Smoke Detector and Relay to Cut Power

I recently purchased a 3D printer to make some of the accessories for the CNC.

There is always the rumor that cheap 3D printers can catch fire. This seems overblown but it didn’t seem wise to not prepare for that circumstance. After all, many prints will need to run overnight when I can’t watch.

So I found a reference somwhere about using a smoke detector and relay to cut power to the printer (Or whatever else) in case of fire. I decided to try it and it works fine. I tested it running a heat gun pulling about 10 Amps. As soon as you press the test button on the smoke detector it kills power to the device.

The only downside is that this is NOT a latching system. In other words, if the smoke detector stops alarming the power resumes. That being said, I don’t run my printer when I am not home. An alarm would wake me and hopefully there would be little damage since the power was cut. This isn’t 100% and use at your own risk.

Here is a crude drawing and a parts list of what I used and did.

First Alert Smart Smoke Detector

First Alert Smart Relay

I simply bought an extension cord and cut it to suit my needs. NOTE: This one is molded and does have the typical Black/White/Green.

Extension Cord

I hid the relay and all of the connections in one of these.


Crude Drawing

EDIT: I soldered and heatshrinked all of my connections.

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Thanks! This could be used with anything sketchy.

@Ziggy - do you have some sort of tutorial you followed for this process? I’ve been meaning to this for my 3D printers and the 1F as well. I don’t really have very good electrical knowledge so the diagram doesn’t make a whole lot of sense.


I don’t have a tutorial but the process is pretty easy. I may just look a little intimidating.

It doesn’t help that I drew the schematic in Paint so it is fairly crude.

In the drawing above, the dots on the lines show connection points. If a line crosses another line and there isn’t a dot it doesn’t connect. For instance, the “L” on the “Male Plug” connects to the “L” on the “Smoke Det” and the “L” and “BR” on the “Relay.” In the drawing it crosses over other lines but doesn’t connect to them. I put dots in the corners but this doesn’t mean you have to have separate wires. It merely means that the “L” connects on those three devices as well as the BR on the Relay.

If you wanted to use the extension cord I listed above you would need a continuity checker since the wires aren’t color coded.

If you wanted to do this but aren’t comfortable, see if you can find a friend who can help. This whole assembly onlyt took about an hour and that is mainly because I soldered and heatshrinked everything.

It really is quite easy but you have to be careful when working with this stuff.

Good Luck!

probably too early for me but your diagram seems a bit overcomplicated to me. I think you just need to connect up the normally open relay contacts to the Onefinity E-Stop pins. That way it will latch off until reset.

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This was made for a 3D printer which as far as I know doesn’t have a breakout box.

But… your suggestion makes sense for the 1F!