Most household appliances generate heat during operation. Some of them are designed and designed for heating (electric iron, electric kettle or boiler for heating water), and for most, a strong increase in the temperature of their body and internal filling is an undesirable side effect of their functioning. To prevent overheating, a thermal fuse is installed in series in the power supply circuit of such devices.
Device and principle of operation
Before checking the thermal fuse for operability, it will not be superfluous to familiarize yourself with its operating principle and device. Indeed, such a situation often happens: the refrigerator or the iron has stopped working, you have to give it in for repair or buy a new one, and the whole fault is a small part, the cost of which is cheap. Knowing how and what to check, you can save significant money.
The principle of operation is based on the property of different metals to expand upon heating with different intensities. The bimetallic plate bends under the action of high temperature, which is used in thermostats to open the supply circuit.
Structurally, this protective element consists of two parts:
- electric with normally closed contacts;
- mechanical with a bimetallic plate connected to the contacts of the electrical part.
The electrical part, as a rule, is enclosed in heat-resistant plastic, and the mechanical part is enclosed in an aluminum case.
Possible malfunctions
As noted above, the contacts should be normally closed - at a heating temperature not higher than the permissible electrical current must flow through the fuse. After reaching the temperature limit value, the thermal fuse trips and the contacts open.
The first possible malfunction is open contacts in normal condition. The second malfunction - when the threshold temperature is reached, the contacts do not open or open when heated above the nominal value.
Health Check Methodology
There are some tips on how to check the thermal fuse. It all depends on whether there is a multimeter or a regular dial at hand.
The first tip is how to check the thermal fuse with a multimeter in resistance measurement mode:
- put the device into resistance measurement mode;
- to attach probes to the fuse contacts - if the resistance is close to zero, then the contacts are closed;
- heat the metal part of the thermal fuse (with a lighter, soldering iron or dip into hot water) and check the resistance again - it should be infinitely large.
In the process of cooling, a faint click may be heard - this is a closed contact. If, before heating, the resistance is zero, and after heating, it is infinity, then the tested part is serviceable.
This verification method is the most accurate, but not always at hand is a measuring tool. The following tip on how to check the thermal fuse gives an approximate result:
- heat the tested part and listen - there should be a slight click when the heating temperature approaches the nominal;
- when cooling, there should also be a click.
If the part is "silent" when its temperature changes above the nominal and below the nominal, then with a high probability it is faulty.
Expert Advice
There are models of thermal fuses that themselves do not return to their original position after cooling. They have a button on the case to put the contacts in a closed state. Before checking the thermostat, make sure that it is not of this type. Otherwise, there will be no click and resistance with a value of zero.
And the last advice from experts: before checking the thermal fuse of a refrigerator, boiler, vacuum cleaner or other household appliance, it must be disconnected from the circuit. Otherwise, shunting through other parts may show incorrect results when measuring resistance or continuity.