/challenges-projects/design-challenges/experimenting-with-thermal-switches/b/challenge-blog/posts/3d-printer-thermal-runaway-thermistor-tester-6---cutting-power-to-the-3d-printer-when-thermal-sensor-detects-thermal-runawayTable of Contents Project Introduction Testing the OHD1-50B Thermal Sensor Testing the OHD1-50B and M-TRS5-60B Thermal Sensors Detecting Transition From ON to OFF on Thermal Sensors Activation of a Fan with a OHD1-30B Thermal Sensor Cuttingen-USTelligent Community 12https://community.element14.com/challenges-projects/design-challenges/experimenting-with-thermal-switches/b/challenge-blog/posts/3d-printer-thermal-runaway-thermistor-tester-6---cutting-power-to-the-3d-printer-when-thermal-sensor-detects-thermal-runawayMon, 14 Feb 2022 20:55:11 GMT93d5dcb4-84c2-446f-b2cb-99731719e767:33b25b94-d552-4c49-b77c-19dff805da32DAB1<p>Nice build.</p> <p>You have room to add some other items to the box.</p><img src="https://community.element14.com/aggbug?PostID=23054&AppID=359&AppType=Weblog&ContentType=0" width="1" height="1">https://community.element14.com/challenges-projects/design-challenges/experimenting-with-thermal-switches/b/challenge-blog/posts/3d-printer-thermal-runaway-thermistor-tester-6---cutting-power-to-the-3d-printer-when-thermal-sensor-detects-thermal-runawaySun, 13 Feb 2022 19:12:39 GMT93d5dcb4-84c2-446f-b2cb-99731719e767:33b25b94-d552-4c49-b77c-19dff805da32Gough Lui1<p>I would highly recommend adding a back-EMF protection diode in reverse across the relay coil as this will avoid a high voltage spike being generated as the relay turns off. Such a spike could stress the power supply and transistor and contribute to eventual failure after an indeterminate number of cycles.</p> <p>- Gough</p><img src="https://community.element14.com/aggbug?PostID=23054&AppID=359&AppType=Weblog&ContentType=0" width="1" height="1">