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Apologies if this is not an appropriate question or if there are answers elsewhere, I am looking for a definitive answer which I have been unable to find.

I want to solder some heavy gauge, insulated, multi-strand copper wire (8 AWG) to a tinned terminal.

What would the correct tools and technique be for this?

I have tried 10's of combinations of solders, soldering irons and fluxes, but always end up with what looks like a dry joint, and/or not all the strands could be soldered, presumably because of what appears to be a residue on the strands from the soldering.

I would like to avoid using a flame torch if possible to avoid damaging surrounding parts. (Or perhaps some how shield surrounding parts from the flame.)

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Typically if you have a wire that big, you design in terminals. –  Matt Young Jul 23 at 12:10
5  
The difficulty in getting that much copper hot enough to solder is one reason to use crimp terminals instead. –  Martin Jul 23 at 12:23
    
A "Soldering Copper" can deliver all the heat you need, without the overheating that can cause tinning problems. Large automobile battery cables can be slid inside a slightly flared copper tubing, and hammered flat on one end with the copper wire inside, then a hole drilled for mounting. –  Optionparty Jul 23 at 13:14

2 Answers 2

Soldering 8 ga multistrand is not a good idea. The problem is that, assuming you can get it hot enough to take the solder, solder will wick up along the individual strands, causing a fairly long region where the cable is essentially solid. The end of this region is susceptible to long-term degradation since it acts to concentrate any flexing stress and work-harden the copper.

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First, clean the wire and the terminal meticulously and tin the wire with Sn60 or, better yet, Sn63 tin-lead solder. Second, crimp the terminal onto the wire. Third, use a vise to gently hold the wire steady several inches away from the terminal. Fourth, using an iron, melt a little solder onto the outside of the terminal sleeve with the iron and hold the iron on the terminal while feeding a little solder into the sleeve-wire joint. When the solder starts to melt, add more until the space between the wire and the inside of the sleeve is full and it's all melted and shiny. Fifth, remove the iron and the solder feedstock from the terminal quickly, and let it cool without disturbing it.

That should do it.

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