Dual PSU, what happens if one turns off?

[SensualSpinach]

Hi everyone,

I recently build a 6 GPU (1080 TI) mining rig using 2x Corsair MR1000x PSUs.

The first PSU is powering 2 risers (both on the same molex cable), 2 GPUS, the MoBo, hard drive, CPU and has an Add2PSU (on its own molex cable) for jump starting the second Power supply.

The second PSU runs the remaining 4 GPUs and two pairs of risers which a share molex cable. The 24-pin cable that normally plugs into the motherboard is connected to the Add2PSU adapter coming from the first PSU.

I have a UPS (1500VA, 900W) which I want to connect the first PSU to as backup but I can't have the whole system on without it drawing too much. I want to have the first PSU on the surge+battery backup and just connected the other to the surge protector. Is this a good idea?

I was wondering what would happen if only the second PSU were to turn off while the other was still on... I can test it but I'm kind of worried to flip the switch. What do you all think?

Thanks in advance!

 

[CountMike]

Only problem would be that GPUs would loose external power and start drawing from PCIe ports which could in theory overload their circuit in the MB but most likely they'd shut shut off before anything bad could happen.