Smoke Detector Auto Power Off for Enclosure

thingiverse

I posted this in the Ender 3 group to share with everyone who might be interested in adding an extra layer of safety to their printer. I recently upgraded my Ender 3 enclosure by installing a smoke detector that automatically kills the printer power if it goes off. This was done by switching to a new detector that can be linked to other detectors and adding a relay specifically designed for use with that style of detector. The smoke detector I used, the First Alert Smoke Detector Alarm | Hardwired with Backup Battery, BRK9120b6CP, cost me $12.25 on Amazon (with prime shipping). The relay I used was even cheaper at $16.89, also available on Amazon with prime shipping, and it's specifically designed for use with First Alert detectors like the one I chose. The specs on the relay looked great for handling the Ender 3's power draw, which is about 15 amps or a third of a horsepower motor. To make sure everything worked smoothly, I spliced the relay leads into a short extension cord that gets interrupted if the smoke alarm goes off. To connect everything, I used some round 3-conductor antenna rotor cable for the connection from the cord to the smoke detector pigtail. The 3-conductor extension cord was cut in half and the wires stripped for easy connections. All my connections were soldered, then protected with multiple layers of heat shrink tubing to keep them secure. I didn't bother making an enclosure for the relay assembly since it was already heat-shrink sealed as a bundle, so I just taped the connections together to make a neat packet. A possible box enclosure has been attached in case anyone wants to use one. The actual wiring wasn't too complicated - the pigtail for the smoke detector needed hot and neutral wires from the plug plus a third for the signal. The input for the relay required signal (from the detector) + hot & neutral (from the plug). On the output side, the relay common got a connection to hot from the plug. The socket end of the cord got ground and neutral from the plug end + the relay's NC wire for the hot side. Before plugging in the printer, I tested out the functionality by pressing the detector test button - it dropped power immediately and restored it about 5 seconds after the beeping stopped. Then I plugged the assembly into my power strip from the UPS I use for the printer and plugged the printer into the assembly. This project doesn't address every possible issue that could come up, but if you need to leave the area for a bit, it's a good safety precaution while you're out of earshot. DISCLAIMER: I am not an electrician, just a hobbyist. If you have any concerns or doubts about your ability to safely do electrical work involving 120v circuits or the safety/efficacy of this project, don't attempt it. Have a professional evaluate the project and do the work instead.