Soldering... clearly I'm doing something wrong
Posted: Tue Jul 12, 2022 8:25 am
You would think that soldering two wires together would be a pretty simple task. I'm self-taught, so any bad habits I have are my own. When I attempt to solder, I've got about a 75% success rate. 25% of the time it just doesn't work. The wires refuse to tin, get hot and oxidise. I get little blobs of solder sticking to the wire rather than solder wicked up into the strands. This happens even if I put enough heat into the wire to melt the PVC insulation. It's made me gun-shy of soldering, and I tend to install crimp terminals instead (my terminals are a lot more professional - bare brass lugs, crimped with the correct forming tool instead of a masher, and heat-shrinked). There are times though (as I found out again this week) where you just have no choice but to solder (in this case, reconnecting a wire back onto a soldered stub of a terminal on the side of a motor).
The wires I work with are typical automotive mult-strand copper (10-30A). I strip the wires, leaving enough for the solder (maybe 5mm-10mm). Sometimes I use new wire, sometimes no choice but to use old stuff when wiring back into an old harness. The new stuff is bright and coppery, sometimes the old stuff looks like either silver (tin?) or is oxidised. I try to cut wire back enough to get clean wire but sometimes you have not enough length to go cutting back much.
I know you should make a mechanical joint (by twisting or braiding the two wires together before soldering) but I usually don't. My wires are under very little load. In any case, the strength of the joint is not the problem... getting the solder to work is.
I use an electric soldering iron (two of them... an old Dick Smith one I've had since I was a kid, and a new one from SuperCheap). I warm the iron up for several minutes, so that it is hot enough to melt solder instantly (or burn the crap out of me when I pick it up by the pointy end). I make sure the tip of the iron is clean by wiping it hot on a damp rag. The entire tip looks clean and shiny before I start. I use one of those spring-type holder things to keep the iron off the floor, and to increase the chances of me using the blunt end to pick the iron up.
I hold the hot, clean iron underneath the stripped wire, giving it ten seconds or so to heat the wire. Doesn't seem to make a difference if I hold it there for longer, though the heat transferring up the wire gets to the point that the PVC insulation softens/melts. Pretty confident its not a cold joint.
I use a roll of plain solder. It looks to be solid core, and I seem to remember using flux core when I was younger. I gently run the solder strand along the top of the hot wire, hoping it will melt and wick in. 75% of the time it does. Other times the solder melts into little blobs and rolls off the wire. The wire gets hot and eventually oxidises. Cut the end off, repeat. I keep the iron under the wire until the solder is on (iron on, solder on, solder off, iron off).
If I eventually get two tinned wires I use one of the little helping-hand alligator clip things to hold the two wires together, heat both until the solder melts, allow to cool. I then pull-test the joint to make sure it is strong.
Looking for advice please on what I am doing wrong.
Cheers,
Harv
The wires I work with are typical automotive mult-strand copper (10-30A). I strip the wires, leaving enough for the solder (maybe 5mm-10mm). Sometimes I use new wire, sometimes no choice but to use old stuff when wiring back into an old harness. The new stuff is bright and coppery, sometimes the old stuff looks like either silver (tin?) or is oxidised. I try to cut wire back enough to get clean wire but sometimes you have not enough length to go cutting back much.
I know you should make a mechanical joint (by twisting or braiding the two wires together before soldering) but I usually don't. My wires are under very little load. In any case, the strength of the joint is not the problem... getting the solder to work is.
I use an electric soldering iron (two of them... an old Dick Smith one I've had since I was a kid, and a new one from SuperCheap). I warm the iron up for several minutes, so that it is hot enough to melt solder instantly (or burn the crap out of me when I pick it up by the pointy end). I make sure the tip of the iron is clean by wiping it hot on a damp rag. The entire tip looks clean and shiny before I start. I use one of those spring-type holder things to keep the iron off the floor, and to increase the chances of me using the blunt end to pick the iron up.
I hold the hot, clean iron underneath the stripped wire, giving it ten seconds or so to heat the wire. Doesn't seem to make a difference if I hold it there for longer, though the heat transferring up the wire gets to the point that the PVC insulation softens/melts. Pretty confident its not a cold joint.
I use a roll of plain solder. It looks to be solid core, and I seem to remember using flux core when I was younger. I gently run the solder strand along the top of the hot wire, hoping it will melt and wick in. 75% of the time it does. Other times the solder melts into little blobs and rolls off the wire. The wire gets hot and eventually oxidises. Cut the end off, repeat. I keep the iron under the wire until the solder is on (iron on, solder on, solder off, iron off).
If I eventually get two tinned wires I use one of the little helping-hand alligator clip things to hold the two wires together, heat both until the solder melts, allow to cool. I then pull-test the joint to make sure it is strong.
Looking for advice please on what I am doing wrong.
Cheers,
Harv