is silver plate found in many flashlights?

I'm new here. A casual search did not turn up the answer.

Is silver plate found in many flashlights? If not, why not?

Why, for instance, do I see gold plated springs in the two Cree lights that I recently bought? Why gold?

Don't the Chinese know of silver's singular virtue?
It's also cheaper, pretty surely.

Yeah, that's a leading question I pose.
Some of you know what I'm driving at already.


:thinking:

Silver oxidizes, but I remember silver oxide being a good conductor as well

I'm guessing that gold looks distinctive, and connotes "high quality". With silver, either it tarnishes (looks like crap), or it looks just like nickel, steel, stainless, etc.

Yes! That's it. Silver is not only the most conductive metal,
it also is the only metal (that I am aware of) whose tarnish/oxidation products are perfectly conductive.

In the era of the vacuum tube: early Western Electric tubes of the WW1 era and beyond, had gold tips soldered to their prong-ends.

Some years later the military determined that silver was far superior and cheaper than solid gold!

All of the mil-spec tube equipment of the WWII era and beyond used tube sockets whose many spring-clip contacts were of phosphor bronze (that's copper and tin) heavily silver plated.


It did NOT matter when and if the silver tarnished.
The electrons passed unimpeded.

The "problem" with silver is that it -looks awful- when tarnished. Human nature wants to polish away the tarnish! Not a good plan--we'd lose the conductor.

Copper oxide is a great insulator. Makers of cheap flashlights have known forever, that their market for replacement lights is secure as long as they continue to output flashlights with -brass- contacts. Brass is just a poor conductor to start with, and it gets an oxide film of zinc and copper oxide= dim light, throw it away.

But in these newer lights with gold plated parts: I wonder, why?

Gold is an indifferent conductor.
Worse, it requires to be plated atop nickel.
Brass or bronze, a layer of nickel, a microlayer of gold.
The base metal will tarnish beneath the nickel in time.
The gold maintains contact with the nickel.
In service where exposure to tarnishing gasses is likely,
there will be some increase in circuit resistance in the case of a gold over nickel on brass or bronze spring.

If instead, the spring is heavily silver plated, the entire path for the current can/could be through the conduction of silver alone--that skin is of the noblest pedigree for current conduction.

Silver plates directly atop base metals. Unlike gold, it does not need a flash of (indifferent-quality-conducting) nickel.

___________

It's pretty clear that today's quality lights do OK without silver contacts. Ah, but if clicky switches are not all silver plated parts, well, that seems like a small shame.
Because if, say, a 1925 Everready flashlight had been made with all silver plated parts (in fact, only the reflector was silvered) then that light would be working today at full efficiency, given fresh batteries.

Silver plate makes connections immortal. IF Maglight
cared, or knew better, they'd silver plate switches (do they?) and contact springs, and they'd issue a directive to end users:

Do not polish silver if you want your shine to last

:thumbsup:

sysadmn said:

I'm guessing that gold looks distinctive, and connotes "high quality". With silver, either it tarnishes (looks like crap), or it looks just like nickel, steel, stainless, etc.

Click to expand...

Right. So what a maker would want to do: make the silver a selling point. The tarnish aspect can be made a selling point: The Forever Flashlight.

Even today...confusion:

http://www.finishing.com/370/45.shtml

Silver vs. Gold:

Yes, they are both important in electrical contact systems. Aside from cost, one of the most significant differences is that gold is very nonreactive. Silver does not oxidize readily in air, but it does form "tarnish" (silver sulfides and silver chlorides).

The question then becomes, how does the conductivity of pure clean gold compare to tarnished silver? The nod goes to the gold.

Here are a couple of quick looks at the use of silver and gold in electrical contacts:

http://www.brushwellman.com/alloy/tech_lit/sep02.pdf

http://www.brushwellman.com/alloy/tech_lit/July02.pdf

Thank you Steve. I need to get Acrobat into this just-loaded Vista OS (PS: stick with XP). Am really keen to read the two articles.

