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cookiejar
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CEO
Are you sure they're silver?
cookiejar   10/24/2013 2:44:21 PM
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I was taught that oxidized silver was a good conductor, especially in this case with the high impedances involved.  I suspect the silvery contact is some other material that needs a minimum wetting current, typically 1mA to 10mA to remain reliable. Replacing contacts inside a relay is not what I would call an elegant solution.  My impulse would be to see if the circuit could be modified to increase the contact current.

P.S. While oxidized silver may be a good conductor, it does resists soldering, hence the preference for gold to gold connectors. 

WKetel
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Rookie
that rlay contact problem.
WKetel   10/23/2013 10:23:48 PM
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One good permanent fix would have been to substitute wercury wetted contact reed relays. But they are a bit expensive and several UNELIGHTENED countries don't allow them any more. Or just plain gold contact reed relay elements could work quite well.

But the fix as posted is quite good, and I would give the detective work a good mark indeed.

ghfarmer
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Rookie
there's silver and then there's Silver
ghfarmer   10/22/2013 12:59:21 PM
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I heard a similar story working in Automotive.  A certain manufacturer had specified silver and German silver for the contacts in the brake switches but the manufacturer had reversed the materials in some of the parts.  As it was explained to me, in the proper configuration when the contacts wiped against each other, any silver transferred between the contacts was essentially plated back onto the correct side.  In the defective switches, the lost material wasn't replaced and additional material was also removed with each wipe.  This caused brake switch field failures in the trucks at 15-20,000 miles.  The situation got very ugly very quickly.  Not recommended process for enhancing your career path.

ost0
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CEO
Inductive load?
ost0   10/22/2013 3:33:27 AM
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If there is an inductive load on the corroded contacts, I'd suggest checking if there is some working reverse current diode to prevent excess of sparks.

 

mhrackin
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CEO
Re: surprising
mhrackin   10/21/2013 4:25:19 PM
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Back in prehistoric times, there was a solution. I don't remember who the supplier was, but they sold "kits" for assembling relays.  This you could "mix and match" power and signal rated contacts quite easily.  In thsi case, you'd use a pair of contacts: one gold-plated NC, the other silver high-current NO, and hook them up as a "SPDT" pair.  Of course, for production you could then have the part as a custom P/N built the way you needed it.  I suspect another of the greybeards on this site will remember who the manufacturer was.  This isn't really that rare of a problem (at least back in the old days when a lot of machine logic was relay-based).

David Ashton
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Blogger
Great Story
David Ashton   10/19/2013 8:27:28 PM
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Excellent work Richard,,,,I have soldered pins back onto ICs before, but this beats that hands down!  

rick merritt
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Author
Re: surprising
rick merritt   10/18/2013 7:01:57 PM
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Interesting

Caleb Kraft
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Blogger
surprising
Caleb Kraft   10/18/2013 12:44:02 PM
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Its a bit surprising that this is the best solution. You'd think there would be purpose built relays for this!



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