DIY 12v Hot Glue Gun

Ever wanted a semi-portable hot glue gun? Yes, I know you can buy them off of Ebay and the like, but if you do there will be a couple of months wait, and they are about the same price as this one. And why are you here? Its because you're a maker! It is a very easy (and inexpensive) task to make one yourself, and you get a pretty cool and useful tool to play around with too- so why wouldn't you want to build one!

This hot glue gun heats up from cold in about 45 seconds, and consumes 1.52 amps at the 13.8 volts of a car cigarette lighter socket, for a power of 21.08 watts. After an initial warm up, I found that you could get about 4 minutes of gluing for every minute of holding the button down, which is very usable. You can go through an entire stick of glue at once after heating it up, without touching the button, if you so wish! This is perfect for field repairs of drones/ radio controlled planes, as well as general repairs or makings if you don't have access to mains power!

Step 1: So, What Do You Need?

The parts list for a 12 volt hot glue gun is actually rather small. I have listed the components (and prices) from Jaycar electronics here in Australia (to support a local business) but I am sure you can find the same parts online if you can't find any at your local electronics store.

Parts required:

Donor hot glue gun- 7mm sticks use less energy to melt- Part number TH-1997, cost: $12.95

Cigarette lighter plug- Part number PP-2008, cost: $4.95

Push-to-make switch SPST (momentary, must be rated for am least 2 amps)- Part number SP-0741, cost: $1.95

White LED, 5mm

Current limiting resistor- suitable for the LED you use

10 watt wire wound power resistor- Part number RR-3352, cost: $1.80

Heat shrink tubing (not essential but nice to have)

Thermal adhesive (not essential but makes assembly easier)- Part number NM-2014, cost: $7.95

Total cost (not including LED and thermal adhesive): $21.65

Obviously, there are some basic tools you will need too:

Side cutters

Soldering iron (and solder)

Scalpel (or a really ridiculously sharp and thin knife)

Phillips screwdriver (or whatever bit you need to disassemble your donor hot glue gun)

Superglue (cyanoacrylate) or similar adhesive

Pliers (not essential but useful)

A second, working hot glue gun (but you can get away with insulation tape)

A rotary tool

Step 2: Don't Turn It On, Take It Apart!

No, seriously. It is much easier (and safer) to work on when the glue gun is cold and there is no glue inside the barrel of the glue gun. It is, however, possible to do this on an older glue gun, it is just simpler to do if the glue gun is clean.

Remove all the screws- you want to be able to take the cover plates off. The stand will most likely have to be removed as well. MAKE SURE THE GLUE GUN IS UNPLUGGED! 240 volts AC is only dangerous if you work on the glue gun whilst it is powered.

After you get in, the trigger assembly has to be removed to access the heater barrel and the (no longer wanted) 240 volt AC heating element. Remove the silicone caps on both the nozzle and the inlet sides- you want to be working with just the metal piece.

Finally, remove the metal clip that holds in the heating element. Make sure you don't damage the kapton tape wrapped around the element as it is reused to make the 12 volt heating element. Also, as can be in the last image, the metal walls holding the 240 volt element in place were removed too. Although not strictly necessary, removing this gives more room in the case of the glue gun.

Step 3: Now, Add Heat

Getting heat from electricity is actually really, really easy. All you need is a source of resistance and a flow of electrons though it. However, if the resistance is too high it will not heat up enough, and if it is too low too much power will flow, resulting in too much heat (and leading to the magic smoke being released).

To ensure we don't release the magic smoke, there are two things to consider: what voltage is being used and how much power you want converted to heat. Since I wanted this glue gun to run off of 12 volts the resistance can then be changed to give the power required.

In the end I decided on a power of 14 watts. This is 4 watts more than the glue gun claims to use from 240 volts, but this isn't an issue, as it will merely decrease the time it takes for the glue gun to heat up.

To work out the required resistance, we can substitute ohm's law into the power equation, giving us r = (v^2)/P. By substituting the given values, this give us a required resistance of 10.2857 ohms.

To do this you could purchase some nichrome wire, and measure out a length resulting in 10.2857 ohms. However, to make it easier I used a pre-made form of resistance: a resistor. The closest wire-wound resistor I could find has a resistance of 10 ohms, giving (from the previous formula) a power consumption of 14.4 watts.

But wait, I hear you say, isn't that resistor only rated for 10 watts according to its own label?!! Well, yes, but that rating is when the resistor has no additional cooling. In this case, the resistor is attached to a large metal barrel, and additional cooling is supplied by the glue itself, as it has to heat up to melt!

To make the new heating element, the first thing you have to do is use a pair of pliers to remove the ceramic casing from the resistor, and carefully unwind the resistance wire. Be careful- it is quite thin and easily broken. I don't know the exact composition, but this resistance wire is good because you can actually solder to it, unlike nichrome wire.

Now, I hope you saved the kapton (polyimide) tape that was wrapped around the 240 volt element. This was wrapped around the hot glue gun's barrel and held in place with thermal adhesive (I held it in place with some electrical tape until the adhesive had dried). This insulates the barrel from the resistance wire.

