Joining Copper Cable

[Baggywrinkle]

One other point .... don't slide the heat-shrink over the joint until it has completely cooled down or it will shrink before it's properly in place.

I know it's obvious but it's caught me out a number of times when in a hurry.

 

[savageseadog]

Movement also puts stress on crimped joints. With adequate cable support, soldering is fine in the context of a leisure boat.

I'm afraid you're wrong and wrong.

Crimped joints have a much less abrupt interface and are less prone to corrosion. What does "fine in the context of a leisure boat" mean? The requirements of a leisure craft, especially a sea going one are no less than any other, perhaps even more so.

 

[lw395]

I'm afraid you're wrong and wrong.

Crimped joints have a much less abrupt interface and are less prone to corrosion. What does "fine in the context of a leisure boat" mean? The requirements of a leisure craft, especially a sea going one are no less than any other, perhaps even more so.

Both crimp and solder joints are prone to failure if stressed in a vibration situation.
A professional crimp is probably better than soldering.
Amateur crimp probably worse.
Mechanical clamp joint is possibly better than a bad crimp joint.
corrosion can be an issue with any of the above, but something sealed in adhesive lined heatshrink should outlive the rest of the cable.

A seagoing yacht is a fairly humid, corrosive environment in places, but even the engine bay is benign by avionics standards.

It's more important to make a good job of whatever method you use, and ensure the cabling is well secured against vibration and flexing.

 

[ffiill]

An easy and I feel satisfactory solution to join large diameter cables, is to use short lengths of copper water pipe. The pipe is available in many diameters. Match the inside diameter of the pipe with the outside diameter of the wire conductors. It should be a tight fit. Clean the inside of the pipe then push the conductors in each end. Crimp the copper pipe around the wire for mechanical strength then solder ( you need a very big soldering iron ) for electrical conductivity. Wrap in a couple of layers of glue lined heat srink and preferably some conduit.
It produces a low resistance, waterproof, mechanically strong, cheap and neat join that is not much larger than the existing wire. It is a less flexible over the join so support it if there is any vibration / movement.

I do the same-I also make up terminal connectors the same way-flatten off end of piece of 8/10mm microbore;take off the corners and drill to required diameter.
I use a beautiful 19thc vintage "heat by blowlamp" tin smiths soldering iron one of a set that belonged to my grandfather.

 

[stephenh]

If you were to use a piece of copper tube ( assuming water / gas pipe from what used to be called Table X) then you must make sure that the tube is totally full of solder as the wall thickness will probably be only 0.7mm which gives a CSA (cross sectional area) of approx. 33mm squared.
Even the thicker walled tube available (and rare) of 1.0mm will only give approx. 47mm sq. These are both way under your cable CSA.

You would be better using the proper crimp / solder joint with the thicker wall as in post no. 10 above.

Good luck.

 

[pvb]

If you were to use a piece of copper tube ( assuming water / gas pipe from what used to be called Table X) then you must make sure that the tube is totally full of solder as the wall thickness will probably be only 0.7mm which gives a CSA (cross sectional area) of approx. 33mm squared.
Even the thicker walled tube available (and rare) of 1.0mm will only give approx. 47mm sq. These are both way under your cable CSA.

It wouldn't actually matter, as the length of the thinner section is so tiny. The reason for large cable is to reduce voltage drop over a long run.

 

[pvb]

Crimped joints have a much less abrupt interface and are less prone to corrosion. What does "fine in the context of a leisure boat" mean? The requirements of a leisure craft, especially a sea going one are no less than any other, perhaps even more so.

I mean that a leisure boat isn't a battleship, or a nuclear sub, or a cruise liner. Home-made crimped and soldered joints are fine on a leisure boat. Maybe "Practical Boat Owner" isn't the ideal forum for your higher standards.

 

[stephenh]

"It wouldn't actually matter, as the length of the thinner section is so tiny. The reason for large cable is to reduce voltage drop over a long run."

pvb - thanks for that.....

 

[lw395]

"It wouldn't actually matter, as the length of the thinner section is so tiny. The reason for large cable is to reduce voltage drop over a long run."

pvb - thanks for that.....

Pedant mode on, cable rating is also about heating of the cable. A short length of small x-section won't matter if the rest of the cable is carrying the heat away. But even an 'acceptable' voltage drop can over heat things if the heat can't escape.

 

[pvb]

Pedant mode on, cable rating is also about heating of the cable. A short length of small x-section won't matter if the rest of the cable is carrying the heat away. But even an 'acceptable' voltage drop can over heat things if the heat can't escape.

You're theoretically quite right of course, but you haven't bothered to assess the practical effect of your theoretical knowledge. Even if the copper tube were only 20mm2 area, and even if there was a gap between the wires of 10mm, the voltage drop with 100A current would only be about 1mV - in other words, the heat produced would be 100mW, just a tenth of a watt. Now, be honest, is that going to create a lot of overheating??

 

[noelex]

As others have said the voltage drop is insignificant and this is generally the limitation on boat DC systems but in practice the cables will be butted together and the void filled with solder so the cross sectional area will be larger than the original wire even if their are a few voids in the solder coverage.