Best Way To Solder Two Wires Together

[bostonman]

Typically my favorite way to solder wires together is parallel in opposite directions. As an example, soldering wire onto a fan with wires too short to reach the power connection.

I've heard of J hooking the wire and various other methods, but feel J-hook may leave a sharp point poking through the heat shrink.

When I solder them parallel, I never seem to get them parallel, instead, kind of a V shape due to not holding them steady. Putting the wire in clips causes the insulation to get crushed.

Does anyone have a preferred method for soldering wires together?

[aeg]

https://en.wikipedia.org/wiki/Western_Union_splice

[edpalmer42]

I agree with aeg that the Western Union is probably the best splice.  One variation I've discovered is that if you're doing a Western Union splice with stranded wire, don't twist the strands before you make the splice.  As you make the splice, the strands will spread out and lie flat.  The resulting splice, even after soldering, will be about the same size as the wire.  A layer of heatshrink over everything and you've got a splice as close to smooth as you'll ever get.

[Ian.M]

For small stranded wires where you cant tolerate the bulk and length of a Western Union splice , strip the ends but do not twist then lay the ends parallel and apply a seizing using a single strand of bare copper wire (or tinned if the wires are tinned) of much smaller diameter than the wires to hold them tight together with the strands parallel.  Apply non-corrosive flux and sufficient solder to wet the seizing and wire ends, without forming a blob.   

However due to the stress concentration at the limits of the solder flow weakening the wire, its seldom worth going to this much trouble and tinning both ends and lap jointing the wires using some sort of jig to hold them aligned is usually sufficient. 

For fans where the solder pads on the PCB are accessible without dismantling, If the wire has to flex at all, I'll change the whole wire rather than jointing it.

[bostonman]

Interesting on the Western Union splice.

I may have seen this in my past (forced) training of IPC standards (and I may still have one of the training manuals somewhere - I'll need to look).

Not sure where I developed the poor technique of the way I've done it. Usually I tin both ends but seldom do I get a nice cacoon of smooth solder and keep meaning to ask the opinion of others..

One technique I keep forgetting to implement is cutting both wires (say a positive and negative) different lengths. This way I can solder both, but the solder connections are at different points eliminating the possibility of the strands poking through and shorting (usually I put a piece of heat shrink over each solder connection and a larger one over both of them). If the solder connections are at different points, then the other wire is protected by the insulation too.

[ajb]

What's the application?  I'm skeptical that the effort and bulk of anything like the western union splice is worth the effort versus a basic lap joint for the vast majority of cases.  Assuming both are done half-decently, anyway, and the splice is protected/reinforced with heatshrink at least.   But it depends on the materials being used and the application/environment.  Proper strain relief of the transitions between the splice and the parent wire on either end is important in any case, particularly for stranded wire which also requires making sure the solder doesn't wick too far along the wire.  Wherever the solder ends, the wire strands will be susceptible to breakage as the wire flexes.  Similarly, reinforcing the splice TOO much -- for example by using some really stiff heatshrink -- can just move the stress concentration problem from the end of the solder joint to the end of the heatshrink.  Mechanically supporting the wires to either side of the splice can also help. 

Not sure where I developed the poor technique of the way I've done it. Usually I tin both ends but seldom do I get a nice cacoon of smooth solder and keep meaning to ask the opinion of others..

Are you using flux?  IME, a liquid flux that can get into the strands works best, especially if the wires aren't in great shape.  Flux and tin each wire end, then flux them again before soldering.  At that point getting a well-formed joint is mostly a matter of iron temperature and timing -- you need to put enough heat into the joint to get the solder to flow and wet out properly, but not so much heat or for so long that you burn off all of the flux. 

If you're soldering stranded wire a lot, a solder pot is a really worthwhile investment, makes the tinning step faster, easier, and much more consistent.

One technique I keep forgetting to implement is cutting both wires (say a positive and negative) different lengths. This way I can solder both, but the solder connections are at different points eliminating the possibility of the strands poking through and shorting (usually I put a piece of heat shrink over each solder connection and a larger one over both of them). If the solder connections are at different points, then the other wire is protected by the insulation too.

You can sometimes save some bulk by only putting heatshrink on one of the two wires before putting the larger piece over both.  The one small piece will be adequate to insulate the one wire from the other, although it doesn't provide as much mechanical/environmental protection (eg against moisture ingress into the wire) if that's important.

[Messtechniker]

These might be an option:
Search for  "Solder Seal Wire Connectors Heat Shrink Solder Terminals"

[tooki]

Interesting on the Western Union splice.

I may have seen this in my past (forced) training of IPC standards (and I may still have one of the training manuals somewhere - I'll need to look).

Not sure where I developed the poor technique of the way I've done it.

There’s nothing inherently wrong with lap joints, as long as they are suitable for the purpose at hand. The Western Union splice had to be strong enough for telegraph wires strung between poles. That’s not necessary for many applications.

Usually I tin both ends but seldom do I get a nice cacoon of smooth solder and keep meaning to ask the opinion of others..

Solder-tinned wires should never have a “cocoon” of solder, that’s way too much solder! Properly solder-tinned wires should still let you see the individual strands.

See section 6.16 “Service Lead Splices” of https://workmanship.nasa.gov/lib/insp/2%20books/frameset.html for great examples of lap splices with the correct amount of solder. It also shows acceptable and unacceptable amounts of angular misalignment. (https://nepp.nasa.gov/DocUploads/06AA01BA-FC7E-4094-AE829CE371A7B05D/NASA-STD-8739.3.pdf is the standard itself, and it’s a great read.)

One technique I keep forgetting to implement is cutting both wires (say a positive and negative) different lengths. This way I can solder both, but the solder connections are at different points eliminating the possibility of the strands poking through and shorting (usually I put a piece of heat shrink over each solder connection and a larger one over both of them). If the solder connections are at different points, then the other wire is protected by the insulation too.

I recently had to extend the wires on a dozen cartridge heaters and a few 4-wire PT100 sensors. Because each of those pairs/quads of wires had to fit inside a fairly thin Teflon tube being used as armor (against chemicals), I had to use lap joints to keep the splices slender, and had to stagger them to prevent a giant bulge. And like you said, it’s an extra layer of protection against shorting if a splice should come apart for whatever reason.

Huge tip for staggered splices: carefully measure and strip the wires, and be very, very careful when soldering to make sure that no spliced conductor is appreciably longer or shorter than any other,. It doesn’t take much length disparity at all between conductors for the bundle to get bulky because the longer conductors have to bow outwards to match the distance dictated by the shortest conductor.

[bostonman]

What's the application?  I'm skeptical that the effort and bulk of anything like the western union splice is worth the effort versus a basic lap joint for the vast majority of cases. 

No application, it was a general question based off coming across this periodically. When I make a lap joint (I would have initially used this term had I remembered it), I like the solder to have a smooth cocoon so the strands don't poke through the heat shrink. As mentioned, this is too much solder, but that's been my typical approach.

Seems I was better at making this. Lately it just seems the are more of a Y than parallel and I don't like leaving it that way.