Sensor-less Soldering Iron Temperature Controller

Inexpensive temperature controllers for soldering irons on the market do not actually control the temperature. Most of them are simply current control using THYRISTOR and TRIAC. Then, I thought about making a Sensor-less Soldering Iron Temperature Controller that uses the temperature resistance characteristics of the ceramic heater.

CAUTION: This product is supporting up to 110V Solder Iron!

The value of the voltage generating resistor RV is selected to be 1/40 thru 1/50 of the resistance value of the ceramic heater at room temperature due to the characteristics of the resistance value-voltage conversion and comparison circuit used.

The soldering iron that I usually use is "goot CXR-41", and the ceramic heater used for this has a resistance value of approximately 175Ω at room temperature.

Therefore,

1/40, 175 ÷ 40 = 4.375

1/50, 175 ÷ 50 = 3.5

So I chose 3.9Ω. A cement resistor of about 5W is suitable for this resistor.

To adjust, first remove VR2 from the connector, and then use TP1 and TP2 to adjust the resistance of VR1 to approximately 600Ω. (In my case, the adjusted resistance was 606.8Ω)

After installing VR2 and RV, attach the soldering iron and power supply to their respective connectors.　Turn on the power and rotate VR2 to about halfway, and wait for the soldering iron to warm up sufficiently.

The green LED lights up while the soldering iron is energized.　When the temperature reaches the set temperature, the power is automatically turned off and the green LED turns off. Therefore, the green LED blinks during automatic temperature adjustment.

Adjust the temperature by turning VR2 using a soldering iron temperature gauge.　It will take some time for the temperature to become constant.

Mark the desired temperature, such as 300℃, 320℃, 340℃.

The temperature of CXR-41 will exceed 500℃ if nothing is controlled.　Using this Sensor-less Soldering Iron Temperature Controller, you can now solder for a long time at your desired temperature.

Good Luck!