Electronics > Repair

Anybody ever attempt to repair a relay?

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uoficowboy:
I have a ~35 year old SPDT relay that isn't working very well. The NO side closes and opens just fine, but the NC side never closes. Oddly enough, I suspect that during this relay's life it was never switched, or at most was switched very few times.

It is completely sealed. Is this fixable at all? I am able to order a replacement for it, but it's more fun to fix rather than replace :)

My guess is that the contacts are corroded and are beyond repair - but I figured I'd ask!

jahonen:
Try connecting problematic contacts to a lab power supply, set output voltage and current limit so that contacts are not overloaded. Switch it few times and that should do the trick. Resulting spark should clean the contacts if at all possible.

Regards,
Janne

uoficowboy:

--- Quote from: jahonen on September 04, 2013, 05:44:15 am ---Try connecting problematic contacts to a lab power supply, set output voltage and current limit so that contacts are not overloaded. Switch it few times and that should do the trick. Resulting spark should clean the contacts if at all possible.

Regards,
Janne

--- End quote ---
Wouldn't a spark oxidize it even more? Also, what sort of voltage/current limits do you mean? I have a 50V, 0.5A supply I use for everything - think that would be reasonable?

David_AVD:
The switching action can blow away the built up surface oxidation.

Skimask:

--- Quote from: uoficowboy on September 04, 2013, 06:51:01 am ---Wouldn't a spark oxidize it even more? Also, what sort of voltage/current limits do you mean? I have a 50V, 0.5A supply I use for everything - think that would be reasonable?
--- End quote ---
You would think it would wreck it even worse, but 'taint the case...
Back in my C-130 days, we had a relay panel, lots of relays, called the 'NIRP' (navigation instrument relay panel), contacts would fail all the time, low voltage contacts.
The NIRP tester was nothing more than a momentary relay coil energizer and would shoot AC across the contacts for awhile until either you gave up or the relay started working.
Seems that generally if you put DC across relay contacts, one side will lose material, and the other side will gain it, and in the process, both sides would be full of garbage and not make contact.  Shoot the current in the other direction basically blasts the crud off the contacts and 'fixes' it, at least for awhile.

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