Fire safety device

After reading about several home made and one professional attempt to make an electrical cutout in the event of fire for safer unattended printing (we all do it even if we shouldn't/even if we say we don't). I decided to get a smoke sensor module, a powersupply and a power relay. Using these it was easy enough to make a circuit that enables the 240v to the printer as long as the smoke sensor isn't triggered, if its triggered then the power resistor switches and the power is cut.

This works well when tested except when the smoke sensor resets which it does after 2-3 minutes, the power comes back on. I did see one person had tried a latching relay instead but this presents the problem that it might switch the power back on, when the smoke sensor changes state after the smoke clears.

So why not use an RCD type circuit breaker, when the smoke sensor triggers it trips the RCD which mechanically disconnects the 240v until it is physically restored? The only thing is I do not know how to trip the RCD using a 9v trigger signal, since it normally works by picking up a voltage in the even of an imbalance between the the live and neutral which triggers a solenoid and trips the switch. Does anyone know what voltage an RCD needs to pick up off the sensing coil to trip? Does anyone know of a high voltage mechanical circuit breaker that can be triggered by 9v to physically disconnect the high voltage until manually reset?

Anyway assuming its possible I will share the design its a pretty cheap device to build and it might just prevent a printer catching fire when unattended. I also intend to connect a trigger signal from this to a home theft alarm GSM dialer which would call or text message me in the event the smoke detector was triggered, that way I could check the camera/turn off the printer remotely or call the fire brigade.

Edited 1 time(s). Last edit at 10/24/2015 06:09PM by DjDemonD.

Use an Arduino a transistor and a relay.

Smoke detector provides a signal to the Arduino which then triggers a transistor to turn a NC relay off. code it so that once the smoke detector is triggered you either press a button to reset or you just reset the arduino.

Be careful with smoke detectors. There are 2 types (cant remember the types). One picks up smoke and the other picks up burning without smoke (or something alone those lines.) Would probably be a good idea to have one of each.

RCD and RCBO's can not be used and they work on over current detection.

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wes1007
Use an Arduino a transistor and a relay.

Smoke detector provides a signal to the Arduino which then triggers a transistor to turn a NC relay off. code it so that once the smoke detector is triggered you either press a button to reset or you just reset the arduino.

Be careful with smoke detectors. There are 2 types (cant remember the types). One picks up smoke and the other picks up burning without smoke (or something alone those lines.) Would probably be a good idea to have one of each.

Optical is the normal used device (and the one that is available in a module) the other is an ionisation detector and are nasty radioactive things to deal with.

What would be better is a normally closed circuit. when powered hold the SSRelay closed providing power to both the heatbed and hotend. This is not perfect unless the SSD is latching as you say because one the detector clears it will reheat the hotend at the cost that the print is already shot.
A better way would be to kill all power to the printer but at the cost that some electronics could be damaged.

My plan is to hack an RCD domestic socket outlet, and connect a DC supply via the relay on the smoke detector, to the solenoid in the RCD, to trigger the solenoid if the smoke detector triggers, thereby killing the live and nuetral high voltage and everything connected to this socket i.e. the printer. It will also kill the power to the smoke detector, as I intend to run it off the 240v out from the RCD via a transformer, so there is no chance of it turning back on unless physically reset. Plus it also should work normally as an RCD. I am working on it right now, just had to find a 12v power supply as I was using a very small 9v one for the smoke detector.

Edited 1 time(s). Last edit at 10/25/2015 04:46PM by DjDemonD.

12v 1A is not enough to trigger the solenoid in the RCD - anyone know what current and voltage these things need to trigger them? I do not have a bench power supply so I am limited in my ability to work it out by trial and error. They trigger from current induced in a sensor coil, which I assume is rectified then passed to the solenoid, there are a bunch of diodes in the RCD. Since the RCD I am using is a 30ma trigger I presume that 30ma @240v is around 7.2w. So I should need at 12v - 1.6A to trigger the solenoid. I am sure this is a bit of an oversimplification, anyone willing to throw their hat in the ring?

Edited 1 time(s). Last edit at 10/25/2015 04:44PM by DjDemonD.

One, this is highly suicidel what your trying and is more likly to cause a fire!
Two, it's all written n the cover!

Calm down, all I am trying to do is trigger a circuit breaker when a smoke detector goes off. I DO NOT intend to have my moistened fingers on the high voltage contacts at any point.The RCD just happens to have everything in it that I need ready-made, a latching double pole contact, a socket, a nice insulated box for it all to live inside and a DC operated solenoid which disconnects them. I am not affecting the operation of the RCD itself merely adding the ability to trip it externally, if my optical smoke detector detects smoke.

