Hardwire a Desktop Pc to Always Turn On.

Introduction: Hardwire a Desktop Pc to Always Turn On.

About: Update 12 September 2017: A very special thanks to Sam Elder, a manager here at Instructables, who tracked down the cause of my lost publications and fixed the issue. Take a bow Sam!

I had lost remote communication with my home pc during my working hours today. Hmm, most curious. The watchdog timer didn't force it to reboot so could it be it was off? Coming home I found it off! Dammit.

Now understand that my pc controls my entire home and also directly powers my WiFi, Internet modem, imatic to allow gate and door control. If this machine is down then my comfort factor drops.

With a clear head I decided to use an old trick to force a desktop pc to always turn back on. All that was needed is a 12V or 5 volt relay with a normally closed contact!

Step 1: Connect the Motherboard Power Pin to the Relay.

I just plain cut out the motherboard power button 2 pin cable and wired it to the relay normally closed contact. If I ever need to turn off the machine I'm gonna unplug it.

Step 2: Tap Into the 12 Volt and 0 Volt Atx Supply Lines.

Once the relay is energized the normally closed contact will open and the pc will function normally doing what it's supposed to do. Once it gets the power off command from Windows it will de-energize the relay and click! The relay simulates the power button being pressed.

Now my machine will always be on doing what it's supposed to do!



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19 Discussions

Decommissioned project. Basically the normally open contact is wired to the power switch header on the motherboard. Use a 2 pin jst female for this.

Most PC's have a "what to do on power fail" setting, and you can just set the CMOS to tell it to turn back on after a power failure.

4 replies

I would however put an electrolytic cap across the coil to give it a small delay to let the power supply settle for a second before it hits the power switch again. Other than that, very easy solution.

If someone instrcuts windows to shutdown, it will. Power would still be available to the ATX PSU but the PC wont immediately start back up. My machine is a home embedded automation controller. It MUST remain on else the world of crap happens with the house.

I really like your solution. I have tried Wake On LAN, but it is very difficult with my router and a dynamic IP. I have managed to get WoL working over the internet from my cell phone so I could remote access my home PC's with my cell phone or another PC whenever I want, but it seems to stop working after a while or the DynDNS would cause conflicts with my PC's access to the internet. My plan is to set up an old junk PC to always be on so I can remote access it, then I can send the WoL packet from that PC to my other PC's over the LAN instead of WAN. Sending the WoL packet over a LAN is really easy and doesn't need a stupid DynDNS. This whole set up relies on the junk PC always being on though, which is is hard to guarantee with BIOS settings. I will set up the relay you did but I'm going to use an ATX 24 Pin extension cable to splice instead of the actual PSU wires.

1 reply

Thanks for the thumbs up. I think you would love my diy watchdog instructable. You won't need a whole pc to monitor another pc... Just use 2 timers like I did plus a lab jack u3 and you never have to worry about a crashed pc.


3 years ago

You can also use Wake On Lan function, assuming wifi is always ON.

1 reply

Good idea but that solution is not robust enough for my system. My pc is actually configured as an embedded system for the home. It also powers the WiFi via the atx psu.

So very true and my bios already has that option enabled. I did this project because if you tell Windows to shutdown it will. If the pc is a remote location machine then how will it come back on except for an rtc alarm on bios? I need my machine to bounce right back into action. If I want it off for maintenance then I will physically pull the plug.

Great idea. Just curious but how do control everything with your computer?

1 reply

I'm using a labjack u3 with FLOWSTONE. It's easy and low cost! Solar power management, dog food water, gate, front door entry, and more.