How to work with (join) extremely thin wire, only a couple of strands in total? - Page 1
Forum section: electronics / beginners

author: pierremontagne
author_rank: Contributor
timestamp: October 15, 2025, 05:30:20 pm
content: I have an android tablet that has been given to me. It charges by 5V/2A so I want to make a usb to barrel connector wire for it. The person who gave it had neither the mains adapter or any other charger that I recall. Just happened to have this spare barrel that fit it lying around somewhere.Annoyingly I bought a whole set of barrel connectors to usb of differing sizes of about 5 or so and figured one of them is bound to fit when I get it. Nope! This one is smaller still than any provided. I hate barrels and their lack of standardization.I have the right barrel connector but it is just 2 pins for positive and negative and no lead. I snipped a spare usb wire and opened it to show the 4 wires.I have figured out which is positive and negative but my first attempt to solder these tiny couple of stranded wires to those large, in comparison, pins was fraught with frustration and I just gave up and not tried again since.Looking online for how some other, lay people, did it it seems I was on the right track in terms of the connection as they were doing similar. I was trying to get some kind of connection with solder and then heatshrinking over it in order to act as a 'mechanical joint' which is what they were calling it.I was using the solderer to contract the heatshrink as heatgun or lighter would very likely melt the plastic barrel casing as well due to the close proximity.This is not the hard part. The hard part is getting the few hairs of wire to stay in place somehow while I solder it.I did it for one of the wires and tested and got continuity with the meter but then couldn't get the other and gave up. Well I did make the connection but could not find continuity on the meter.So suggestions for how to manage the holding in place while soldering part please.

author: MrAl
author_rank: Super Contributor
timestamp: October 15, 2025, 06:08:44 pm
content: Quote from: pierremontagne on October 15, 2025, 05:30:20 pmHi,I have run into these problems myself in the past because I tend to try to fix everything even the very hard to fix stuff.The two cases I remember like yours is 1. Antenna wire for a car radio, and 2. A computer mouse cable.After years of doing this, my first and best recommendation is to continue to try to find the right connector. I say this because (1) it is hard to keep the wires from breaking off, and (2) the flux eats up part of the copper sometimes which makes it even thinner. And (3) you can get a variety of connectors when you buy a general purpose wall wart that comes with maybe 12 or more connectors.Your connector is probably 3mm outside by 1.1mm inside diameters.Check this out on Amazon:5V 2A Power Supply Adapter 10W AC100-240V to DC 5 Volt 2Amp 1A 1.5A 0.8A 0.5A Replacement Power Cord with 9 Interchangeable DC Plug for Baby Monitor TV Box Tablet Camera Webcam Router, etc. (1 Pack)It comes with a 3mm/1.1mm plug. You do not have to use the wall wart just the connector and wire, but you may even be able to use that too.If you still want to try to solder and fix the old thing, then you must find a way to anchor the wires coming in from both sides.For a cheap example, if you had a popsicle stick you would hot glue the two wires to the stick, then solder. Then maybe cover will a layer of hot glue.That's a really cheap and not that good of a way to do it, but that shows how you have to anchor the wires because you have to reduce the strain on the soldered joint and loose wires. The main forces have to be on the outer jackets, or at least on the wires somewhere away from the joint.If the force is not only on the cable jackets there is a reasonable chance it will break again.

author: pierremontagne
author_rank: Contributor
timestamp: October 17, 2025 09:28:55 am
content: Quote from: MrAl on October 15, 2025, 06:08:44 pmYes I experienced something similar with a voltage regulator I used between source and device. In this case it is screw in terminals as they were the only thing holding the wire to the device that became a tension point and constantly pulling out when moving the wire around. I stuffed some wood glue into those screw terminals.Anchoring is the word I was looking for when writing the post.I was thinking of doing something similar to just do the soldering job, like using crocodile clips to hold the wires down to something but didn't also think of anchoring after that as well to some dedicated implement which is a good suggestion you made.

