Category Archives: Raspberry Pi

3D Printer Fire Safety

I have a sneaking suspicion that Santa is bringing me a 3D printer for Christmas. (I sat next to Teri while she ordered the right one, so it isn’t a real stretch to think that it might happen. ūüôā

Until next week when I can actually play with it er… investigate the capabilities of this new tool, I’m trying to get everything ready. ¬†During this preparation, I read a few items about printer malfunctions that either caused a fire or nearly did so. ¬†3D printers have high-temperature components and hardware problems can result in fire, though this is admittedly rare.

My doctor says I’m allergic to fire and should try to avoid it so I’m putting together a fire detection circuit that will cut power to the printer if it detects fire or even an overheated environment. ¬†I’ll post more when it is done but check out these cool little bits I’m using.


First up is an AC cord that has a built-in relay that can be controlled with a low-voltage signal.  The printer will plug into this and can only be turned on if my safety circuit sends a signal to close the relay.

 

 

 


Next is a Mini Flame Sensor that can be read from your favorite micro-controller or embedded computer. ¬†In my case, I’m using a Raspberry Pi. ¬†This boards pulls a digital signal low if it detects light in the same spectral range as fire.

 

 


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This temperature sensor will give you the current temperature over I2C. ¬†I’m using several of them at various places around the printer.

When the detected temperature exceeds some pre-determined limit (say 60 degrees Celsius), or when the flame sensor detects fire, the Raspberry Pi will turn off the control signal to the relay, thereby cutting power to the printer.


Software solutions are fine and dandy but sometimes software or the computer it is running on don’t behave as intended. That’s why you should always have a hardware-only layer of protection.

This is a replacement thermal fuse for a clothes dryer.  I plan to put this inline with the mains supply inside the control unit of the 3D printer. If the ambient temperature gets too high, it will break the circuit.

 

 


These thermal fuses are another layer that operates independently of the software. ¬†I’ll put these at various points on the printer, along with the temperature sensors. ¬†But these won’t be used as input to the Raspberry Pi so a software problem won’t keep them from working. ¬†Instead, they will be in series in the control signal¬†going to the relay. ¬†If one of these blows, the relay will lose its signal and cut off power to the printer.

 


 

So what is my total investment in fire safety?  Disregarding the Raspberry Pi because I was including that anyway so it can provide a web interface to the printer, the components add up as follows:

  • PowerSwitch – $26
  • Flame sensor – $5
  • 5 temperature sensors – $25
  • Thermal fuse for dryer – $12
  • Inline thermal fuses – $8

That adds up to $70. ¬†Throw in shipping on those items I didn’t get from Amazon Prime and it is closer to $80. Is that worth it? ¬†Lots of people (most) operate 3D printers without any sort of fire detection circuit. ¬†Is this degree of safety unnecessary on my part? ¬†Obviously I don’t think so. ¬†Anyway, it was fun sourcing the parts and putting it together and since the whole purpose of this hobby is to have fun, it is a win-win.

Comments?  What would you have done differently?

 

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