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From the Q&A

With TJ Byers

Iron Keeps Its Cool


Most of us in the shop work with an 80 W solder iron and would like to control its temperature in order to prolong the tip and iron life by preventing overheating. Can you please provide a simple yet effective diagram for a solder iron heat control device with a 120 VAC socket? This would also make a great project for beginners in electronics!

D. Zillbermann
via Internet


If you're talking about turning down the heat when the soldering iron is in the holder, then turning it back up when it's removed, the Tip Saver circuit below is what you want. This design simply inserts a diode into the AC line to reduce the average voltage to the iron. The thermal switch (available from All Electronics, 800-826-5432, is positioned so that it opens when in proximity to the soldering iron with the iron in its holder. The heat from the soldering iron causes the switch to open and reduce the AC Out voltage. When the iron is removed, the switch closes, shorting out the diode, and applies full power to the soldering iron.

If you're looking for a variable temperature controller for the soldering iron and want to keep it simple, check out the Temp Controller circuit below. This is your run-of-the-mill triac dimmer that's been reduced to the minimum number of parts. The temperature is controlled by varying the phase angle of the sine wave, creating a "dimming" effect just like in a light bulb. The limitation is that you can only guess at the temperature (or measure it and calibrate the dial) because there is no temperature sensor to control a feedback loop, as would be the case with a true thermostatic controller.