By George Dowell, K0FF
Weller soldering guns operate as a transformer with a single turn short loop secondary. A low voltage developed in the secondary loop is essentially short circuited by the copper tip. The tip is smaller in diameter than the main loop, so has higher resistance, therefore gets hot faster (Kirchhoff's Law).
Near the tip, very strong magnetic fields are created. Since they are alternating, we can do a couple of things unintended by the inventor, all non soldering related!
If an object that is capable of being magnetized is placed within the loop, the power turned on for a moment, then suddenly turned OFF, with the object held stationary, the object will become magnetized by the sudden collapsing of the magnetic field.
On the other hand if the object is already magnetized and you wish to DEmagnetize it, first apply power to the soldering gun, with the object at a distance. Then bring the object into the loop, and slowly withdraw it again, all the while, the power remains ON.
This slow decreasing of the magnetic field will effectively DEmagnetize the object.
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