I think that you could make a relay with bifurcated contacts where one fork
of the contact had a contact button made of some material suitable for high
current (like silver) and the second fork was gold plated. You then arrange
the contacts so that the silver contacts mate first and then the gold. When
you are switching high current, the arcing happens when the initial
contacts meet and so would be handled by the silver, protecting the gold
contacts which have not yet closed. If the current is very low, then there
is a chance that the resistance will be high even after the silver contacts
mate. Then, when the gold contacts close, there will be a good connection
for low current.

Relays with bifurcated contacts are common. I don't know whether any use
the system I mentioned above. I also don't remember where I got this idea -
I don't think it was mine, I think I read it somewhere.


On Sun, Oct 20, 2013 at 5:46 AM, Brent Brown <brent.brown@clear.net.nz>wrot=
e:

> Interesting what the article says about gold not being as durable as
> silver under
> arcing conditions.
>
> I had wondered once if gold plating over standard contacts in a power
> relay might
> bring some benefit... allow them to be used at microamp levels without
> oxidisation
> problems, or if used at high currents the gold might disperse harmlessly
> and fall
> back to working on the silver alloy underneath. Thoughts? For the
> application I had
> in mind the current was not known precisely as it depended on the
> equipment the
> user would install it into... could be some hundreds of uA, or some 10's
> of Amps, but
> whatever it was once installed the conditions would remain consistant.
>
> On 19 Oct 2013 at 12:49, John Ferrell wrote:
>
> > As an old time relay mechanic at IBM my diagnosis is simply proper
> > adjustment is needed.
> > There should be enough over travel of the moving contact to assure ther=
e
> > is a little "wiping" action of the contacts.
> >
> > On 10/19/2013 11:57 AM, Peter wrote:
> > > http://www.eetimes.com/author.asp?section_id=3D30&doc_id=3D1319831&
> > >
> > > Worth reading for anyone using relays in small signal circuits. My
> solution
> > > would have been to analyze the circuit and add small caps (100n)
> across the
> > > low current contacts, assuming the rest of the circuit would have
> worked
> > > with the additional delay. These will charge to supply voltage and
> provide a
> > > nice tiny cleaning arc upon contact closure, keeping the low signal
> side
> > > reasonably clean. No idea if it would keep like this, it is a hack,
> but ...
>
>
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