Date sent: Tue, 23 Feb 1999 16:00:29 -0800
From: dlhough@vegas.infi.net
Subject: Re: [TowerTalk] burnishing tool
To: Scott M Cronin <lefty@bc.seflin.org>
Copies to: "towertalk@contesting.com" <towertalk@contesting.com>
>
> Also might check out an auto parts supplier or a Sears store where
> they keep the tools. That's where I got mine. It's also possible to get
> an 800 or 1200 grid emery paper and do the job.
Agggghhhh!!!!!!!
NEVER ever ever use anything abrasive on a plated relay contact!!!
The contacts are either gold flashed, or silver flashed, with various
alloys added to modify the surface for different current requirements.
If you remove even a few tenths of an inch (meaning ten-
thousandths in plating slang) of surface, you'll absolutely destroy
the alloy that keeps contact resistance low.
The MOST you should ever use on a plated relay contact is
something about as abrasive as cardboard. I use a thin cardboard
like off a matchbook cover soaked in toluene, xzylene, or one of
the other nasty solvents that evaporate without any residue to
clean crud out of the contacts.
This does not apply to starter solenoids, or other hundred ampere
non-plated contacts. They can be cleaned with a grinding wheel
since they are not plated, but don't try that on gold or silver alloy
flashed contacts typical in low or medium current relays.
As long as I am on the box, relays get "dirty" for two main reasons.
1.) They are not plated.
2.) They have had the plating ruined by hot switching or "cleaning".
3.) They have debris trapped on the contacts.
4.) They aren't in an application where they carry a required
minimum current that "wipes" the contact.
Number four is a major problem with amplifier relays. The receive
contacts technically require a different alloy than transmitting
contacts, because one carries virtually no current while the other
carries several amperes. Since they are in one relay, your stuck
compromising. An antenna relay is the same.
When they "get dirty", and they usually will because the material is
a compromise, all they need is a VERY light wiping (like with
cardboard) to remove surface contamination. Just be sure to blow
any paper fibers out with air or freon when you are done, and
NEVER coat the contacts with any "stuff".
What type of relay is it that is the problem? Maybe it's the wrong
type? Relays rated for hot switching higher currents, while
impressing customers, make very poor antenna relays. They are
great for starting motors, but not designed to maintain low contact
resistance under conditions of low current flow.
73, Tom W8JI
w8ji@contesting.com
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