this post was submitted on 27 Aug 2024

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6800XT connected to PSU via single cable (lemmy.nz)

submitted 2 months ago by [email protected] to c/[email protected]

32 comments fedilink hide all child comments

I saw this picture while looking at overclocking guides and I wondered if I may have my power setup incorrectly. My GPU is currently connected exactly like the don't do this diagram.

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[–] [email protected] 35 points 2 months ago* (last edited 2 months ago) (1 children)

The concern is that really running too much current / many amps through too thin of a cable risks melting the cable, which can in turn cause a short and fry things.

For a cable meeting the minimum specification, for one 8-Pin PCI connector it would be rated to handle about 12A / 150W. L

Your card can draw up to 300W. If your second PCI power connector is a “pigtail” off of the first, then the first run of cable is taking about 25A at full load.

If the cables are thick and overbuilt, that’s bot really an issue. If the cables are thinner and have a lower current rating, they could melt.

Best practice is to split the connections across the power supply’s available ports.

[–] [email protected] 14 points 2 months ago (1 children)

A well built power supply will have a current limit on the connector to prevent the cable melting problem, but that means if you have a card that needs 200w, but only power it via 1 connector you are going to run into problems

[–] [email protected] 12 points 2 months ago (1 children)

12hpwr/6+6 will do 600 watts using a lot less copper than what you'll find in 4 8 pin pcie cables.

The ATX standard allows for a 5% voltage drop. This shitty 2.1 star rated extension cable uses 18 gauge wire which is typically the worst you'll see in a cable. Using this calculator 30 amps on an 18 gauge 3 foot cable leaves you with 0.1v of drop which is within spec. And there's 3 +12v wires in every 8 pin cable. You'll be fine.

[–] [email protected] 2 points 2 months ago

Yes, this is the way. I've had to do the maths manually without one of those calculators before, but people still wouldn't believe me.

Best advice is to always do what your PSU maker recommends. If they put the connector on there it probably means they want you to use it.

[–] [email protected] 17 points 2 months ago (1 children)

If your GPU has two power connectors you should always use two runs from the PSU.

You only have to ask yourself why they would bother with the second connector if it was okay to just attach a little extension to the end of a single cable.

Some cards may run fine with this setup, but you're going to be increasing fire risk by potentially running more amps down a wire than is safe to.

[–] weker01 19 points 2 months ago (2 children)

You only need to ask yourself why the PSU manufacturer would bother including the second connector on the same cable if it wasn't ok to use it.

If you use a third party extension/splitter that would be another story but it doesn't look that way in the diagram.

[–] captain_aggravated 3 points 2 months ago

I seem to remember they started doing those daisy chain power connectors back in the SLi days. Take the GeForce 6800GT for example, which was a single slot card rated for 67 watts and had a single 6-pin power socket. You could safely drive two of them in SLi on a single 150 watt PCIe power cable. Hell they'd probably both run fine on motherboard power.

[–] [email protected] 2 points 2 months ago

Many cards used to use 3 connectors so you'd run two lines and a third from the second connector of one of the lines.

The diagram op posted is from nvidia and seasonic and fixes many stability issues, not fire hazzards

[–] [email protected] 14 points 2 months ago (1 children)

The manufacturer is concerned that they will be pulling a ton of power from both connectors. Sometimes the second connector is just for ancillary power silly or balancing, in this instance they are saying that they're planning on your card pulling as much power as possible.

You might find that in heavy situations, or on hot days, your power supply overcurrent will trip out and your system will crash. If you have the second connector, I'd connect it, and if you're worried about having a plug dangle around just tie it back with a tywrap or some electrical tape so it's nice and clean.

[–] [email protected] 2 points 2 months ago

Not all PSUs even have a second cable. Mine sure doesn't.

Technically it's fine to use daisy chained connectors. People get into trouble though with badly built power supplies, extreme overclocking, or cards like the R9 295X2 that blatantly violate the specifications.

Older PSUs sometimes have trouble with new GPUs. It generally happens because new cards have large power transients that the older spec didn't take into account. Sometimes running a second line fixes this for one reason or another, but not always. 12VHPWR actually uses similar current per wire or per cross section area of wire as a daisy chained setup, if not a little more.

[–] [email protected] 9 points 2 months ago

Yes. I too did this once with a friend's build, scratching my head why performance was terrible and power usage didn't go above 250W.

[–] [email protected] 6 points 2 months ago (3 children)

Is this a thing with new GPUs? I've always connected my GPUs with 1 cable there was no option for 2. I currently have a RX5700 XT.

[–] [email protected] 2 points 2 months ago (1 children)

I have a 7900 XTX, having upgraded from a 5700 XT, yeah it's a thing, and it is also a much chonkier boi. Weighs like 2.5 kilos, barely fits my case.

[–] [email protected] 2 points 2 months ago (3 children)

I knew GPUs had gotten bigger but then I built an all new PC, upgrading from a 2080 to a 4090.

Holy shit. That thing is fucking huge, man. I was literally stunned pulling it out of the box. Just set it down and stared at it for awhile trying to process technological progress. It's like 8 times the size of the GPU I had in 2006.

[–] [email protected] 2 points 2 months ago* (last edited 2 months ago)

The volume of the PCB should be the same in both GPUs, the difference is that the 4090 has an enormous cooler/heat dissipation.

