Thermal Fuses
(332)Thermal fuses protect a system against excessive ambient temperature. After reaching the set maximum degrees Celsius (in contrast to fuses which react to electric current), the thermal fuse disconnects the circuit and as a consequence protects the device or installation from being damaged. This element works only once which means that after interrupting the electric current flow, you have to replace the component before restarting it. Its construction is based on a meltable input (from metal or polymer compounds) that holds a spring. After reaching the set temperature, the spring is released and separates contacts, which in turn interrupts the circuit. Thanks to the development of technology, the range of safe working temperature is really wide - it can reach even up to 240 degrees Celsius. The thermal fuse can be characterised as having a very low resistance and ability to conduct large alternating currents, up to 15-20A. Its price is usually low but at the same time it is efficient in many systems. Fuses of this type have been used in transformers, industrial machines and everyday equipment like a dryer or a coffee machine.
What are thermal fuses used for?
Unlike electrical fuses, thermal fuses protect circuits and devices not from excessive current directly, but from overheating. Both are large concerns for the longevity and safety of electrical systems and appropriate types of fuses should be used to prevent malfunctions. Without it, you're risking possibly starting a fire. Until the trigger temperature threshold is reached, the fuse acts like a regular part of the circuit and does not disrupt normal operation. When high temperature levels are detected, the fuse springs into action and breaks the circuit to disconnect power from the system.
A thermal fuse, also called a thermal cutoff, does not work like standard circuit breakers - they can’t be reset after triggering and must be replaced with new safety devices instead, similar to electrical fuses that blow after reaching a certain current threshold.
See also: Fuses and Circuit Breakers
How do I know if a thermal fuse has blown?
As you might know, fuses blow after reaching dangerous levels of temperature. The first obvious sign of a thermal fuse blowing is that the device has stopped working. However, since there are potentially countless possibilities for why a given appliance has stopped working at a time, you’ll have to manually check if they have blown. Some devices might also continue working after their thermal fuse is blown, with some functionality missing - for example, if a thermal fuse has blown in a dryer, the dryer might continue to work, but won’t produce any heat. These fuses are also used in coffee makers or in a fan motor, and a blown fuse might also be the cause of a defective thermostat.
Sometimes, you’ll be able to tell that a fuse has blown just by looking at it - but not all types of fuses show that they’ve been triggered. If you can’t tell whether a thermal fuse is blown from looks alone, you’ll need a multimeter to test it. Your multimeter will have two probes - a black one, and a red one. Set up your multimeter for measuring Ohms (use the lowest possible setting), and turn the multimeter ON if it has a separate power switch.
Before testing the thermal fuse, place it on a non-conductive surface like laminated wood or plastic - do not test it on a metal surface! Touch each end of the fuse with the probes - it shouldn’t matter which lead touches which end, since there is no polarity. If the multimeter reading shows resistance, the fuse has not blown and should be good for use. If the reading doesn’t change after touching the fuse with the probes, indicating no resistance change, the fuse is blown and will need to be replaced.
See also: Polymer PTC Fuses
How do thermal fuses work?
Depending on the specific type of thermal fuse you’re using, their method of working might be slightly different. Organic thermal fuses use an organic element in their construction, as the name might suggest. It melts after the surroundings reach a certain temperature level, loosening up a spring hidden inside the fuse and breaking the circuit. Other types of fuses utilize a thermal compound, which liquifies at excessive temperature. After that, the compound shrinks and separates, gathering around the lead on each side and breaking circuit continuity.
Whenever a current flows through a thermal fuse, it generates heat because of the resistance it introduces. Each fuse is built to dissipate heat at a certain rate, which itself depends on the material, shape, and structure of the thermal fuse. If the fuse is heated faster than the heat dissipates, the safety device will eventually reach its temperature threshold and blow. When choosing a thermal fuse, carefully look at its characteristics, including the rated current and rated voltage, as well as operating and melting temperatures, and maximum temperature.
In contrast to a circuit breaker, thermal fuses can’t be reset when the temperature drops or open and close as you see fit - they’ll only blow once the temperature threshold is reached, causing the conductive element inside of the fuse to melt and stop the current flow. Breakers, on the other hand, can be easily controlled and turned on and off, but lack the technical capabilities to detect exactly when that needs to happen - they need to rely on sensors and other elements to determine when to break.
See also: Miniature Fuses
Are there universal thermal fuses available?
Short answer - no, there are no thermal fuses that can be universally used for all devices.
Long answer - thermal fuses come in a variety of types and temperature ranges. They also differ in size and material used. Since various devices use ranging current and voltage, it would be impossible to create a single thermal fuse that would work for all of them, since what would be a safe operating temperature for one appliance is going to be damaging to another. If you’re looking for high-capacity fuses for a demanding appliance, consider using Industrial Fuses.
You might not find one thermal fuse that fits all appliances, but the range of available types of thermal fuses makes it easy to find the one you need. If you’re simply replacing a blown fuse, buy a thermal fuse that offers the exact same properties the previous one did. If you’re placing a new fuse into a circuit without knowing what kind of fuse it used before, you’ll need a good knowledge of the operating details of the device.
See also: Automotive Fuses
Thermal fuses in thme offer
The TME offer includes a wide range of different types of thermal fuses. The basic criterion in the selection of the product should be its working temperature - this is a single-use item, so it is important to choose appropriate temperature value (the burnout value can reach even 240 degrees Celsius.). It is also advisable to look at current rating which ranges from 1A to 16A, depending on the variant. Transfer Multisort Elektronik distributes components of such manufacturers as Eska, Proffuse or Schott.
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