Inductive relay "kick"

[Carl, WCØV]

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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[jferg977]

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  <[hidden email]>
Subject: [Elecraft] Inductive relay  "kick"
To: <[hidden email]>
Cc:  [hidden email]
Message-ID:  <001e01c9b539$4f37cc70$0202a8c0@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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