Electrical Contact Material

In a critical situation I would use reed relays and small magnets. A totally closed system, no maintenance.

Oh, and if you insist on contact fingers, try hammered silver. It produces nice springs, and even the oxide conducts. They might come to 4 dollars a piece, but satisfaction guaranteed.

What's wrong with plating? It's not that expensive. Maybe nickel plating. (We got a tray full of stuff for

Not sure about Platinum but IIRC Rhodium was used for some special relays.

Or, $olid $ilver ;-P

And I'd use BeCu before I'd use phosphor bronze; just a personal whaddayacallit. ;-)

Cheers! Rich

What's the quantity? Is it a one-off? If so, just get a relay and hack it for the contacts.

For production, see my other post (gold-flash over nickel plate, or $olid $ilver, BeCu for the springy part).

Cheers! Rich

That's a perfect storm: no high voltage, no wiping, means that any dust mote will prevent contact. That can only work reliably if you have high contact forces, or if you use reed switch parts (for the sealed glass envelope).

One possibility you might consider is zebra-stripe elastomer conductors; these are compliant enough to make a connection even if that dust mote shows up.

Zebra-stripe elastomer conductors would be too "exotic", expensive and would require a lot of redesigning, *if* they would work for what I'm doing.

I might however be able to incorporate wiping if I can determine a good material to use, outside of the contact material itself.(I can make it part of the switching mechanics).

Thanks.

Darren Harris Staten Island, New York.

Zebra-stripe elastomer conductors would be too "exotic", expensive and would require a lot of redesigning, *if* they would work for what I'm doing.

I might however be able to incorporate wiping if I can determine a good material to use, outside of the contact material itself.(I can make it part of the switching mechanics).

Thanks.

Darren Harris Staten Island, New York.

Good nickel plated brass should do. As an example, for a gas furnace with a millivolt relay, I had problems with a standard "Decora" switch designed for 120V. There was enough surface oxidation to cause an open circuit at such low voltages (about 500mv max) A

Don Kelly

Well, unless nickel plating means I'll never have to worry about "dirty" contact problems, I'll stick with Phosphor-Bronze + wiping to keep things clean.

Thanks.

Darren Harris Staten Island, New York.

And can anyone suggest a material I can use for wiping? (A material that isn't conductive).

Thanks.

Darren Harris Staten Island, New York.

..

TP? (sorry)

A piece of tinplate (tin-plated steel) cut from the lid of a "tin" can.

You could either use two, or the other contact could be a brass nail.

The action of the movement of the contacts will knock off the oxide when they make contact.

Good Luck! Rich

Usually the contacts are arranged so that they wipe against each other.

And can anyone suggest a material I can use for wiping? (A material that isn't conductive).

Thanks.

Darren Harris Staten Island, New York.

----------------------------------- Nickel plating so far has gone for over 13 years without a problem while the standard switches lasted under a year. Gold plating works but is expensive As to "wiping" that is a function of the way the contact is made- the contacts rub a bit when closing. This acts to clean them. No need for external wiping with some cloth or emery.

Don Kelly cross out to reply

Contact "wipe" is the term used for how much the contact travel overlaps and is not a material.

After a contact initially touches any further action will cause the contact arm to bend and thus "wipe" or scrape the contact bump against the other contact side bump. This effectively keeps the contact surfaces clean and free of dust specs between the mating surfaces.

For reliable contacts the usual techniques are bifricated (dual arm ends and contact surfaces), dual contacts in parallel, silver or gold (best) contact surfaces, seal them in a dust enclosure or vaccum (best= no dust or oxide), wet them with mercury or other liquid conductor (slow acting) or any of the above in combination. The arms need to be a different material for spring action.

If you want to actaull wipe a contact clean use isopropylene or a good isopropyl alcohiol with low water or oil content and a good lint free cloth wrapped around a contact burning tool, or just a burning tool designed for that usage.

Reed relay contacts are sealed in a vacuum bottle and can be operated via a magnetic field.

Thanks.

Darren Harris Staten Island, New York.