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thermal-runaway [2019/02/18 20:07] – [Introduction] samuelpinchesthermal-runaway [2019/02/18 20:30] – samuelpinches
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-===== Introduction =====+==== Introduction ====
    
 <alert info>Note: I am going to use the term ‘thermistor’ interchangeably, to cover both thermocouple and thermistor types of temperature sensors throughout this document.</alert> <alert info>Note: I am going to use the term ‘thermistor’ interchangeably, to cover both thermocouple and thermistor types of temperature sensors throughout this document.</alert>
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 In Marlin firmware, there are a series of settings that enable the firmware to monitor the temperatures and thermal progress of the hot-end(s) and heated bed of a 3D Printer. Should a condition occur that is outside the ‘safe boundaries’ set in the firmware, it can shut down the heaters and all printing processes to help prevent damage to the 3D Printer, and avoid dangerous situations such as a potential fire. In Marlin firmware, there are a series of settings that enable the firmware to monitor the temperatures and thermal progress of the hot-end(s) and heated bed of a 3D Printer. Should a condition occur that is outside the ‘safe boundaries’ set in the firmware, it can shut down the heaters and all printing processes to help prevent damage to the 3D Printer, and avoid dangerous situations such as a potential fire.
  
-I need to stress here, however, that **these settings, and the Marlin firmware itself, cannot guarantee absolute Thermal Runaway Protection under all circumstances**. These are not absolute fail-safes, nor are they idiot proof. The final section in this document covers some basic safety precautions in situations beyond the control of the firmware and the controller.+I need to stress here, however, that **these settings, and the Marlin firmware itself, cannot guarantee absolute Thermal Runaway Protection under all circumstances**. These are not absolute fail-safes, nor are they idiot proof. The final sections in this document cover some basic safety precautions, as well as  situations beyond the control of the firmware and the controller.
  
 <alert danger>Thermal Runway Protection in Marlin only provides one level of protection, and there are some circumstances that it cannot prevent. One very important hazard to be aware of are **[[#MOSFET Shorts|MOSFET Shorts]]**</alert> <alert danger>Thermal Runway Protection in Marlin only provides one level of protection, and there are some circumstances that it cannot prevent. One very important hazard to be aware of are **[[#MOSFET Shorts|MOSFET Shorts]]**</alert>
  
-===== Thermal Runaway Safety Monitoring Settings in Marlin ===== 
  
-Let’s now go through each of the settings in the Marlin firmware (as of release 1.1.9) and cover what they are each for:+ 
 +---- 
 +==== Enabling & Disabling Settings ==== 
 + 
 +Many features in Marlin can be enabled or disabled by modifying the configuration files in the source code. In most cases, features are disabled when they are 'commented out'. This is done by inserting two forward slashes at the start of the line to be disabled, like ‘%%//%%’. See the examples below: 
 + 
 +**Here's an example of an enabled feature:** 
 +<code>#define THERMAL_PROTECTION_HOTENDS</code> 
 +**Here's an example of a disabled feature:** 
 +<code>//#define THERMAL_PROTECTION_HOTENDS</code> 
 + 
 + 
 +---- 
 + 
 + 
 +==== Thermal Runaway Safety Monitoring Settings in Marlin ==== 
 + 
 +Let’s now go through each of the thermal runaway settings in the Marlin firmware (as of release 1.1.9) and cover what they are each for. 
 + 
 + 
  
 ---- ----
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 What it is:\\ What it is:\\
-**These are the two most important settings for thermal protection in Marlin**. If these are disabled (having two slashes in front of them ‘%%//%%’), then there is no Thermal Runaway Protection at all – regardless of any of the other items covered here. +These are the two most important settings for thermal protection in Marlin. If these are disabled (by commenting out - see [[#Enabling & Disabling Settings|above]]), then there is no Thermal Runaway Protection at all – regardless of any of the other items covered here. 
  
 What it does:\\ What it does:\\
-When enabled (no slashes before the ‘#define’ statements), it enables Thermal Runaway Protection to help keep your printer, and you, safe. +When enabled (no slashes before the ‘#define’ statements), these options enable Thermal Runaway Protection to help keep your printer, and you, safe. 
  
 How to use it:\\ How to use it:\\
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 ---- ----
  
-===== Additional Settings =====+==== Additional Settings ====
 These are additional safety precaution items in Marlin that while not tied directly to Thermal Runaway Production, they still help keep the printer safe from over-driving the heaters and potentially causing a fire. These are additional safety precaution items in Marlin that while not tied directly to Thermal Runaway Production, they still help keep the printer safe from over-driving the heaters and potentially causing a fire.
  
