Alternative options for replacing the thermal fuse in the event of a malfunction

To protect equipment from damage, bimetallic elements are used that break the power circuit when overheated above the permissible threshold. If you repair household appliances yourself, you should know how to replace the thermal fuse without the risk of ignition of the device due to a short circuit. The jumper is installed temporarily, since it is impossible to calculate the resistance and provide the necessary protection parameters.

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The concept of a thermal fuse

A thermal protective element is a device that breaks the power circuit when heated. Excess heat is released during the passage of current with increased strength through the conductor.

Features and purpose

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The element is installed in electrical and electronic devices and provides protection of components from damage. For example, fuses are used in the air conditioning fan control units of a car. The thermal element prevents fire when the rotor of the electric motor is jammed. On the cases of products there is a type marking that allows you to specify the operating voltage, current and response temperature.

Fuses are characterized by simple design and low price, provide reliable protection of equipment.

Device and principle of operation

The disposable element is equipped with a metal jumper that burns out when overloaded. The product has contact legs necessary for installation in the electronic module of the equipment. In bimetallic reusable elements, the circuit is opened by a plate that deforms when heated. After cooling, the integrity of the line is restored automatically; in some models, pressing a button is required.

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Main varieties

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Fuse modifications:

1. Standard disposable with Rose or Wood alloy filament installed in a protective housing. The wire is soldered to the contacts that are attached to the electrical circuit. When the current rises above the allowable threshold, the jumper melts and protects the equipment from irreversible damage. An example is the element TF1081-105, designed for a current of 15 A and heating up to +105°C. There are powerful fuses for electrical installations with ceramic cases filled with quartz sand, which extinguishes the arc.
2. Disposable, used in the toner heating unit in laser printers. The design provides a spring with contacts filled with solder. Under normal operating conditions, the fuse will withstand numerous warm-up and cool-down cycles. When the temperature rises above +180°C (the parameter depends on the printer model), the solder melts and the spring opens the contacts, preventing the equipment from catching fire.
3. Reusable bimetallic fuse, triggered when the threshold temperature is exceeded. After cooling, the integrity of the circuit is restored automatically. The advantage is the ability to permanently protect equipment without replacing or maintaining components. The disadvantages include an increased price due to the complicated design and the risk of failure due to jamming or burning of contacts.
4. Resettable polymer-based fuse used in electronic devices. With an increase in current and heating to + 80 ... + 90 ° С, the resistance increases sharply, which leads to an opening of the circuit. After a while, the temperature of the fuse drops, the resistance returns to its normal value, and the electronic device is restored to working order. Similar products are used in USB or FireWire port circuits and other powered interfaces.

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Possible problems with the thermal fuse

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The main problem is the destruction of the fusible thread due to the excess of the threshold temperature. You can check the condition of the fuse with a test device switched to the resistance measurement mode. On a working insert, the multimeter will show a value within 0.2 Ohm, on a burnt one, the device will display an open circuit. Occasionally, the cause of incorrect operation is poor contact between the copper-plated leg of the element and the printed circuit board. In this case, you will need to crimp the metal sleeve or re-solder the fuse to ensure heat dissipation.

If you find problems with the operation of devices equipped with thermal fuses, you must check the condition of the power supply and the cord from the AC outlet. The procedure is performed with a multimeter switched to the circuit ringing mode. The master must make sure that power is supplied to the fuse input, and then test the operation of the protection.

If the equipment is equipped with a bimetal fuse, then you should check the resistance, and then make sure that the device is working correctly. When heated and cooled (for example, with a lighter flame), a click should be heard from the housing, indicating the operation of the contact group.

In domestic conditions, it is impossible to find out the temperature threshold for breaking the circuit; for an accurate check, you need a stand that simulates the operation of the load and a thermometer.

What can replace

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For emergency repairs, instead of a regular thermal fuse, use:

• fusible type standard protective elements;
• pieces of aluminum or copper wire of a suitable diameter;
• a steel spring from a lighter (an emergency method that does not provide protection).

For a regular fuse

Instead of a thermal fuse, you can use a standard protective element with a metal jumper, closed by a durable glass case. The product is selected according to the strength of the current in the circuit. If the wire does not burn out during the test switching on of the device, then the equipment is considered suitable for further operation. But the fuse does not provide normal protection, it is recommended to install a thermal type product as soon as possible.

wire

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As a temporary solution, it is possible to install a jumper made of aluminum or copper wire. It is necessary to find out the peak value of the current strength, and then select the cross section according to the table. With an erroneous choice, both premature operation of the protection and failure of the device are possible. The table shows the ratio of wire diameters to the maximum allowable current, if the parameter is exceeded, the jumper burns out.

Do-it-yourself replacement nuances: important rules

Thermal fuses burn out when the temperature rises, so the elements are installed using clamps, contact welding or brazing with refractory solders. Standard mixtures based on lead and tin may not withstand overheating and melt. With self-repair, the wire is wound on the legs of a burned-out element, ensuring the integrity of the wiring. If tin-lead solders are used in the design of the device, then when installing a new fuse with an electric soldering iron, a reliable heat sink should be provided.

After mounting the element, it is necessary to check the integrity of the jumper, since protection may be triggered when heated.

Testing requires a multimeter switched to resistance detection mode. The probes should be attached to the fuse terminals, a serviceable element will show a resistance of about 0.1-0.2 ohms. If the indicator shows an open, then a new thermal fuse will need to be installed, taking extra precautions and using a reinforced heat sink.

Household fan heaters use disposable riveted fuses. For dismantling, you will need pliers with long narrow jaws that allow you to bend the legs. The contacts of the new product are pre-bent in place, the wire supports should form rings for installation on rivets. After installation, it is necessary to additionally crimp the connections with pliers, ensuring tight contact. If installed incorrectly, sparks can occur, leading to the formation of carbon deposits and breaking the power circuit.

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Thermal fuses are often used to protect the primary or secondary windings of transformers. To remove the element, you will need to dismantle the voltage converter and remove the protective coating from the windings. After soldering a new fuse, it is necessary to restore the insulation. The procedure may not be economically feasible as it is easier to purchase and install a transformer with suitable performance.

If you need to change the fuse mounted in the car air conditioner, then first find out its location. On most machines, it is necessary to remove the glove box or partially disassemble the instrument panel or center console. The fuse is installed on the contacts of the resistor, which provides step switching of the fan speed. Pliers are used to remove and install the element. If the resistance fails, a new regulator assembly with a fuse will need to be installed.

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