I suppose the point is made, and you obliquely hit on the point, that our gold plated contacts in lights are likely to be micron-thin depositions atop nickel plate (tarnishes under the gold, and therefore reduces -current in current conduction capacity in time, if and when the nickel is exposed to tarnishing agents.

Platings are mostly quite porous. As a for-instance, old nickel plate (which is put atop a flash plating of copper, always) will turn somewhat dark in time. This is due to the copper below taking a tarnish. A soak in ammoniated water will brighten the nickel plate to new condition, by brightening the copper substrate. Platings are porous and for current handling---I think silver's corrosion byproducts will handle current. Need now to read your cite articles, to learn just how and to what degree the findings translate over to flashlight efficiency.

Reid, FYI, the articles come from Brush-Wellman, who is a well-known vendor of materials used in electrical contact systems, especially beryllium-copper and related materials. You might find the articles a bit too brief and generic, but I hope they shed some light.

There's a lot more to engineering a contact interface than just material selection. Contact area plays a major role among others. And contact area breaks down into apparent area vs actual area of contact, where actual area is a strong function of contact force.

If you're designing a switch, the norm is to incorporate wiping motion between the contacts during transition to help them "self-clean". In circuits carrying higher current, cleaning can be accomplished thru the natural arcing that occurs during switching. At higher voltages, thin layers of contamination are irrelvant since they'll be overcome by the voltage. But if it's a static low-energy connection (plugging a printed circuit card onto a motherboard for example) forces aren't all that high and wiping is a nonissue. This is where you tend to find the gold for its inherent long-term stability.

Hi Steve,

"This is where you tend to find the gold for its inherent long-term stability."

I suspicion that is due to sales and fashion. Silver is a hard sell. But, long-term stability? I've got boxes of porcelain tube sockets, or did, and their contacts never made a crunch or crackle in audio tube work. Yes, to all you said about contact actions.

Say, I made a tube preamp, moving coil input, all triode, esoteric little peanut tubes. The attenuators to balance stereo channels, were/are fifty position wiping contact switchable resistors. All very primitive. The contacts are all silver. The signals are critically sensitive to the noise that imperfect contact would induce.

There is no noise. Old school silver, I really think, is much neater and more basic and more suitable for flashlights--particularly for switch contacts. That's just my opinion today.

But we know: opinions like this, based on simple observation and common sense, will never displace the gold bug.

Gold sells. Gold is sexy.



Silver can turn gray or black.
Silver...not sexy. But, what a magical metal for wiping contacts. Ductile, but not excessively soft. Homogenous-can be directly plated to brass or bronze.

Think outside the gold plated box, guys, I say,

gold in flashlights is snake oil.
I won't object to it in my computer; those seldom-parted connections are happy in a micron's cladding of gold.

But if all that gold were silver? I wouldn't mind. I think it would all work the same,

but, in a flashlight? Better and forever.

This talk has got me thinking about putting an old Mercury dime in the bottom of the battery tube of a couple twistie lights.

Geoff

Geoff, a Roosevelt dime from 1964 or before might be easier to find and less costly if lost. Same silver content.

Interesting thread. I didn't know silver oxides and sulfides were conductive.

years ago... when I was working in a production plating shop.

one of our contracts was plating bus bars for power plants. these were not little bars, but huge solid copper buses used for power plant transmission and contact switches.

what spec's required was heavy silver plate. which was applied directly to super cleaned and activated with nitric acid (very briefly) copper. We used a cyanide vat with solid silver (99.9 fine) anodes.

the engineers explained silver was chosen over gold due to superior contact abilities.

One of my ham radio antenna books stated that silver will conduct 105% of the electricity that copper will conduct.

cy said:

years ago... when I was working in a production plating shop.

one of our contracts was plating bus bars for power plants. these were not little bars, but huge solid copper buses used for power plant transmission and contact switches.

what spec's required was heavy silver plate. which was applied directly to super cleaned and activated with nitric acid (very briefly) copper. We used a cyanide vat with solid silver (99.9 fine) anodes.

the engineers explained silver was chosen over gold due to superior contact abilities.

