Noob Soldering Problem - Which Wire To Use?

[electronub]

Hello there,
My first post about my first electronics project.
I am soldering away to attach a very thin wire to my CR2032 battery holder pin. This is more difficult than I expected (as said: my very first project of this kind...). I do manage to get some soldering in more or less the right place, however the wire just breaks off from very little movement. To be clear: it is not the solder that breaks, it is the wire itself that breaks where it is soldered to the battery pin.
What is the best way to handle this? My project does require resistance to movement.

 

[bushtech]

What sort of wire, single/multistrand, thickness?
What type of soldering iron and what heat are you soldering at?
Please post some photos

 

[hevans1944]

From your description of "a very thin wire" and the fact that it breaks, it is obvious you are using a single strand of solid wire to make the connection to your CR2032 battery holder pin. There are two frequent problems that occur with this practice: tiny nicks in the wire caused by poor wire stripper performance and mechanical fatigue at the wire/solder junction caused by movement of the free end of the wire.

The nick problem is especially difficult to avoid if cheap, opposing "V"-groove, strippers are used. Try using strippers that close to form a precise-diameter round stripping hole. These are available for both solid and stranded wire, so be sure to use one specified for insulated solid wire. If this is 30 AWG insulated wire-wrap wire, it should be stripped using a stripper designed for that purpose. Wire-wrap connections are extremely susceptible to failure from nicks in the wire, which is why the final two or three turns on the wrap post must be made with insulated wire. The insulation provides a form of strain relief. Surprisingly, the single-blade "V"-groove stripper, attached to common and inexpensive hand wire-wrap/unwrap tools as a flat "spring," works reasonably well. If you are stripping Teflon insulated wire, special wire stripping blades are usually necessary to assure a clean cut through the insulation without penetration of the undelying wire. I often use a new single-edged razor blade, rolling the wire under the blade while carefully controlling the downward pressure. Always inspect stripped solid wire under a magnifying glass for the presence of nicks before using it.

The fatigue problem, usually caused by vibration and movement of the wire after it is soldered, is solved by applying a stiff conformal coating to both the joint and a short length of the insulated portion of the wire extending from the joint. A quick-curing two-part epoxy, or even hot-melt glue, will work for this. Avoid using soft elastomer coatings such as RTV (room-temperature vulcanizing) adhesives.

In an earlier life, I used a viscous red substance called glyptal varnish. See image below. This was a common substance on the bench of every radio and TV repair shop in the 1950s, often used to solve corona discharge problems in the high-voltage section of TVs and to fix in place the adjustments of tuning coils and potentiometers. It dries to a hard, brittle, consistency.

If you decide to use glyptal varnish, allow plenty of time for the solvents in the varnish to evaporate and the coating to harden before disturbing the solder joint. Purchase only as much as you think you will need in a few months. This stuff slowly hardens in the bottle once opened. You can try to slow the process by wrapping the screw-on cap with electrical tape, but I have had spotty results with that. Hot-melt glue might be a quicker and better alternative. Your mileage (or kilometers) may vary.

 

[CDRIVE]

Hop, I will put my wire stripping skills up against any of the contraptions developed of the last 50 years. I've used the same Miller "V" groove stripper ,...like forever. No nicks no cut strands. And I'm still FAST!

BTW, nail polish (I like enamel) works pretty good too but doesn't hold up well to tight bends.

Chris

 

[hevans1944]

I have used the Miller stripper for years also, but prefer the precision round-hole type. The Miller V-jaws require some skill to either set properly or "feel" properly. The Air Force issued me an abomination that had a complex mechanism that gripped the wire as you closed the handle grips, then chomped down on the wire with a pair of round-hole blades, but not with any force to speak of because the pair of blades came together and were mechanically stopped facing each other. Further squeezing was supposed to separate the insulation from the wire, whereupon you were supposed to release your grip on the handles, allowing the tool to retract the blades and spring open. Most of us flight-line techs left that useless POS back in the shop and carried Miller-type V-blade strippers for the few times we actually needed to strip a wire on the flight line. I don't know of any techs in the shop who used them either. But Teflon insulation is a whole 'nother ball game. Best tool I found for that used two V-blades in a scissors-like closing action, but it was too expensive to purchase for personal use... hence the suggestion to use a single-edged razor blade for stripping Teflon.

 

[CDRIVE]

Hop, my Dad bought me one of those contraptions (still have it) over 50 years ago. I didn't have the heart to tell him I'll never use it. BTW, I've never used the stop screw on the Miller. Totally feel and experience. On the other hand the Teflon insulation you mentioned is a different animal. Like you said, razor blade or sharp exacto-knife!

Chris

 

[hevans1944]

Chris, I once had one that I had (by trial and error) set for 30 AWG wire-wrap wire. Used that tool a lot back in the day, but one had to develop a "knack" for squeezing, slightly twisting, and pulling the insulation off without nicking the wire-wrap wire. Hopefully I will never have to do that again. My last wire-wrap design involved several hundred connections, which a technician did for me without error in about a week, IIRC. This guy was much better than I ever was at wire wrapping, and I was fortunate to have him assigned to the project. Nowadays, the only time I strip 30 AWG wire-wrap wire is to create a short jumper for circuit board repair.

The larger solid gauges, 24 AWG to 20 AWG, I stripped by "feel" only. When I had teeth, I would sometimes strip solid two-pair (red/black, green/yellow) telephone wires with them. This worked for solid wire, but not so much for stranded wire. I also carry an "electrician's knife" that I sometimes use for stripping insulation from heavier gauge wire, usually 14 AWG to 10 AWG. Even more problematical is stripping coaxial cable... I've tried all sorts of tools but usually end up using the good ol' Gillette Blue Blade single-edged razor blade to get the job done.

As far as the OP's original problem is concerned, a finely stranded insulated wire of appropriate gauge will solve most of the breakage problems, or at least reduce them to breaking one strand at a time if strain relief isn't used. Experience helps a lot too.

 

[(*steve*)]

Nowadays, the only time I strip 30 AWG wire-wrap wire is to create a short jumper for circuit board repair.

I had to admit it, but for quick one-off things, it where I need something a little better than a breadboard, I use matrix board and wire wrap wire.

Making a 1cm link with two stripped ends can be really fiddly.

I think I spend more time stripping wire than anything else. I'd love to find a fast and reliable method that works for really short lengths of wire.

Stranded wire (back to the OP's question) can also be problematic as you can get a lot of stress at the point where the tinning of the wire stops. At this point the wire changes from stiff to flexible. You need to consider strain relief so that stress is not concentrated at one point.

 

[hevans1944]

Making a 1cm link with two stripped ends can be really fiddly.

Which is why I have a spool of tinned bare wire of various gauges and another box (somewhere) of insulation tubing sized to fit over the bare wire. My favorite "go-to" stock is a small spool of 22 AWG solid tinned wire and a spool of Teflon tubing that fits nicely over it.

For any newbies reading this, shrink tubing also works well, is available everywhere in a huge range of sizes, but it is a bit pricey for the purpose. You can often salvage what you need for insulation purposes from scraps of wire you have saved for "just in case" situations like this. Strip one end of the scrap wire to a length of an inch or so, eyeball the length of insulating tubing you need, and then cut the insulated portion of the scrap to that length. Now grab the exposed wire with a pair of long-nose pliers or secure it in a bench vise. Pull off the insulation you need. A hot-air gun or hand-held hair dryer sometimes helps to loosen the grip of the insulation on the underlying wire. This works for short lengths of insulation, up to a foot or so.