The Winners of Experimenting with Thermal Switches

We have completed the Experimenting with Thermal Switches Design Challenge, sponsored by KEMET, and featuring its Thermorite® Thermal Switches. We had 15 participants with 13 finishers, including our Grand Prize and Runner Up Prize winners. Our judge has read all the blogs and tallied up the points, and in this blog we will announce the winners of this competition!

First Things: Let's Talk About Thermal Switches
Many people know all about bimetallic thermal switches, but not everyone may be familiar with Thermorite® Thermal Switches. So, let me provide you with a brief background.

Thermal switches (also called thermal sensors) are used in industrial, appliance, and HVAC products. They are typically used as protection against overheating, overcooling, or overloads when used in a motor protection circuit. The most widely used thermal switches are bimetallic thermal switches and thermistors.

Bimetallic thermal switches consist of two strips of different metals that are bound together. Bimetallic thermal switches leverage the expansion of metals when they are heated. As the strip is heated, the different metals bend in different directions, opening or closing a switch contact (NO/NC).

A thermistor is a type of resistor whose resistance changes with temperature changes. Thermistors are widely used as inrush current limiters, self-resetting overcurrent "fuses," and self-regulating heating elements.

The bimetallic thermal switches have been a mainstay for the design of thermostatic temperature controls and over-temperature protection over many decades. Thermistors have also been widely used, but neither type offers the high accuracy or stability needed to meet the latest demands of consumers and industrial end users.

In response to the drawbacks of the traditional products, thermal ferrite materials such as KEMET’s Thermorite® have emerged to enable a new generation of thermal switches that deliver greater accuracy, faster response times, and better stability with respect to ageing and environmental conditions such as humidity. For a detailed discussion of Thermorite® Thermal Switches, go here.

How Does the Thermorite® Thermal Switch Work?

The thermal reed switch contains a pair of Fe-Ni (iron-nickel) reeds encased in a glass tube filled with inert gas. Encasing the reeds in this way ensures the switch is dust proof, explosion proof, and corrosion resistant. A Thermorite tube surrounds the reeds, and acts as a magnet at temperatures below the set point determined by the material composition. When the temperature rises above the set point, the Thermorite loses its magnetic properties and the magnetic field collapses, allowing separated reed contacts to touch (make-type switch) or close contacts to separate (break-type switch). The mechanism shows very little degradation due to metal fatigue. Tests under standard conditions have demonstrated switch lifetime based on metal fatigue of 500,000 on/off cycles.

element14's Experimenting with Thermal Switches competition was an opportunity to provide our participants with a kit of KEMET’s Thermorite® thermal switches so that they could conduct experiments and blog about what they learned. Our judge has made his decisions, so let's meet the winners!

Grand Prize Winner of the Experimenting with Thermal Switches Challenge: Gough Lui

Gough Lui wrote seven blogs during the experimenting period. Even though only two blogs were required, given the breadth of experiments he had planned to conduct, I'm not surprised at the extra blogs he felt were needed. What did he attempt to do that had him write these extra blogs? I'll let him explain in his own words: "I proposed focusing on characterising the thermal switches provided in the kit. I attempted to characterise as many as I could for the temperature cut-in and cut-out thresholds and temperature hysteresis over many cycles, to see if there is any drift in parameters as the switch ages under a working load. Initial contact resistance and final contact resistance will also be measured in case this yields any further insights. Upon the conclusion of the tests, I may even repurpose the switches to create a simple temperature-controlled chamber by controlling a resistive heater, or to control heatsink temperatures by directly controlling a brushless-DC fan."

His second blog featured an unboxing and an introduction to his experiments, including load handling, thermal coupling and distribution, measurement speed, thermal thresholds, contact resistance, and more. His third blog is where it really gets interesting; he discusses Magnetic Characteristics, External Magnetic Influence, Overload Behaviour, and does a Teardown. In the fourth blog, he goes into Vibration Induced Resonance, Contact Bounce, Overvoltage Behaviour, and offers some thoughts About Switching Inductive Loads. I would describe the fifth blog as his data analysis blog, and he has plenty of data! Blog 6 is a must read, as he discusses his Latching Fault Circuit Design – A Thought Experiment. The final blog covers problems and conclusions.

