[Boatanchors] Relay Repair - Demagnetization Question

[Carl]

I just dont care for that much voltage to clean the contacts; the idea is to 
use just enough to remove the oxide without leaving pitting. Its comparable 
to using a burnishing tool versus a points file.

There are a couple of methods used or championed by the vintage car people 
and Ive been happy with the one I use for many decades.

Most auto vibrators run at 115 cps and there is a fairly even distribution 
between 6V and 12V radios arriving here. The big rush to 12V systems started 
in 53.

Carl
KM1H


----- Original Message ----- 
From: <WA5CAB at cs.com>
To: <w7qho at aol.com>; <boatanchors at mailman.qth.net>
Sent: Wednesday, February 03, 2010 2:14 AM
Subject: Re: [Boatanchors] Relay Repair - Demagnetization Question


> That's correct.  As my third sentence said (the post I replied to had
> referred to age-related chemically caused relay failures), I was referring 
> to
> vibrators that don't work after decades long periods of inactivity (as in 
> never
> used).  And Carl, I got this trick from Tom Horsfall 30+ years ago.  He 
> got
> it out of a West Coast antique car collectors monthly journal sometime in
> the late 80's.
>
> Most antique cars use 6 volt systems.  So that's what the original article
> said to use.  For those (and the 2-volt and 4-volt military units), you 
> need
> a 40 watt lamp to get enough current through the coil once the switching
> contact starts work again.  For 12 volt units, a 25 watt lamp is adequate.
> For 24 volt ones you can usually use a 12 watt one.  For all contacts that
> don't switch the coil, 12 watt ones are fine.  They all allow roughly 170 
> VAC
> peak across open contacts.  Only the one in series with the coil has to 
> carry
> enough current to operate the coil.  I've also found that for the lamp in
> series with the coil (especially on shunt type vibrators) time to clear 
> the
> contact is reduced if you put a diode in series with the whole mess.
>
> I've always assumed that the most efficient "fixer" would have the AC
> running at the vibrator's natural resonant frequency.  Apparently, it 
> works a
> little better (in a 60 Hz world) if the dirve voltage is running slower 
> rather
> than faster than the vibrator wants to run (typically 100 CPS).  At least
> until the switching contact clears.
>
> In a message dated 2/2/2010 11:10:32 PM Central Standard Time,
> w7qho at aol.com writes:
>> A distinction has to be drawn here between vibrators  that fail in
>> service and vibrators, military or otherwise, that fail to operate
>> following long periods of non-use.  The latter problem as Robert
>> points out is due to a chemical buildup on the contacts.  I am certain
>> this is not limited to military units and is the type of problem most
>> commonly encountered today.  This buildup is very hard and some
>> significant mechanical burnishing effort is required to remove it.  I
>> have never tried the 115vac/series lightbulb treatment that several
>> claim to have used with positive results.  I 'm skeptical (given how
>> hard the gunk is to scrape off mechanically) but plan to give it a
>> shot one day.
>>
>> Dennis D. W7QHO
>> Glendale, CA
>>
>>
>>
>> On Feb 2, 2010, at 5:37 PM, Carl wrote:
>>
>> >I wouldnt know about military vibrators as Ive no interest in them.
>> >Nor do I know if they are constructed any different than civilian
>> >versions.
>> >
>> >Automotive type whether used by hams, public safety, or whatever
>> >often have the contacts stuck together and 6 or 12VDC often wont
>> >budge them loose. Trying it too long is guaranteed to damage the
>> >contacts.
>> >
>> >It only takes a little AC, no string of lamps or 120VAC involved; a
>> >6 or 12VAC filament transformer works fine. Ive been doing this
>> >since the 60's when I started rebuilding vintage auto radios for
>> >owners. Many hundreds also including the 38 Buick I finished 2 days
>> >ago.
>> >
>> >
>> >Carl
>> >KM1H
>> >
>> >
>> >  ----- Original Message -----
>> >  From: WA5CAB at cs.com
>> >  To: km1h at jeremy.mv.com ; boatanchors at mailman.qth.net
>> >  Sent: Tuesday, February 02, 2010 5:04 PM
>> >  Subject: Re: [Boatanchors] Relay Repair - Demagnetization Question
>> >
>> >
>> >  No.  At least not the military ones.  The problem with them, after
>> >decades of inactivity, is that the contacts are covered with a non-
>> >conducting layer of tungsten sulfide (or maybe supphate, I never
>> >looked up the relavent valences) caused by sulfur outgassing from
>> >the sponge rubber sleeve inside all the cans.  I've "fixed" hundreds
>> >of them.  You can open up the can and burnish the contacts but it's
>> >a lot less trouble to use an array of 120 volt 12 to 40 watt lamps
>> >and the 120 VAC line to do the job.
>
> Robert & Susan Downs - Houston
> wa5cab dot com (Web Store)
> MVPA 9480
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