[TowerTalk] Lightning protection and control wires

[Jim Lux]

On 10/5/12 4:38 AM, Julius Fazekas wrote:
> This topic is interesting and I have played with a few different HB
> options. Which is the source of my question, what is the best method
> (how?) of determining the value of MOVs, TVSs, flash tubes or other
> options? Or is it any value is better than nothing, which seems to be
> the case in most ham related writings (which seem to be few and far
> between) on the topic.



IN theory, you choose the highest voltage that won't damage the 
downstream equipment.  What you don't want is "normal" events hitting 
the MOV repeatedly.  This is one of the causes of fires in "surge 
suppressor plug strips".... Advertising a low clamp voltage, which 
actually isn't needed, and periodic "swells" in line voltage hit the 
threshold and dissipate power in the MOV.  (and killing the MOV a bit 
each time).

the back to back zener schemes (TransZorb, for instance) are better than 
MOVs (but more expensive), because they don't have the incremental life 
consumption of MOVs.


A study some 10-20 years ago by, I think, a Canadian organization, 
looked at the response of consumer electronics to line transients 
(Canada has lots of above ground distribution AND thunderstorms) and 
found that almost all modern equipment can tolerate 2000V spikes on the 
power line (a wall wart, for instance, will block that with no sweat, 
either common mode or differential, as will most anything with a power 
supply either linear or switching.)  There's very little sold these days 
that operates directly off-line in the All-American 5 tube radio scheme 
or older TV designs.

What kills things today is big differentials between "chassis" and 
"signal"; and they're getting tougher.  For instance, the parallel 
printer port is notorious: the connector pins went  right to the 74LS244 
or similar, and these days, right to some ASIC.  It doesn't take much to 
kill that.  Cheap serial ports (that don't use RS232 line drivers, which 
can easily take 30V spikes and have current limiting on the signal 
leads) get killed too.    USB is much tougher, of course.


If you want to know what to really do, and to get good explanations.. 
get Ronald Standler's book "Transient Protection of Electronic 
Circuits".. it's something like $17 in paperback from DOver and has both 
theory and cookbook "what do you do in situation X".  ANyone who is 
*designing* equipment should read it, because doing the "right thing" is 
no more difficult than the "wrong thing" (and he has lots of examples of 
poor design from a transient damage standpoint... some of which are 
straight out of *old* editions of the ARRL handbook..)

As the cover blurb says: "This text presents practical rules and 
strategies for circuits designed to protect electronic systems from 
damage by transient overvoltages"

http://books.google.com/books/about/Protection_of_Electronic_Circuits_from_O.html?id=5-NEmE1EhYQC


I see that Dover now charges $27...
http://store.doverpublications.com/0486425525.html

Still worth every penny.

Standler's website has useful information too, but the book is better.






>
> So far I've been lucky with only a few popped diodes or transistors
> and two fried UPS units, but would prefer fewer incidents.
>
> 73, Julius
>
> Julius Fazekas
>
> N2WN
>
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