[Top] [All Lists]

Re: [TowerTalk] Lightning protection and control wires

Subject: Re: [TowerTalk] Lightning protection and control wires
From: Jim Lux <>
Date: Fri, 05 Oct 2012 07:44:10 -0700
List-post: <">>
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"

I see that Dover now charges $27...

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


Tennessee Contest Group

Tennessee QSO Party

Elecraft K2     #4455

Elecraft K3/100 #366

Elecraft K3/100 #4461

_______________________________________________ TowerTalk mailing


TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>