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Electrical Contact Material for Small Battery

goldenfab

Cast Iron
Joined
May 25, 2016
Location
USA Prescott , Arizona
I am looking for some recommendations for an electrical contact material.

I am basically picking a design change from prototype to production where someone else left off. I am re-designing a small sheet metal part that needs to also function as a spring to keep electrical contact with a watch battery. The original drawing simply calls out "Nickel Plated 3/4 Hard Bronze" for material. I have no reason to change the material other than specifying an actual bronze alloy. What bronze alloys are better suited to this application and which are not?

Thanks in advance.
 
I am looking for some recommendations for an electrical contact material.

I am basically picking a design change from prototype to production where someone else left off. I am re-designing a small sheet metal part that needs to also function as a spring to keep electrical contact with a watch battery. The original drawing simply calls out "Nickel Plated 3/4 Hard Bronze" for material. I have no reason to change the material other than specifying an actual bronze alloy. What bronze alloys are better suited to this application and which are not?

Thanks in advance.

Phosphor bronze was the go-to for a hundred years. Hard enough. Conducts well-enough. Most of all, retained spring tension superbly.

Decent spring Stainless - allegedly not as good, but proven "good ENOUGH" - has de facto taken-over most of the market, starting well over fifty years ago. CAVEAT - some changes to dimensions & c. may be in order.

That was partly to eliminate the cost and delay of the plating step, and partly to reduce damage when, not IF, batteries are left to wither, die, and corrode-nasty.

2CW, but I have, and would again, use Stainless.
 
Thanks for the info. I forgot to mention the part will need to be soldered to a PCB. I'm guessing stainless would not be the best choice due to that.

Stainless is soldered "somewhere" on this Earth every hour of the day. Also riveted. Also riveted AND solder-flowed. Also pressure resistance welded.

What do you think applying Nickel plate makes Bronze act like?

Yup. Becomes very similar to Stainless w/r soldering...
 
Another good contact material is tin plated nickel-silver (it has no silver in it).

Stainless is good enough, though.
 
Another good contact material is tin plated nickel-silver (it has no silver in it).
OTOH, Alpaca metal makes rather poor springs, AND is not usually hard enough to "scratch through" the Oxides that form on a watch (or hearing aid) battery case itself, so...
 
If I was doing it, I would use half hard beryllium copper, formed, then vacuum heat treated and silver or if the budget would stand it, gold plated. Beryllium copper is tricky to plate, but if you decide to use it, I will give you the method that really bonds it.

In the interest of full disclosure, my judgement is somewhat slanted because I have a lot of experience with beryllium copper and little with phosphor bronze. Either way, gold is the best contact material.

Bill
 
OTOH, Alpaca metal makes rather poor springs, AND is not usually hard enough to "scratch through" the Oxides that form on a watch (or hearing aid) battery case itself, so...



That is as may be.

In the commercial audio world, a very large number of connectors are used which have nickel-silver contacts. The entire contact, from solder tag to contact material, is nickel silver, used as the spring which makes contact with the inserted plug. No other spring material is used. They have to (and do) scrape off any corrosion on the plugs as the plugs are inserted.

They have been used for decades and are still used, very successfully. The best variety (as I proved for our own use in products by actual testing) has tin plating, which drastically reduces the incidence of "fretting corrosion". That corrosion causes loss of contact in the "bypass connections", which are made when no plug is inserted. But the plating would likely also be useful in preventing corrosion at the battery contact.
 
Be careful with tin plate. Matte tin will oxidize over time and become a semiconductor. If you must use tin, use bright acid tin.

Tom
 
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I have always used stainless, mostly for replacement of corroded ones. I keep an assortment of stainless hose clamps and they are my sacrificial goats for this. I find I can cut them, drill them, form raised buttons on them, and solder to them (with some patience). And they last a lot longer than most commercial battery contacts when exposed to battery chemicals.

On forming a raised button on them, I carve a recess in one piece of wood (oak?) and drill a hole in another piece that fits over it. Clamp the contact between them and use a punch through the hole. One whack and I have an instant button. Works great and lasts a long time.

If this is for a production situation, you may have to use a different alloy. But if it is for production, I would buy a commercial battery holder for the cells you are using. They will be made for soldering and that problem will not exist.
 
