Dual Power Supply Mining Rig

[abbtech]

Hey Guys,

Sorry for the crap links below, the spam filter thought I was spamming if I left them as clickable URLs. What is left is the last part of the tinyurl.

Just curious about a few things. I am currently selecting some parts for a mining rig and would like to use 2 quality 750 watt power supplies instead of a single large one. I can see lots of mining rig builds where this has been done (like the linked video below) but I have a few questions.
https://www.youtube.com/watch?v=UWu2d6_bF5M

I haven't built a computer for many years but have an electronic background. The goal is to power the motherboard and some GPUs with power supply 1 and the rest of the GPUs with power supply 2.

I have seen lots of ways people activate the 2nd power supply that is not connected to the motherboard, simply jumpering the power on pin to ground, using a cable that connects a ground and the PS_ON pins together or using a relay to short out the PS_ON and ground on power supply 2 when the relay is powered from power supply 1.

Cable style:
tinyurl y8s7e9do

Relay style:
tinyurl yawr8pej

To me it seems that the cable style that simply connects both power supply ground and PS_ON pins together is dangerous since I am assuming the the PS_ON is probably using a simple pull up resistor to sense when that pin is shorted to ground. You are then mixing that voltage with the 2nd power supply and connecting it to the motherboard of the PC. I would like to hear some input on this since maybe I am missing something here.

Should the ground of both power supplies be connected together. With the simple cable style connection there would be 1 small wire tying both power supply grounds together but should there be something more substantial? I guess potentially each USB cable ground might be common to the GPU power connection so potentially there are a bunch of small ground connections that are inherently made.

Last question. Obviously you don't want to tie outputs of both power supplies together anywhere, is the large power feed that large GPUs have on the top isolated from any power they might get from the PCI bus? When using riser cards, obviously their will be a USB connection between the card and the PC but what about the riser card power, does this need to be fed from the same power supply as the PC or should it be the same power supply that powers that GPU?

Riser card.
tinyurl y7c9dhev

Sorry for all the questions, just trying to get a better understanding so I don't go blowing stuff up!

 

[Red Squirrel]

The PSUs are ground referenced already, but I imagine it would not hurt to tie the grounds on the DC side too.

I'm curious myself about the effects of two different PSUs though, like if one is 12.0 volts and the other is 12.1 is that going to create a high current 0.1v difference between two parts of the system or cards or whatever and cause issues. My guess though is that the cards have their own regulators so it all gets regulated down to 5 volts or even 3.3v anyway after the connector. So voltage differences probably don't matter.

What I want to eventually do is built my own large buck converter so I can have one or more super large PSUs instead of a bunch of smaller ones. Like say a 10kw 12v power converter that can just power several rigs worth of cards, which would then only have their own smaller 500w psu to power the motherboard etc.

From the risers I've seen, the part that connects to the card has it's own power connector, so the power comes from whatever source you choose, and not the motherboard, so that's good.