[Elecraft] Inductive relay "kick"

[Jferg977 at aol.com]

Carl,
It appears that my K2 is the only one in the universe to have  experienced 
this problem.  We don't really know what caused the problem,  but it may have 
been due to vagrant high-voltage under the heat sync resulting  from unchecked 
ESD.  Since the two failed caps must have been the weak  links in the area, 
replacing the 50 volt type with 100 ought to improve  things.
 
John
 
 
 
Date: Sat, 4 Apr 2009 10:23:29 -0500
From: Carl, WC?V  <wc0v10 at embarqmail.com>
Subject: [Elecraft] Inductive relay  "kick"
To: <w3fpr at embarqmail.com>
Cc:  elecraft at mailman.qth.net
Message-ID:  <001e01c9b539$4f37cc70$0202a8c0 at NEWDESKTOP>
Content-Type:  text/plain;    charset="iso-8859-1"

Don, seriously  disagree about the magnitude of the "kick". For years I 
taught a course on  industrial installations and demo'ed the "kick" issue by 
soldering two bare wire  to the coil of a small Potter and Brumfield "ice cube" 12 
vdc relay. I would  pick the biggest guy in the class to hold the wires while I 
touched them to a  nine-volt transistor radio battery. And then watch as he 
would throw the relay  across the room. A reverse diode would vastly reduce the 
effect.

Well, I  got yelled at and was told "Hey, Stupid (and stupid wasn't the word 
they used)!  Put that on a storage scope to see what you're messing with." The 
scope showed a  spike of 450 vdc! The diode reduced it to less than 75 vdc. 

The  magnitude is due mainly to the large inductance of the coil, but until 
some  measurements are taken, some caution is advised. The inductance of any 
coil  inside a K2 or K3 is bound to be much smaller. But the phenomenon is the  
same.

73, Carl WC0V
 
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