1.Types of thermal protection devices
Bimetallic strip type overheat protector: The most common, it utilizes the temperature characteristics of bimetallic strips.
Current type overload protector: Triggers protection based on the magnitude of the induced current.
Combined type (temperature + current) : Simultaneously monitor temperature and current.
2. Working principle of bimetallic strip overheat protector
Core components:
Bimetallic strip: It is made by pressing together two metals with different coefficients of thermal expansion and bends when heated.
Contact: Connected in series in the compressor circuit to control on-off.
Work process:
1. Normal state:
When the temperature/current is normal, the bimetallic strip remains straight, the contacts close, the circuit conducts, and the compressor operates.
2. When overheated or overloaded:
Excessive temperature: Due to poor heat dissipation or prolonged operation, the temperature of the compressor rises, causing the bimetallic strip to bend due to heat and the contacts to break, thus cutting off the circuit.
Excessive current: When overloaded, the heating element inside the protector heats up, indirectly causing the bimetallic strip to bend and break the contacts.
3. Reset after cooling:
After the temperature drops, the bimetallic strip returns to its original state, the contacts close again, and the compressor restarts.
3. Working principle of current overload protectors
Induced current through electromagnetic effect or resistance heating:
When the current exceeds the set value (such as when the compressor is locked), the resistance inside the protector heats up more intensely, triggering the bimetallic strip to deform and break the circuit.
After the current returns to normal, the protector resets.
4. Application Scenarios
Air conditioning compressor: Prevents overheating caused by insufficient refrigerant, poor heat dissipation or unstable voltage.
Refrigerator compressor: Avoid burnout caused by frequent starts or excessive load.
5. Other protection mechanisms
PTC thermistor: Some modern devices use positive temperature coefficient thermistors. The higher the temperature, the greater the resistance, thereby limiting the current.
Electronic protection module: It monitors temperature/current in real time through sensors and cuts off the power supply by the control board (more accurate).
Post time: Jun-13-2025