Click to expand...

wow! i never knew the stuff on busbars was silver.
i thought it was copper with a nickel plate.
this is all very interesting.

exampling old mil-spec stuff they nearly always silver plated, often quite heavily:

a ganged fuse holder
http://tinyurl.com/3xnzqc
_____

Angela Instruments sells new and NOS tube sockets.
I used to build vacuum tube audio stuff; used to buy from Steve. Good guy.

Silver plated contacts were and are preferred in the DIY audio field:
http://www.angela.com/catalog/tube-sockets/4.5.6.pin.html

_____

Caswell is the leading supplier for DIY metal finishers.
I've never used their kits.
http://www.caswellplating.com/kits/silver.htm

Many years ago I taught myself basic plating technique so I could restore the bright nickel plate of antique Mills Violano machines. There was no Caswell Supply then; I had to buy five-gallons of this and five pounds of that--all out of scale with the needs at hand.

Yet, I have never silver plated....wait:

When we were kids in junior high, we noticed that used-up photo print fixer solution would strike a micron-thin layer of bright silver on the metal tips of our BiC pens. Just polish and dip! That's not a useful result, but it was true electrodeposition of a primitive kind.

fwiw,
r.

I mentioned the following in a PM with Reid, and he asked me if I would post this info to this thread. Here goes:

I spent 13 years of my career working for a major manufacturer of precision circuit breakers and switches used in aircraft, HVAC, automotive, and other markets. The "gold" standard (sorry about the pun) in contacts was silver-cadmium-oxide. Very high conductivity, coupled with very high resistance to erosion and welding. Cad of course is a toxic material and I believe its usage has probably been superceded by other systems such as silver-tin-oxide or silver-tin-oxide-indium-oxide. However I'm now ten years out of touch with the state of the art.

I note in some of the design data that pure silver's environmental resistance is considered very good because it slowly forms a relatively innocuous conductive silver oxide. It more readily forms silver sulfide which is non-conductive but very weak and easily displaced by wiping action or high contact force, or "punched-thru" by voltage.

Thanks Steve. Therefore, presuming O-rings contain no sulphur, there's not much reason, then, for silver sulphide to form upon any silver-anything that might be found inside flashlights.Partial quote:

soffiler said:

...I note in some of the design data that pure silver's environmental resistance is considered very good because it slowly forms a relatively innocuous conductive silver oxide. It more readily forms silver sulfide which is non-conductive but very weak and easily displaced by wiping action or high contact force, or "punched-thru" by voltage.

Click to expand...

Do switches often bear silver plating?

------
Now for the biggie-question: What's with this tailcap spring in my new Fenix P2D-ce?

It's a relatively fine bronze (?) wire, bearing what appears to be thin gold plate.

I would think that pure silver plating would be a lot better than a few mere microns of gold, atop a substrate of nickel plate that in turn is atop the base metal wire.

Why, if it were a sufficiently-heavy plating of silver on that spring, the silver skin could become the prime path for the current
(bronze isn't so suave a conductor, and brass is positively bad).

Thanks in part to you, Steve, I now feel bold enough to state flat-out: Gold plate is liable to be found in places where it does not rightly belong. Tailcap springs?
Can you do some sort of evaluation? I don't know,
I guess the Fenix P2D spring is what, a few inches long,
and bears some kind of minor current, eh?

I have zero skills to determine just-what-and-how-much;
I can only work on broad concepts and intuitive logic.
Good engineers work from basic facts, and so get the job done right.
And, engineers who have both your intuitive genius
(I've seen your product design skills), and your mathematical skills;
such men are the golden....no!...the SILVER Sons of the Scientific Arts.



In desire of more data, thanks Steve,

Reid

It could simply boil down to diminishing returns in regards to many commerically-produced lights. Assume everything conductive in a light was silver plate. What would that give us, 5-10% increased output, maybe? It generally takes a 50% increase in output for the human eye to see the increased output. There would be little practical benefit to the customer.

Good engineering is all about choosing the right compromises. Good marketing, however, is all about capitalizing on public perception, and they often win out over the engineers. Thus we have gold were it doesn't belong, probably partly because someone with insufficient knowledge saw that it was good in certain situations and assumed that it would be good in other, un-related situations where the systems are completely different.