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 ---- ----
  
-=====Basic Safety Precautions, Best Practices, and other Dumb Things you shouldn’t do...=====+==== Basic Safety Precautions, Best Practices, and other Dumb Things you shouldn’t do... ====
  
 **Thermistor Type:**\\ **Thermistor Type:**\\
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 Typically, this thermistor type is set to ‘1’ : 100k thermistor - best choice for EPCOS 100k (4.7k pullup) Typically, this thermistor type is set to ‘1’ : 100k thermistor - best choice for EPCOS 100k (4.7k pullup)
 However, if you do not know what thermistor your printer has installed, consult the printer manufacturer or the seller of the sensor to find out. However, if you do not know what thermistor your printer has installed, consult the printer manufacturer or the seller of the sensor to find out.
 +
 +==== Best Practices & Safety Precautions ====
  
 **Here are some precautions and best practices when operating your 3D Printer.** **Here are some precautions and best practices when operating your 3D Printer.**
  
-  * Do not turn on your printer’s heaters if the thermistors are not reporting temperatures near your room’s temperature (when fully cooled) or the thermistors for the heaters are not installed or attached to their bases (the print bed or the heater block).+  * Ensure you have a **fire extinguisher** (pick one suitable for electronic fires) within the room your printer is operating. 
 +  * Ensure you have a **working Smoke Alarm** within the room your printer is operating. 
 + 
 +  * Do not turn on your printer’s heaters if the thermistors are not initially reporting temperatures near your room’s temperature (when fully cooled) or, if a thermistors is not connected or physically attached to the heater it is responsible for monitoring (e.g. stuck down to the the print bed or mounted in the nozzle heater block).
  
   * Do not exceed 250c hot-end temperature for those printers with PTFE (Teflon) in their throats (most 3D Printers) as out-gassing of toxic fumes can occur.   * Do not exceed 250c hot-end temperature for those printers with PTFE (Teflon) in their throats (most 3D Printers) as out-gassing of toxic fumes can occur.
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   * Do not purposefully bypass the Thermal Runaway Protection of your 3D Printer for any reason. If you are having issues with it erroneously triggering a Runaway fault, find out why and fix it.    * Do not purposefully bypass the Thermal Runaway Protection of your 3D Printer for any reason. If you are having issues with it erroneously triggering a Runaway fault, find out why and fix it. 
  
-  * Do not purposefully ‘burn’ the filament or its residue from the hot-end of your printer – through disengaging the thermistor or any other means. Burning of plastic, any plastic, produces toxic, possibly carcinogenic, fumes (which is why you don’t burn plastic in your fireplace). And 3D Printer filament contains various unknown compounds to enhancing its color, print-ability, and durability – most of which there is virtually no information on what chemicals are released when it is burned. +  * Do not purposefully ‘burn’ the filament or its residue from the hot-end of your printer – through disengaging the thermistor or any other means. Burning of plastic, any plastic, produces toxic, possibly carcinogenic, fumes (which is why you don’t burn plastic in your fireplace). Beyond the base plastic, 3D Printer filament also contains various additive compounds, such as colour dyes, flow enhancers, viscosity modifiers – and there is virtually no information available on what chemicals are released when these are burned. 
  
   * Do not purposefully trigger a Thermal Runaway event. There are no guarantees the Thermal Runaway Protection will engage before PTFE starts out-gassing toxic fumes, filament starts burning, or even a fire.    * Do not purposefully trigger a Thermal Runaway event. There are no guarantees the Thermal Runaway Protection will engage before PTFE starts out-gassing toxic fumes, filament starts burning, or even a fire. 
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-===== MOSFET Shorts =====+==== MOSFET Shorts ====
  
 MOSFETs (metal-oxide semiconductor field-effect transistors), are solid-state (non-moving) components on your printer’s controller board. Their job is to switch power to the various heaters (e.g. bed heater, or hot-end nozzle heater) on and off. These MOSFET devices can fail either open (no power delivered) or closed (power is delivered). If the MOSFET fails open, this simply means the heater it controls will appear to not work at all. MOSFETs (metal-oxide semiconductor field-effect transistors), are solid-state (non-moving) components on your printer’s controller board. Their job is to switch power to the various heaters (e.g. bed heater, or hot-end nozzle heater) on and off. These MOSFET devices can fail either open (no power delivered) or closed (power is delivered). If the MOSFET fails open, this simply means the heater it controls will appear to not work at all.
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 A 3D printer with a shorted MOSFET will immediately start to heat up once power is turned on - and will not obey any instructions from the safety systems to turn off. In that circumstance Thermal Runaway will occur, and this may generate smoke, toxic fumes and can potentially cause a fire.  A 3D printer with a shorted MOSFET will immediately start to heat up once power is turned on - and will not obey any instructions from the safety systems to turn off. In that circumstance Thermal Runaway will occur, and this may generate smoke, toxic fumes and can potentially cause a fire. 
  
-A MOSFET short can occur randomly at any time, without any apparent cause. For this reason, lastly, and absolutely:+Since a MOSFET short can occur randomly at any time, without any apparent cause. For this reason, lastly, and absolutely:
  
 ==== NEVER LEAVE AN OPERATING 3D PRINTER UNATTENDED ==== ==== NEVER LEAVE AN OPERATING 3D PRINTER UNATTENDED ====
 +
 +Stay safe, and happy printing!
  
 -- //DaHai Zhu// -- //DaHai Zhu//
thermal-runaway.txt · Last modified: 2020/12/25 02:13 by 127.0.0.1
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