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Converting A Soldering Gun to Resistance Soldering

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  • #16
    Apparently an AC RSU doesn't need the power switching off before removing the probe...

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    • #17
      I have been using mine for chassis building for 3 years, no variable power, just use the foot switch to control the time,the carbon tip helps control the heat.

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      • #18
        If the output is AC it means the current is turned off 100 or 120 times per second, and greatly reduced maybe 10% or 20% of the time. That should give you a chance to break the circuit without striking an arc.

        With a DC output the current is continuous as long as the power is on and the contact is not broken. Break the contact with the power still on and you run up against a phenomenon known as "inductance". One way to think about inductance is that electrical current has a momentum -- it will not start or stop instantaneously. Open a circuit with a current still flowing through it and the current will attempt to "jump the gap" Dukes of Hazzard style, causing a spark, or in the worst case, an arc. This is how spark plugs work. Also arc welders.

        An arc is an electrical current flowing through superheated ionized air, which is highly conductive, unlike normal air which is a great insulator. Electrical arcs can be destructive. In high-powered circuits they can result in an "arc flash"-- an electrical explosion which has been known to kill people! This is one reason why we have licensed electricians who get arc flash safety training.

        A resistance soldering setup shouldn't have the power to blow you across a room with an arc flash. But if you have a DC setup using a power supply you should probably turn off the power before breaking the contact. It will be kinder to your power supply, if nothing else.

        Ed Bianchi

        PS - Reading this posting earns you 0.1 credit towards an online degree in Electrical Engineering.

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        • #19
          i already have one. but I like your insight, Ed.
          speedy

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          • #20
            Well shoot!

            I tested my concept today, modifying my Weller Model 8200 soldering gun to use it as a resistance soldering setup. But I couldn't get any heat at all out of it! I checked my continuities -- all good. Still nothing.

            When I put the soldering gun back together it worked just fine.

            So now I'm confused. I was prepared to see too little heat. I was not prepared for NO heat!

            I'll step back from it for a while. Maybe I can figure out what the problem is. But for now I am completely stumped.

            Ed Bianchi

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            • #21
              Arc flash... never mind kinder to your power supply, arc eye is painful!!!

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              • #22
                I don't really understand the very low open circuit voltage you measured on the gun. Perhaps there was some significant resistance in the circuit. A common failure mode for soldering guns is a tip not firmly clamped in the mount. I'll measure the open circuit voltage on my Luma set-up and report.

                EM

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                • #23
                  The specs that I have seen call for 1.5 - 3 volts. My rechargeable battery operated iron uses 2 NiMH batteries = 2.8V

                  EM

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                  • #24
                    If you try to turn down the AC input voltage to the soldering gun with a dimmer that works by turning the power on and off you may burn out your gun. I have a couple of autotransformers, also known as Powerstats or Variacs, hanging around that I can use to reduce the voltage, but still have a 60hz sine wave. I have always had good luck using a regular 45 watt chisel tip Ungar iron with everything from 1/24th scale brass and piano wire chassis to attaching wires to surface mount LEDs. I do have an old Weller gun hanging around and I will have to try modifying that to do resistance soldering.

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                    • #25
                      i always experience poor connections between the Weller barrels and the copper electrodes on my guns, so I'm always loosening and retightening them to get a better contact. don't know it that helps or not. the internal connections have always been trouble-free.

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                      • #26
                        Just to be clear, we're not supposed to be using the tandem resistors on the gun. The conversion utilizes the transformer only.

                        Plenty of schematics on-line, but I wont hook us up for fear of scrambling the link police.

                        As noted, the foot pedal or dimmer goes on the primary side.

                        ******

                        As 'speriments on You Tube go, Im not sure that opening the "iron", leaving its ends lugged into the heaters, and using the work to complete the circuit; qualifies as resistance soldering in the true sense.

                        For fine work the nifty bit is the carbon rod holder that allows you to incrementally feed the carbon probe forward in the holder, as it is gradually consumed. Micro mark has a basic two step unit for a buck eighty three, with the foot switch. Available accessories include ground clips, grounded work plates, probes and replacement carbons ....etc.

                        Plumbing capable big boy units are well over a K.


                        Last edited by model murdering; 06-21-2019, 08:48 PM.

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                        • #27
                          Has anyone used a Cold Heat soldering unit?

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                          • #28
                            A soldering gun IS a residence soldering unit, take the bit out and pull the trigger...nothing will happen but there is low voltage across the bit holders.

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                            • #29
                              The Weller soldering gun is a transformer with a large number of primary turns and one (or maybe two) secondary turns. Because of the primary and secondary turns ratio the secondary current is very high (to heat up the tip) but the secondary voltage is also very low.. My guess is that the Weller cannot develop sufficient secondary circuit voltage to operate the resistance concept. You need a transformer with a bit more secondary voltage.

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                              • #30
                                This thread has certainly fascinated me this last few days, I have loads of new bookmarks, one of the best is this one ->

                                I have a broken microwave in the boot of the car for a couple of weeks...now rather than take it to the tip I can make use of the transformer

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