If a technically superior component doesn't yield a noticeable improvement for the end user, then it's a prime candidate for compromise in commercial manufacturing.

In the world of custom, high-end lights, such as the Alephs, high quality silver or silver plated parts, including springs, are more common.

Reid said:

Thanks Steve. Therefore, presuming O-rings contain no sulphur, there's not much reason, then, for silver sulphide to form upon any silver-anything that might be found inside flashlights...

Click to expand...

Chemistry is not my strong point, but I'll just mention that most types of cells, both primary and secondary, tend to outgas and of course those gases are trapped within the flashlight. Corrosion due to alkaline cells is legendary. Solvent-type aromas inside flashlights have been associated with primary lithium cells. Is there any sulphur? Honestly I don't know. There are traces of sulphur in the atmosphere, which is why silverware and silver jewelry tarnishes over time, but there's not much atmosphere getting into an O-ring sealed flashlight.

Do switches often bear silver plating?

Click to expand...

It depends on the switch, but, yes, silver plating is VERY common in the contact areas inside many switches.

Now for the biggie-question: What's with this tailcap spring in my new Fenix P2D-ce? It's a relatively fine bronze (?) wire, bearing what appears to be thin gold plate...

Click to expand...

I suspect the spring is made of music wire, which is a steel alloy.

... I would think that pure silver plating would be a lot better than a few mere microns of gold, atop a substrate of nickel plate that in turn is atop the base metal wire. Why, if it were a sufficiently-heavy plating of silver on that spring, the silver skin could become the prime path for the current (bronze isn't so suave a conductor, and brass is positively bad).

Click to expand...

I have taken some measurements of my P1D-CE spring and done the math. It's conical with a larger OD of .75" and smaller OD of .30". Average OD is .525" and there are 7 coils. The total length of the spring wire is therefore about 11" but I'm going to use 10" (25cm) as an effective length because the contact is not made at the literal tips of the wire, but rather around the circumference of the end coils.

Next, resistivity of music wire is 11.8E-6 ohm-cm and resistance = resistivity*L/A. The wire diameter is .028" and area (converting to metric) is .004cm^2. Resistance works out to 0.074 ohms.

Now, let's plate it with a .001" layer of silver. This "skin" results in what is effectively a tube of silver surrounding the music wire spring, the tube measuring .030" OD and .028" ID. The area of this tube is .0006 cm^2, length is the same 25cm and resistivity of fine silver is 1.6E06 ohm-cm. Resistance works out to 0.067 ohms.

Rounding both to 0.07 ohm, we see that a .001" layer of fine silver plate will literally cut the bulk resistance of the spring in half, not to mention the improvement in contact resistance.

But is this signficant? Let's say we pull an amp through this spring. Power dissipated is I^2*R which is .07 watts without silver plate, or .035 watts with the silver plate. My P1D-CE running on high does indeed pull roughly an amp from the cell, and cell voltage is about 2.5V under these conditions. We're taking 2.5 watts and losing .07 watts to heat in the spring, which works out to about 3%. Or 1.5% if we silver-plate the spring.

To be honest that's bigger than I thought but still not sure if it's big enough to call "significant".

Oh, and you are being a bit too hard on brass as a conductor. Here's a list of some comparative resistivity values referenced to pure copper. Most people probably think solder is a pretty good conductor, but look where it constituents (Tin and Lead) fall on the chart below:

Silver 0.95
Copper 1.00
Gold 1.42
Aluminum 1.64
Tungsten 3.20
Zinc 3.34
Brass 4.07
Nickel 4.53
Iron 5.81
Platinum 5.81
Tin 6.69
Music wire 6.86
Lead 12.79

soffiler said:

It depends on the switch, but, yes, silver plating is VERY common in the contact areas inside many switches....Lead 12.79

Click to expand...

Excellent analysis soffiler!

Thanks for taking the time to write this up. CPF is a better resource because you choose to share your expertise.

.