[–] [email protected] 1 points 2 months ago

I installed another fan into my case just so that monster is not resting solely on the back mount and the PCIE port.

[–] captain_aggravated 1 points 2 months ago

As I type this I"m in the process of building a new computer, going from a GTX-1080 to an RX7900GRE, and it's relatively small, I got a 2-fan Asrock Challenger one and while it's bigger than the 1080 it's not as big as some I've handled. It's amazing how they managed to pack the 1080 into such a small package. I guess the blower fan helps.

[–] [email protected] 2 points 2 months ago* (last edited 2 months ago)

I changed it when it kept crashing on me. Then I bought a new power supply and the crashing stopped. That's what I get for ordering the 7/7/7nm/'700xt from XFX...

Edit: they should be on separate rails, so it's not a bad idea, especially if you're having stability issues.

[–] [email protected] 2 points 2 months ago

I am using a RX 6700 XT on one cable as well and it's perfectly fine. If your PSU has a second cable you can run that to be sure, but if not like mine don't worry about it. It's only certain corner cases like extreme overclocking, or certain cards and PSUs that violate the specifications that actually cause issues. The Radeon R9 295X2 would be an example of this. 12VHPWR actually runs a similar amount of current per wire, with an even smaller connector, as a daisy chained 8 pin setup. You should not use third party splitters though if you want to be safe.

[–] [email protected] 5 points 2 months ago* (last edited 2 months ago)

Haha mine too! I recently upgraded my gpu so I opened it up and realized I daisy chained it. Lesson learned!

[–] [email protected] 4 points 2 months ago

Its been years I ain't checkin' that shit. I'll make sure to forget this for the new build.

[–] [email protected] 4 points 2 months ago

When I bought my last PSU and GPU it also came with a diagram like this, so that's how I plugged in the cables. I guess its better to balance the power draw for the GPU over both the GPU ports on the PSU, rather than try to pull it all through one cable.

The annoying thing for me was that my PSU (a Seasonic) didn't come with single GPU power cables, and only came with the ones with 2 ends, so they're a little ugly just hanging there.

[–] [email protected] 3 points 2 months ago* (last edited 2 months ago)

I could be wrong here, but I think the common interpretation here is wrong. The risk is not that the wires overheat and cause a fire. The risk is that the card draws too much current from a single 12V power rail on your PSU, sustained for a long time, and that burns out the power rail on your PSU.

I have a 6950 XT that I used with a 850W PSU that was connected incorrectly according to the diagram, with multiple connectors coming off a single rail. After about 6 months, one day my SSD stopped working, and after some tinkering, I realized that if I plugged it into a different 12V connector, it started working! I had burned out one of the 12V rails on my power supply, and I strongly suspect it was my incorrect wiring into my 6950 XT that caused it. (edit: I got a new PSU and never looked back)

[–] [email protected] 2 points 2 months ago (3 children)

If the GPU has two power inputs, you don't do the “don’t do” diagram. Period.

Like other commenters have input, there are specific situations where you’re probably fine.

If you have to ask, just fix your wiring to one of the green check configs.

This is literally how house fires start.

[–] weker01 5 points 2 months ago

Only if you buy a shitty PSU. Quality ones have lots of protection circuits so worst case the PC would randomly shut down in high load situations.

Even then if the manufacturer put two connectors on the end of the cable they made sure to put large enough conductors to handle at least the max load of the connectors specifications. Again if it's not a shitty no name brand. Probably with a good safety factor as well.

It's not like 300-400W is that much energy in the grand scheme of things, so thicker wires wouldn't even be expensive.

[–] [email protected] 2 points 2 months ago

This is straight up wrong. There are people here who have done that maths for you, if you look hard enough.

This diagram was probably created by a specific PSU builder and intended to illustrate their recommendations for their PSUs, not as a general rule.

[–] [email protected] 2 points 2 months ago (2 children)

Crap I was hoping someone wouldn't say this. Rewiring its going to be a mission.

[–] [email protected] 3 points 2 months ago

For what its worth, I've ran 1 cable to my RX 6800 from a seasonic power supply for years without issues

[–] [email protected] 0 points 2 months ago

Yeah this person you are replying to is wrong. Using two lines where possible is a best practice, but in most cases isn't necessary at all. This diagram was created by a specific PSU manufacturer I think, and should only pertain to their PSUs.

[–] [email protected] -4 points 2 months ago (1 children)

As long as you’re not overclocking you’ll be fine. If you can share a cable for 2 3 8 pin gpus then why wouldn’t you be able to do the same for 2?

If you’re trying to overclock the snot out of it then you should theoretically get better performance out of two cables.

[–] [email protected] 1 points 2 months ago* (last edited 2 months ago) (1 children)

I don't know why you are getting downvoted to hell. This is actually correct. They put the second connector on there for a reason. People including myself have done the maths on this before and it's all above board. Only fringe cases involving power transients, out-of-spec cards, and obviously overclocking should actually make this a problem. Even then the 12VHPWR uses the same current density if not more than a daisy chained 8 pin setup.

[–] [email protected] 3 points 2 months ago

The duality of lemmy

The PC community is full of FUD/just straight up ancient information that's no longer applicable. I'm definitely not perfect, but it doesn't take a rocket surgeon to figure out a lot of these things if you sit down and double check your info.