Soldering... clearly I'm doing something wrong

[Harv]

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

[gledge]

Try using bakers flux on the older wires that is the only way you will get the old wires it take solder..


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[funkyscooter]

Soldering sucks with modern led free solder - just doesn't flow and stick like the old lead stuff as you describe.

Had a big roll of Dick Smith wire from the 90's which only run out a couple years ago. Have not been able to find a half decent alternative since.

Melted my share of pvc sheath trying to get heat into the wire too. I find that if you melt the solder onto the iron tip and let it flow onto the wire to tin it rather than putting the solder on the hot wire seems to work a bit better. End up wasting a lot of solder as it drips off the tip.

[Brett027]

Need flux Harv. Solid solder wire is useless unless you add flux - like Bakers fluid flux, or a paste flux used to be available in a little tin. Best bet is to go to Jaycar and grab a roll of resin cored solder. If you just happen to have some muriatic acid on hand you could try dipping wire end in that, but resin cored solder is easiest.
Solid solder is useful for lead work but nothing much else I reckon.

[BILLY BLACKARROW]

Harv
I am no expert but what I tend to do is i have some liquid flux buy from( Bunnings or hardware store) and i ether dip the bare wires in it or paint on with a brush i do use a fair bit of flux it cleans the wire to prepare for soldering but after you make the joint clean with water as the flux will still be active and may corrode the wires hope this helps oh I do still us flux core wire

[fb delivery]

Have you tied useing vinegar to clean the old wires ? to remove the oxidation
And i always use a flux core solder
i use Weller General Purpose So0lder
5 core rosin solder , 60% tin ,40% LEAD
I have just rewired a 1965 Pontiac


Rob

[Blacky]

What wattage is your iron ? I have a 100W soldering iron that is way better to use then the pissy little 15 or 25 W ones, although now my weapon of choice is my 12V Milwaukee battery iron. If the wires are not accepting solder try scraping the strands with the back of your stanley blade to help remove old crud and get them clean , I have found that helps. Every now and then I find a cable that just will not accept solder, then the crimper comes out.

[EK283]

Flux impregnated solder, flux flux flux !!
Hold the iron on the wire and push down on the wire with the solder, when the wire is hot enough the solder will melt into it and thats it !

Greg

[Brett027]

Yes, I was thinking a bit more about this today. Best to have the iron behind the join and heat the solder through the wire. With flux. 100% with you here Greg.

[Blacky]

Yes, I was thinking a bit more about this today. Best to have the iron behind the join and heat the solder through the wire. With flux. 100% with you here Greg.

Thats how I have always done it.

[BILLY BLACKARROW]

You MUST have clean wires to start or it just wont flow

[ardiesse]

Using a Metcal soldering iron fitted with the b.f.t.*, and paste-flux for surface-mount components, the wire tinned, and I could resolder it.

Admittedly this is the sort of equipment that your home hobbyist doesn't have . . . that's why I did it at work.

Rob

* the largest chisel-point tip I could find. The Metcal soldering stations are interesting beasts. They're effectively short-wave radio transmitters. The tip absorbs the radio-frequency energy, and gets very hot very quickly. When the tip gets hot, its impedance changes, and it reflects the RF power instead of absorbing it. Instant temperature control results.

[Errol62]

Wiring sucks.

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[Blacky]

Wiring sucks.

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agree.

[Harv]

Thanks gents. Seems like my lack of flux is the problem. Will get some new solder and have another go.

The SuperCheap iron is an 80W job. The Dick Smith one is a lot smaller.

Many thanks to Rob for soldering the unsolderable. You don't want to know what a second-hand VL Calais headlight lid motor is worth

Regards,
Harv