3D Printer Thermal Runaway / Thermistor Tester #1 - Project Introduction

Table of Contents

1. Project Introduction
2. Testing the OHD1-50B Thermal Sensor
3. Testing the OHD1-50B and M-TRS5-60B Thermal Sensors
4. Detecting Transition From ON to OFF on Thermal Sensors
5. Activation of a Fan with a OHD1-30B Thermal Sensor
6. Cutting Power to the 3D Printer when Thermal Sensor Detects Thermal Runaway
7. Project Report Updated

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Project Introduction

I am a communications and electronics engineer, and writter about electronic and robotic solution. I´m interested in KEMET thermal sensors, because I want to experience their potential in solving hardware problems and compare them with traditional solutions already known.

What experiments I plan to perform?

The global 3D printer manufacturing market is experiencing strong growth, the market is expected to reach $25.26 billion in 2025.

Regarding technical support, You should never leave your 3D printer unattended. This solution can activate an alert and cool your 3D printer´s drivers, or cut power to your printer when it senses thermal runaway.

PROBLEM:

Thermal runaway is a safety feature designed to prevent the printer from accidentally catching fire. If the thermistor in the printer was disconnected in any way, the electronics would get a lower (incorrect) temperature reading. In an attempt to compensate for the lower temperature, the heater would reach dangerously high temperatures and the printer could turn into a dangerous fire. Thermal runaway prevents that from happening. Most 3D printer firmware includes some sort of thermal runaway protection, a feature that monitors the heaters and shuts the printer down if it notices something gone wrong. However, most printers use MOSFETs to switch power to the heating element. Unfortunately, when MOSFETs fail, they usually fail closed (i.e. conducting). This means that, even if the firmware detects something has gone wrong, it won't be able to do anything about it. Solid State Relays (SSRs) can fail in the same way. This can be dangerous if you have a powerful high wattage heated bed. Examples:

• In the image below you can see a bottom view of the damaged 3D printer heated bed.

Now we zoom in on the heated bed, and we can see the thermistor burned out and being soldered.

• In the image below you can see a 3D Printer Heated Bed Power Module High Current 210A. This device is damaged due to the high temperatures it takes after many hours of using the 3D printer.

SOLUTION:

This device provides extra protection against such failure by monitoring the temperature independently and control the printer power with its own KEMET thermal sensor as follow:

1. Its primarily designed for monitoring the heated bed, which normally works with temperatures of 60 degrees celsius;
2. It also can be used for monitoring other parts of the printer that heat is of concern, such as the hotend. The hotend is the component of a 3D printer that melts the filament for extrusion and helps maintain a consistent and accurate temperature for successful prints at 200 degrees celsius approximately; and
3. The step motor drivers to prevent hardware damage or fire.

 HOW DOES IT WORK?

• Once powered up the device, the screen will display the current temperature and the maximum temperature that has been observed;
• The screen also will display the current temperature target in the setting according the thermal sensor used, and the 3D printer´s part monitored; 
• If the thermal runaway is detected, the KEMET thermal sensor will shut off the printer power, and the device generate alarm sound for 1 minute. The power will remain off until the the device is manually reset;

HARDWARE:

1. The Thermal Switches Experimenter’s Kit;
2. Arduino NANO 33 BLE Sense;
3. Grove-LCD RGB Backlight;
4. Grove-Buzzer;
5. Grove Relay;
6. Relay RAS-0510;
7. BC547B Transistor;
8. LEDs x 3;
9. Resistors 10k;
10. Thermistor; 
11. Cable gland x 4; and
12. Fan 12v 0.1 A.