[time-nuts] DC distribution

Sun Oct 6 03:16:08 UTC 2019

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.

Larry McDavid
40 years experience in electronic packaging and formerly engineering 
manager for a well-know connector manufacturer.

On 10/5/2019 3:03 PM, MLewis wrote:
> The bulk of my wiring experience is with residential electrical (VAC) 
> and audio signal cables & speaker cables, with some VDC in amplifiers. 
> Most of the computer cables I needed I could order, so I wasn't usually 
> terminating them myself.
> 
> With audio, it's pretty straight forward. A number of people figure 
> they'll save some money and avoid the snake-oil cable sellers and make 
> their own cables. So they buy the materials that others have found work 
> well, they'd make some cables, and report they don't sound good. The 
> sound simply isn't clear. Many don't seem to be able to make a quality 
> solder joint. When they get their friend who knows how to solder to redo 
> the connections, and the sound is clear. Others get steered to the 
> crimping connectors, but use pliers or cheap crimping tools. Again, 
> despite quality materials, not a clear sound. They're just not a quality 
> connection. So they can learn to solder properly, and be at risk of the 
> typical stress failures of soldered connections, or the more robust and 
> much easier to learn path, buy a proper quality crimping tool and learn 
> to use it. Great connection and repeatable.
> 
> Then there's the soldered crimp. It's astounding the number of times 
> such a connection fails and the wire: moves back and forth, turns in 
> place or pulls out. The heat from soldering expands the crimp, lowering 
> its crimping pressure, for a poor crimp connection, but it's still tight 
> enough while heated that the solder can't wick in. You end up with the 
> combination of a poor crimp connection and a poor solder connection. I'd 
> guess that with a poor enough crimping, there could be enough space to 
> wick solder in...
> 
> An engineer told me what was up, and I cut open some connections that 
> seemed solid to check. In each case there was a gob of solder at the 
> end, but only some trace solder within the first part of the strands, 
> with minimal contact between the wire and the crimp. I've cut one open a 
> number of times over the years since, to show such to people. (Note: 
> NASA will not accept crimped connections of tinned stranded or tinned 
> solid wire. I've no idea why, but I figure it's a given that they know a 
> lot more about terminations and connections than I ever will.)
> 
> So my first-hand personal experience is that I've seen dozens upon 
> dozens of examples over four+ decades where an audio cable terminated 
> with soldered crimps that did not sound clear, but replacing the 
> terminations with properly soldered or properly crimped connections and 
> the sound was then clear. Not a subtle difference, but at minimum a 
> strong improvement, and usually a night and day difference. Now for 
> quality consistency, I only use crimps for audio connections and choose 
> connectors accordingly.
> 
> I've heard a lot of speculation over the years as to why this difference 
> in clarity, but nothing that seems completely credible. The closest to 
> credible speculation I've heard is:
> - a poor connection results in multiple signal paths resulting in a 
> sightly overlapped signal so the signal is no longer clear, or
> - a poor connection has multiple connections and combined with eddy 
> currents in the connector you can get tiny RC paths instead of a single 
> long connection, so you've got multiple re-injections of a delayed 
> signal that smooths tiny changes in voltage, which is your signal.
> Causation is clear. The explanation? No idea.
> 
> I've heard people say that all this analogue cable stuff doesn't matter 
> for digital signals because it's digital. Except that if one reads the 
> specs, the "digital" signal is really an digitally encoded analogue 
> signal. Back in the main-frame era, a number of times I was able to 
> correct throughput degradation or outright failure by addressing cable 
> issues (poor connections, shielding grounding, co-located cables of 
> identical length so they're sometimes surprisingly effective as 
> sending/receiving antennas, etc.) that techs thought would only apply in 
> analogue signals.
> 
> So where someone is transferring a timing signal down a cable, depending 
> on the frequency a quality termination/connection may be important, not 
> only to the longevity of the cable, but to the quality of the signal, 
> hence the ease, speed or consistency with which it drives and triggers 
> what is reading it.
> 
> And for power connections, you don't want to hope you detect the signs 
> of a failing loose connection due to heat, arc smells, etc. (like the 
> mushroom-cap screw heads on terminations for containment & detection), 
> before it outright fails, nor a conductor that comes free if the 
> wire-to-solder connection breaks. The welded connection is new to me, 
> but sounds like it could befit in some applications. If you've enough 
> power and the connection is not tight, I have seem some conductors weld 
> themselves to a terminal, often with a thin connection; but usually it's 
> material gets blown away and the conductor is now loose. Lithium battery 
> packs can deliver some surprising current.
> 
> So again, I don't think doing a proper (or poor) crimp connection, then 
> expanding it with heat to try and wick some solder into gaps that would 
> have been reduced by crimping and then with heating, is a very good way 
> to go, along with taking on the risk of the stress failures of soldered 
> wires.
> 
> 
> On 05/10/2019 2:10 PM, Wes wrote:
>> On 10/4/2019 12:17 PM, MLewis wrote:
>>> With audio signals, a soldered crimp is one of the worst possible 
>>> connections.
>>
>>  Please explain.
>>
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-- 
Best wishes,

Larry McDavid W6FUB
Anaheim, California  (SE of Los Angeles, near Disneyland)