Smoke Detector Auto Power Off for Enclosure

My Ender 3 LACK enclosure has had a smoke detector installed pretty much since I built it. I recently got around to upgrading it a bit so that printer power would automatically be killed if the detector went off. This was done by changing over to a detector designed to be linked to other detectors plus adding a relay specifically designed for use with that style of detector.

The smoke detector I used was $12.25 at Amazon (prime) First Alert Smoke Detector Alarm | Hardwired with Backup Battery, BRK9120b6CP
(https://www.amazon.com/gp/product/B00O8MVW3U/ref=ppx\_yo\_dt\_b\_search\_asin\_title)
The relay I used was $16.89 at Amazon (prime) BRK RM4 Smart Relay for First Alert
(https://www.amazon.com/gp/product/B0039PF21U/ref=ppx\_yo\_dt\_b\_asin\_title\_o00\_s00)

The specs on the relay looked to be plenty adequate for the Ender 3 power draw (15 amp resistive or 1/3 HP motor). I spliced the relay leads into a short (2') extension cord so the printer power gets interrupted if the smoke alarm goes off.

I used some round 3 conductor antenna rotor cable for the connection from cord to smoke detector pigtail. The 3 conductor extension cord was cut in half & the wires stripped for the connections.

All my connections were soldered, then protected with multiple layers heat shrink tubing. I didn't bother with an enclosure for the relay assembly as it was already heat shrink sealed as a bundle, so I just taped the connections together to make a neat packet. I could have printed a box, but this was adequate for my needs. A possible box enclosure has been attached.

The actual wiring was pretty straight forward. The pigtail for the smoke detector wanted hot & neutral wires (from the plug) plus a third for the signal. The input for the relay needed 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 & neutral from the plug end + the relay's NC wire for the hot side.

I tested out functionality before plugging the printer in (after already checking wiring cold for continuity & shorts). It dropped power on the detector test button being pressed & restored power about 5 seconds after the beeping stopped. The assembly then got plugged into the power strip from the UPS I use for the printer & the printer plugged into the assembly.

It doesn't address everything that could go wrong, but if I need to leave the area for a bit it makes for a bit of insurance while I'm out of earshot.

DISCLAIMER:

I am not an electrician, just a hobbyist. Replicating this project is at your own risk.

If you have any concerns, or doubts, about either your ability to safely do electrical work involving 120v circuits or the safety/efficacy of this project, you should not attempt it. If such is the case, but you are still interested, have a professional evaluate the project and do the work.

Category: 3D Printer Accessories