Hi!

How about automatic powering off your printer when printing is done?

*Update! New, better, safe version is published. Go there for it!
https://www.thingiverse.com/thing:3335522

I want to share my upgrade for 3D printer which gives Auto Power Off functionality.
Some printers, equipped with ATX PSU may do this by simple M81 command. Lucky owners!!!!
All others, or almost all others, know these timers to switch off the printer after printing is finished. We also know that expected finishing time may be different than calculated by slicer software. So we add one or two hours to not switch off the printer too early.
I started to be tired of this solution and invented my way of secure switching off the printer just after the printing. Tested with Ender 3. Should work with similar printers.
After finishing printer cools down and raises printhead frame to the maximum height. It triggers switch and disconnects power from printer.

What do you need to upgrade your printer?

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MOST IMPORTANT IS TO KNOW HOW TO WORK WITH POTENTIALLY LETHAL LIVE VOLTAGE.
You will not need to take a risk, but mistake can always happen!!!
SO PLEASE, ASK PROFFESSIONAL TO HELP YOU WITH CABLING.

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• about 1/2 meter of two-wire cable. 2 x 1mm2 at least.
• soldering iron
• soldering skills (not advanced)
• some insulating tape or themorshrinking tube
• two screws for fixing to frame. I had hammer nuts (T-nuts) with 4x14 screws.
• two screws with nuts to fix microswich. Mine are 2x12mm but it's not so important.
• microswitch with lever, capable to take more than 2Amps. Mine is 5A (size 20x10mm distance between the holes 9,5mm). Unfortunatelly, these small switches used by Ender (you may have one free after installing BLTouch or 3DTouch) are 1Amp which is not enough. Printer takes almost 2Amps in full load - heaters, electronics and motors.
• some time :-)

Assembly instruction:

• Print V2 arm. PLA or any other material except of TPU. Fancy colour is highly recommended! 20% infill. Layer 0.2mm is OK. No supports. No rafts. No brim.
  V1 arm is fine too, but there is a risk of collision with some models of head in very rare cases of high and wide prints

• prepare all parts

• power off the printer

• UNPLUG POWER CABLE!

• unscrew PSU from the frame

• remove plastic cover of PSU cables

• disconnect one of power cables from PSU (L or N). In my Ender 3 it's first from the right.

• solder one wire from your new cable to just disconnected wire

• solder end of second wire of new cable to make it hard (cover with tin).

• attach and screw this wire to PSU in place of the original one

• guide new cable through PSU cover hole

• install PSU plastic cover back
  

• you may add extra tube to the cable, just in case

• mount PSU leading new cable through frame as seen on the photo below
  

• assemble printed arm to the frame. Fix it high as possible for a start.

• install microswitch

• bend microswitch arm as seen on pictures. Do not bend whole arm from switch, bend arm in the middle, to trigger the switch earlier. It helps to securely stop Z motor and frame before hitting the switch body. PSU has big capacitors which extend the move of the fraction for a second after disconnecting the power.
  

• move frame up by hand and check if it push the switch lever with any part. Adjust arm if necessary. It may happen that your printer needs different shape of arm. Ask me for help or make remix. Up to you.

• measure needed cable length to the microswitch

• weld cables to pair of connectors which are normally closed (NC) IMPORTANT

• secure connections with tubes or insulating tape.

• IMPORTANT! Secure also third, not used pin of microswitch. It may have live voltage when the printer is turned off by the switch
  

You are done with electro-mechanics. Now it's time for software and adjusting.

• Add "special" commands to end sequence in your slicer (i.e. Cura--Settings--Printer--Manage Printers--Machine Settings--End G-Code window). Disable M84 command with ";"

  G4 S300 ; wait 5mins to cool nozzle
  G0 Z250 ; go up to max height
  

You may adapt commands to your needs. Decrease Z250 part if your printer is smaller than Ender3 which has 250mm max height
5min pause is really needed. Too much heat from hot nozzle without cooling fan active may cause filament jamming in the head.

• print anything. Small one for sure

• wait until frame goes up
  use of terminal is also OK. Octoprint or any other one. Just send commands:
  G28
  G0 Z250

• adjust printed arm with microswitch to trigger it. It should power off your printer!

You are done!!!

Congratulations. No more power waste.

You are GREEN now!

Starting printer is simply by pushing the frame little down. Power is coming back.

In case of another microswitch you may adapt holes in the arm or ask me for help with it.
.stp files enclosed

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Good luck!