How Do I Know If the KSD301 Temperature Control Switch Is Broken?

Understanding the KSD301 Temperature Control Switch

The KSD301 temperature control switch is a bimetal-based thermostat widely used for automatic temperature protection in household and industrial appliances. It operates by opening or closing a circuit according to the temperature threshold, ensuring safety and performance stability.

When the appliance is at normal working temperature, the bimetal disc remains free and the contacts stay closed or open depending on the circuit design.
As the temperature rises to the operating point, the disc rapidly deforms due to internal stress, causing the contacts to open or close - effectively cutting off or connecting the current. Once cooled to the reset temperature, the contacts return to their initial state.

 

 

How to Test If a KSD301 Thermostat Switch Is Broken

Step 1: Measure at Room Temperature
Use a multimeter to measure the two terminals. At room temperature, most KSD301 normally closed models show connected contacts.

 

Step 2: Apply Heat to the Switch
For switches rated below 100°C, place them in hot water of the corresponding temperature.
For 100°C-rated models, gently heat with a soldering iron.
When the temperature rises to the operating point, the contacts should open - indicating that the thermostat is responding correctly.

 

Step 3: Cooling and Resetting
After removing the heat source, allow the device to cool.
If the contacts reconnect when the temperature drops, the KSD301 switch is functioning properly.

 

Alternative Test Method (With Multimeter and Heat Source)

To confirm the operating temperature:

• Connect both ends of the KSD301 pins to a DC power circuit (about 10V).
• Touch the lower shell to a heating object (like a hot water surface).
• Monitor the temperature when disconnection occurs.
• If the contact opens around 97°C ±5°C, the thermostat is within a qualified range.
• All KSD301 thermostats are tested in ovens during production to verify this "operating point" before leaving the factory - ensuring reliable performance in real applications.

 

Common Faults and How to Identify Them

Symptom	Possible Cause	Suggested Action
No response when heated	Damaged bimetal element	Replace the switch
Always disconnected	Contact failure or corrosion	Clean or test continuity
Temperature deviation > ±10°C	Calibration issue	Replace with accurate model
No "click" sound	Mechanical fatigue	Verify with multimeter

 

 

Where KSD301 Thermostat Switches Are Commonly Used

Electric kettles

Coffee makers

Irons and heaters

Water dispensers

Industrial temperature control units

Adding proper temperature protection helps ensure longer product life and safety compliance in all these devices.

 

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