PSU PCIe power cables with dual inline 6+2 connectors

[swaaye]

Power supplies these days frequently come with PCIe power cables with two inline 6+2 pin connectors per cable. Until I read some posts about this being bad, I assumed it was safe because the PSU companies surely designed the PSU with their cables in mind. But apparently these cables are not safe. If your GPU actually pulls around the 300W of 2x 8-pin connections, connector resistance might cause enough heat to melt and burn.

Anybody else have some thoughts on this?

 

[Davros]

Are you saying a 6+2 pin connector is bad compared to using an 8 pin connector?

 

[Albuquerque]

The question becomes: why do people think it's bad, and what details are they using to support their conclusion?

Safety of wiring usually comes down to just a few things: conductor material, conductor length, conductor circumference, number of conductors, amperage load typical (sustained) and maximum, insulator material and thickness, and environmentla factors such as temperature, humidity, and will it be freestanding in air or buried or underwater.

Let's just get to the meat of it: For a six-wire power connector to move 300W, this means we need each pair (+/- DC) to carry 100W sustained and a little bit more (25% maybe? So 125W) at peak. At twelve volts DC, that's a maximum of ~10A for a length of say 36 inches absolute max?

16 gauge wire is absolutely sufficient to carry that load. I suspect any power supply worth a shit is using at least 16ga wiring for their PCIe power connectors.

 

[Davros]

Just a little note :
A 6+2 pin connector is a 8 pin connector

 

[swaaye]

It's not the wire gauge that causes problems. It's the resistance at the contact points of the connector. They wear from each plugging, get dirty/oxidized, maybe weren't great to begin with, etc.

Lots of nice images of melted power connectors out there to view. I've cooked a 4 pin CPU power connector from overclocking. Seen melted ATX connectors.

 

[Albuquerque]

It's not the wire gauge that causes problems. It's the resistance at the contact points of the connector. They wear from each plugging, get dirty/oxidized, maybe weren't great to begin with, etc.

Lots of nice images of melted power connectors out there to view. I've cooked a 4 pin CPU power connector from overclocking. Seen melted ATX connectors.

It's still a conductor whether it's a wire or a conductive pad inside a connector. If a 16ga copper wire terminates at a 22ga-width aluminum post that's been flattened to form a conductive "pad" inside a connector, then you're going to have problems because the conductive surface area is still too small. The sizing math and metallurgy for the conductive pad still works out the same as the conductive wire, even if it's smashed flat into a post or pad.

More math: four pairs of wires at 300W (with a 25% buffer, same as my original example) only reduces the amperage load by about 2.2A -- each pair of 12V leads would still need to carry 8A instead of 10A. If the powersupply is using shitty cheap pot-metal for their connectors, it's still likely to burn up under duress.

 

[swaaye]

I have been running a 1080 Ti with dual 8 pin connectors on one of these PSU cables with 2 inline connectors and it has been fine. But a 3080 uses the same dual 8 pin configuration and some people appear to have melted the PSU end of the cable with that load.

 

[Albuquerque]

Yeah, and I 100% believe there are PSU's out there having problems for all the reasons we've discussed.

I'm running one of those EVGA 3080Ti FTW3 Ultra models which comes with three 8-pin sockets and a maximum board power draw of 450W. If we trust MSI Afterburner, then I've run the card in excess of 400W more than a few hours. My Corsair HX850 doesn't even seem to care, it just piddles along quietly with the rest of the 5950x @ 5GHz + 64GB CAS 4 @3800MHz sucking down the airflow through the Arctic Liquid Freezer 280 AIO loop at full whack.

Nobody deserves a fire in their PC, but anyone who doesn't buy a quality powersupply unit should re-evaluate their life choices as a PC builder Of all the things to skimp on, don't start with the part which feeds power to literally every piece of your PC!

 

[BRiT]

They can make up for skimping on the psu with Water Cooling, but only if they skimp on that too.

 

[swaaye]

I am currently running a Corsair TX750M and another PC has a EVGA 650 GQ. Both of these have the 2x 8pin connectors per cable thing going. I ran a second cable to the GPUs now instead of using those two in one cables. Why risk it. I'm going to get a 3080 which is what got me thinking about this because it is +100W over a 1080 Ti.