NNTP-Posting-Date: Wed, 08 Jan 2003 08:24:06 -0600
From: firstname.lastname@example.org (John Fields)
Subject: Re: Reducing contact resistance for low volt use?
Date: Wed, 08 Jan 2003 14:29:19 GMT
Organization: Austin Instruments, Inc.
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On Tue, 07 Jan 2003 21:44:19 GMT, DarkMatter
> *That* was the "nominal" quoted figure. Since plating thickness for
>all but solid silver wire is measured in percentage of the whole wire,
>and runs only through a three percent range from 1 to 3 percent, I
>doubt much change would be noted.
The plated wire data sheet from www.mwswire.com shows a plating
range of from 1.25% to 6%, with the 6% coating thickness yielding
265 microinches for a #24 wire with a nominal diameter of 0.0201".
That gives us a silver right circular cylinder with an ID of
0.0201", an OD of 0.02063", and an annular area of 0.00001696"²
bonded to the copper core. With a resistivity of 10.31 ohms per
circular mil foot, the 24 gauge core will exhibit a resistance of
25.67 milliohms per foot at 20°C, while the silver cylinder, with a
resistivity of 9.95 ohms per circular mil foot will exhibit a
resistance of 480.25 milliohms per foot at 20°C. 480.25 milliohms
in parallel with 25.67 milliohms yields a total resistance of 24.47
milliohms per foot, a decrease of 1.2 milliohms per foot, or about
> That kind of says that solid silver strands bundled up into a custom
>feed line would be the best solution.
I doubt it, since just a little more cheap copper would have to be
added, in parallel, to handle the current that less of the expensive
silver wire could. But, depending on the tempco of Ag VS Cu, it
might be worth it.
>>> For copper (bare) at the same gauge, it is 25.67 ohms per 1000 feet.
>>> As for the reasons for silver on wire in the military, it was
>>>originally used soled in transmitter equipment initially because the
>>>cost for silver was a lot higher back then.
>>Your argument that it was used originally because it was more
>>expensive back then is nonsensical _and_ untrue. Check the Silver
>>Institute website for the facts.
> Bullshit. If it were not an issue, they would have made transmitter
>coils from solid silver, not just plated silver.
Bullshit bullshit. Elemental silver is _very_ soft, and would have
easily failed to maintain dimensional stability in that military
application; detuning the transmitter, ruining the antenna matching,
etc., etc.,. While cost _is_ important in any application, it
becomes less and less important as performance and reliability
become more and more important.
> The corrosion
>problems for silver plated copper would be gone as well.
You know not of what you speak. From one of your other posts you
indicated that it was your belief that a paucity of plating would
result in gaseous oxygen intrusion and corrosion when, in fact, a
humid environment would be all that what was required to allow the
galvanic corrosion to occur since, with the intrusion of a water
molecule into the Cu Ag electrolytic cell, it becomes dissociated
and starts tearing shit up.
>definitely used it only in radios for that reason. Then it became
>apparent that it would benefit power transmission lines as well.
I'm not aware that siver is used extensively in power lines on the
grid. Would you please supply some references?
> Again, not solid, but plated strands. Were cost not the factor in
>that, they would have opted for pure silver as we always use the best
>for mil spec. Their "best" was silver plated. Sounds good enough for
Just because it's good enough for you doesn't mean it's good enough
for the military.
>>As I recall, silver was/is used to plate the wire used to make coils
>>in HF equipment in order to minimize skin effect.
> No. It was in fact, to optimize it. Silver is a better conductor.
>Plating HF components in it, particularly coils, make them work better
>*WITH* the skin effect, not abate it, which is impossible anyway.
Perhaps I should have written "in order to minimize the effects of
skin effect." Happy now?
>> I don't recall
>>silver plated chassis wiring or cables on vintage military radio
> As I said. Originally, it was only used in the RF sections. It is
>STILL used to this day to plate output tube connection rings, etc.
> Yet another proof that silver oxides are far more desirable in
>contact faces than copper oxide would be.
You have a remarkable grasp of the obvious.
>>>It has since migrated to
>>>power cabling for corrosion resistance reasons, mainly.
>>> One of the mentions in the mil specs are susceptibility to "rd
>>>plague" corrosion, A galvanic response at the copper/silver interface.
>>>No electrical stimulus needed. It surround plating thickness and
>>>integrity as oxygen seems to be the culprit. I guess that is why they
>>>call it "oxidation".
>>"Red plague" isn't oxidation, it's a form of galvanic corrosion
>>which occurs in the presence of humidity because of the location of
>>copper and silver in the electrochemical series.
> Yes. Note that I said this above. That galvanic response is due to
>the porosity of the plating. It takes form in the way of allowing
>oxygen into the area where the two metals interface. Though the
>mechanism is galvanic, the product is copper and silver oxides.
>> It is exacerbated,
>>but not caused by the presence of oxygen, and occurs when the silver
>>plating is too thin, allowing moisture to form an electrolyte
>>between the two metals, which then become a shorted battery.
> No. The sole motivator is the presence of oxygen. That is why
>heavier platings do not exhibit the problem... at all.
No. the sole motivator is the presence of ionizable water, and
heavier platings prevent the intrusion of water into the interface.
In a gaseous O2 free environment corrosion will still occur, but in
an oxygen-rich, dry environment it won't. While the products of the
corrosion may well be oxides of silver and copper, the oxygen is
obtained from water, not air.
>>> I'm sure there are many other factors. Another good one is that SPC
>>>is far more solderable (especially over time and environ)than is TPC
>>>or straight copper even. It remains "wettable" longer.
>>Since it's the flux in the solder which is responsible for removing
>>the chemical contaminants from the surfaces to be soldered, I don't
>>think there's a really big difference between tinned copper, copper,
>>or silver plated copper.
> I guess that you have never tried to wet a TPC HV wire then.
Sure I have.
> We have spools of it on the shelf where it was improperly purchased.
>It hasn't aged, it has a reaction with the teflon. making wetting
If it hasn't aged and the problem was there from the beginning, then
I doubt it was the Teflon which caused the problem, since Teflon is
_very_ stable. More likely the processing reguired to get the
teflon around the wire is the culprit. Do you know what the
> The SPC versions, however, tin right up. A well
>known fact in HVPS circles.
> Did you take a prozac, Zanex or something? You seem more calm.
>Are you bipolar?
Neither. I'm reacting to your newly found semi-civility and finally
getting back on a technical topic.
As an aside, I've looked high and low for any information to either
prove or disprove your claim that "pure" silver oxide is a better
conductor than elemental silver. Do you have any data to support
Professional circuit designer