On Thu, 13 Dec 2012 11:17:12 -0800, Searcher7 wrote:
On Dec 12, 1:15Â*pm, Tim Wescott wrote:
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. Â*No one who actually knows is answering. Â*Here's my two bits, but
take them with a large grain of salt, 'cause I'm no expert.
I know that "wiping action" is an advertised feature on many switches.
There is probably some minimum normal force that you want to achieve to
make sure that the oxide is wiped off, and probably some minimum wiping
distance to boot. Â*I absolutely couldn't tell you what the necessary
forces and/or distances are, but I'll bet you that there's standards
out there, and probably huge amounts of tribal knowledge at the various
switch manufacturers.
None of that will be a problem, since I can adjust the wiping force and
number of times.
If you can get a good thick silver plating on your contacts then your
required forces will go way down -- silver is a pretty good conductor,
and silver oxide is both mechanically weak and (I understand) not a bad
conductor in its own right.
Electroplating silver onto Phosphor-Bronze would require redesigning and
and result in an increase in complexity and cost of the project. The
idea is to stick with a material that I wouldn't need to plate. If it is
conductive enough, then wiping would take care of the oxidation. (The
switch of course will be used under "normal" environmental conditions).
There are certainly switches that are made of phosphor bronze.
There are no "normal" environmental conditions -- only the environmental
conditions that people of limited imagination assume is normal.
Silver does however have the best conductivity of all metals, but not
the *spring* of Phosphor-Bronze. Copper also has more electrical
conductivity than Phosphor-Bronze, but not it's corrosion resistance.
Gold has excellent electrical conductivity, but is not as wear
resistant.
Yes, I think we all understand that. What we didn't know until this
moment, though, is that you had considered silver plating and decided
against it for cost reasons.
Because, you see, we can't read your mind.
Finding a switch that has about the same ratings as what you need,
taking it apart, and copying it's actions and forces may not be a bad
way to go. Â*You won't be able to duplicate their metallurgy, but you
can't have everything.
Nope. This is a switch that doesn't exist in any form yet and will
incorporate unorthodox connections. (One particular version will allow
switching between a dozen 40 pin connections). The wiping will actually
be in the mechanical action of switching from one connection to the
next.
If you can't replicate _just the forces and actions_ of an existing
switch at the contacts, then you're in a different universe from me, and
no advise that I can give you will help. In fact, no amount of advise
that you get from any of the regulars here will help, because as far as I
know they're all in the same universe as I am, too.
Perhaps this is why you thought that the help you got on s.e.b was all
from trolls? Getting sound engineering advice from the wrong universe
can do that.
Here in this universe, how you _connect_ to a switch is largely
independent of how the _switch's contacts come together_, and with what
forces. This applies in particular if your switch is currently just a
connection diagram, and has not been reduced to practice in a way that
involves any means of making the contacts come together, with or without
any forces.
You might try asking this question on sci.electronics.design, since you
don't seem to be getting much info here.
I actually tried a similar question at Sci.Electronics.Basics two or
three years ago, only to have to deal with personal attacks by a group
led by a "John Fields" because I wouldn't give them *detailed* plans of
what I was working on. Specifics that had nothing at all to do with the
question concerning wiping material.
I'd think that lot of the same trolls who hang out at
Sci.Electronics.Basics also frequent Sci.Electronics.Design.
John Fields is pretty astute, and engineers learn early not to answer
general questions with specifics. "How much paint does it take to paint
a door?" should be immediately replied to with "How big is the door, and
what sort of paint?", because any specific answer is only going to be
correct if the questioner and respondent both share all the same
assumptions.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com