Anonymous wrote:
Plain, un-tinned copper will corrode at the joint, would solder tinning the wire ends before crimping be a good idea? Likewise a copper strap.
I used to be a follower of the solder faith, and I suppose none are as devout as the converted, so please excuse me if this sounds like I'm once again mounting a soap-box :-) If you don't have extra time on your hands due to Covid 19, then the bottom line is crimps are great with glue lined heatshrink, otherwise, hopefully what follows is either entertaining or informative.
Glue-lined heatshrink can be used for insurance for crimped terminals. Heat it not just until it shrinks, but until you see a little glue ooze out of both ends. However, the crimp itself is almost as good as the wire are resisting corrosion. Keep in mind, there are millions of cars driving around on salt-laden roads in the winter. All of their connections are crimped and most are less protected than you will do on your boat. Lots of folks have seen, made or inherited poor crimps and this probably makes them more concerned than necessary. A proper crimp matches the ferrule to the wire size so there is little extra space before the crimp. During the crimp both the wire and the terminal deform to create a join that should not have any gaps. It should be air tight. I've actually gone to the trouble to cut a lug in half, acid etch it, and view it under the microscope to confirm that I can make crimps this well. But, for those that are wiser with the use of their time, here is one example of what a good crimp should look like. Here is another example, the pic on the left is made with an indent crimper, like I mentioned earlier in this thread and the pic on the right is made with a hexagonal die, like the kind David bought.
For a person at home, or on their boat, most industrial means of inspecting crimps are impractical (expensive, specialised equipment, etc.). However, there is a pretty good relationship between mechanical strength and electrical conductivity in crimps. So, buy a couple extra lugs and make a test piece. If you can come between the UL and Mil Spec tensile strengths listed in this table, you're making good crimps. Your test apparatus need be no more complicated than the rafters of your garage (or a tree branch), a bucket, a bathroom scale, and a way to keep yourself (especially toes), away from danger should the connection fail. Weigh things on your scale and add them to the bucket until you meet the spec weight or the connection fails. Please use sense in testing, don't use something stretchy (use chain rather than nylon line) in the test rig so that things don't fly about if they break, wear some safety glasses, be responsible for your own safety. If you use a plastic bucket, think about how strong it and its handle are.
For the copper strap. The strap itself should be fine left bare, but the mechanical connections are best with something to exclude air and liquids. Silicone dielectric grease is the gold standard, but has the drawback that it is silicone. Maybe it's just me, but silicone seems to like to go everywhere and also has the property of being impervious to virtually all solvents and cleaners. Thus, years later you may wonder why you are getting fish-eyes when you refinish your brightwork because you have long-forgotten the silicone fingerprints you left behind. I keep a small tube of silicone dielectric grease for things like VHF coaxial connections that need the very best. I've used a fair bit of Grote Ultra Seal, mostly because it is easy for me to get locally. It is some kind of petroleum based grease. It seems to get thicker and darker as it ages on the connections. However, I've pulled apart stuff more than ten years old and it still seems to be doing its job. Get the tube version for less mess. Lanolin is another alternative. Lots of us have experience with Lanocote. This is Lanolin with petroleum distillate added to make it workable through a wide range of temperatures, it may have other additives. I'd just as soon not have the petroleum distillates, so I've been using straight anhydrous lanolin for a while now. It seems to work just as well, and your hands are silky smooth at the end of the project. During Canadian winter temps you need to keep the container in your pocket or it gets too cold and hard to work with.