[ARC5] Troubleshooting Tips from the Late Nick Broline, #3

[Brian Clarke]

I agree with Scott. Here's why:When you have a lightning strike with a
typical current rise rate of 30,000 A / 1.2 usec (that is, 25,000 MV /
s) [note capital M as a multiplier means Mega, million or 10^6], even
1 mH  inductance in a lead gives |25 MV| rise. Even if your leads are
1 nH (e = |25 kV|), do this often enough to your MOV rated at 400
V and it will be cactus - and you won't know. I reckon you're better
off using a spark gap.
73 de Brian, VK2GCE
BE, MBA, PhD, CPEng, APEC Engineer, IntPE(Aus),
 FIEAust, MASTC

----- Original Message -----
From:
 scottjohnson1 at cox.net

To:
"Christopher Bowne" <aj1g at sbcglobal.net>, "David Stinson"
<arc5 at ix.netcom.com>
Cc:
"ARC-5" <arc5 at mailman.qth.net>, <milsurplus at mailman.qth.net>
Sent:
Wed, 12 Jul 2023 07:08:15 -0700
Subject:
Re: [ARC5] Troubleshooting Tips from the Late Nick Broline, #3

 The leads should be as short as possible, the longer the leads, the
less effective the MOV is at shunting fast rising transients.
 It is sometimes advisable to add a utility box on the side of the
panel, so the leads have a direct short, direct path to the main lugs.
Splicing should be avoided.
 This was shown graphically in a recent issue of EC&M, and electrical
trades safety magazine.

 Scott W7SVJ

 -----Original Message-----
 From: arc5-bounces at mailman.qth.net <arc5-bounces at mailman.qth.net> On
Behalf Of Christopher Bowne
 Sent: Tuesday, July 11, 2023 03:02
 To: David Stinson <arc5 at ix.netcom.com>
 Cc: ARC-5 <arc5 at mailman.qth.net>; milsurplus at mailman.qth.net
 Subject: Re: [ARC5] Troubleshooting Tips from the Late Nick Broline,
#3

 Thanks for all these tips! I only recently became aware of the
availability of “whole house” MOV protectors that can be installed
across the incoming power line in one’s circuit breaker/distribution
panel. Super easy to install - 4 wires - to neutral, ground, and to
each hot side of the incoming 240 via a spare circuit breaker. 

 We once had the pole pig across the street from the house take a
lightning strike that caused a lot of damage to loads that were on
service during the strike - blew up light bulbs, a clock radio, and
the refrigerator. And blew out a hole around the ground rod at the
service entrance about a foot in diameter. According to my wife (I was
out of town on work travel at the time), the concussion of the
thunderclap actually made window shades that were pulled down wind up
all over the house, just like in a horror movie. Luckily, this
happened in mid 80s, before we had any really expensive electronic
stuff in the house and Diane had gone around and unplugged or turned
off as many loads, including my ham gear, as possible in advance of
what sounded like was going to be a whopper of a storm when it came
through.

 If you buy one of the whole house protectors, make sure they have
enough lead length on the attached connection wires. The GE one I
bought had a only a very lqshort neutral pigtail that would have
required making a spliced connection to add enough length to reach the
neutral bus bar within the circuit breaker panel. I ended up returning
it and went with one made by Square D.

 73 de Chris AJ1G
 Stonington CT

 Sent from my iPhone

 > On Jul 10, 2023, at 22:22, David Stinson <arc5 at ix.netcom.com>
wrote:
 > 
 > Choosing MOVs to protect your power supplies:
 > 
 > This is a long treatment of what you are asking for in your MOV
selection.
 > Depending on how your MOV manufacturer specifies the device, it may

 > not be what you want.
 > 
 > Your 122V power system has a peak voltage of 1.4 x the rms value 
 > (122V)l, or 173V. This peak voltage should be the voltage used in
selecting the MOV.
 > One with a lower rating would mean it would be attempting to
conduct 
 > on the peak of every half cycle.
 > 
 > Looking at an offering from the Mouser catalog for the Bourns MOV 
 > products I see they have provided application assistance by
specifying 
 > the RMS voltage design center, the DC hold-off voltage, then more
data 
 > that gives us insight as to how they turn on, or start conducting,
and how hefty it is.
 > 
 > Their line for part number
 > MOV-20D201K is called a 130V rms MOV that can operate across a 170V
dc 
 > source without drawing significant current.
 > Continuing down the listing, they specify the voltage at which it
will 
 > draw
 > 1 ma: 185V min, 200V nominal, and 225V max. Now we can see these
are 
 > not precision voltage devices, so we need to select one with some
"elbow room"
 > at the top voltage. They do no go to full conduction at the
threshold 
 > voltage, either. They turn on gradually Increasing the voltage just

 > causes them to draw incrementally larger currents, and the voltage 
 > across them also rises. Note that the lowest threshold voltage at 1

 > ma. is comfortably below your peak line voltage.
 > 
 > MOV's are not anything like back-to-back Zener diodes, which will
have 
 > sharp knees at turn on. They would certainly try to clamp a
transient 
 > at their rated voltage.....once......unless one uses very large 
 > honkin' diodes. For a transient like a lightning strike somewhere 
 > distant from the protected product they would clamp the transient 
 > once, then possibly be destroyed by the peak energy they are
subjected 
 > to. Most likely they would short, and that would blow the fuse.
 > 
 > MOV's are designed to take such transient "on the chin" and
continue 
 > protecting without destroying themselves.....but they are limited
in 
 > the number of times they can do that, and that is normally not a 
 > problem. A good way to think of them is their ability to absorb a 
 > relatively large amount of energy instantaneously and will draw a
very 
 > high peak current (6500 A in this part number) for a few
microseconds 
 > in the process. This makes them a good and cheap circuit protector 
 > that knocks off the sharp edges of transient waveforms.
 > 
 > The product I used as an example is about 1" in diameter and is a 
 > fairly typical size. It looks like it would be a suitable selection
for your needs.
 > 73
 > Nick Broline W5FUA

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