author: Gyro
author_rank: Super Contributor
timestamp: October 17, 2025 10:03:59 am
content: Barrel connectors normally have holes in the tabs that you can fold the wires though before soldering. Presumably your doesn't. Normally you can just hold the lead and connector in stable relative position with a pair of clamps, self closing tweezers etc.One concern. If the strands are really that thin and so few, it doesn't sound as if lead will withstand the 2A charge current demand of the tablet. You should probably look for a more robust USB lead to modify. The original charging lead would almost certainly have been a 2 core coaxial construction, similar to (but thinner than) a Laptop charging lead. You might find that a smartphone (or tablet!) cable is a better candidate.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: October 17, 2025 12:57:56 pm
content: Good Morning Pierremontagne, My experience is that the tiny multi-strand wires have a small, fabric string entwined among the copper strands. I subjected the stripped end to a flame and burned it off,('m thinking I ran into that trick 'somewhere'). Then the wires would twist together nicely. Use some good flux to clean up the bundle and solder delicately. OH, and don't forget to slide on your shrink wrap before you twist the wires together, like I always do. Good luck, Pierre

author: pierremontagne
author_rank: Contributor
timestamp: October 17, 2025 06:21:47 pm
content: Quote from: Gyro onYesterdayat 10:03:59 amOh I didn't know that usb cables were created different? I thought they were just standardized.

author: pierremontagne
author_rank: Contributor
timestamp: October 17, 2025 06:23:03 pm
content: Quote from: BILLPOD onYesterdayat 12:57:56 pmIndeed I have forgotten myself a good few times but starting to learn...

author: tooki
author_rank: Super Contributor
timestamp: October 17, 2025 11:05:43 pm
content: Quote from: MrAl on October 15, 2025, 06:08:44 pmJust a little correction: it’s not the flux that eats away at the copper. It’s the molten solder itself. It dissolves the copper.

author: MrAl
author_rank: Super Contributor
timestamp: October 17, 2025 11:14:03 pm
content: Quote from: tooki onYesterdayat 11:05:43 pmHello there,Flux can be aggressive with copper, although the solder itself could play a part depending on some other factors like heat and repeated thermal cycling. The solder forms a compound at the interface though so that involves some of the copper. I think what happens is the wire becomes more brittle and then is easy to break apart. I guess it depends how much of the copper gets 'mixed' with the solder near the surface. The heat causes oxidation too, so it's really a combination of things.Thanks for bringing that up

author: tooki
author_rank: Super Contributor
timestamp: October 17, 2025 11:14:46 pm
content: Quote from: pierremontagne on October 15, 2025, 05:30:20 pmTheyarestandardized. You just forgot to measure and made assumptions instead!Quote from: pierremontagne on October 15, 2025, 05:30:20 pmA good USB cable has thick power conductors inside.Additionally, some very cheap USB cables use copper-clad aluminum wire, where the wire has only a very thin layer of copper on each strand. Speaking from experience with that crap: if you don’t solder itveryquickly, the hot solder will actually dissolve away the copper entirely, leaving only the aluminum core of each strand, which cannot be soldered to with ordinary soldering methods/materials.I would seek out the correct cable, or build your own using a high-quality USB cable. (I would offer to mail you such a USB cable with bare wire ends, but Swiss Post would cost more than the price to just buy one at Aldi or Lidl…)

author: tooki
author_rank: Super Contributor
timestamp: October 17, 2025 11:21:49 pm
content: Quote from: MrAl onYesterdayat 11:14:03 pmElectronics flux isn’t that aggressive. The solder itself (AFAIK, mostly the tin) is much, much worse in that regard. You can easily test this with some very thin magnet wire or a strand out of very finely stranded wire: just keeping it in a big droplet of molten solder will eat it away.I don’t think the soldering process hardens the copper (if anything, I think it would lightly anneal it?), but repeated flexing most certainly would, and I’m sure that’s part of why repeatedly overflexed wire breaks.

author: MrAl
author_rank: Super Contributor
timestamp: «Reply #11 on:Todayat 12:59:53 pm »
content: Quote from: tooki onYesterdayat 11:21:49 pmHi,Well we can think of hardening in another way, if we have two fine wires entering from the two sides of a solder joint, the solder joint is structurally harder than the wires. That means we now have two interfaces: one at each end, and that means when the wire is flexed the interface is going to stress the wires in very small areas which tend to break with time. This actually happens with any soldering when a wire is soldered to something else. The interface where the wire enters the solder blob causes extra stress on that small part of the wire.I think the way the tin reacts with the copper though does create a harder alloy. That may be at the surface only, but if the wire is thin it will have more effect than if the wire is thick because then a more significant part of the diameter is affected.I guess we can look at the alloys that are created after soldering copper wire and how deep it goes into the wire.Silver solder would be better for these thin wires I think.The most important point though is mechanical support for the two wires being joined. It has to be somewhat soft too. We might think about this in a way similar to how we use rubber grommets when running wires through a hole in a chassis. If we used a ceramic grommet the wire would tend to break easier near the grommet while a rubber grommet allows the wire to bend with a larger radius. It's kind of like folding a piece of paper back and forth to create a weakness at the fold so it can be neatly torn along the fold ... if we folded with a much larger radius it would not tear as easily.