After the thermal adhesive had dried, the resistance wire was then wrapped around the barrel. This was secured at each end by wrapping it around itself a few times.

The finished 12 volt heater assembly can then be tested by connecting it to a 12 volt source. I saw a current draw of 1.323 amps at 12 volts, for a power consumption of 15.889 watts. Now, we did work out a power consumption of 14.4 watts. However, I did end up shortening the resistance wire a bit when it was wrapped around itself, giving a resistance of 9.03 ohms. The added power sees the glue gun heating up even quicker, useful for something that operates portably.

The power consumption of something like this, with very low resistance, will change quite a lot with small changes in voltage- I measured 1.323 amps at 12 volts, but 1.52 amps at 13.8 volts!

Finally, reassemble all the silicone parts back onto the heater barrel.

Step 4: Just Add Power!

A resistor will not produce any heat unless you apply a potential difference (voltage) across it. Since this hot glue gun was designed to run off of the12 volt circuit of a car, a cigarette lighter plug makes perfect sense as a power connector.

A cigarette lighter plug was purchased- I got one that came with a fly lead attached, terminated to a 2.5mm DC socket- but because I didn't want a removable cord, and wanted the build to look neat, I had to modify it.

The wanted component is the cable strain relief, from either the cigarette lighter plug or from the 240 volt mains cable (that came with the original hot glue gun). I found that the strain relief on the cigarette lighter plug looked easier to remove- so that's the one I worked on.

The aim is to remove the strain relief from the red and black wires that the cigarette lighter plug comes with and install the strain relief on the sheathed cable that comes with the hot glue gun. This results in a nice looking finished product, as the strain relief on both the cigarette lighter socket and the hot glue gun looks professionally done.

The only way (I found) to remove the strain relief from the cigarette lighter socket it to cut it away from the cable its attached to. You will have to desolder the original wires from inside the cigarette lighter socket, and remove them and the strain relief from the actual connector.

If you look closely, you can see the seams from its molding process. To remove it, simply cut down those lines. If you use a thick knife (box cutter etc), you are left with a wide gap that is not too pleasant to look at! Instead, use an x-acto knife or a scalpel, which gives a much narrower cut.

After having split the two pieces, you need to measure the length of wire inside the cigarette lighter plug, as well as the length of the strain relief. Then, cut off the mains connector and strip this length from the cable's outer sheath- DO NOT cut into the insulation of the conductors inside, as they will be next to each other inside the strain relief.

Then, glue the strain relief halves around the conductors of the mains cable. Make sure the end of the strain relief is flush with the end of the cable sheath for a professional look.

The final part is to strip the ends off the actual wires and solder them to the positive and negative contacts of the cigarette lighter plug, and then reassemble the cigarette lighter plug.

Step 5: Add Light to the Mix

Although not necessary, a light is a good thing to add, and the ease of doing this with a voltage as low as 12 makes it a no-brainer to install.

The only components required are a white LED and a current limiting resistor of an appropriate value. You could, of course, use any colour you like, I just happened to have a 5mm high brightness cool white LED on hand. White light is probably more useful than a coloured LED, but not as aesthetic!

You need to know two things about the LED, its forward voltage and its forward current. The LED I used has a forward voltage of 3.4 volts, and a forward current of 20mA, or 0.02 amps. To work out a value for the resistor, we can apply Kirchhoff's voltage law, which states that the sum of voltages around a circuit should equal zero. Thus, the voltage dropped across the resistor must equal 12 - 3.4 = 8.6 volts. We can sub this into ohms law, where r = v / i. Solving this gives us 430 ohms. The nearest value I had on hand is 470 ohms, so this value will be fine, giving the LED a current consumption of 18mA.

A hole was drilled in the plastic just below the nozzle. The case was screwed together for this- ensuring the hole was centred and keeping a high quality look. This was drilled parallel to the nozzle, meaning the LED points in the same direction as the nozzle, making the LED actually useful!

The LED was glued in with hot glue. If this is your first glue gun that you are modifying, then this can be held in pace with superglue too, just ensure the LED is a tight fit because superglue has no gap filing properties.

Step 6: Switch It Up

To turn stuff on and off, you need, well, a switch. There are two main kinds, momentary and latching. A momentary switch is what's wanted for this glue gun.

Whilst a latching switch sounds like a good idea, the form of heating element that's been added to this glue gun is not suited to such a switch. Because resistance wire has no thermal coefficient, the resistance does not change in accordance to the temperature. This is a very good thing for a resistor, but not for a heating element.

The 240 volt heating element has a positive thermal coefficient- as the temperature increases, so does the resistance. As this occurs, less current flows, and the element cools. This lowers the resistance, and the process repeats again and again. This is a self-governing process.

However, the resistance of the wire does not change as the temperature increases. This means a constant power flows, and so the element doesn't cool down. I left the power connected for 3 minutes and the barrel heated up to over 250 degrees! This is probably (read: definitely) not an ideal temperature for a hot glue gun.

