Hi,
I’ve added a 1200 watt server PSU per 6 rigs. The rigs were made to run at default clock which took about 85% of the PSU capacity, so the PSU’s can’t keep up with overclocking.
I needed to spread some load to a second PSU (GPU high power input is 7.5amp = 90 watt x 2 GPU's = 180 watt per rig x 6 rigs is 1080 watt).
I’ve read a lot what to do and what not, but nobody has a straight forward explanation.
The problem is that the ground differential is conducted though:
1. The GPU
2. The motherboard
3. PSU to PSU wire, 1 card
4. PSU to PSU wire, max cards.
https://i.imgur.com/jrFxxZX.pngIf you would take the same brand and type PSU’s, the chance both grounds are equal is bigger than you take a b-brand desktop PSU and combine it with a b-brand server PSU.
To start of you can measure the difference in current by turning them on without the second PSU connected. Hook up a multimeter and measure the amps running between the two grounds. This is the load your GPU, motherboard or straight wire needs to conduct.
The ground on a GPU circuit board should be pretty strong. If the PSU’s are wired like option 1, the current is spread across the 4 cards. It could run, maybe unstable. It depends on the difference between the PSU’s.
If all is hooked up like option 1, but only one GPU’s high input is powered by PSU 2, all 3 amps will run through 1 GPU. Could be bad.
Let’s say you got 3 amps between PSU’s and wire everything up by option 2, your motherboard needs to conduct 3 amps on top of what it was already conducting and it will eventually burn.
If all is wired by option 3 with a thick wire between PSU’s, the most of the current will run through the wire. Do the same with a thin wire and most of the current will go through the single GPU’s, risers and motherboard.
Make the wire the least resistance and get most of the current run though the wire.
Best option is number 4. Get the current though the cable and spread the rest over the GPU’s.
4 or 6 mm2 (12 or 10 AWG) per amp difference should be good.
A dual PSU setup wired the wrong way could work perfectly because the PSU’s ground voltage is equal.
A dual PSU setup wired the right way could run unstable because the PSU’s ground voltage varies too much.