How is anything supposed to be invented/discovered or hacked if people fly into a blind panic at the mere thought of adapting something to work in a slightly different way?

Edited 1 time(s). Last edit at 10/25/2015 05:03PM by DjDemonD.

As it turns out this is much more difficult to do than it appears. Here's where I have got to. I cannot trigger the dc solenoid in the RCD without sending it 50v so this is not very practical as I would need a rather cumbersome power supply for the 50v and another for the 9v smoke detector. I have tried to trigger it using the test button contacts but this was not very good either as it creates a momentary high voltage short (albeit through a resistor to limit the impact of this) which triggers the RCD but also triggers the RCD on my home consumer unit.

So perhaps the arduino based solution is the one to go for, I am sure it will offer massively more flexibility, the only issue is I do not have any programming/coding abilities to speak of which is why I was aiming for a more electrical rather than electronic solution.

It surprises me that I have not been able to find any commercially available mechanically latching circuit breaker which can be tripped using a 9-12v DC pulse. Does anyone know of any such device?

Your printer is plugged into the power outlet. You want kill the power if the smoke detector sees smoke (which it might do all the time under normal printing conditions, and depending on the filament material and temperature). Have you considered a "crowbar" circuit that shorts the AC power input- that will trip the circuit breaker in the house wiring. That can be as simple as a relay connected to the smoke detector. It will probably destroy the relay when it operates, but that's a small price to pay. Keep a few spares on hand... There is exactly zero chance that the power will come back after the thing is tripped, but somehow I don't think this method will get UL/CE approval, (I don't think many 3D printers do, anyway).

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Hi, I have thought about this, and in my previous comment above this is the equivalent to shorting the RCD test circuit, which I have done using an insulated screwdriver, this tripped the house RCD also, but I have not tried using the relay, though I am sure it would work, as I suspected it would destroy it and I only have 2 smoke sensor modules at the moment.

However I figure that if a genuine smoke event triggers the detector (tuning the sensitivity to minimise false positives will be a key part of getting this right I suspect) I do not want the whole house to be shut down as I want my cameras and lights in the workshop area where the printers are to be running so I can assess the problem. Especially if I am not at home at the time, I then have the option of logging into the pc controlling the printer/s remotely shutting off the heaters, or rushing home and dealing with it or in extremis calling the fire brigade. This is why I wanted to link the system to an alarm that would dial/text me in the event of a trigger, most of which I fully expect to be false alarms.

I understand many people at this point will be thinking - just don't do unattended printing - but realistically this is impossible to avoid under all circumstances many prints are long processes, and a 3d printer is immensely more useful if it can be safely left printing without a human hovering over it in case it catches fire. I doubt many Stratasys owners are poised with fire extinguisher in hand at all times. My goal is safe (safer) unattended printing using a reprap printer.

Does anyone know if there are any plans/experiments to use some pins on the Ramps or other controller boards as trigger for smoke detectors which would immediately kill the print, shut off the heaters/motors and essentially remain in an off state until manually reset. It seems odd that with these versatile devices no one is doing this already? I would try this myself but I am not at the point of being able to modify marlin to do this even if it is possible with the hardware I have (ramps 1.4).

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DjDemonD
Does anyone know if there are any plans/experiments to use some pins on the Ramps or other controller boards as trigger for smoke detectors which would immediately kill the print, shut off the heaters/motors and essentially remain in an off state until manually reset. It seems odd that with these versatile devices no one is doing this already? I would try this myself but I am not at the point of being able to modify marlin to do this even if it is possible with the hardware I have (ramps 1.4).

I plan to implement an input pin for an emergency stop button in RepRapFirmware shortly. RepRapFirmware runs on Duet, RADDS and Alligator electronics. However, one cause of fire could be a short within the electronics itself. So IMO it is preferable by far to cut the power.

You could use two relays. First, a relay with NC contacts that can be driven from the smoke detector - possibly a reed relay to keep the current requirement low (you can get reed relays with changeover contacts). Second, a relay with a 12V coil (assuming you are using 12V power) and mains voltage NO contacts. Drive the coil from your 12V supply, with the contacts of the first relay in series with it, and a flyback diode across the coil. Use the contacts of the second relay to switch the mains supply to the printer. Connect a mains-voltage push button in parallel with those contacts, so you can start the printer by pushing the button. This will cause the second relay to energise and continue providing power for as long as the first relay is not triggered.

Edited 1 time(s). Last edit at 10/29/2015 07:43AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I am not familiar with flyback diodes but will do some research. What I am unclear about is how will putting a mains voltage switch in line with the supply to the printer energise the second relay to switch the current on?

I have enclosed a back of fag packet diagram to see if I understand what you're saying.

Relay 2 controls the power to the whole printer. When you press the button in parallel with the contacts of relay 2, you feed mains input to the printer PSU so it produces 12V. This energises the coil of relay 2, which is driven from the printer's 12V supply through the NC contacts of relay 1. So the relay 2 contacts close, and when you release the push button, the printer is still powered.

When the smoke alarm triggers, it energises relay 1, disconnecting relay 2 coil from 12V. So the relay 2 contacts open and the printer is powered off, until you press the push button again.

HTH David

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thank you, I was presuming I would power this device from its own power supply, this makes much more sense now. That's really helpful and looks like it will work very well.

btw the reason I suggested a flyback diode across the coil of relay 2 is to be kind to the contacts of relay 1 - especially if it is a reed relay. You probably need a flyback diode across the coil of relay 1 as well, to protect the smoke alarm electronics.

If the smoke alarm is battery operated, then there are options for replacing relay 1 by a small amount of electronics.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I'm thinking that this would be a suitable job for something like an Arduino Nano. They're cheap as chips. Have the Nano watch the smoke detector and control a Normally Open relay which provides power to your printer(s). At startup, the Nano closes the relay and watches the smoke detector. When smoke is detected it opens the relay and halts. To reset, you would power the Nano down and up again. You could even have the relay control power to the Nano itself, if you added a manual Normally Open pushbutton switch in parallel. To reset, hold it down, the Nano starts up, the relay clicks closed, release the button.

See Instructables.com for ideas on smoke detectors. There's even a Wifi based one that texts you if it detects smoke. This one includes relays to control power (but no notification comms)

My day job is safety critical software. Yes you could use an Arduino Nano; but IMO there is no way that a critical function such a fire prevention should be implemented by any programmer not experienced in writing critical software, on a poorly-written (from a safety perspective) software platform (i.e. Arduino). Also there are additional hardware failure modes if you use a microcontroller, and you should quantify the associated hazards and either accept them or mitigate them with more electronics.

So my advice is to stick to simpler components which have few failure modes, that you have some hope of understanding.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I think I am going to go along with the relay option - it is simpler and much more likely to be something I can execute well, the idea of using an arduino or other programmable board does appeal but my programming and skill with these things is limited so far to printers and configuring ready written software.

My smoke detector module which is 9v has a relay built in so this will be relay 1 and I have a 9v coil - 240v power relay module which will be relay 2, I will use a voltage regulator to tap 9v from the printers 12v supply, I have the momentary switches and flyback diodes. I will put this together this evening and see how well it works.

Given how potentially simple this is and how cheap the components, assuming I can tune the sensitivity and position of the smoke sensor to give the optimum between false alarms and genuine detection I am amazed that such things are not at the top of the build list for a reprap 3d printer, given that realistically unattended printing is ubiquitous. The question over whether cutting the power at the first sign of appreciable smoke will actually prevent ignition of any part of the printer is something that I will only be able to test by potentially destroying one of my printers, however even a small layer of safety is better than literally none at all.

If my printer were in my living room I might be less inclined to do something like this, but its in an outbuilding so even a regular smoke alarm would be of no use, if I were in the house. I considered a networked smoke alarm but these are very expensive, and do nothing to address the issue of what if I have to pop out. With this option I can use a trigger from one of the relays to also activate an alarm/sms dialer so I can be alerted to the problem and take action.

I have built a smoke sensor device that cuts the power to the printer and I have been using it now for about a year.

[forums.reprap.org]

It has a latching relay and the way I have got it wired, the device can only be reset by turning it off and back on at the mains plug.

The smoke alarm will not put the power back on automatically when the alarm condition clears, that would be dangerous.

Many thanks to those who contributed especially to dc42 for the schematic and dave3d for doing this already which is what encouraged me to make a similar system. I have made two of these devices, and enclose photos. Now to test and set the sensitivity to ensure they trigger when they ought to.
I will try to post a full write up of all parts and the circuit diagrams etc.. at some point, if they prove to be reliable/useful.

Edited 1 time(s). Last edit at 10/31/2015 11:39AM by DjDemonD.

I have included a diagram of how it goes together in case anyone is interested in making something similar and like me wasn't sure how to do it without a bit of messing around and a lot of help and advice. Apologies it is not a proper circuit diagram.
Fix the smoke detector on your printer somewhere where it will be able to detect smoke from the extruder and/or electronics board, since these seem the most likely sources of ignition.

