Soldering gun
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A soldering gun is in effect a transformer. The secondary winding has very few turns of heavy copper wire or bar, and generates a high current at a very low voltage. The bit is made of thinner copper wire, and so has a relatively high resistance. This causes the bit to heat up. One of the advantages of soldering guns is that they take only a few seconds to heat up, and also cool down rapidly after being switched off. They are also powerful, making them ideal for tasks such as soldering together small metal sheets and tubes. They typically produce from 50-200 W of heat.
One disadvantage is the heat regulation must be done manually; if the worker fails to regulate the temperature by releasing the button heat-damage to printed circuit boards may occur. Another disadvantage is that copper wire loop slowly dissolves in the solder and has to be regularly replaced. Third disadvantage is that the soldering gun generates electromagnetic spike when the button is released, this is not good for static sensitive devices. The spike can be seen when a high-efficiency LED is soldered - the LED flashes.
Soldering guns may also be used to solder the small SMD components, after replacing the default thick wire with a thin one. If the wire loop is bent into a rectangular shape, the gun can be used to solder 14- and 16-pin 1.27mm pitch SMD packages in about 8 seconds by heating all pins at once.
The tip shape in form of wire loop is advantageous for getting into confined space - the tip can be rotated to get into a gap between neighbouring components. This is not possible with the cone shape of usual soldering iron. This advantage is more pronounced if working with thin wire loop and SMD components.
Temperature in soldering gun is regulated manually by holding the button until the solder melts, and then releasing it. When it's about to start solidifying, the button is pressed again and so on. An experienced worker develops automatic feedback reflex to regulate the temperature according to immediate need.
