Remote start of PC on applied AC power

I am starting on my vertical mill retrofit and I want to start all the electronics with one switch. Normally I turn on the 220 Phase convertor which applies power to the mill in general, then I flip on the mill's main circuit breaker once 220 power is steady, and then I turn on the 110 switch on the control pendant which powers on the display and the old Dynapath controls. I want to keep the same idea of having one switch on the pendant which will apply power to the monitor as well as the PC (which will be located inside the electronics cabinet so it will not be convenient to access) and start everything going. I can wired one switch to a contactor to turn on the AC power to the monitor, my 24VDC power supply, all the other electronics and the PC, but that does not get the PC itself to boot up. I looked at the bios setting for PC start on AC power, but that only works if the PC shutoff due to a power loss. If I do a normal shutdown and then remove AC power and then plug the AC back in, the PC does not start. I know from building PCs that on the front panel header on the motherboard there are two pins which the front panel power switch connects to boot the PC. I can set up a relay that on AC power will make the same connection between those two pins, simulating the front panel switch closing, but a simple relay would continue holding those two pins connected which would be like holding in the front panel power button which would then turn the PC off. What I think I need is a relay setup that would close for about 1-2 seconds upon AC power on, simulating press the front panel power button, and then open. I guess there is a way to figure out how to do this with maybe a RC circuit that cuts off power to the relay after a couple seconds, but I was wondering if anyone had a better solution.

What you need is a mother board that has a bios setting for turning on when power is applied. (some do and some don't)

sam

I am not sure this is better, but it is how my mill is configured.

Mains power to the 24V power supply is switched through a relay with a 5V coil. That coil is controlled by the PC USB power.
A switch on the front panel bypasses the relay.

So, press the switch, 24V comes on, a DC-DC converter provides 12V to the PC motherboard. After a second or so that wakes up and energises 5V power on the USB header, which latches the relay.
When the PC shuts down it turns off the relay.

Motor / Servo power is all run through a contactor controlled by LinuxCNC.

I _think_ that my PC is configured to wake on power-up regardless of shutdown mode, though it is possible that I used a double pole switch to simultaneously bypass the relay and trigger the PC wake-up pins. This does mean mixing 5V and 230V in the same switch, which is not something I normally like to do.

If you are using a PC power supply these normally expect to be permanently connected and running in standby. In that case you only need to trigger the wake-up pins then let LinuxCNC operate the other relays and contactors.

Unless your BIOS is odd, usually there are a few power options, one is like you said, it returns to the last power state when power is replied, but there usually is another choice that is always on. Another possibility is the cmos battery is low and when power is removed it is resetting to default settings?

Failing that, when using a contactor sealed circuit for your main power is triggered by a momentary contact button, (off button breaks that seal). Can you use the momentary signal from the main power button to also start your PC?

andypugh wrote: If you are using a PC power supply these normally expect to be permanently connected and running in standby. In that case you only need to trigger the wake-up pins then let LinuxCNC operate the other relays and contactors.

As a further advantage of this, you can then configure wake-on-LAN. This can be convenient to wake up a machine to send a G-code file from the CAM system before you walk out to the workshop.

There may be specialty motherboards which will boot up as soon as power is applied, but the normal motherboards one buys at the electronics stores do not have this feature. I have played with all the power settings in the bios and nothing will turn the computer on when I unplug and plug in the power cord, if the computer was properly shutdown. If there was such a feature, I would think that if you set that option you could never turn your computer off. I did like the idea from AndyPugh about tying a relay into some power signal on the motherboard. I think I will try closing a relay when the power switch is turned on which would then simulate the switch closure of the power switch on the front panel and turn on and boot the PC. I can pass the relay's energizing signal through a second relay that is normally closed and which would be opened by either a 5v or 12v signal from the PC's power supply or by a 5V signal from one of the extra usb headers on the motherboard. There should be enough of a time lag for the PC to start before the second relay disables the first. I do need to think this over to consider any possible failures in the circuit and what would happen. If the second relay was to fail, then the PC would see the power switch on the front panel being closed and the PC would shutdown. Once the PC would start to shutdown Linuxcnc and everything else would also stop, but that would not be catastrophic. Since I am using a MESA 6i25/7i77 configuration, I could probably power the second relay off of some point on the mesa card; although, the time lag before the mesa card powers up and opens the first relay may be too long.

I have 3 machines out in the shop running now with very ordinary off the shelf PCs (not for Linuxcnc controls though) all of which I was able to set the bios to start when power is removed and re-applied (even after shutting down the PC normally and correctly). 2 of them are on their 2nd replacement in the last 10 years. One of the current pcs is a Dell, another an HP the 3rd ??? some generic pos. (all might be P4s or Pentium D cpus.) Nothing special or industrial about them or their BIOS in any way. Oh and my hometheater/DRV PC at home running an Asrock J1900-Pro3 mother board is also configured for always on. I have not ever ran into a PC I could not set up like this (But I've only ever looked into 20 or so PCs).

Well you got me on this one. I have not been able to solve this through the bios. I have a Trak1630 lathe that comes with a PC based control system and it will power up the PC when power is turned on, but I think it does it because it has some extra modification. On my stock gigabyte motherboard, the only setting I have in the bios under power management is the ability to have the PC reboot when AC power is restored after AC power loss, and it does not work if I do a normal shutdown before remove and reconnecting the AC power. There are two settings to power on the PC via the keyboard and via the mouse, but those are to wake the system up from C-state, not from applying AC power.
If there is a way to do this in the bios could you give me a hint what to look for. Doing this in the bios would be easier than having to build a startup circuit, but I have looked under the power management setting in the bios (and all the other setting tabs) and as I previously said, I found nothing that works.
Thanks.

What gigabyte board do you have? What bios? The board I repaced in my HomeTheater was a gigabyte board and It could be set up that way to. (Some times these things are not in the most intuitive location in the BIOS.)

jwsigler wrote: There are two settings to power on the PC via the keyboard and via the mouse, but those are to wake the system up from C-state, not from applying AC power.

What behaviour do you get if you jumper the startup pins together?