On Dec 12, 6:17*pm, "Jim Wilkins" wrote:
"Tim Wescott" wrote in message

...









On Tue, 11 Dec 2012 22:06:24 -0800, Searcher7 wrote:

I'm working on a project that is a mechanical switch of sorts, and
it
entails running electrical signals through Phosphor-Bronze
contacts.

Now since *all* alloys will oxidize to an extent, I was wondering
if I
were to wipe the phosphor-Bronze contacts with the same
material(Phosphor-Bronze), would that be serve to keep the alloy's
surface clean? (The wiping action will be part of the mechanics of
the
switch).

Wow. *No one who actually knows is answering. *Here's my two bits,
but
take them with a large grain of salt, 'cause I'm no expert.

Or no one actually knows. The question is like "How long will this
bearing last" without giving the load, speed, misalignment,
temperature, contamination, etc.

How do you figure?

In this case the main electrical conditions that matter are the
voltage and current the switch makes and breaks and how much
resistance increase is too much. *Mechanically the contact force and
opening speed affect the life. I've seen contact lifetime ratings
range from 10 to 10 million cycles, and occasionally seen and heard
the number be 1.

Wiping makes the resistance stay low longer and the contacts wear away
faster.

None of that matters. I have control over the contact thickness,
number of wipes between connections, length of wipes between
connections, pressure of wipes between connections, and "Break" and
"Make" will only occur when there is no current, so there will be no
arcing.

I was just concerned about using a different material/metal to wipe
the Phosphor-Bronze contacts. If I can just use the same material then
problem solved.

Thanks.

Darren Harris
Staten Island, New York.