DIY Hot Air Soldering Iron Using 12-18volts DC at 2-3 Amps

This is my first eva posting of a DIY article on the web. So excuse me for some typo stuff, protocol etc. The following instructions show how to make a WORKING hot air soldering iron suitable for ALL uses requiring soldering. This hot air soldering iron is not limited to SMT (surface mount technology) devices or super thin soldering wire. In under 15 seconds from turning this baby on, I reached in excess of 300 degrees centigrade hot air. I still had room for more...lol. The cost for me was under $10 Australian dollars. plus petrol for my car to get to the local dump and back home again. If you don't have a regulated power supply, I am sure an ATX power supply or two hooked up in series together would deliver enuff gutz to power up your version. If you do it this way, a potentiometer is essential for adjusting amperage output as well as DC voltage. This hole unit is SAFE from electrical shock due to high voltage/current hazards typical of mains powered AC supplies, but if you have a poor ticker...use protection :)

Step 1: From the Rubbish Dump Into My Home

I didn't have much faith that I would be able to get anything useful out of these hot air guns when i bought them at the local dump for next to nothing. After I pulled them apart, some bits worked and others did not. It was just a matter of throwing away the useless bits and keeping the good and then some more for spare later on should my iron fail in years to come. Once I had collected what I thought could be useful to make my idea reality, I laid them all out before me and pondered over them with a few coffees and cigarettes.

INTRODUCTION: Yesterday morning, my 50 watt soldering iron shat itself. Tragic I know...lol. The main tragedy was that I had no $$$ to get another. Well I had sum money, but not enuff to get me another one. I am a freelance photographer, a poor one at that and am working on using PWM (pulse width modulation) to regulate voltage supplies from small lead acid batteries scavenged from old battery powered scooters. The electronic stuff to make my PWM voltage regulators I get from desoldering old ATX power supplies and televisions etc.. Linear regulators are too inefficient to meet my portable needs for power, as this power will ultimately be used to control my off camera flashes and other stuff. Anyways, back to the meat of this presentation :)
A two hour Google search on the WWW revealed sum people converted their soldering irons into hot air solder irons. But they were all working before they modified them and mine was deadfrom the outset...lol. Also the other creations I saw on the web were largely confined to removing the smaller SMT electronic bits. I did notice that in my quick review of other peoples "creations" that they all had the same basic flaw and problem: exposing enough cold air passing through their devices to heat at the element before leaving the solder iron. Most people came up with ideas of inserting copper or iron mesh into the barrel near the element to increase the surface area of the heating element exposed to the passing through colder air.
My experience with this method used by others, reminded me of my earlier Peltier cooling experiments I later used for my marine aquarium....that was with heat transfer problems. Oopsy...got side tracked ;) Anyways, I always wanted to remove bulk components from PCB boards using those coal guzzling paint stripping hot air guns. But I haven't got the $$$ for that either! So I figured on making a soldering iron that could act like a hot air gun and also a delicate soldering iron. So after several cups of coffee and many cigarettes and many more Google searches, I had in the back of my mind some idea of all the gadgets I needed to get myself a working soldering iron...off to the local dump. I love the dump...so much useful stuff and cheap too!! Much like going into a hardware store to window browse. $10 ozzy dollars later I left the dump with 2 laptops and three paint stripping hot air guns. The guns had seen better days and I didn't have much hope at getting anything out of them that might work. The laptops I am keeping for their LCD screens that I will use for my DIY movie projector :) But that is another project. At home, I pulled the the air guns apart. I love pulling things apart...something I never grew out of as a kid. SORRY mumsy and dad!!!

Step 2: The Fan

Part of the fan assembly from the paint stripper blowers. 17VDC fan shown here. I removed the bridge rectifier and capacitor and used this type of fan, as it was all I had to deliver air into the soldering iron. This proved to be a lucky situation later, as I had the right amount of air flow passing through and in direct contact with the heating element.

Step 3: Blower Unit

This is the essential blower unit that delivers cold air through to the heating element. I used this entire assembly as the means of pumping air. How I was going to connect this thing, I had no idea.

Step 4: Heating Element

Don't forget the heating element. When making the long lengths of straight wire, crimp out the curves and make sure you don't have any sharp bends. Current does not like turning sharp corners.

