FridgeTroll

An ESPHome-based smart controller for SECOP compressor-driven refrigerators, providing advanced temperature management, stall detection, and telemetry.

Overview

FridgeTroll is designed as an off-the-shelf, installable firmware primarily targeted at the SECOP 101N2000 compressor controller (though it should work with most modern SECOP controllers). It replaces the standard mechanical thermostat with an ESP32, offering fine-grained control over compressor speed, dedicated fridge and compressor fan management, and rich telemetry for Home Assistant via InfluxDB and native ESPHome APIs.

Installation

You can use the button below to install the pre-built firmware directly to your device via USB from the browser.

Bill of Materials (BOM)

To build the FridgeTroll hardware interface, you will need:

• Microcontroller: Wemos S3 Mini (or similar ESP32 board)
• Power Supply: Wemos DC Power Shield (or similar 5V USB-C power supply)
• Fridge Fan: Coolerguys 12vDC Waterproof IP67 Fan (High Speed, 25x10mm) (or similar 12V DC fan)
• Compressor Fan: Noctua NF-P12 redux-1700 PWM (or similar 120mm PWM fan)
• Temperature Sensors: DS18B20 1-Wire sensors (x4 recommended: Fridge, Freezer, Compressor, Ambient)
• Optocouplers: PC817 (x3)
  • Compressor Enable Pin (T)
  • Compressor PWM Pin (P)
  • Door Switch Pin
• Transistor: 2N2222 NPN Transistor (for driving the Fridge Fan)
• Diode: 1N4007 or similar (Flyback protection for the Fridge Fan)
• Resistors: Various (for optocoupler LEDs, pull-ups, and pull-downs depending on your specific board layout)

Interfacing with the SECOP Controller

The SECOP controller provides several pins that need to be interfaced with the ESP32. Due to voltage differences (the SECOP can Output 12V/24V on some pins), opto-isolation is required for the compressor control signals and the door switch to protect the ESP32.

1. Compressor Enable (Pin T)

The compressor turns on when Pin C is connected to Pin T (or driven by a PWM signal).

• Circuit: Use a PC817 optocoupler. Connect the ESP32’s compressor_enable_pin to the optocoupler’s anode (via a current-limiting resistor). Connect the optocoupler’s collector to the SECOP Pin C, and the emitter to Ground.

2. Compressor PWM (Pin P)

This pin dictates the compressor speed.

• Circuit: Use a PC817 optocoupler. Connect the ESP32’s compressor_pwm_pin to the optocoupler’s anode (via a resistor). Connect the optocoupler’s collector to Pin T and the emitter to Ground (Pin P).

3. Compressor Fan

Controls the cooling fan for the compressor itself.

• Circuit: The Noctua PWM fan can be driven directly by the ESP32. Connect the 12V and Ground pins of the fan to a 12V power supply and common Ground. Connect the fan’s PWM pin directly to the ESP32’s fan_pwm_pin. Connect the fan’s tachometer pin directly to the ESP32’s fan_speed_pin (the ESP32 will handle the pull-up internally).

4. Door Switch

Monitors if the fridge door is open.

• Circuit: Use a PC817 optocoupler. Connect the switch across the optocoupler’s LED side (with appropriate resistor). The output side connects to the ESP32 door_pin (using INPUT_PULLUP) and Ground.
• Sensing Logic: To sense the door status, solder a +12V lead to the switched side of the stock door switch (the one that controls the fridge light). Ensure the “input” side of the switch has constant +12V. This allows the optocoupler to detect the 12V signal when the door is open/closed, isolating the 12V circuit from the ESP32.

5. Fridge Fan (Internal)

Controls the circulation fan inside the fridge compartment.

• Circuit: Use a 2N2222 NPN transistor to switch the fan’s ground connection. Connect the ESP32 fridge_fan_pin to the transistor’s base via a resistor (e.g., 1kΩ). Connect the fan’s negative lead to the transistor’s collector, and the emitter to Ground.
• Critical: Place a flyback diode (e.g., 1N4007) across the fan’s positive and negative terminals (cathode to positive, anode to negative) to protect the transistor from voltage spikes when the motor turns off.

Physical Installation & Wiring

Component Mounting

A successful FridgeTroll installation requires precise placement of sensors and fans for optimal thermal control:

• Fridge Sensor: Mounted inside the main refrigerator compartment to monitor food-safe temperatures.
• Freezer Sensor: Mounted inside the freezer compartment.
• Compressor Sensor: Mounted directly against the compressor body (using thermal tape or a clip) to monitor for overheating.
• Ambient Sensor: Mounted in the air intake path, directly in front of the compressor cooling fan, to measure the temperature of the air being used to cool the coils.
• Compressor Fan: The stock fan should be replaced with the high-performance Noctua PWM fan to allow the ESP32 to ramp cooling based on compressor temperature.
• Fridge Fan: This fan should be mounted to facilitate air exchange between the freezer and fridge. A great location is in one of the existing baffle holes in the drip tray between the two compartments.

Parasitic Wiring for DS18B20

To simplify wiring, the DS18B20 sensors are intended to be used in Parasitic Power Mode. This allows all sensors to share a single data line and ground.

• Wiring: For each sensor, tie the VDD (+) and GND (-) pins together and connect them to the system Ground.
• Data Bus: All DQ (Data) wires from the four sensors are connected together and run to the ESP32’s one_wire_bus_pin.
• Pull-up: Ensure there is a ~4.7kΩ pull-up resistor between the Data line and the ESP32’s 3.3V rail.

Cable Routing Tips

Reusing existing paths can save significant time and avoid drilling into the fridge chassis:

• Thermostat Rewiring: You can often reuse the wires from the original mechanical thermostat to carry the 1-Wire data bus into the fridge compartment, as well as the door sensor +12V.
• Freezer Access: Use the existing temperature probe tube (that originally housed the mechanical sensing bulb) as a conduit for the freezer DS18B20 wiring.
• Fan Cables: Fridge fan wires can often be sneaked through the same hole used by the refrigerant tubes to get from the compressor area into the internal compartments.