Topband: Beverages, Lightning and Moose

[Tom Rauch]

I have miles of cables and dozens of switching relays spread over a 
large area. Making matters worse, I have some very tall structures 
attracting occasional hits. 

Because of the number of cables and area, I can't unhook anything 
during a storm.

What I use is a diode clamp with fast 3 ampere dodes (1N5408) on 
all the control lines in the house. On each control conductor, one 
diode goes to ground (anode to ground) and another goes from the 
line with the cathode into a "dump capacitor" of several thousand 
microfarads that is grounded. The dump capacitor positive terminal 
junction with the diode cathode is held just above control line rail 
through a leak resistor to the supply voltage.
  
I use only relays in the field, although they are configured for BCD 
control voltages. 

I drive the control lines directly with transistors and have never lost 
a transistor while the dump circuit is connected. If I disconnect a 
diode, I will lose the transistors on that line in every storm.

MOV's were ineffective, as were series resistors (they always 
opened up). The diode clamps have let me go for years now without 
replacing parts.

73, Tom W8JI
W8JI@contesting.com 


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