Cycling UK Forum

Anyone else had issues tinning the coaxial cables that SON use? I'm trying to extend my elderly Edelux front light cable but I really can't get any solder to stick to the copper wires. I've got a half decent soldering iron and I've tried low and high temperatures, short and long soldering times, lead free and leaded solder, flux and no flux. Nothing works, the wire just goes black and the solder just wicks onto the iron. I've also previously tried to solder a SON waterproof connector onto a piece of SON coaxial cable and had the same issue. I'm not having any issues soldering anything else so it doesn't seem to be my iron. Any tips to get my solder to stick?

Are you sure it's copper wire? It could be copper coated aluminium - which depending on the thickness of the copper coating can be tricky to solder.

I don't remember having any problems, but that was with the insulation stripped reasonably well back from the wire when fitting the spade connectors (old-style leaded solder with core flux). The wire itself has to get hot enough to melt the solder.
If it's for extending the cable, you could consider using the coaxial connectors.

I've had similar issues with copper cables on a pretzel headtorch. A combination of water and corrosion had made the copper cable very brittle. I ad the same experience as you trying to resolder it. I eventually replaced the cable with twin core which I had to hand.

I'm going to sound like a GB News presenter here, but I never had a problem soldering with lead/tin solder. The new lead-free stuff doesn't easily wet anything in comparison.

if you have copper wire that is old, it may already be oxidised, in which case much stronger flux might do the trick. For plumbing, they sell three different strength fluxes with rules about which ones can be used in potable water systems (the strongest fluxes leave residues that are both corrosive and poisonous). I have occasionally used my plumbing flux for other purposes.

Difficult tinning problems can be solved with a drop of hydrochloric acid, also called muriatic. Ruby's Soldering Flux containing hydrochloric acid can be used, but that's a commercial name used in the US, and there should be something similar for the UK. I always keep those for tinning stainless steel with silver solder, such as cable ends, but they can be used anywhere else. After the soldering, you should wash off the flux, preferably using soapy water.

Thanks for all of the suggestions. I'll try plumbing flux first as it seems likely the cable has oxidised given it's used for commuting and been ridden through 7 salty splashy winters.