Settle an argument

Scenario facts: a piece of stranded copper battery cable about 3.5" long with two soldered connectors at each end, used for ground connection on a motorcycle battery. The cable broke in the middle with what looks like a stress fracture. Cable was flexed many times, every time battery had to be taken out or when battery had to be disconnected for electrical tests or electrical modifications to motorcycle wiring.

Son contends it is the fault of soldering connectors onto cable, which heat stressed the cable. I think it is copper work hardening when flexing cable, thinking that heat if anything (maybe to low) would help anneal copper.

Your opinion welcome. cheers T.Alan

Reply to
T.Alan Kraus
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Dad is correct. Heat anneals, flexing work- hardens. That's why copper tubing is forbidden for aircraft fuel line.

Reply to
Jim Stewart

Solderless crimp connections are said to be more resistant to severe vibration because stress concentrates at the point where the solder stops wicking up the wire. Sometimes a tapered rubber boot is used to distribute the bending stress.

If the break was in the middle, maybe it was at a vibration node?


Reply to
Jim Wilkins

Soldering the terminals didn't "heat stress" the copper however it is possible that in soldering the cable solder wicked up the cable which turned that portion of the wire into effectively solid wire thus making the flexible portion of the cable shorter and contributed to the work hardening of the cable due to flexing.

Annealing copper is usually done by heating it until it turns red and either quenching it or leaving it to cool slowly. This is far above the temperature necessary to soft solder copper wire. Thus the question of "heat stress", if it exists, doesn't apply.

Try making the new cable longer and perhaps bending a loop into it to allow more flexibility.



Reply to

You may find the flexing and breaking is caused by the vibration from the engine work hardening the copper. Just because you can't see the flexing doesn't mean it is not there. You need to encase the new cable with some type of heavy insulation which will dampen the vibrations. Perhaps instead of stranded battery cable, use a short length of heavy welding cable. The copper strands are quite small and will not vibrate near as much and the heavy insulation will dampen the vibration even more.


Reply to

Stranded cable that breaks AT the soldered joint can (rightly or wrongly) be blamed on soldering More than an inch or 2 from the solder, no way.

Reply to

And for automotive brake lines, and a miriad of other applications. SOP in years past (antique cars) was to remove and anneal the fuel lines every year or so to prevent vibration stresses cracking the fuel line.

Reply to

It's a combination of factors. Just bite the bullet and buy a new cable.

Yes, it shouldn't had been soldered, and yes, every time you screw around with it, it work-hardens the copper, and probably didn't do the insulation any favors, so it's shot. Unless you're destitute, the new cable will be your best bet; otherwise, you'll be dicking around with kluges for the remaining life of the bike.

Cheers! Rich

Reply to
Rich Grise

T.Alan Kraus wrote: ...

The heat was probably too low to do anything one way or the other. If the solderer went crazy with the heat, it would have softened/annealed the copper.

Soldering is a problem though. Or can be. What often happens is the solder wicks up the cable beyond the connector, making it stiff and creating stress risers. I.e., flexing the cable will create a sharp bend where the solder ends. A crimped connection allows a more gradual transition during flexing. Because the actual crimp is in the middle of the connector, allowing some wiggle room between the crimp & end of connector.

That's my story & I'm sticking to it, Bob

Reply to
Bob Engelhardt

It has been replaced with a longer conductor made from much smaller gauge individual copper wires built up into strands, and a stress relief loop is now incorporated. thanks

Reply to
T.Alan Kraus

Son's right on this one - the solder will wick an inch or two up the wire when it's heated. If the whole cable is only 3-1/2" long there's only about an inch in the middle that can do any flexing. And when you concentrate all the bending flex like that...

And I'll bet the battery was moving relative to the chassis while riding, so it wasn't just from removing and replacing the battery. You can't make it too rigid or things will break over time.

Saw your post already about making a longer cable and leaving a slack loop, that should be a permanent repair. Don't solder the new lugs, but seal battery acid out of the crimp connections. Heat-shrink tubing with hot-melt glue sealant inside might be the ticket.


Reply to
Bruce L. Bergman

What I used to do with battery connections was to splay the copper strands slightly, force some silicon grease between the strands, twist the strands back together, and crimp or bolt the terminal onto the wire. The clamping pressure forces the grease out of the actual contact areas, allowing metallic contact, while the grease fills the space between the strands, excluding the acid.

It also helped a lot to smear the battery post and the inside of the battery clamp with this same grease, keeping the acid from wicking up into the space between post and terminal.

The silicon grease I used was made in the 1970s by GE as a dielectric grease, to exclude water and dirt on the insulators of high-tension transmission lines, and is now available as for instance Permatex Dielectric Grease .

Joe Gwinn

Reply to
Joseph Gwinn

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