[time-nuts] DC distribution

[jimlux]

On 10/5/19 8:16 PM, Larry McDavid wrote:
> I've used Power-Pole connectors for many years successfully and I've 
> always crimped them with appropriate Power-Pole crimp tools. I never, 
> never solder crimped connections! Heating a crimped connection to 
> soldering temperature will relax the crimp force in the crimp zone and, 
> if properly crimped, there is no gap among the wire strands for solder 
> to flow into. The result is always a loss of connection quality.
> 
> Stranded wire can be tinned or coated with solder by the wire 
> manufacturer and crimped successfully so long as the wire is 
> "non-fused-tin-coated." But, much stranded tinned wire *is* fused to 
> keep the strands together after removing the insulation; this type of 
> stranded wire should not be crimped. Much MIL Spec wire is silver 
> coated, inherently non-fused and crimps well.
> 
> Professionally (in both aerospace and high-rel automotive air bag 
> applications), I've had the "crimp zone" of very many crimped connector 
> contacts metallurgically mounted, cross-sectioned and examined 
> microscopically after polishing and etching to reveal the individual 
> strands even in the crimp zone. This is the ultimate method to "qualify" 
> a crimped connection. A "gas-tight" crimp shows under microscopic 
> examination no air gaps within the crimp zone--the crimped wire bundle 
> has gone solid and is "gas tight."
> 
> "Crimp pull force" is another, production level, crimp quality control 
> method but the proper method requires making numerous crimps at various 
> "crimp heights" (how reduced in dimension is the height of the crimp 
> zone) and pull force testing the resultant crimps. The requires crimping 
> by a machine or qualified hand crimp tool that is adjustable. The pull 
> force values are plotted against crimp height and the shape of the curve 
> examined. A crimp height resulting in a pull force just as the pull 
> force begins to *decrease* after reaching a peak value is selected. A 
> "looser" crimp is not "gas tight" and a "tighter" crimp reduces the 
> cross-section area of the wire bundle enough to weaken the crimped 
> connection. Crimped connections have to be crimped within a narrow zone 
> of compression and only the appropriate crimp tool, appropriately 
> calibrated, can provide this. Forget about all types of "crimp pliers;" 
> these are worthless tools.
> 

interesting...

And I assume, then, that the degree of compression (set by the dies and 
their position in the crimper) is wire gauge dependent - that is, the 
crimper doesn't crimp to a specific force, it crimps to a particular 
mechanical dimension, so if the number and size of strands is different, 
then the degree of crush is different.

That sort of makes the "crimping a tiny wire by folding it back on 
itself" or "crimping a tinywire by putting it with a big wire" a tricky 
operation.