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  1. #1
    3D Printer Noob
    Join Date
    Jul 2019
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    Lightbulb Power Interrupter From Smoke Detector

    I think this is an answer for a simple, cheap and effective way to interrupt power to an unattended 3D printer that is overheating to the point of smoking or even fire.

    No software required, and parts under $35. Here's what you need:

    - 2 x L7805 5v voltage regulators to convert 9vDC to 5vDC.
    - 1 x SRD-5vDC-SL-C 5v / 120v Relay
    - 1 x Wired (120vAC) and network capable smoke alarm
    - 2 extension cords
    - 4 wire to wire connectors to splice 120v wires together
    - 1 x small perforated circuit board (PCB)
    - 1 x wire terminator to PCB
    - Basic soldering skills

    1. Cut off the female end of one of the extension cords and splice it to the smoke detector power wires.
    2. Solder red and black wires to the smoke detector battery terminals.
    3. Solder the red battery wire (9vDC) to the PCB connected to the (+) terminal of one of the voltage regulators.
    4. Solder the black battery (ground) wire to the PCB and then to each of the voltage regulator's (-) terminal, and also to the Relay (-) terminal.
    5. From the battery powered voltage regulator, solder it's output terminal to the Relay (+) terminal.
    6. Solder the smoke alarm sensor (network) wire to the other voltage regulator's (+) terminal. It will power the voltage regulator when the smoke detector alarms.
    7. Solder it's output terminal to the Relay sensor input. It will provide the sensor input to the Relay when the smoke detector alarms.
    8. Take the second extension cord and mark the positive and negative wires. Then cut it in the appropriate place as dictated by your install requirements.
    9. Connect the male end (+) wire to the normally open terminal on the Relay.
    10. Connect the female end (+) wire to the feed terminal (middle) on the relay.
    11 Splice the two ends of the (-) wire.
    12. Splice the two ends of the ground wire.
    13. Insulate (tape, etc) the splices and package up the PCB (I put mine in a junction box).
    To operate:
    Plug in the smoke alarm to the wall (120vAC).
    Plug the spliced extension cord to the wall.
    Plug your printer into the spliced extension cord.

    Voila! When normal power is in place, the printer is powered by the normally closed circuit in the Relay. The 9vDC battery wires power the first voltage regulator, which in turn powers the Relay, which maintains it's normally open state. When the smoke detector alarms, the sensor (Network) wire sends 9vDC to the second voltage regulator which then outputs 5vDC to the sensor input on the Relay. That sensor input now opens the relay (interrupts) power and thus shuts off the printer power.

    Note: After the smoke detector quits alarming (Smoke clears...), the power to the printer will be re-established. This is OK if your printer stops printing with a power interruption.
    (I have a CR10S, and this is the case.)

    Again, this is very simple, cheap and easy. Enjoy and be careful!

  2. Thanks TommyDee thanked for this post
  3. #2
    Super Moderator
    Join Date
    Nov 2016
    Post Thanks / Like
    Welcome jward and thank you for the hack. Comes with its own built-in warning ;p



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