Question Dual power supply with mini itx

[zamehan]

Hello,

I built a small pc with a mini-ITX Z270I motherboard, a i7 8700 cpu, a nvme ssd and 16go of ram. The power comes from a small 160 watts picopsu

I can put this pc in my backpack and bring it everyday to work.

When I am home, I would like to quickly plug a graphic card so that I can game with this pc. The GPU would be a high end one like a rtx 2080.

It is obviously not possible with 160 watts. Therefore, I want to plug the graphic card to another external 600w psu.

I would use an adaptor like a add2psu so that both psu start at the same time. I would connect the second psu to the VGA power connector of the graphic card.

However, this article https://www.thegeekpub.com/11955/using-dual-power-supplies-mining/ says that the second psu has to power the whole graphic card so that it is safe. But as we know, the graphic card also takes 75w of power from the PCI port from the motherboard.

Therefore, I would like to know if there is a possibility that the graphic card takes its whole power from the second psu and not from the motherboard anymore.

I thought maybe I could use this : https://www.overclockers.co.uk/ocuk...ble-inc-molex-power-cable-19cm-cm-14e-ok.html

Thank you for your answer

 

[Barty1884]

Assuming you mean Z370I?

No, it's not possible to power the PCIe a slot AND the GPU from the secondary PSU. The molex on that riser cable is not powering the original PCIe slot.

 

[zamehan]

Ok. I thought that as it says the molex "must be connected to the power supply to replace the power supply of the plug-in card, which normally takes up to 75 watts directly through the PCIe slot" it meant that the card doesn't take 75w from the motherboard anymore but from the molex.

 

[Barty1884]

Hmmm, you might be right .... at least, that's what it appears to claim.

I have no clue why that product exists. PCIe risers, especially at 19cm, do not need to be powered.

Yes, molex by spec is rated to handle 11A on the 12V rail (132W) so could replace PCIe power... I'm at a loss as to why the product exists.
Of course, the wiring needs to be capable too. I think 18G would be fine there.

 

[zamehan]

Does it mean that as PCIE riser is not powered, the graphic card takes all its power from the VGA power connector when there is a riser?

 

[Barty1884]

No. That listing is claiming the GPU can still pull 75W from the PCIe slot, but would come from the riser (via molex) opposed to the PCIe slot.