OVERVIEW: I found two fans had worn bearings and one was just fine. I had two broken heating elements and some ceramic insulating disks and tubing. There really is not much to these babies at all...makes me wonder why they are so expensive. All they are is a heating element and a motor. A bridge rectifier stood between AC mains voltage and the air blower motor. This was encouraging as I wanted to run my power supply for the idea in my head from low DC voltage. I don't like playing with mains 240 volts AC. The motors were rated to 17volts DC. That is close enough to my desired 12volts DC. I powered my chosen fan that didn't have rattling bearing and it worked. Kewl.
I also saw that one of the guns had hollow cylinders of ceramic that were used to hold the heating elements. I inserted one of the cylinders into my soldering iron metal tube. It fit perfectly. That was very encouraging too. I still had no idea as to what the final idea would be like. Be adaptive and use what is available is my motto. I had earlier pulled my dead soldering iron apart too to see how it worked and if I could fix it. It's element was stuffed. I also noticed that it relied on conductive heating to heat the tip. My concept from the beginning was to pass cold air through the hollow barrel, expose it to a heating element and have hot air forced out of the tip. Much like a mini hot air paint stripper. This concept never changed, but the ideas as to how I reached this end were constantly changing, as I engineered numerous new ideas with what I had available in front of me on my work bench.

Step 5: Close Up of Element

The idea in keeping the straight lengths long is to have some room to play with when putting it all together. The final length decided on was slightly larger than this one. I shorted this out on the 12 volt battery and even though the battery was half dead, I was able to get some kewl heat from it. I figured some extra lengths of coil may help desensitize temperature fluxes during slight voltage changes.

Step 6: Ceramic Tube

I thought this tube would be the best thing since bacon and eggs, I wasn't disappointed :) This is one of the insulator rods used to separate the heating elements from each other inside the hot air guns. The element ran over the outside of this rod. I aimed to place the element inside the rod and have cold air passing into it and super hot air passing out of it. How this would all come together, I still had no idea as yet...except some wild images of what the end product could do and look like.

Step 7: The Element and Ceramic Tube

This is essentially the operating end of everything.

OVERVIEW: First off, I needed a heating element. I figured I could down size the broken heating elements rated for 240 volts AC to fit inside the ceramic tubing and have it run quiet well on twelve volts. The amperage was an issue to worry about and could be fixed by varying the length of coil to get the desired heat output. Too much coil and I will need to use more volts and/or amps...too little and I overheat the coil and snap the link. I experimented with a few lengths of coil using power from my small 12 volt lead acid batteries and found a length that gave off enough heat (145 degrees centigrade) as a starting figure. I inserted the coil into the ceramic tubing, ensuring I had no sharp bends and sufficiently long lengths of straight wire running from the coil. The long lengths were to give me enough room to play with when I go to fit this baby inside the shaft of my soldering iron. Also the long lengths enabled me to place the heating element further away from the handle of the iron. It would seem that the entire solder iron was made to be reverse engineered for use with hot air flow. I notice other people on the web have had similar thoughts.

Step 8: The Gutz

The basics of it all. Not much really. But damned effective beyond what I expected.

OVERVIEW: With the element inside the solder shaft I noticed I had to isolate the the lead running up the outside of the shaft from the metal casing. I had several different sizes of heat insulating tubing that would fix this. Next, I had to reshape the shaft slightly into an oval shape to fit the ceramic heating element with the added wire heat insulation tubing. The next step was to see if I could still have air pass through the element with the added insulation. I could see light through the other side of the shaft that said to me it was all good. Now the easy bit was to use the wire terminal joiners previously used by the iron to join the heating element ends to the battery power wire ends. I used the 240 volt AC cable previously used for the iron as I wanted a thick wire capable of handling some amps.

Step 9: The Nozzle

The nozzle is actually what used to sit inside the iron. The heating element for the 240v AC supply was wrapped around this and the copper heating rod used to solder stuff sat inside the hollow tube.

OVERVIEW: I marked on the handle of the plastic cover where there would be a hollow space for me to drill a hole and insert some tubing once the unit was together. Air would later be pumped through this tubing. This was important to get right, so I used calipers and a few marks to get the right length. The next problem I encountered was to get a nozzle for the tip. I reversed the inside shaft previously used to hold the heating element and dremelled the flange and it fit perfectly. I now have a nozzle!! Next step was to use a nozzle from my aquarium that would fit into the handle and fit also the plastic tube that will have air flowing through it. I drilled a hole where "X" marked the spot, being careful I didn't have too much pressure on the drill. I would have done this with the gutz removed but felt I could get away with not perforating the innards if I was careful. This arrangement worked, but is only temporary as I want to see if the concept worked. I will later add some mechanical retention here by using a screw nipple or something. With the solder iron nearly fully together, I needed to tackle the issue of getting air into the thing. I had no air pump used for an aquarium. I have an aquarium, but don't use them, they are so inefficient. What I do have is the bad ass air blowers from the hot air guns I got from the dump. These babies are huge compared to the small tube I have to run into the solder iron.

Step 10: Square Peg in a Round Hole

My biggest challenge was deciding how to fit my small hose to a huge blower outlet with what I had lying around the house.

