Advice Downsizing my NAS with a custom case - PSU help


Shrink Ray Wielder
Original poster
Jan 20, 2018
Hey everyone! It's been a while since I've been around here all of a sudden. After moving back to Norway and some overall habit/lifestyle changes I'm downsizing my NAS - the Node 304 it currently lives in is simply overkill, especially as I've consolidated the storage drives into two higher capacity ones. The other harware is massive overkill too, really, but that just means I can keep it until it stops working, whenever that will be. Another decade of use would be nice. I'm planning to throw together a simple plywood box to house the components, as it'll sit entirely out of sight in my apartment, and I've got a 4-bay 3.5" HDD cage with sleds to hold the drives. The only real question: the PSU. Currently the NAS has a Silverstone 500W SFX-L PSU, which ... well, that's way more than I need for a NAS. I've got a 200W 80+ Gold PSU scavenged from an old Dell Optiplex USFF that I'm hoping I can use instead (alongside a PicoPSU that I have lying around too). I know it works, it's free, and the form factor is pretty great, so it has a lot going for it.

Being a proprietary Dell PSU this is of course not entirely simple, as it's not ATX or simple 12V. Rather, it has two 10A 12V rails (one for the 4-pin EPS connector, one for the proprietary 8-pin power connector), a single -12V rail (really, Dell?), and PS_ON and Power_good signal pins. When the PSU is off, PS_ON reads ~4.3V, and the PSU turns on when it's shorted to ground. +12VA (the one on the 8-pin) seems to act as a 12VSB rail, as it reads 11.9V even when the PSU is off (I haven't tested any current draw in this state, nor does the label tell me anything useful).

The question: is there any way to wire this so that the PC can turn the PSU on and off like a regular ATX PSU? Could I somehow connect the PSU's PS_On pin to the one on the motherboard's 24-pin, or would this interfere with the PicoPSU? Should I just go the simple route and either short this pin directly or put a latching switch on there and call it a day?

Other than this, the wiring is pretty simple:
12VA (8-pin) -> PicoPSU input
12VB -> 4-pin EPS
-12V -> not connected
HDDs and SSDs run off the PicoPSU (I might branch the 12V for either HDDs or SSDs off the EPS connector for load balancing across the rails if I can make the PSU turn off properly).

The power draw of the system under normal usage is in the ~35W range, and adding up the components I'd estimate a peak (never going to happen IRL) power draw of ~120W, so with the CPU on its own rail I see no problems with the relatively measly output of the 12V rails.

The rest of the build, for those interested (already up and running for a while):
OS: TrueNAS Core
CPU: Ryzen 5 2400GE (changed from my old Ryzen 5 1600X for power savings)
Motherboard: Biostar X370GTN
RAM: 2x16GB 2666MHz unbuffered ECC
Storage controller: LSI 9210-i
Boot drive: 120GB Samsung 840 Evo
Storage: 500GB Samsung 850 Evo, 2x8TB WD whitelabel (shucked) HDDs
NIC: Generic 2.5G Realtek NIC (on a PCIe riser from the m.2 slot)
Cooling: currently a CM TX3 Evo ducted to the 140mm exhaust fan of the case, likely moving to a Noctua L9a or AMD Wraith Stealth.