Re: strange behavior of laptop during thunderstorm

From: w_tom (w_tom1_at_hotmail.com)
Date: 08/21/04 

Date: Sat, 21 Aug 2004 09:52:32 -0400

  If nearby lightning fields could do to a laptop as others
have suggested, then every nearby automobile radio and every
nearby cell phone is also damaged. Nearby strikes do damage
because they make direct connections through the electronics.
A camping lesson:

  They were sleeping near a tree that was struck. Those
sleeping parallel to the tree were not harmed. But two
sleeping perpendicular to (pointed towards) the tree required
emergency medicial assistance. Lightning traveled down tree
seeking earth borne charges some kilometers away. A shorter
electrical path to those charges was out of ground, through
the feet, and back into earth via the head. Only those
campers were harmed.

  Same could have happened to your laptop. Charges up out of
a conductive concrete, through fingers, into laptop, then back
into earth via table. Was table non-conductive (glass) or
conductive (plastic or wood)?

  Furthermore, was anything else connected to that computer -
printer cable (even withtout a printer), modem, etc? Was
there an insulated wire draped out back of machine onto
floor? These could have been conductors to complete the
circuit.

  One way to avoid future problems would be a conductive
plastic (anti-static) sheet on floor underneath both computer
table and human.

  To have a transient, one must first establish a complete
circuit. Often a destructive transient will enter computer on
AC electric, pass through motherboard and modem, then leave
via phone line. The transient would have been in contact with
virtually every semiconductor IC on motherboard. Why were
those others IC (ie RAM) not damaged? No outgoing path means
no electric current and therefore no damage; as was taught in
elementary school science.

  So yes, there must have been a complete circuit - incoming
and outgoing - via the laptop. The most interesting question
remains what that circuit was.

  It gets more interesting. I setup a computer on a glass
table top. Then build up static electric charges with leather
slippers on a nylon carpet. I then static electric shock the
computer case so that charges must pass across chassis and
down a wire back to nylon floor. If motherboard is mounted on
multiple conductive standoffs, then computer crashes. If
mounted only on one standoff, then computer operates
unaffected. Why? Again, the complete circuit. With multiple
standoffs, then static electric passes across motherboard
logic ground. But with only one conductive standoff, an
incoming path but no outgoing path exists for that static
electric discharge. Ergo, no computer crash.

  So yes, a transient need not even go through semiconductors
nor do damage to make a computer crash. A potential
difference across the motherboard's large copper ground plane
can cause strange computer actions.

  This becomes too complex for some. So they speculate that
nearby lightning creates these mythical, massive, destructive
fields. Problem remains that numbers are never provided to
prove that speculation. We call that junk science reasoning.
Many materials they 'think' are non-conductive are, instead,
conductive to high voltage, high fequencey transients such as
lightning. Hope this helps.

Allan Adler wrote:
> I was using a laptop a few weeks ago during a thunderstorm. I knew
> about the storm and was running the laptop on battery for that reason.
> This laptop runs RedHat Linux 9 and for reasons I don't understand
> won't use the full screen for X, but only about half of it, but one
> can still use it, and that is what I was doing during the thunderstorm.
> At a certain point, there was some lightning nearby and suddently
> the computer display was occupying the full screen. But it also
> was hanging and wouldn't respond to commands, so I turned it off
> and rebooted it. It's tempting to think that this had something
> to do with the storm, but I was running the laptop on battery.
> Still, I remember when I was a kid hearing stories of electric
> lights dimming when someone took their sweater off, apparently
> due to the static charge from the wool, so I don't entirely
> rule it out. I was using the laptop in a basement apartment
> and maybe there was a very slight change in ground potential
> during the storm, which got transmitted through my feet and then
> my fingers to the laptop. Or, when I use an oscilloscope sometimes
> (my old EICO 460) the signal displayed on the scope depends on how
> close I am to the probe; I've been told that this is due to the fact
> that the body acts as an antenna somehow. So maybe instead of
> changing ground potential, it was my body acting as an antenna and
> transmitting some electrical disturbance due to the lightning. I
> don't like to speculate about these possibilities since I really
> don't know what I'm talking about. The laptop has shown no signs
> of damage since then.
>
> It was always my impression that it is perfectly safe to operate
> a laptop under battery during a thunderstorm, but this experience
> is making me wonder. Can someone please clarify this point?

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