One of the advantages of beryllium copper is that you can form it into a fair example of the desired shape and heat treat it in a fixture that holds it exactly where you want it. I have made thousands of contacts from beryllium copper strip stock with end shapes punched out and bent, then clamped in a stainless fixture for vacuum heat treat. Because of the difficulty of transferring heat from a heater to the fixture in a vacuum, I run the current through the 18" bar with a bunch of pieces clamped on it, a couple of volts and up to 800 amps. The parts come out perfectly shaped and bright, none of the oxide that is really tough to remove. I electrolytically strip the beryllium out of the surface, leaving a pure copper one to plate on. I go into cyanide silver plating without a strike and get a bond that doesn't peel in bead blasting. The silver just slowly wears away. Riveted on silver buttons complete the part.

Bill
 
If the print says 3/4 hard nickel plated bronze" there's about a 99% chance they mean 510.

Unplated stainless isn't appropriate in a PCB application, the flux or plating you'd have to use will corrode the PCB or cost more than phosphor bronze.

BeCu is great stuff if you need longer spring throws or better conductivity, but a watch battery is not a high drain application and it's costly and does require some precautions when processing.

Gold flash over your nickel plating would improve solderability and not cost that much if that becomes a problem.
 
BeCu is great stuff if you need longer spring throws or better conductivity, but a watch battery is not a high drain application and it's costly and does require some precautions when processing.

When I was doing machine work, the lathe guys made tens of thousands of BeCu parts, mostly electrical connectors and RF couplers, and I believe nearly all of them were gold plated. Worked rather nicely, but not cheap. As for precautions, don't sand or grind it. Wash your hands. That's it. We never did anything different safety-wise, just don't make dust and don't eat the stuff.
 
Some woods - oak is one - will off-gas something that will oxidize tin/lead. Had a church with a large audio mixing board that a member build a beautiful oak cabinet for it. Very intermittent problems started to manifest themselves that after several months I finally came to the conclusion that the mixer itself was the cause.
Another example, I built a carrying case for a hunting rifle made of oak. I was using lead/tin cast bullets and left a couple of boxes of ammo in the case with the rifle. The cast bullets took on a strange flat gray color after a period of time.

Bob
WB8NQW
 
At least some tin oxides are conductive, so the issue of fretting corrosion in air is not serious, although heavy pollution may produce non-conductive compounds.

We found that the problem of open connections essentially disappeared 100% with the use of tin plating. It had become a serious issue prior to the plating. The big culprit was apparently sulfur compounds.
 
I remember having an email from occupational hygiene in work regarding guys working in the carpenters shop, there were complaints about asthma, rashes and all sorts, they were sawing huge quantities of oak, I found out it was toxic but never got round to figuring what was toxic about it, there was a book I started think it was woods injurious to health, from what I remember just about all of them were toxic.
Anyway I detract, a long time ago I had to make a 2 stage press tool for a firm, it was to form battery contacts, they were using the previously mentioned beryllium copper strip, it was a simple tool, just a strip a bump one end and a couple of barbs to grip the moulded case, don't think it was plated after due to the mentioned difficulty getting plating to adhere.
Beryllium copper is an amazing material in itself, I used to have a set of slogging spanners, open Enders, chisels punches and hammers given to work inside gas holders and oxygen galleries, cutting steel with a copper chisel is nuts but you can with that stuff, amazing.
Said tools got stolen unfortunately but I don't plan on working inside a full gas tank again, ever.
Mark
 
I remember having an email from occupational hygiene in work regarding guys working in the carpenters shop, there were complaints about asthma, rashes and all sorts, they were sawing huge quantities of oak, I found out it was toxic but never got round to figuring what was toxic about it,

Oak contains a tannin, from the tannic acid family. From Wiki,

Quercitannic and gallotannic acids[edit]
Quercitannic acid is one of the two forms of tannic acid[2] found in oak bark and leaves.[3] The other form is called gallotannic acid and is found in oak galls.
The quercitannic acid molecule is also present in quercitron, a yellow dye obtained from the bark of the Eastern black oak (Quercus velutina), a forest tree indigenous in North America. It is described as a yellowish brown amorphous substance.

Matter of fact, the word tannin is derived from an old German word for oak and leather is tanned with oak bark.

Bill
 
One more question. Is H03 510 0.2mm thick going to have much springiness in it without deforming? I am planing on prototyping a part with it that is 4mm by 10mm and it will have up to 90 degree bends. Will there be any issue forming bends with a makeshift die and/or pliers in the H03 state without it breaking and expecting some springiness left in it?
Spring_Contact.jpg
 








 
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