Description
The Smart 12V Thermistor Relay Switch – Automatic Temperature Protection is a rugged, industrial-grade temperature monitoring and control module designed for 12V DC systems. Operating on a standard 12V supply—common in automotive environments, solar installations, battery-powered equipment, PLC panels, and industrial control cabinets—this module combines a sensitive NTC thermistor temperature sensor with a built-in relay to automatically switch external devices based on ambient or surface temperature.
When the temperature rises above or falls below your preset threshold, the onboard comparator circuit (LM393) instantly energizes or de-energizes the relay, allowing you to control high-power devices such as cooling fans, exhaust vents, heaters, pumps, compressors, or alarm systems up to 10A. The module features an adjustable potentiometer for setting the temperature trip point, a green LED indicator showing relay status, and both Normally Open (NO) and Normally Closed (NC) output terminals for flexible fail-safe design.
Unlike the 5V version, this 12V module offers superior noise immunity, longer cable runs (up to 30 meters for the sensor), and direct compatibility with automotive and industrial control systems. The module operates standalone—simply apply 12V power, adjust the potentiometer to your desired trigger temperature, and connect your load. No microcontroller, no programming, and no software required. The onboard LM393 comparator provides stable, noise-immune performance with a built-in flyback diode to protect the circuit from relay coil spikes.
Whether you need to activate a radiator fan in a vehicle, turn on a heater in a chicken coop, protect a solar battery bank from overheating, automate greenhouse ventilation, or provide temperature backup protection for industrial equipment, the Smart 12V Thermistor Relay Switch delivers reliable, plug-and-play temperature protection in a compact, easy-to-use package.
Key Features
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12V DC Operation – Compatible with automotive, marine, solar, PLC, and industrial control systems.
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Standalone Operation – No microcontroller or programming required; works immediately after power-up.
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Adjustable Temperature Trip Point – Onboard potentiometer lets you set the exact temperature for relay activation.
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Dual Mode Operation – Use NO (Normally Open) for “turn on when hot” applications, or NC (Normally Closed) for “turn off when hot” or fail-safe applications.
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High-Power Relay – 10A/250V AC or 10A/30V DC contact rating controls fans, heaters, pumps, and more.
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Sensitive NTC Thermistor with Extended Cable – Fast response with included external probe; supports cable runs up to 30 meters.
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LM393 Comparator IC – Provides stable, noise-immune threshold detection ideal for industrial environments.
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Status Indicator LED – Green LED illuminates when relay is energized.
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Flyback Protection Diode – Protects circuitry from voltage spikes when relay de-energizes.
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Wide Operating Temperature – Module and sensor rated from -40°C to +100°C.
Technical Parameters
Usage Guide
How It Works
The module continuously monitors temperature via the NTC thermistor. As temperature increases, the thermistor’s resistance decreases. The LM393 comparator compares the thermistor voltage to a reference voltage set by the onboard potentiometer. When the temperature crosses the threshold, the comparator triggers the relay, which switches the connected load ON or OFF depending on your wiring configuration.
Wiring Instructions
Step 1 – Power Connection
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Connect a 12V DC power supply to the VCC (+) and GND (-) terminals.
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Suitable sources: 12V battery, 12V automotive system, 12V industrial power supply, or solar charge controller 12V output.
Step 2 – Load (Device) Connection
Wiring Example (Cooling Fan – Turns ON when engine compartment is hot):
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Connect fan’s positive wire → NO terminal
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Connect 12V battery positive → COM terminal
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Connect fan’s negative → battery negative directly
Wiring Example (Heater – Turns OFF when temperature reaches setpoint):
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Connect heater’s positive wire → NC terminal
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Connect 12V power supply positive → COM terminal
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Connect heater’s negative → power supply negative directly
⚠️ Safety Warning: When working with 110V/220V AC loads, ensure all connections are properly insulated. Use appropriate gauge wire and mount the module in an enclosure. For automotive applications, use automotive-grade wiring and fuses.
Setting the Temperature Threshold
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Power on the module with the sensor placed in the target environment.
