Oct 172012

I actually never have my own station. I always have been using cheapest soldering iron without any regulator. Of course I has access to such equipment in work, but it’s not the same. And I quit that work lately.

My first attempt to improve my iron was to add a diode serially with heater. It cut out half of the supply sine, so the iron works with the half of its power. I’ve added also a switch parallel with the diode which allow me to use also the full power. That improvement let me to decease power when the bit becomes too hot.

About a week ago I decided to build a real station. I bought an iron (Solomon SL10: 24V, 48W with thermocouple). Most expensive part – transformer I already have, thanks that I’ve saved a lot of money.

Here is the schematic (click to enlarge):


P1 is where you set the temperature, with P2 you could calibrate the device. It could also display temperature using attached panel voltmeter. I’ve selected resistor values to work with digital voltmeter in range of 20.00V (0.01V correspond with 1°C). IC1A amplify voltage from thermocouple to achieve this range. Using S2 you could select which temperature you’d like to measure (real or set).

P1, R1 and R2 makes the temperature range which you could set to about 150-460°C. IC1B works as comparator, it powers up OK1 whenever the amplified voltage from thermocouple is smaller from the voltage from P1. I’ve used this optotriac instead of connecting T1 directly to cancel out the noise generating during heater powers up (MOC3041 have build-in zero detector).

Because my transformer has 2x12V output (not a single 24V) I was able to install power selector switch (S1). I could select heater voltage (12V/24V) by this switch. In practice it turns out to be very useful, especially that I have build such simple regulator without thermocouple compensation. With full power iron gains heat quickly but if I need stable temperature to solder some SMD I could switch to 12V and it is able to hold selected temperature very accurate (it changes +/- 2°C).

Only thing that I want to improve is to change the soldering iron. Solomon SL10 has termocouple too close to the heater. In result the bit temperature is significantly smaller than measured one. But what to expect from 10$ iron.


Q29 noticed that C1 capacitor polarity was reversed, I’ve corrected the schematic.