Need to pick some brains, best compromise metal for electrical contacts?

[mdocod]

Ok.... so I'm working on building some battery carriers for 6AA>2D, ( http://www.candlepowerforums.com/vb/showthread.php?t=175879 )

I've got the design almost completely figured out, but I'm at a loss for what type of fastener material would be the best compromise between corrosion resistance and conductivity. I'm going to be using the heads of screws as contacts for the ends of the cells, and then planing on using copper sheet cut into sections and drilled, the fasteners would then hold down the copper plate to make contact with the next "stack" to get em all in series. The contacts on the ends of the pack will be the end of a machine screw and nut holding down a washer.

I was reading around on the internet, and it looks like basic steel and stainless steel is pretty poor in comparison to copper for conductivity, but then again, exposed copper has it's downsides as well, (oxidation? sets in and the surface develops poor conduction in time anyways, as I understand). I was reading that brass and aluminum are commonly used for electrical fasteners that are required to carry current, but still wouldn't be nearly as good as copper. Was also reading that zinc plating improves steel conductivity slightly. Read that Silver, Gold, Cadmium, and various tin and electro platings are great for electrical conductivity.

The biggest problem, is the limitation of what seems to be available on the market. I've been scouring the internet constantly in search of a source of the ideal fastener, (a plated copper would be best I think), but such a fastener is hard to come by. Aluminum isn't available in small the sizes I need, copper fasteners are very rare and only available in a few screw head types that aren't what I am looking for, brass is the only material I have seen that I can get the size I need in a standardized size. I could go with custom fasteners, but they are cost prohibitive unless ordered in quantities in the tens of thousands or more.

So how is steel, or stainless steel as far as conductivity goes, is what I read true? is it pretty lame? Is brass up to the job? Any input on the resistivity of metals would really be appreciated. In 2 parts of the carrier, the length of the fastener will carry the current over the length of about 1/2 inch, the diameter of the threaded portion of the fastener will be the equivalent of approximately 9 gage wire, which, if copper, would be able to carry a maximum ~60 amp, but copper is probably out of the question unless I find a source of copper fasteners.

Any guidance would be greatly appreciated, I know we have electrical guru's and engineers all over the place here. Throw me your words of wisdom. !

 

[Norm]

copper fasteners are very rare

But brass isn't.
Norm

 

[bfg9000]

Silver plating should conduct great, and home silver plating kits aren't that expensive. Silver may tarnish, but silver oxide conducts virtually as well as pure silver.

Copper nuts are traditionally used because they stick and won't loosen, handy for high temperature applications that would damage plastic Loctite/nylon locknuts or cause spring lockwashers to lose their temper--exhaust pipes, for example. This sticking may not be desirable in a battery carrier intended for frequent disassembly.

Gold plating the copper would take care of that problem, but since copper isn't too strong mechanically anyway, I'd prefer to use silver plated steel for an "ideal fastener." When contemplating the price of "ideal," please remember that we do have plenty of Deoxit so some compromise may be called for in order to reach a more ideal price point.

Else you could set up a side business in silver plating parts (Mag springs, etc) to recoup the costs

 

[richdsu]

If you are looking for copper fasteners -- try out hardware suppliers selling "Stud Welders", they should carry assorted types of copper fasteners and nuts that you can modify to suit your applications.

I would also recommend that you send you screws & nuts be it copper, brass, stainless steel to be plated with Blue Zinc plating process ( or rainbow zinc plating).... as I am aware most power connectors' fasteners employ this plating process.

:twothumbs

 

[paulr]

I thought cobalt gold was supposed to be the best for these contacts. It's also used on relays that have to open and close millions of times. It's used in some flashlights and you can find some posts about it using the search feature.

