My glue gun gets fitted with a white LED light to show that it is plugged in and switched on.

 My cheap glue gun has the bare minimum of parts, and did not include any means to indicate its power status. Several times I had assumed that my glue gun was ready to use, and strained at the trigger, only to realise that it was cold.

  The reverse would happen as well: I would have finished with it, and assumed that it was switched off, while in reality it was hot and just waiting to burn me when I handled it carelessly, without realising that it was hot and dripping with molten glue.

 The solution to this was obvious: Fit it with a light that would be shining whenever it was plugged in to the mains. This would be great for discovering those pesky loose mains sockets, which would accept the plug and hold it in but (treacherously) not supply power to it.

 The glue stick is transparent - the ones I use are, anyway - so the light is arranged to shine into the glue stick , making the part sticking off the rear of the gun glow brightly.

Warning:    The entire circuit is connected directly to the mains, and so is a shock hazard. All circuit components are at high potential with respect to ground. If using it in a device with exposed metal parts extra insulation with a minimum creepage distance of 6 mm is required between parts of this circuit and the metal parts that can be touched.

Step 1: Dismantle the gun

The first step was to unfasten the six screws holding the glue gun together and pull it apart. Inside the glue gun, there are only two shrink wrapped joins, where the mains cord gets connected to two teflon insulated wires coming from the heater. If you are careless while trying this and break off the wires like I did you will have to crimp the wires on again.

 On the underside of the glue chamber is a thermistor which heats up to a constant temperature. It has a positive coefficient of temperature, and self regulates its temperature to the melting point of the glue. If it is colder, it draws more current and heats up. When it gets hotter, its resistance increases and so it draws less current and thus cools down. Thus the glue is effectively held at a constant hot temperature.

Since it gets hot solder would melt off, so the wires are crimped on to two metal plates contacting the heating element.

The modification involves soldering on two more wires to the mains cord so that the added lamp can run off the voltage coming into the glue gun.
Great instructable! I like also like how you used hot glue to fix your hot glue gun.<br><br>How much can the circuit be simplified? Could I use two LEDs in antiparallel and omit the rectifier (would then need a non-polarized smoothing cap)? What would be the consequences of removing the tantalum capacitor?
You don't know if that works until you try it out, do you?
Works great thanks for the 1 hour project!
Would the LED and the other components be able to stand the heat that build up in the glue gun?
what type of capacitor is the one with 250v 0.15microfarad. I like your project and i wanna do it for my glue gun too. But im stuck with the capacitor. Help me out
It might be &quot;metallised polyester&quot; Googling for &quot;150n 250V capacitor&quot; might bring up a few suppliers.
Very nice, and the gluestick takes the light well. Wish they would come with this. Or else colour changing like those shower heads so you can tell if it is hot or not. Me, I would just use a neon rather than an LED, because I am lazy...
This would work for one's cheap soldering iron (pencil style) too
I have to admit, this is a LOT more elegant than my solution to the problem....I added a switch to the line (mine was so cheap there was no &quot;switch&quot;), and placed a resistor and neon bulb in series with the switch (on the outside of the switch case), so I knew when it was on or not.
This is a really good idea. I've lost count of the number of times I've left my glue gun on by accident!
Really nicely done. Thanks for the extra info for the 110v folks. I can think if about 4 places I want to make use of this circuit, starting with my hot glue gun (Which has a light, but I never see it) and ending with my sewing machine (Which has a light but it's really weak.)
Be really, REALLY careful about insulating it if you are using it on an appliance with exposed metal parts (like a sewing machine).
how did you use hot glue if the glue gun is in pieces??? lol just kidding, you must have another. great instructable! i might do this with my glue gun, since it has done this to me before. thanks!
I placed scraps of hot melt glue around the wires, and used my warm (not hot) soldering iron to melt it into place. I have just this one glue gun, but I used to work with hot melt glue even before buying it, melting it on the tip of a warm soldering iron.
I like the idea of shining it into the glue stick so you can see it at a glance. Going to do this to mine, as I always end up forgetting if I left it plugged in or not. This way, I can just glance over and see if it is on.
Very nice instructable! I like your explanation of the circuit and the role of each part.

About This Instructable


35 favorites


Bio: Employed as an Engineer in Electronics. Interested in building small circuits around tiny chips (the electronic kind).
More by neelandan: Wireless L E D 9V battery case for projects Stereo amplifier, dead bug style
Add instructable to: