I have some specialised electrical copper cable which has broken and I wish to solder the broken ends back together. Easy enough you may think, as did I, until I stripped the insulation back and discovered the cable has been seriously overloaded for some time and the copper cores have discoloured to dark brown. For some reason, way beyond the knowledge of this electronics engineer, solder will now not adhere to the cable and I can neither tin nor join them.
I have no idea whether the cable's atomic structure has changed irreparably or whether the discolouration is simply a coating which can be removed. In hope of the latter I have the cable ends sitting in white vinegar (apart from lemon juice the only acid I have) - am I wasting my time or is there a solution to this problem?
PS. For the safety conscious: normally, passing excess current through a cable is a "Bad Thing" - in this case it's a controlled situation and I know what I'm doing... well... most of the time anyway :)
rgren2 said
12:22 PM Feb 8, 2023
Ive had a dark discolouration on wires on my boat, its not always overloading, can be a chemical reaction, I scraped the wire to get some bright copper showing, this I dipped in an acid (probably Bakers Soldering Fluid as that would have been the only stuff around), the copper became bright quickly, I slid some glue heatshrink up the wire, twisted and soldered. Slid the heatshrink over the join and heated it to seal the join. There is another school of thought to use crimps and heatshrink.
Tony LEE said
02:54 PM Feb 8, 2023
It isn't normally an indication of overloading. I've seen brand new, but long-time stored cable just about black inside) Possibly a reaction with the sheathing. Doesn't seem to happen with tinned conductors
Only way I know that doesn't run the risk of even worse corrosion later is to mechanically remove the tarnish with fine steel wool.
Years ago in my first job out of uni, an old electrician showed me how it was done - joining a 2" diameter cable. Every strand was separated and polished to a mirror finish before laying it all back neatly to fit into the socket before soldering. No hydraulic crimper available then.
Triggy said
04:47 PM Feb 8, 2023
Just a thought is it multi strand all copper or like sat cable steel core copper coat
.
Mike Harding said
10:57 PM Feb 8, 2023
Triggy wrote:
Just a thought is it multi strand all copper or like sat cable steel core copper coat
It is a multi strand cable and I believe it to be all copper.
----
This discolouration is definately from current overload and thus high temperature - I knew I was pushing my luck with cable this small when I chose it :)
Yes, crimping is certainly a possibility but it will change the characteristic impedance of the cable at that point - this may not matter a lot but I'd rather not do it if possible.
It's been in vinegar for about 10 hours and I think it looks more "coppery" but that may be wishful thinking?
Whenarewethere said
07:20 AM Feb 9, 2023
A few thoughts.
Marine cable is tinned to minimise corrosion (used to have a yacht).
I have resoldered 40 year old welding cable for jumper leads (brilliant fine copper gauge) cleaned up a bit & used lead/tin solder. Tin only solder is a pain in the neck.
Rather than trying to join the cable directly. Can you add a jumper section with multiple crimped or soldered points for either end. Then heat shrink the overall section.
Mike Harding said
09:16 AM Feb 9, 2023
Whenarewethere wrote:
Rather than trying to join the cable directly. Can you add a jumper section with multiple crimped or soldered points for either end. Then heat shrink the overall section.
The issue with using repair methods (that I can think of) other than simple solder joints is that they will likely change the characteristic impedance of the cable this may, or may not, be significant but I would prefer to just solder if possible. As this cable is working at high frequencies things are electrically very different than is the case at DC or 50Hz.
deverall11 said
10:31 AM Feb 9, 2023
All that is required is a cleaning of the surfaces. Copper does not change its chemical structure. Actually no metal
does unless you melt it. That's a whole discussion in itself.
Acetic acid is all you need to remove the oxide layer. As soon as it is shinny, it should be ready for soldering.
The issue with soldering is that is a relatively low heat, compared with welding or brazing, and therefore unable to penetrate through the oxide layer.
The oxide is what is preventing the solder from sticking.
