So I've been performing upgrades on my homelab over the past few days. I consolidated several Xeon servers into a single large server. When I switched over to the new rig, I treated myself to the new Gen5 Hyper M.2 card .
Card arrived today from Amazon. Before I move forward, I should highlight some of my jankiness in my setup: I run 2x EVGA 1000W power supplies daisy chained together using an add2psu module. (Looking back, it was a horrible idea..)
My setup was as follows: PSU1 powers my MB, CPU, 2x CPU 8 pins and a GPU. PSU2 provides power to about 24 drives.
This new Gen5 Hyper M.2 card requires 6x PCI power, like a GPU. This is where things go down hill. I provided this power from the 2nd PSU. I guess I never realized, but since the HDDs are 'isolated' within the second PSU, I guess things were safe. But once I added a new lead from PSU2 to power a card that likely is also receiving some power from the motherboard, I probably created a grounding loop? (I'm just guessing).
1st power supply: I complete the upgrade, flick the power switch and go upstairs to my office. By the time I sit down, I'm able to ping the IPMI management interface...but then it goes offline. I start smelling a faint burning smell... I rush down to the basement. It smells NASTY, but no drama: Server is off. Some quick troubleshooting and I determine the 1st PSU is dead, the second one is fine. I swap in a spare 1000W PSUs (Old mining equipment FTW). I look around and don't see anything weird. I ASSumed I wasn't careful and shorted out the add2psu module on something. I fix this potential issue.
I power up the 'new' PSU and sit by and watch.. The computer powers up but the case LEDs are off. Before I can react there's a POP and TONS of smoke starts pouring out the PSU, being blown around by the fan. I quickly cut the power.
Anyways, it was the nastiest smell ever.. and funnily enough, the power supply had some sort of liquid coming out of it from whatever got melted. I was super lucky that none of my equipment got damaged in this process. I learned my lesson and consolidated to a single PSU. I also sent the Hyper M.2 card back as possibly defective.. I'm not going to try a 3rd time!
TLDR: My janky 2PSU system blew up dramatically. But luckily I didn't lose any gear besides the PSUs.
I needed to rant. Sorry for the long post. I have PTSD every time I turn on that computer now...
This wasn't a ground loop issue, both grounds are connected to house grounds, so were almost certainly at the same level, and would equalize potential when plugged in, not when powered. What happened was that the power rails on one psu had a different potential than the other, think like 11.5v vs 12.5v is technically possible. 1v Across solid copper traces and wires would go through the mobo and GPU when powered.
What happens here is that one power supply 'wins', that is the one with the higher voltage, and it provides current to the second. PC Power supplies are not designed to accept or 'sink' current, and are destroyed quickly.
When using dual PSUs, you can only use them with GPU risers to isolate the power from the motherboard, or with sata sds with no power connections. A m2 port or pcie port has 12v power traces.