 

[Bushman5]

try copper rivets ...., not sure how your designing your battery tubes, but i have seen copper rivets used in small battery pack holders (using thin plastic for the box)

 

[sysadmn]

If you're looking for a cheap, good enough solution, it's astonishingly easy to to copper-plate. It's the reverse of the process used to homebrew PCBs using copper sulfate, battery acid, and a 6V lantern battery. You could plate the components or the completed assemblies.

http://steampunkworkshop.com/altoid-etch.shtml

If you do use steel, stainless steel, or nickel-plated steel, I wouldn't worry too much about cross-sectional area of the screw increasing resistivity; I'd concentrate on making the battery/screw points of contact as large as practical.

 

[chesterqw]

916 gold

 

[mdocod]

well, looks like a mixed bag of ideas here as confusing as the ideas I had originally.

I don't want to get into the business of plating, from what I just spent some time reading, a quality plating job is not something you can pull out of your hat with a simple trick. I also don't really want to deal with the chemical hazards involved.

 

[lctorana]

Funny, I would have used tinned copper - so solder would have been my contact metal.

 

[VidPro]

for what your making, in the quantity your making it, i would use locally purchaced brass. Clean it (like sanding with 400-1000), or chemically cleaned, then silicon it with a light silicon spray which will keep the oxidation off, Or de-oxit stuff.
Unless i could get ahold of copper ones, then i would do the same thing, have them shine with raw metals, then silicon spray it so most of it didnt oxidize.

the quantity of the connection point, could be a bigger issue than steels conductivity ability.
whatever you can do to increase the number of (metal to metal) atoms that make the battery to adapter contact, the better.
soft copper, soft silver or softer gold accomplish that. not soft lead though, that dont work AS good.
meaning the steel screw wont squish into the battery ends as well as something softer, and THAT could be a bigger issue than the steels resistance/conductivity.

but how the heck you gonna trot on down to the plating store to have them do just 50 screws? seems like it would increase the price, time, and trouble above the value of the project, Who else already did that?
so if your going to get gold plated screws mabey it would be a "different" clientel that would want that item? so i am sure sombody wants a 75$ battery adapter oh wait, the candlepower people would WANT that one

the other issue, be it an advantage (less chance of shorting) or a disadvantage (less heat capable) your making it in plastic, so there should be some reasonable level of "hotwire" that it can be used for, the people using it wont want to turn it into a blob from heat. umm that means they probably wouldnt want to torture the batteries in them. then a bad connection in a plastic holder, the heat hits that ONE place where the metal is at, making the mounting to the plastic there subject to heat.
an example of that is crappy radioshack holders , when attempted to be used for 50+ watts, the wire, the springs high resitance, the plastic just turns to a blob. Far worse than anything that can happen with the substantiability of the items your making, but all within the concideration of its maximum heat use.
improve the connections at each battery point, and you decrease the heat that can occur there, WHEN a connection isnt working as well as was intended, and sombody thinks they can get 50amps out of it

riveting or pressfitting things eventually get loose, in just about everything :-( so because i like to be able TO maintance something, i wouldnt recommend them. but that is just ME, a screw i can retighten in 2 seconds,some of the crappy manufactured riveted stuff, get loose, then you have to smash it with a hammer, and hope that tightens it up before it falls apart again.
examples of that are those Cruddy adapters that we can already buy, and try and fix to become something usefull.

well me, i like the idea of dissasembleable and fixable, vrses manufactured. i have had many riveted pressfit plastic junk get high resistance when pushing more power through than was intended. I WISHED it was made with bulkey hardware instead, cause then it would HAVE BEEN fixable. so if something cant be perfect, its nice if it can be maintained.


plus screwing it up like your doing means i can Rewire it :huh: to parellel or series or something. Here we screw everything up :duh2: and good too.

 

[DM51]

Silver bullion is not actually too expensive, but then you would have to cast it or work it, or plate it on to something else, so it could be a PITA unless you can find something ready-made. Copper would probably be your best bet.

