Thanks Herman,

I also prefer the DC  for my current application and especially your idea of
the constant current with the LM317.

I have upload a schematic of the LM317 connected to the pic at
http://www.eskulaap.co.za/schem.gif . Please
comment.

How and where should I connect transorps, MOV's, caps or inductors (short
circuit and bypass)and what values?

Thanks

Francois

> I would use constant current (say 1 mA) through the (steel wire) loop.
>
> This puts you in the best position to keep lightning away (from your
electronics). Because :
> Capacitors give you bypass or shorting (short-circuiting) capability ...
> Inductors give you blocking capability ......
>    ...... both without basically affecting your constant-current system.
>
> Then there are MOV's (Metal-Oxide-Varistors). I see the telephone-company
using them. Between wires (not sure) and from each wire to ground, in the
terminalbox at every house. There is a wire to a groundrod. Our tel.system
is mostly overhead wires.
> We have serious lightning here in the tropics. I have regular twinlead
wire here to show it. Insulation melted away by lightning in many spots ...
while in use for telephone service.
>
> With only 12Volt (max) you can stop lightning getting in (capacitors,
inductors) and whatever gets past the capacitor/inductor protection you can
clamp with 12V MOVs.
>
> For 1 mA and 200 Ohm loop resistance (resistance assumed), you would need
less than a Volt to maintain the 1 mA current (plus voltage-drops over poor
connections in the loop).
> The voltage-drops serve to find the poor connections with a voltmeter.
>
> If you generate the constant-current from the 12V powersupply you
mentioned, the voltage will shoot up to 12V when the loop is broken.
> You can make a 1 mA constant current generator with just 2 parts .....
>  an LM317 voltage-regulator and a 1200 Ohm (1 to 2 kOhm) resistor.
>
> Herman in PHL.


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