KJB said
10:33 AM Feb 9, 2023
deverall11 wrote:
All that is required is a cleaning of the surfaces. Copper does not change its chemical structure. Actually no metal does unless you melt it. That's a whole discussion in itself. Acetic acid is all you need to remove the oxide layer. As soon as it is shinny, it should be ready for soldering. The issue with soldering is that is a relatively low heat, compared with welding or brazing, and therefore unable to penetrate through the oxide layer. The oxide is what is preventing the solder from sticking.
Good, simple explanation...........
Mike Harding said
12:31 PM Feb 10, 2023
Forty eight hours in white vinegar brought the copper colour back to the wire and I've now soldered it together.
Many thanks for your responses people :)
bruceg said
12:08 PM Mar 18, 2023
To prevent re-occurance of the black oxide coat the first few cm of the copper strands with tin and then use a glue type heat shrink over the soldered joint.
See this video for a cheap DIY tin coating solution. Make sure the solution is rinsed off and the wire strands are dry before sealing with the heat shrink.
https://www.youtube.com/watch?v=Hsw3lOnHaas
As an electrical engineer you may already have a supply of (expensive) proprietry tinning solution ?
I have some specialised electrical copper cable which has broken and I wish to solder the broken ends back together. Easy enough you may think, as did I, until I stripped the insulation back and discovered the cable has been seriously overloaded for some time and the copper cores have discoloured to dark brown. For some reason, way beyond the knowledge of this electronics engineer, solder will now not adhere to the cable and I can neither tin nor join them.
I have no idea whether the cable's atomic structure has changed irreparably or whether the discolouration is simply a coating which can be removed. In hope of the latter I have the cable ends sitting in white vinegar (apart from lemon juice the only acid I have) - am I wasting my time or is there a solution to this problem?
PS. For the safety conscious: normally, passing excess current through a cable is a "Bad Thing" - in this case it's a controlled situation and I know what I'm doing... well... most of the time anyway :)
Just a thought is it multi strand all copper or like sat cable steel core copper coat
.
It is a multi strand cable and I believe it to be all copper.
----
This discolouration is definately from current overload and thus high temperature - I knew I was pushing my luck with cable this small when I chose it :)
Yes, crimping is certainly a possibility but it will change the characteristic impedance of the cable at that point - this may not matter a lot but I'd rather not do it if possible.
It's been in vinegar for about 10 hours and I think it looks more "coppery" but that may be wishful thinking?
A few thoughts.
Marine cable is tinned to minimise corrosion (used to have a yacht).
I have resoldered 40 year old welding cable for jumper leads (brilliant fine copper gauge) cleaned up a bit & used lead/tin solder. Tin only solder is a pain in the neck.
Rather than trying to join the cable directly. Can you add a jumper section with multiple crimped or soldered points for either end. Then heat shrink the overall section.
The issue with using repair methods (that I can think of) other than simple solder joints is that they will likely change the characteristic impedance of the cable this may, or may not, be significant but I would prefer to just solder if possible. As this cable is working at high frequencies things are electrically very different than is the case at DC or 50Hz.
does unless you melt it. That's a whole discussion in itself.
Acetic acid is all you need to remove the oxide layer. As soon as it is shinny, it should be ready for soldering.
The issue with soldering is that is a relatively low heat, compared with welding or brazing, and therefore unable to penetrate through the oxide layer.
The oxide is what is preventing the solder from sticking.
Good, simple explanation...........
Forty eight hours in white vinegar brought the copper colour back to the wire and I've now soldered it together.
Many thanks for your responses people :)
To prevent re-occurance of the black oxide coat the first few cm of the copper strands with tin and then use a glue type heat shrink over the soldered joint.
See this video for a cheap DIY tin coating solution. Make sure the solution is rinsed off and the wire strands are dry before sealing with the heat shrink.
https://www.youtube.com/watch?v=Hsw3lOnHaas
As an electrical engineer you may already have a supply of (expensive) proprietry tinning solution ?
bye