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Converting A Soldering Gun to Resistance Soldering

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  • Converting A Soldering Gun to Resistance Soldering

    I have been lusting after a resistance soldering setup for a long time now, but have always been put off by the price of commercial units. Even the cheap MicroMark setup -- on sale for the summer at US$139.99 -- gives me pause. The more industrial American Beauty (?) units cost upwards of US$400!

    Now I have this bug in my brain telling me that a classic Weller soldering gun should be easy to convert to resistance soldering. Such guns are available used on eBay for US$13 to US$30.

    The classic Weller brand gun I have in mind has two power ratings -- 100 and 140 watts -- depending on how far you pull the trigger. It has two electrodes which connect to the ends of a loop of copper -- the heating element that is used to contact and heat the work.

    So, remove the heating element, connect a ground wire to one electrode and insert a carbon electrode in the other. Connect the ground wire to the work, place the carbon electrode where you want to apply heat, and pull the trigger. Why won't that work?!?

    If you need a better way to throttle the heat, install a dimmer switch on the house-current side of the soldering gun.

    Now of course I have been all over the internet trying to see if this type of setup has been tried successfully. I have some indications it has, but not nearly as much as I would have expected.

    I'm this close to performing the experiment myself, but thought I'd ask here if anyone has built and used such as setup.

    So I'm asking...

    Ed Bianchi

  • #2
    I've not seen the soldering gun approach but have seen several battery charger/jump starter conversions.

    EM

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    • #3
      Some use a glow plug as the carbon rod...
      Last edited by Kevan; 06-19-2019, 01:14 AM.

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      • #4
        If you have a weller soldering gun just cut the end off the tip so you have two prongs not joined, the heat is then generated in the metal it touches.
        ... I'm going to try this tonight...

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        • #5
          I have built my own RSS using an old Scope transformer. I think it is 30 Amps at around 4 volts.It is great for chassis work.There is a good how to on the web somewhere.

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          • #6
            I took a look last night. The soldering gun I own is a Weller model 8200. I'd buy a used one to convert.

            Its electrodes are bored out a bit over 1/4 inch. McMaster-Carr has carbon-gouging electrodes in that size, with copper sheathing or without. I think I can arrange to hold the carbon rod in place with a set-screw. The copper sheathing might be needed to prevent the carbon from breaking at the set screw.

            The open-circuit voltage across the electrodes is only 0.375 volts AC. If the power output is to be 100 watts, theoretically the current would be 267 amps (!) I've got a strong suspicion that number is too large. Internal and external resistance should cut that way the heck back.

            Just how much wattage shows up at the solder joint is the question here. The rated power of the 8200 is 100 and 140 watts, depending on the trigger position. That should be way more that needed if it actually does show up at the joint. TBD.

            I'm going to have to decide whether to raid my lunch money and take this deal further...

            Ed Bianchi


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            • #7
              I love reading about something new, much googling find plenty of DIY options out there, transformers, battery chargers, pc power supplies...maybe a sewing machine foot pedal can be used as both a variable power control and on off switch feeding the mains side of it.

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              • #8
                I like the sewing machine foot pedal idea! Do you mind if I -- oops! -- I've stolen it already! Sorry...

                Ed Bianchi

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                • #9
                  Originally posted by HO RacePro View Post
                  I like the sewing machine foot pedal idea! Do you mind if I -- oops! -- I've stolen it already! Sorry...

                  Ed Bianchi
                  I have one ready...

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                  • #10
                    Sewing machine pedal works fine IF it is just a switch,many have speed control in the pedal.

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                    • #11
                      The thinking is vary the voltage to the primary rather than the secondary.

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                      • #12
                        As Kevan noted above, its the speed control feature of the sewing machine foot pedal is what I find attractive. The electronic speed control 'chops' the incoming AC voltage waveform, rapidly turning on and off to reduce the power supplied to the soldering gun. Since it doesn't work by adding resistance, the amount of waste heat created is minimal.

                        I've ordered a pack of copper-sheathed carbon electrodes to experiment with. Should see them tomorrow. Then I'll run some soldering tests.

                        Ed Bianchi

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                        • #13
                          This project is getting interesting. I have a fairly large transformer with bridge rectifier I used to power r/c battery chargers, it's been redundant for years...it may have a job to do

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                          • #14
                            You do not need variable temperature as the heat is controlled by the time the foot switch is held on.

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                            • #15
                              You need variable output voltage though so you don't burn holes.

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