[ARC5] All Electronics Closing
Richard Knoppow
1oldlens1 at ix.netcom.com
Wed Jul 12 23:50:45 EDT 2023
All Electronics, one of the last old fashioned surplus stores, is
closing at the end of August.
I will try to visit their walk in store in van Nuys soon.
On 7/12/2023 6:47 PM, Brian Clarke wrote:
> 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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--
Richard Knoppow
WB6KBL
SKCC 19998
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