PeachParts Mercedes-Benz Forum - View Single Post

micalk · #12 07-17-2010, 10:49 PM

You do realize, of course, that almost all the connectors in your car are soldered and none of them were crimped first, right?.

It would seem that you are suggesting either to crimp and solder or simply crimp without soldering for the best joint, since soldering without crimping can lead to delamination.

A cold solder joint is another matter, but I'd assume that you are comparing a proper crimp to a proper solder joint. I've never seen nor heard of a properly formed solder joint delaminating. I've seen plenty of cold joints where there was either contaminants in the joint (not cleaned properly prior to soldering), not enough heat was applied to flow the solder properly on all connection areas, or a connection was moved when cooling. I've never seen it but was trained not to blow on a solder joint to cool it since a joint that is cooled too quickly or unevenly can be a source of failure. (Years ago I was ISO 9001 certified in soldering and circuit card repair, so I have a little experience in this arena.)

I agree that the best solder joints begin with a mechanical connection between the parts. So a wire may be wound around a pin or stud before soldering to it instead of just laying the wire up against it. The goal is to have solid contact between the two materials before soldering. A 6ga wire in an 8ga lug has plenty of contact. Normally one would 'tin' the wire before soldering. I tried that first but it added too much diameter to allow the wire to enter the lug. So the mechanical side of the joint is pretty much there to begin with. Since the 6ga wire barely fits into the 8ga lug, I'm not sure how much deformation you could get if you tried to crimp it. Besides that, a tool to crimp that size lug is not in too many people's tool box. (I know it's not in mine.) And it would take a _huge_ amount of solder to fill in the space between a 6ga wire and a 6ga crimp lug.

An additional benefit of soldering over a crimp is the greatly increased surface area that conducts the current between the wire and terminal. Soldering the wire into the lug in this instance provides an incredibly strong joint with excellent conductive properties.

A crimp is a simple mechanical connection that exposes a portion of the connection to the atmosphere. Oxidation and corrosion can occur in the connection especially when exposed to the salt and water of winter driving. On top of that they are not as mechanically sound. Twist a crimp connection and the wires will shift around into more optimal positions in response to the stress imposed on them, which results in a looser connection. Vibration can produce the same results. I've seen many more crimps fail than solder joints.

You mention that solder has higher resistance than copper and you are correct. I think it is about ten times as high as copper. Solder would not make a worthwhile conductor if you wanted to wire your house with it. It is the length of the run and the circumference of the conductors that make a difference in that case. Solder connections, though, are fractions of a millimeter at most. The amount of resistance added to the circuit is on the order of .0001 ohms, and takes special equipment to measure accurately. If you pumped a thousand amps through it you would see a 0.1 volt drop.

Sorry for the rant. Must be getting old and crotchety.