 

[VidPro]

Silver bullion is not actually too expensive, but then you would have to cast it or work it, or plate it on to something else, so it could be a PITA unless you can find something ready-made. Copper would probably be your best bet.

so isnt there such thing as 100% silver jewelers solder?
a bit of flux and a few buck into that, and one could make the contact points silver coated , and Better silvercoated than cheap silverplated jewlery?

that sounds more like something I (myself) could try and crank out in a garage at home, without much effort or trouble?

i have seen a lot of gold coatings completely rubbed off from use in some things, a "layer" of silver could be thicker than a plating of it?

the stuff on e-bay "silver solder" is only 5-15% hmmm
http://tinyurl.com/yovp5r
this claims a big 45% ooooohhh

cant find nothing on a search. time to grab grandmas sterling silverware, and make yourself a Pool on the stove dip the screws in flux, then dip them in a pool of melted silverware

 

[DM51]

Yes, you'd probably need to mix pure silver with some other metal - not sure what the ideal mix is, or what silversmiths use for soldering - but it's pretty pure IIRC.

 

[NiOOH]

High silver content solder to cover copper rivets should work OK. I wouldn't get to carried away with this. Let's don't forget that cells contacts themeselves are not made from super low resistance alloys.

 

[VidPro]

High silver content solder to cover copper rivets should work OK. I wouldn't get to carried away with this. Let's don't forget that cells contacts themeselves are not made from super low resistance alloys.

you dont have them gold plated batteries
hmm, so should we get into the dissimilar metals discussion and the effects of low emissitivity because its not painted black.

 

[NiOOH]

you dont have them gold plated batteries
hmm, so should we get into the dissimilar metals discussion and the effects of low emissitivity because its not painted black.

Exactly. Actually, gold-plating is not as expensive as it may sound. Just look at audio hardware, where gold-plating is lamost a standard even on the lowest price segment. IMO, contact area is the more important factor. Sanyo, for instance, have recognized this. Their AA cells have larger, flatter tops allowing for a larger contact area between cells.
IMO, at the voltages discussed here and currents up to 2-2.5 Amps conductor resistance is a secondary factor. Contact resistance is more problematic IMO. That is why, I'd put more thought into ensuring firmer contact.

 

[mdocod]

Really great points being made here, this is excellent, I'm really developing a better idea of what I want to do with this..

Vidpro I agree with you 100% on all counts. I'm going to try to avoid rivets because I like you, prefer to have the OPTION to modify or repair products in a DIY fashion. I am also of the belief that the majority of CPF type folks are not afraid to get out a screwdriver from time to time. I'd much rather have a product that is user serviceable. Being able to replace the contact surfaces by simply buying some new screws for it would be ideal. The point about the $75 battery carrier is so true, I could have custom gold plated copper end-caps and fasteners made for the entire assembly, but you're right, I would have to sell them for at LEAST $75 a piece, (I've already checked into the cost of the "best" solutions). And the cost of an initial run would be several thousand out of pocket for myself. I'd much rather find a compromised solution that makes a good quality magmod accessible to MORE people. I'm trying to strike a balance between quality, functionality, and price.

 

[Scott Packard]

I think you'd be happy with phosphor bronze. Great corrosion resistance, takes solder well. I don't see it used outside of aerospace much. Boat owners talk about it, so it may well be widely used in marine applications. Those shiny connectors you see in APC UPSes are phosphor bronze.

 

[sysadmn]

I don't want to get into the business of plating, from what I just spent some time reading, a quality plating job is not something you can pull out of your hat with a simple trick. I also don't really want to deal with the chemical hazards involved.

I can't argue with your decision, especially since it sounds like you want production quantities.

Have you considered buying a tap&die and threading the appropriate gage wire? Interesting - this place sells tap&die, burrs, and bits for fine gage wire (14-18ga). They also sell miniature brass nuts and bolts plated with silver or gold.


Marine HW, mostly SS:
http://www.iboats.com/

As an aside -
you might have been reading about someone looking for a pretty plating job. If you want a mirror finish, or to electro-etch, you have to watch closely and fuss with time and voltage. If you're just looking to reduce resistivity, it's really not that hard. If you're putting copper down, the 'hazardous substance' is CuSO4, which you buy by the pound - it's used by gardeners as a root killer, and as a wood preservative. You do have to be careful about disposing of the solution.