Therefore, a momentary switch MUST be used if you use a heating element of this style. This ensures the element cannot be left turned on, and reduces the risk of fire and other heat-related accidents. It just means the button has to be held down to supply power to the heating element. The power of the heating element means it doesn't have to be held for long to get hot enough to glue stuff.

A push-to-make switch must be used- this will send power to the heating element only when it is actually pressed. It must be rated for at least the maximum current of the heating element, in this case 1.52 amps. However, remember the 80% rule, such that you don't use more than 80% of a given component's capacity. The switch specified at the start is rated for 3 amps.

A hole must be drilled for the switch- in this case a 12mm one. A step drill ('Christmas tree bit') makes neat work for this. The switch can then be installed.

Step 7: Wire It Up

Electronic devices tend to not work very well without a way of actually getting electrons into the circuit!

The first part here is to ensure that the modified barrel fits into the original slot. If it doesn't, then remove just enough plastic so that it does fit. I had to remove a part of one of the screw posts at the top (as the new heating element increases the thickness of the barrel), but be careful to not cut into the threads, or the screw cannot be secured properly.

Then, the cable (and strain relief) was glued into the base of the modified glue gun. This was only glued on the bottom, so that the glue gun can still be disassembled (just in case). The positive wire (connected to the tip of the cigarette lighter socket), was then soldered to one pole of the switch. The negative wire had two extensions soldered to it (and the joint covered in heatshrink). One of these is a thicker cable for the heating element, and the second is a length of thin (30 AWG) wire to power the LED. The same thing (two different wires) was done to the second pole of the switch, one for the LED and one thicker wire for the heating element.

The two thicker wires were then soldered directly to the heating element. Hot glue (or superglue if this is your first hot glue gun) can then be used to route the wires, ensuring they cannot touch the heating element. Use a little bit more glue than necessary, because if the wires touch the element it will burn through the insulation and could cause a short. I also added some extra kapton tape around the heating element later, to help insulate even more (not shown). I would recommend you do the same (if you have any spare kapton tape). I did not put any heatshrink over these connections, as the maximum temperature of heatshrink is normally 180 degrees Celsius, whereas in extreme circumstances the heating element could be double that.

Next, the LED is wired up. Firstly, the previously calculated resistor can be soldered directly to the LED's positive pin (the longer one, or the rounded side). The thinner positive and negative wires can then be soldered to the LED, ensuring the polarity is correct (positive to the resistor, negative to the shorter leg/flat side). Heatshrink can then be used to neaten up the connections, and again when securing the wires ensure they cannot touch the heating element.

I'm not super satisfied with the way I wired up the LED, as it is only on when the button is on. In the future I may end up rewiring the LED, so that it is on whenever the glue gun is connected to 12 volts, which should be much more useful.

Step 8: Finishing Up

Almost done! Just a few more things to do to make the finished product look neat.

Firstly, we need to reinstall the trigger assembly. This is fairly simple to do, as its mounting method shouldn't have changed from when the glue gun was new, and should just slot together. Also, DON'T FORGET the little silicone O-ring that guides the glue sticks in. If you forget this you will forever be wondering (and cursing) why the new glue sticks keep falling out of the back of gun. Not that I know from experience or anything....

Next, the other side of the glue gun case can be reinstalled. This is where I made the mistake, as the switch was installed right where one of the screw holes was! Something that probably should have been checked before mounting the switch, and I would recommend you do the same. Removing the offending screw post (which was in the way of the switch) left a large and unsightly hole, which I wanted to fill in.

First, a rotary tool can be used to rough up the plastic and to neaten up the hole. Then, blue painters tape (but really any low-tack tape, can be used, but ensure it is low tack or you never get it off) to cover the hole from outside the case. This can then be smoother out so it follows the rest of the case exactly. Then the hole can be filled in form the inside of the case. You could use wood filler, epoxy, bog or a specially designed product, but I didn't have any of those to hand. Instead, I tried using hot glue to fill the hole. When the glue has cooled (give it at least 10 minutes or you'll have to start again), the tape can be removed, leaving a nice finish that follows the case lines well. The hot glue can then be coloured black with a permanent marker to integrate it even more seamlessly into the case shape and colour.

Finally, refit the top case half and screw in the remaining screws. Since I had removed a screw post, I used a very small amount of superglue to hold the handle together (only use a very small amount if you wish to ever get back inside the glue gun again). Add the stand and you're done!

Step 9: And Finally...

If you have followed this instructable, you will now have yourself a working 12 volt powered hot glue gun! I have found that this is a very useful tool to have- it is more useful than it sounds. This is because hot glue in general is a useful adhesive- it is waterproof, relatively strong, can be removed (with effort) and is quick drying. A 12 volt hot glue gun makes this useful adhesive even better- want to repair your RC plane at the field? Easy! Fix something while your camping? Done!

Thank for taking the time to read my first instructable, I hope you learnt something or gained a few ideas of your own! Let me know in the comments if you used any of the ideas presented here in any of your own projects!

Bye for now,

Jeremy