The parts needed are:

-Smoke detector (optical) - DYP-ME0010-A (amazon/ebay/aliexpress)
-Voltage regular 9v 1A LM7809 (available almost everywhere)
-Power relay module [DC 9V 10A 2CH High Low Level Trigger Relay Circuit Module] (ebay) there are other types that will do this job, this unit just seemed easy and has LED's to indicate its status.
-240v Push to make/momentary/non latching switch (available everywhere)
-lots of wire/heatshrink/cable ties etc..
-insulated junction box type enclosure

Total cost £13.18 ($20) and a few hours of soldering etc..

I am not claiming this device will prevent a fire, won't trigger falsely occasionally and I am NOT encouraging unattended printing but if you do have to step away from the printer for a short while it seems better to have a little bit of a safety rather than none whatsoever.

Edited 1 time(s). Last edit at 10/31/2015 05:27PM by DjDemonD.

DjDemonJ,

Thank-you for this thread and sharing your schematic. I'm rebuiliding my 3D printer (Raise3D N2) for a 120VAC heated bed and will include this smoke detection/safety circuit when I rewire everything. However, I have a few questions:

1. I'll be using the same 9V power relay. However, I cannot find a spec sheet for it after much searching. What is determines if the jumper should be set for "H" (high) or "L" low? Is it current, voltage, or other? The reason I ask is I'm in the USA with 120VAC mains, so I'm not sure if the jump should be H or L.

2. Your circuit doesn't show any fuses to protect the wiring. My IEC 120VAC mains plug has a 10A fuse. However, I'm wondering if each 120VAC "hot/live" wire (to heater, to 9V power relay, to momentary switch, to 24VDC power supply) should have seperate fuses to protect the wires. I'm more mechanically inclined than electrical, so perhaps fuses aren't necessary other than the 10A one at the 120VAC mains plug.

Attached is the re-wiring schematic for my printer. If I'm missing anything, please let me know.

Thank-you!

loddie

I have not done much with any of this stuff for a while but yes leave the jumper on H this tells the relay you are using 9v or thereabout not some lower voltage for the trigger. I believe set to L you can trigger the coil to close (using the 9v dc supply) but with a very tiny trigger signal I only used 9v as that's what the smoke board needed. I would have gone with a 5v or 12v smoke detector and relay if available, it would have been much easier (or 3.3v for 32bit electronics or 24v if your printer psu is 24v) but I couldn't find one. The 9v voltage reg manages fine stepping down from 12v to 9v it doesn't get too hot.

Add fuses wherever you wish, the most important are the psu mains fuse and the thermal fuse on the mains bed.

I am not claiming to have checked your schematic comprehensively, but it looks well thought out. Just make sure you have plenty of grounding so all parts of the machine are grounded and use an rcd or rcbo type device on the mains supply to trip power in case a wire or the heat bed shorts to anything. Make sure the heat bed thermistor is secure, and that the bed is evenly bonded to the heat spreader or hot spots can occur.
The keenovo beds are very high quality and have never let me down.

Edited 2 time(s). Last edit at 04/08/2020 03:46AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Hi Simon,

Thank-you for your thorough reply, especially as it has been a while since you wired your 3D printer. I will leave the jumper on "H" as you have explained it well. As yours was 240V and mine is 120V, I wanted make sure the jumper wasn't for switching those voltages.

Also, thank-you for the other safety advice both here and other threads (e.g., here). I've take careful notes of yours and the_digital_dentist's advice. So I'll be using the same components you did except with a buck converter for the step-down to 9V. And as suggested, will be using reliably quality Thermal Cut Off (TCO). I already have a Keenovo replacement heater and will follow their recommended "sandwich" bed frame (aluminum top plate, heater, silicone insulation, aluminum bottom plate) - that is why my diagram has two ground wires to the heated bed frame.

I found an error in my diagram, so is now are correct (Rev 3) in case anyone is looking at it. The wiring color may be confusing for some as it does not follow convention, but that is the color of the wiring of the existing components so it makes wiring together easier for me.

Thanks again,

loddie

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DjDemonD
...use an rcd or rcbo type device on the mains supply to trip power in case a wire or the heat bed shorts to anything.

I'll be using a GCFI outlet to plug the printer into. Is a GFCI outlet functionally equivalent to an RCD/RCBO?

water sprinklers are pretty much %100 reliable. no electricity. everything is metal.

Quote
loddie

Quote
DjDemonD
...use an rcd or rcbo type device on the mains supply to trip power in case a wire or the heat bed shorts to anything.

I'll be using a GCFI outlet to plug the printer into. Is a GFCI outlet functionally equivalent to an RCD/RCBO?

Yes it is equivalent.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Quote
DjDemonD
Yes it is equivalent.

Thank-you!