Power Supply 12VHPWR adapter cable for HDPLEX 250W GaN

[protocolsix]

Unfortunately, it seems even low/moderate-wattage models of latest GPUs use 12VHPWR power connectors. For example, 4070 Super models which require 12VHPWR connector but draw max ~220W.

I plan on dedicating a HDPLEX 250W GaN PSU to power solely a 4070 Super GPU. Using all the included adapters would be extremely bulky so I am considering making a custom cable for my specific use of this particular GPU/PSU.

Notably, the HDPLEX PCIe to 2x 6+2 pin cable uses a daisy chain configuration with just 7 strands of 20AWG wire (4x grounds and 3x +12v) coming from the PSU. For my use case, splitting this into more wires/pins with adapters seems completely redundant:

• The per-pin amperage limit of 12VHPWR is over 9A (higher than the other molex connectors). 3 pins at 9A is 324W, far higher than either the OCP of the PSU or the maximum draw of the GPU.
• I have read that the 12vHPWR spec requires all 6 power header pins be joined together on the GPU PCB [source]. So there is no requirement that each power pin is connected to power. Obviously, redundancy would provide extra safety buffer, but for this GPU and PSU combination, even 2 pins should be sufficient (2x 9.2A = 220.8W). I could double crimp the pins on the 12VHPWR side, but this seems unnecessary to me.

My plan is to create a 1x PCIe to 12VHPWR cable with that supports equivalent load as the included adapter combination.

I found a manufacturer the makes a similar 8-pin to 12VHPWR cable (https://pactech-inc.com/product/new...x-eps-8-pin-or-pcie-8-pin-psu-to-mini-12-pin/) but my use case doesn't need as much power.

Obviously this cable would be potentially risky in situations with different power requirements (different GPU and/or PSU), but for this specific situation I think this cable is equivalent to the extremely bulky adapter combination.

I am wondering if anyone else would like to see a cable like this or if I am missing something critical.

 

[robbee]

Have you considered taking an existing 2x8pin to 12VHPWR and repinning it to use both the PCIe and EPS on the HDPlex? If you use a reputable brand, you're sure that all the cables and crimps are done well and it's a minimal mod. You'd only have to buy a PCIe and EPS connector.

 

[SFFMunkee]

Have you considered taking an existing 2x8pin to 12VHPWR and repinning it to use both the PCIe and EPS on the HDPlex? If you use a reputable brand, you're sure that all the cables and crimps are done well and it's a minimal mod. You'd only have to buy a PCIe and EPS connector.

Then where do you source the 12V for ATX12V/EPS?

::EDIT:: I just read it says "power solely a RTX4070" and assumed that was a PC with a 4070, but maybe it's JUST the GPU so not a problem, in which case I'd absolutely do the dual 8-pin repin. Super easy mod, all you need is one of each connector and a few staples to depin the original connectors.... and maybe a multimeter to cover your ass before you plug it into any GPU

 

[Tyrael]

In the same boat, Any update to this @protocolsix ?

 

[protocolsix]

I finally got my 4070S and did some preliminary testing to validate this concept.

Things I found:

• The GPU would not power up without both sense pins grounded
• Grounding the sense pins to ground pins on the GPU power connector itself works (no need for connection to PSU)
• The GPU operates fine with just three 12V wires (not all 6 pins on 12VHPWR need to be connected to power), although I did not do any rigorous safety testing.

So this validates the design with the exception of needing to ground both sense pins. I was hoping the 4070 Super would be aware of its lower power requirements (compared to other 40 series models) but it appears this is not the case.

 

[protocolsix]

I found several similar premade cables: https://www.moddiy.com/categories/12VHPWR-PCIe-5.0/12VHPWR-Server-Cables/

A few options are fairly short (~30cm) so I am considering buying one (and just re-pinning if needed).

 

[puffdotbusiness]

Have you considered taking an existing 2x8pin to 12VHPWR and repinning it to use both the PCIe and EPS on the HDPlex? If you use a reputable brand, you're sure that all the cables and crimps are done well and it's a minimal mod. You'd only have to buy a PCIe and EPS connector.

This is what I’ve done in my build to power a 4080 with the GaN 500 using a repinned 2x8 to take power from the pcie and eps connectors on the GaN. I then used a j-hack to bring power to the CPU.