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Author Topic: Lightning Storm Damage (Jan 2020) - Modems 2 and 3 Down  (Read 7071 times)

sevenlayermuddle

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Re: Lightning Storm Damage (Jan 2020) - Modems 2 and 3 Down
« Reply #45 on: January 21, 2020, 11:27:03 PM »

My understanding is that the momentary currents that flow as a consequence of indirect lightning can be regarded as almost ideal current sources.   

That being the case, the current will flow come what may, but the greater the resistance it encounters, the greater the voltage that will arise across the resistor.   That is why higher resistances generally result in higher damage.  For example a discharge from a cloud to a church spire’s lightning conductor creates a huge voltage and makes a big bang whereas the corresponding current down the spire’s earth conductor is the same current, but creates just a tiny voltage along the length of the conductor, so passes unnoticed.

If the firebrick has a half decent (normal household earth) connection to ground, and has protection devices to provide a safe discharge path from the inputs, that would explain why it survived undamaged.

A modem with an earth connection, but without the input protection devices, would more likely follow the model of ‘cloud to spire’ with a very big flash and bang.

Repeat... just my understanding. :)


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Weaver

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Re: Lightning Storm Damage (Jan 2020) - Modems 2 and 3 Down
« Reply #46 on: January 22, 2020, 12:04:11 AM »

The current source may be ideal but it isn’t necessarily undivided and I think 7LM is talking about lightning strikes rather than induced currents? All such currents have a choice of where to go in some situations; so I would assume that some fraction of the total current takes candidate path A some fraction takes candidate B. We indeed see this division in photos of lightning strikes.

I think 7LM is essentially correct but I think we’re at cross purposes possibly?

If the firebrick and MUX switch are lower resistance than the ethernet cable then we have a potential divider and most of the voltage drop would be in the thin ethernet cable and in the modem, if indeed it is thin enough wire to be of higher resistance.

I wonder why two modems appear ok? Should I get shot of them anyway?
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sevenlayermuddle

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Re: Lightning Storm Damage (Jan 2020) - Modems 2 and 3 Down
« Reply #47 on: January 22, 2020, 12:25:23 AM »

I wonder why two modems appear ok? Should I get shot of them anyway?

Personally I’d say no, if they seem ok keep using them.   But keep an eye on performance and if adverse symptoms subsequently emerge them as well as fixing them, be prepared to attribute the damage, retrospectively, to the storm.   That might add data to future cost/benefit analysis of installing protective devices.
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Weaver

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Re: Lightning Storm Damage (Jan 2020) - Modems 2 and 3 Down
« Reply #48 on: January 22, 2020, 12:42:34 AM »

Replacement modems are now down to £15 each - the price has dropped by 70% in the last six months (v approx) as the initial high demand seems to have been dated and more second hand units are coming into the market for some reason. I think new units can still be obtained, but Mrs Weaver will have words me if I buy any more modems than the pile I already have.
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sevenlayermuddle

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Re: Lightning Storm Damage (Jan 2020) - Modems 2 and 3 Down
« Reply #49 on: January 22, 2020, 12:59:50 AM »

If you replace them now, without waiting to see if they are damaged, you also lose the data for cost/benefit analysis.

I have also recently had my own spending habits reviewed by other half, following unexpected appearance of a bench PSU and umpteen bags of bits for a little project I’m working on.  I’ve now been allocated a budget of £x per month beyond which, it seems, written purchase approval will in future be required. :'(
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Weaver

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Re: Lightning Storm Damage (Jan 2020) - Modems 2 and 3 Down
« Reply #50 on: January 22, 2020, 04:17:39 AM »

> I’ve now been allocated a budget of £x per month beyond which, it seems, written purchase approval will in future be required. :'(

Snap. Exactly. I ask my beloved about all substantial planned purchases seeing as I’m not earning anything now and she looks after me. It’s a great thing that modems are so cheap now.
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Alex Atkin UK

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Re: Lightning Storm Damage (Jan 2020) - Modems 2 and 3 Down
« Reply #51 on: January 22, 2020, 02:00:12 PM »

I haven't been following closely enough, was it discovered the Zyxels on your lines performed better than the HG612?
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benji09

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Re: Lightning Storm Damage (Jan 2020) - Modems 2 and 3 Down
« Reply #52 on: January 22, 2020, 04:08:29 PM »


  In the S.E. where I live, storms are rare. But when I know that a storm is due, I disconnect the ethernet cable from the Sky modem/router, and from the Netgear router in the other room. I then connect between the two via a wireless link for the duration of the storm. I hope by doing this that the only router to be blown up will be the Sky one. Also the Sky router is left floating from earth, apart from any capacity coupling to the mains supply via the double insulated mains supply. Not had many storms were I live to see that my idea does or does not work though.......
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Weaver

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Re: Lightning Storm Damage (Jan 2020) - Modems 2 and 3 Down
« Reply #53 on: January 22, 2020, 07:20:13 PM »

I don’t have a HG612, never tested one. Has anyone tried one on ADSL2 ?
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burakkucat

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Re: Lightning Storm Damage (Jan 2020) - Modems 2 and 3 Down
« Reply #54 on: January 22, 2020, 08:36:16 PM »

I don’t have a HG612, never tested one. Has anyone tried one on ADSL2 ?

Yes, way, way back in 2011 (when Asbokid produced the first unlocked firmware image).

First a HG612, then a HG610 and finally a HG622. Subsequently used a VMG1312-B10D and when that went weird on me, moved onto the superior VMG1312-B10A.
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Weaver

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Re: Lightning Storm Damage (Jan 2020) - Modems 2 and 3 Down
« Reply #55 on: February 18, 2020, 06:12:59 PM »

Earlier in this thread, I referred to my hardware lightning warning unit as a "skyscanner" - that is incorrect, it is in fact a "Skyscan" model "Skyscan P5-3".
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