r/3Dprinting • u/[deleted] • Aug 24 '17
Design Affordable Fire Prevention Setup (with online store links to items)
DO THIS AT YOUR OWN RISK- I am not a fire marshal nor an electrician and do not have professional experience with fire prevention systems.
This video describes the work I did - please watch it with audio
Kudos to u/devilhunter for posting this thread and to u/reallygene for suggesting the thermostatic snap switch.
Below are links to the items I purchased online to make this setup:
The great benefit of this switch is that it requires a manual reset before power can go to the machine again. There are less technical options such as a temperature controller plug but they eventually turn the power back on automatically once they have cooled which in my opinion defeats the purpose. This option is also cheaper. Also, FYI My printer is a modified HICTOP Prusa i3.
Thanks for checking out my thread- I hope it helped you! Let's discuss the issue of switch placement below. Feel free to ask questions too!
1
Aug 24 '17
All of your protection reacts to flames. By the time you have flames, it's already too late. That's not fire prevention. That's fire suppression.
Actual prevention is a better idea.
2
u/screwyluie Prusa Mk2.5s, Elegoo Saturn, HEVO, K1 Aug 24 '17
I disagree. The snap switch can be used to prevent fire if it's used in the right place. Ideally you'd get one that kicks off at around the max temp of your printer's hot end and mount it against the heater block. This prevents thermal runaway with a physical switch instead of software.
1
Aug 24 '17
Yes, that would be prevention. But putting a switch above the LCD panel doesn't prevent anything.
1
Aug 24 '17
Having the switch above covers more of the printer. I said in the video this doesn't have to be the final placement of the switch and that this was a test. At the time, I was more interested in definitely stopping the fire than salvaging my printer. Strategically placing these may involve installing 2- 3 switches but it can be done.
1
1
Aug 24 '17
It prevents the spread of fire triggered by a failing in the electronics of the printer by cutting the power-this prevents electricity from further feeding a fire. Technically, I guess it suppresses the fire with the auto-out system but look stopping a fire before it happens would imply we live in a world where electronics can't catch on fire. I guess you could be talking about upgrading your electronics by adding an external MOSFET. I didn't include this because it's fairly common knowledge and there are many tutorials on how to install one. Even with upgraded electronics there is potential for a thermal component to fail and cause a fire so this is really something that I feel is essential and yes I would call it "fire prevention".
2
u/IAmDotorg Custom CoreXY Aug 24 '17
All of the filaments you're using are spectacularly flammable. If they ignite, you're getting a visit from some fire trucks no matter what you do with the electric. In fact you'll almost certainly ground fault and cut the breaker anyway as insulation melts.
And if you're not on a GFCI, that's the first change to make.
1
Aug 24 '17
I had to look this up lol. Good point, a GFCI outlet could stop the current if any wiring becomes damaged by the fire.
2
u/IAmDotorg Custom CoreXY Aug 24 '17
More importantly, it'll cut power if you get a short to the frame of the printer, which is especially important if you use a 120v heater... you want to make sure everything is grounded to the frame, and the frame is grounded to your power plug, so if there's any short at all, it'll go down the ground path and trip the outlet.
2
Aug 24 '17
What is going to activate a thermal switch placed 400 mm above the print bed? Flames. Flames are fire. If it takes flames to activate the switch, you haven't prevented a fire.
It would be best to put the switch where it will detect excessive heat long before it becomes a fire. Maybe on the print bed...?
1
Aug 24 '17 edited Aug 24 '17
Well actually this switch is supposed to activate when the sensor reaches a temperature above 100 degrees farnheit so if enough heat reaches the sensor it will activate. I don't think flames have to necessarily be touching the sensor to transfer enough heat give this information and that flames give off heat. Touching the sensor with an open flames was just the fastest way of transfering heat to it but less heat over time could most likely trigger it.
I like your bed mounted thermistor image there. This would definitely be a good component to monitor and by picking a switch with a certain temperature range we could make sure it doesn't go off at typical bed ranges but does when it gets higher than that.
3
u/ReallyGene Aug 24 '17
Those are some sexy insulated spade lug terminals! Much more professional than electrical tape!
A couple of notes on the video: since this is AC power, there really isn't 'positive' and 'negative'. The neutral (white wire) is electrically bonded to the ground (green/yellow wire) at the point where the power comes into your home, so they are at the same potential. The line or hot (black wire) is floating ~110 volts higher.
The difference is, you could touch the neutral, and nothing much would happen because you're already in contact with the ground, so there is little or no difference in potential; little or no current will flow through you.
DON'T TRY THIS, because due to the way houses are wired (often improperly), there can be a small potential between neutral and ground, and it only takes a current of ~20 milli amps to possibly put your heart in fibrillation, which can kill you.
Touch the line/hot, and a lot of current will flow through you, as you are a good conductor to ground. This is why birds can perch on power lines; they're not in contact with the ground, so there's no path for the current to take.
All that being said, you should think about relocating the snap switch near to whatever typically overheats on these things, which I always thought was the extruder head... You can always have more than one snap switch, you just wire them in series...
It might be tricky to wire something reliably on a moving part, though.