Powering a GPU with 1 or 2 cables from the PSU?

[mihailt]

Hi guys,

So I've finally procured all my components for my new build. Below are my specs:

Intel i5-8400
Gigabyte H370 Aorus Gaming 3 WiFi
HyperX Fury 32 GB RAM @ 2666MHz
MSI GTX 1070 Gaming X
Samsung 970 EVO 500 GB
Seagate Barracuda 2TB (ST2000DM006)
Seasonic Focus Plus Gold 550W (SSR-550FX)
CableMod Basic ModFlex™ Cable Extension Kit - Dual 6+2 Pin Series

Now, my PSU comes with a single PCIe power cable that has a splitter at the other end to plug into two slots, while my GPU has one 6-pin slot + one 8-pin slot.

I recently read that it's better to use two separate PCIe cables to power 2-lot GPUs, with some people claiming this way makes their GPUs perform better, while others complained that their GPUs reached higher temps when powered by a single split cable rather than two separate cables.

So I guess my question is, is there any truth to the above claims? Do you think my power supply will do just fine if I connect the two PCIe cable extensions from CableMod on a single power cable? Will there be any benefits if I had two separate PCIe power cables from Seasonic? JohnyGuru has done a review of my exact PSU model and he mentions something about trying to talk Seasonic into giving an extra PCIe cable. Should I try talking to Seasonic, or do you think I won't have issues with using a single cable for my GTX 1070?

 

[madmatt30]

No issue at all.

That single cable from the focus will be species,to carry up to 300w total.

A 1070 (depending on model & overclocks) is 170-220w absolute max.

Go ahead as you are.

 

[justin.m.beauvais]

It depends. With a Seasonic I wouldn't worry too much about not getting enough power. They make some quality stuff. You should be fine.

The idea that you must be using two separate cables, as in two separate rails, doesn't apply nowadays as much as it did back when video cards were much less power efficient. In those days when a video card would pull 300W or more, a single rail wouldn't provide enough power for dual GPU setups. Nowadays video cards sip power compared to those monsters.

As for the GPUs getting hotter running on a single cable... I don't see how that is even possible unless they were stressing things so hard that their fans couldn't reach full speed... and I think you'd see card instability before that.

The GTX 1070 should be fine to run two of them off of one rail. That said, if it sketches you out too much there is always the second cable option or a splitter to take power off the SATA connectors.

 

[smashjohn]

A single cable carries more wattage, which will concentrate more heat in one place (in terms of the cable, not the GPU). The only reason I know of to use 2 cables instead of one is that you have a multi-rail PSU. Something like the Corsair AXi series will let you monitor power draw on separate cables by assigning them to separate rails through the corsair link software.

Other PSUs (though pretty rare these days), split the 12v into multiple rails; if you have 2 x 20amp 12v rails, you'd want one cable to come from each rail. Again, I don't see this happen anymore, pretty much everything is single rail unless you're talking about something like the AXi PSUs.

The other consideration comes with after market cables, which can have different AWG wire. Cheap aftermarkets might have thick insulation, but cheap out on the actual copper inside. The wire gauge determines the maximum power draw that the cable supports. Running a single cable with split plugs and substandard wire can be a fire hazard. Generally speaking, you shouldn't have this problem with the OEM cables.

Update: Your PSU has one 45Amp rail, so it's all coming off that one rail either way.

 

[ko888]

If you're unable to convince Seasonic to give you an extra PCIe cable you can always buy one:

https://www.btosinte.com/Seasonic-8pin-to-62pin-PCIe-Cable-w-inline-capacitor-SS-IN-8-62PCIe.htm

 

[madmatt30]

Mid wattage dc-dc units (like the focus you own) are all single rail by nature.

18 awg cable (used on the modular cables) is 10amp at 12v in a worst specced scenario (high temp/long 3-4m runs)

That's 120w per live wire , the modular has 3 live cables,3 return grounds, so in t's absolute worst case it can run 360w.

We'd all love 12 or 14awg cable specs but on a psu where there are 8 cables on a single connector it's impractical - trying to route higher gauge cable through your case would be like trying to bend an iron bar.

 

[mihailt]

Hey guys,

Many thanks for all of your replies.

As you picked up, my main concern was using the extensions from CableMod (which are allegedly quality products).

So, my PSU uses 18awg cables and while CableMod doesn't publish such specs, I was able to gain their cables were 16awg. However, I'm not sure is this good or bad? Would 30-cm 16awg extensions be of any hindrance to the original 65-cm 18awg PCIe cables?

 

[justin.m.beauvais]

Hey guys,

Many thanks for all of your replies.

As you picked up, my main concern was using the extensions from CableMod (which are allegedly quality products).

So, my PSU uses 18awg cables and while CableMod doesn't publish such specs, I was able to gain their cables were 16awg. However, I'm not sure is this good or bad? Would 30-cm 16awg extensions be of any hindrance to the original 65-cm 18awg PCIe cables?

Generally the smaller the number the bigger the wire. So CableMod uses thicker wire capable of carrying more current with less resistance. So they are better wire and shouldn't hinder your existing cables at all.

 

[mihailt]

Alright, I'll go with your recommendations and not look for extra PSU cables, as I do not plan to overclock my 1070 at all.

Once again, many thanks to all for your input!