[Boatanchors] Relay Repair - Demagnetization Question

Carl km1h at jeremy.mv.com
Tue Feb 2 20:37:01 EST 2010


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.  

  This works on all of the military vibrators except for the VB-5, which can only be fixed by opening the can.  Which always comes open in little pieces of brittle aluminum and has to be replaced.

  In a message dated 2/2/2010 2:21:57 PM Central Standard Time, km1h at jeremy.mv.com writes: 

    Automotive and other vibrators do not have coil problems. The contacts are 
    "welded" together from basic chemical reaction after decades of storage. 
    Applying 6-12VAC across the proper actuator contacts will get it swinging 
    again.

    Carl
    KM1H



  Robert & Susan Downs - Houston
  wa5cab dot com (Web Store)
  MVPA 9480 


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