OVERVIEW: I journeyed into the back shed and gathered all the tubing and bitz that I thought would be useful and began to fit a square peg into a round hole. I ended up using a piece of tube from an old washing machine, a garden hose connector, a small piece of 1/4 inch tubing and a brass gas nozzle and heaps of surgical tape. I turned the air blower on and got a nice breeze of strong air at the end of the tubing. The design will be fixed up later concerning the airflow obstructions etc that exist with this contraption. I aim to work on the venturi effect to further increase air output at the nozzle without increasing fan speed. I then simply hooked up the small tube into the nipple protruding from the solder iron handle.

Step 11: All the Stuff Is Here

The blower and soldering iron is all there is to this.

Step 12: Candle Blower :)

The strength of the hot air is the key to removing all that good hotness from the heating element inside the soldering iron. Trial and error should get you the right amount of airflow through the heating element that will effectively heat up the cold air blown into the heating chamber and out of the nozzle to a desired temperature. Too fast an airflow and the air will not have enough time to heat to the desired levels. I think I struck it lucky as I did not have to worry about this bit. The added benefit of having a coil used for heating with air flowing into the chamber containing the heating element, is that the resultant turbulence distributes the air more evenly reducing energy losses during heating of the cold air.

Step 13: Regulated Power Supply

This old faithful ex R.A.A.F. unit will live beyond my years. So many features and made in Australia. This is the desired peak operating stats that reached 310 degrees centigrade. It took me under 15 seconds to reach this temperature from a cold start. Far better than waiting several minutes for a stock standard soldering iron to heat up. I note that at 16 volts, peak temp was at 270 odd degrees centigrade. At 18 volts, peak temp was 310 degrees centigrade. So I can figure out the maths as far as predicting temperature ranges exiting the nozzle at assorted voltages and amperage. The linear distance between theses ranges is of course determined by gauge of element wire, it's length and also the CFM of air flow through the nozzle.

Step 14: Temp #1

Temperature of room. Ready for the big show...lol

Step 15: Temp #2

Switched on and rising. Watching those numbers rise was a real rush. I noted the element inside the shaft was not glowing at all yet when I looked up the spout, showing me that I could substantially reach higher temperatures before element failure, using the heating element wire from the butchered paint hot air guns. Once I have made a more permanent work piece, I will be experimenting with various nozzle diameters, as I think a smaller nozzle would be excellent for removing single components and a broader nozzle for IC chips and stuff.

Step 16: Temp #3

I got 310+ degrees centigrade. Could have got more but wasn't needed for what I intended to use this baby for. Also was getting too paranoid about watching those numbers rise...rofl

OVERVIEW: I turned on the blower and found several air leaks. I sealed them up with solid setting putty. The moment of truth is near. Now I needed a a power source. I thought of small transformers but wanted variable supply of voltage and amperage, so I could figure out peak operating conditions. I retrieved my old AUSTRALIAN MADE voltage regulator (ex R.A.A.F. stock) and hooked her up to my iron. All the stuff made today that we get is made in China and is unreliable as all hell. This baby was made to last and work. I had the fan connected to my battery pack separate to the solder heating element. The reasons were obvious :) I lit up a smoke and prepared for the worst....
I started at low DC voltage...the amps are automatically calibrated by the regulator. I had my multimeter set aside to measure temperature of hot air. To make a long story short (lol), at 16volts DC and just over 2 amps...temperature reached was 275 degrees centigrade...KEWLIES!!! I reached my target temperature. I cut through 1mm solder wire like swiss cheese. I was able to remove LED's from a PCB board without even frying them or my fingers which held the LED's from the other side of the board. The metal shaft on the soldering iron was much COOLER than it was when running under 240 volts. I could touch the metal shaft without burning my fingers. It was rather hot where the element is though, but still cooler substantially. What makes mine different from the other creations I saw on the WWW? I have a coiled heating element with a huge surface area of good hotness (lol) that has cold air passing directly through them. The other units I saw use the heating element from the original solder iron, a copper conductor rod that absorbs heat from the element and sends the heat to the tip, some wire mesh in the air cavity to increase surface exposure to cold air exposed to heat. I removed all those conductive barriers and increased efficiency by heaps.

Step 17: Melting Solder Wire

Melted this bundled ball of solder wire like ice cream in the summer sun

Step 18: First Ever Job

I removed these from an old PCB in no time flat.

OVERVIEW: Once I get some longer plastic tubing and rework this prototype into more permanent arrangement, I will have enough spare parts to look after this baby for years to come. Improvements I will make are to rig up temperature settings via trim pots and use my other bitz and pieces to rig up an LCD panel with settings displayed such as temp, voltage and amperage and of course a few fuses and maybe a capacitor across the motor. I already know the mean operating condition and can adjust accordingly from there. One point to remember, is that when turning off the unit, turn the element off first, let the air pass through for a minute to cool the unit down. I will implement a timer for this bit later. Of course I cannot do this without a working soldering iron, but now I have one...