A hot glue gun is one of those standard tools of the hardware hacker’s bench, called upon to provide adhesion between an astonishing range of materials, and to provide a handy filler and strain relief in the form of blobs of polymer glue. We’ve all got one, but how many of us have taken a look inside it?
[Andrew Lorimer] bought a super-cheap eBay glue gun, and subjected it to a teardown. As you might expect, he found it to be a pretty simple device with only a trigger mechanism and a dumb heating element, but his write-up is of passing interest because he’s characterised its heating element. It has a positive temperature coefficient, which means that its resistance increases from around 2.5 kΩ at room temperature to about 7 kΩ at its 150 ºC operating temperature. This limits the current, and provides a very simple thermostat action.
The build quality is surprisingly good for such a cheap appliance, and he notes a surfeit of screws holding its shell together. But the quality of the insulation and strain relief leaves a lot to be desired, and he wonders whether it truly qualifies for its double-insulated logo. The LED pilot light is simply fed from the 240 V mains supply through a 250 kΩ resistor which he replaces with a 12 kΩ component for a brighter result.