processor).

 

However, even in the non ideal way where you use just one strip with two plugs to power a single card, the cables themselves are thick enough and the power supply is quality enough to power each video card just fine. The only downside would be that the wires between the power supply and the video card will heat a bit more and so will the connector on the power supply end.

 

If you want to get technical, the Vega64 should use at most around 280w on the stock settings, maybe around 350w when overclocked.. let's go with 360w since it's easier to do the math.

So assuming 360w from the pci-e connectors, that's 360w / 12v = 30A from two pci-e 8 pin connectors.  Each connector has 3 circuits, meaning there's three pairs (12v+GND) wires between the power supply and the plug, therefore the video card receives those 30 A through 6 pairs of wires, or each pair of wires carries 5A of energy into the card.

 

The connector standard guarantees 9A per pair inside the connector, and the AWG18 wires themselves can handle quite a lot of current over short distances. For AWG18 I think the allowed value is somewhere around 10-12A with heating above ambient of less than 20-30 degrees Celsius or something like that (if you don't care about heat, they can handle more)

 

So considering the connectors can do 9A per circuit, we're perfectly fine since we only have 5A per circuit.

Whether we use two plugs per strip (so 10A through the strip between psu and card) or we use one plug per strip (5A through strip), we're also OK since the wires are thick enough to carry more than 10A.

 

The only potential problem could be right by the power supply in the connector, where in theory, each pin must push 10A of current which is slightly more than the 9A rating of the connector, but in practice it's not a big deal since the connectors on the power supply are soldered really well to thick circuit boards which pull heat away from the connector and the psu fan also moves air around keeping the connectors reasonably cool.

The Seasonic X series also uses some special connectors for each pci-e strip, so there's more than 3 circuits for each strip, so in reality each circuit has less than 10A of current on the power supply side, so it's well within acceptable limits.

 

The wires themselves have some resistance, so between the power supply and the video card, there will be some losses which manifest as heat, and at the end of the cable at the video card the voltage the video card sees will be slightly smaller.

Using two plugs from same strip, the video card may see 11.8v instead of 12v , because 0.2v are lost in the cables. Using two strips and one plug from each strip, the video card would see maybe 11.9v instead of 11.8v and the wires in the strips and the plugs will heat a bit less.

That's the whole difference.