Our judge noted that Gough Lui "provided a lot of results which will be absolutely useful for any organisation looking to use thermal switches. It's an extremely valuable resource." Gough Lui's blogs were high quality and they clearly demonstrated what he learned from his participation in this Experimenting with Thermal Switches program. For these reasons, he was selected as our Grand Prize Winner. You can read all of Gough's blogs by going here.

Runner Up Prize Winner of the Experimenting with Thermal Switches Challenge: Ambrogio Galbusera

While our grand prize winner chose a test-the-limits approach to his thermal switch experiments, as evidenced by his "Torture Test" title, our runner up prize winner took what I would call an applications approach to his experiments with thermal switches. Spanning four blogs, Ambrogio used thermal switches in two projects related to energy efficiency that he called the Energy Squeezer. His projects were designed to be the following: (1) a device to extract heat from boiler fumes and (2) a mixer for the hot water generated by solar panels.

In the first blog, he articulated his personal goal, which was "... in this challenge, I would like to evaluate whether the Kemet thermal [switches] suit two projects I have in mind to improve the energy efficiency of my house." He describes his two projects as (1) a fume energy extractor and (2) a solar panel water mixer, along with his testing plan. His second blog covers test setup and the specific thermal switches he plans on using. He covers a lot of useful information that you should take the time to read. Blog 3 covers the details of his fume energy extractor, and Blog 4 covers the water mixer. As our judge indicated, Ambrogio "came up with very clever solutions that should save a lot of energy. His solutions are (on the face of it) reliably designed, and make good use of the inherent reliability of the thermal switches for heating scenarios where reliability is essential/required." For these reasons, he was selected as our Runner Up Prize Winner. See his project blogs here.

I'd like to thank all the element14 members who participated and completed this challenge, and who will receive a Finisher Prize for their work:

ARDU-TEMPE BEACON (ARDUino + TEMPErature)
Synopsis: use thermal switches in an alarm beacon and a greenhouse fan heater
AlfredC's project blogs

The Cozy Cat House
Synopsis: focused on characterizing the thermal switches in the kit, with the design, build, and operation of a specific application. The application would be a heated and instrumented hutch for a cat.
Doug Wong's project blogs

Experimenting with Thermal Switches
Synopsis: build an aluminum heating plate heated back power resistors and controlled by the TRS break type switch under test. I would also try a steel heating plate to test the effect on the thermal magnetic performance of the TRS.
Gordon Margulieux's project blogs

3D Printer Thermal Runaway / Thermistor Tester
Synopsis: experiment with thermal switches to prevent thermal runaway in 3D Printers
guillengap's project blogs

LED Life Booster/Extender
Synopsis: developing a circuit using a thermal switch to control the power/ switch between LED light panels, to optimize the life of LEDs in LED bulbs.
Karthik Rajagopal's project blogs

Thermal Protection Circuit Experiment
Synopsis: use thermal switches for motor control and PCB heating control.
Leow cheah wei's project blogs

Maintaining Temperature of Plating Solution
Synopsis: use thermal switches to maintain the temperature of an electroplating solution
manoj roy's project blogs

ThermoPID
Synopsis: use thermal switches switches with a DC/DC converter IC to catch the component's operational temperature value and initiate active cooling with a fan on overheat.
Navadeep Ganesh U's project blogs

Auto-Cutoff System for Room Heaters
Synopsis: use thermal switches for experimenting and interfacing them with a room heater.
Rushiraj Jawale's project blogs

Thermal Monitoring and Protection System
Synopsis: build a temperature monitoring system featuring Thermal protection.
Vinay YN's project blogs

Making Electric Geysers Smart
Synopsis: using an external smart device made with KEMET's Thermolite thermal switches to send information to wireless Plug which can in turn control an electric geyser.
Vishwas Navada's project blogs

Last Word: A Big Thank You to Our Judge
I'd like to thank Top Member Shabaz for judging the Experimenting with Thermal Switches Challenge. His input on the projects was invaluable to our final decisions.

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