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Use a small screwdriver to adjust the potentiometer on the board:
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Turn clockwise (CW) – Increases the temperature trip point (relay triggers at higher temperature)
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Turn counter-clockwise (CCW) – Decreases the temperature trip point (relay triggers at lower temperature)
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The green LED illuminates when the relay is activated.
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Test by applying heat (e.g., warm breath, hairdryer, or heat gun on low setting) to the thermistor to verify the relay switches at the desired temperature.
Sensor Placement Tips
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Place the thermistor probe in the area you wish to monitor (engine bay, enclosure, greenhouse, refrigerator).
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For liquid temperature monitoring, use a waterproof thermistor probe (sold separately).
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Avoid placing the sensor near the relay or power components, as they generate heat.
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For surface temperature monitoring, attach the thermistor to the surface using thermal tape or epoxy.
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Sensor cable can be extended up to 30 meters using 2-conductor shielded wire (22–24 AWG recommended).
Q: Does this module require programming or an Arduino?
No. The module is completely standalone. Simply apply 12V power, adjust the potentiometer, and connect your load. No coding or microcontroller is required.
Q: What is the difference between the 12V and 5V thermistor relay modules?
| Feature |
12V Version |
5V Version |
| Supply Voltage |
12V DC |
5V DC |
| Typical Applications |
Automotive, industrial, solar |
USB, Arduino, hobby |
| Sensor Cable Length |
Up to 30 meters |
Up to 5 meters |
| Noise Immunity |
High |
Moderate |
| Automotive Compatible |
Yes (direct 12V) |
No (requires regulator) |
Q: What is the difference between NO and NC outputs?
For safety-critical applications (e.g., heaters, engine cooling backup), using NC is recommended because a power failure will stop the load.
Q: Can I control a 220V AC fan or heater with this module?
Yes. The relay is rated for 10A at 250V AC, which is sufficient for most fans, small heaters, pumps, and lights. Always ensure your load current does not exceed 10A. For AC loads, connect the live (hot) wire through the relay terminals; neutral connects directly.
Q: Can I use this module directly in a car or truck?
Yes. The module operates on 12V DC automotive systems (10.8V–13.2V). Connect to a switched 12V source (e.g., fuse box, accessory power). For continuous monitoring, connect directly to the battery with an inline fuse (1A recommended). The module can control radiator fans, auxiliary cooling fans, or interior heating.
Q: What is the temperature accuracy of this module?
The module provides approximately ±2–3°C accuracy. For precise temperature control applications, calibrate the trip point using a reference thermometer. The potentiometer allows fine adjustment.
Q: Why does my relay click on and off rapidly near the setpoint?
This is normal if the temperature fluctuates exactly at the threshold. Unlike digital controllers, this analog comparator module does not have built-in hysteresis. To prevent rapid cycling:
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Adjust the potentiometer slightly to move the threshold away from the fluctuating temperature
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Add a small heater or cooler to create temperature separation
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For applications requiring precise hysteresis, consider our digital temperature controller module
Q: Can I extend the thermistor sensor wires?
Yes. The 12V version supports sensor cable extensions up to approximately 30 meters (100 feet) using standard 2-conductor shielded wire (22–24 AWG). Longer runs may affect accuracy due to wire resistance and noise pickup. For best results, keep wires away from high-power cables.
Q: What is the maximum temperature the sensor can measure?
The NTC thermistor can measure up to approximately 100°C (212°F). For higher temperature applications (e.g., ovens, engines, exhaust manifolds), consider a K-type thermocouple-based module or a high-temperature thermistor probe (sold separately).
Q: Can I use this module for both home and business applications?
Home users: Automotive auxiliary fan control, chicken coop heater, greenhouse ventilation, aquarium temperature backup, 3D printer enclosure cooling, garage heater control.
Business users: Server room cooling fan control, telecommunications cabinet temperature protection, solar battery bank thermal management, industrial control panel cooling, laboratory equipment protection, food storage monitoring, printing press temperature control, refrigeration backup.
