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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