strange behavior of laptop during thunderstorm

Coincidence?

Probably.

-- Ignorantly, Allan Adler

• Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and

• comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

It is hard to answer your question about the laptop. But, it is possible for electronic equipment to be damaged with a lightning storm near by, even if it is not plugged in to the AC.

One strong reason for electronic equipment damage from being close by to lightning, is from inductive pickup. Lightning consists of a very rapid array of sparks, which comprise of many harmonics, and have a very high intensity of an electrical noise discharge. Since the sparks are very rapidly varying in its intensity, they can be very reactive in their nature. Even a trace on a circuit board, if it can act as a resonant receiver to the lightning induced electrical energy, the trace can become like a tuned receiver and transfer some electrical energy to anything connected to it. Many of the characteristics, and the way that the particular lightning strike may occur can be very random.

I have seen lightning damage to sensitive instruments and electronic equipment, that were completely disconnected from the AC, and not even turned on. Most of the time, when this occurs, the lightning strike has to be very close.

--

Jerry G. ==========================

"Allan Adler" wrote in message news: snipped-for-privacy@nestle.csail.mit.edu...

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?

-- Ignorantly, Allan Adler

• Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and

• comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

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 lightn> I was using a laptop a few weeks ago during a thunderstorm. I knew

True, but incomplete and misleading. Nearby strikes also do damage because of induction and RF transmission.

-- John Miller Email address: domain, n4vu.com; username, jsm

He: Let's end it all, bequeathin' our brains to science. She: What?!? Science got enough trouble with their OWN brains. -Walt Kelly

snip

You hit the screen expansion key combination or XFree's screen mode-resolution key combination? The freezing up and less than full screen suggests the mode change..

w_tom writes (among other interesting things):

Wood.

Allan Adler wrote: []

------------------ Y'know that "click" you often hear right before a lightning strike that is REALLY close to you, a real window-banger? Well, if you recorded the sounds with a shielded recorder you wouldn't hear it!! It's neurological EMP artifact in your BRAIN from the induced broad-spectrum signal!! Same in your laptop, its circuitry is an antenna!! It's bound to lock it up sometimes!

If you want a lightning-proof laptop, then put it in a Faraday cage!

-Steve

Then again, put up those numbers. Explain how all nearby car radios and cell phones with external antenna connected to the most sensitive transistor were not damaged by the same field that penetrated the computer. Again, where are these numbers that prove such damage occurs. If nearby strikes do damage because of induction and RF transmission, then lets see those numbers, all those damaged walkmans, and all those routinely damaged portable phones.

Using the same reasoning, I could even claim that airplanes cause computer damage. I am asking for numbers since everyone who makes claims about 'induction and RF transmission' cannot even provide basic electromagnetic field numbers to prove their point.

It nearby strikes do such damage, then the devices most susceptible - especially portable AM radios - would be rout> True, but incomplete and misleading. Nearby strikes also do

Has it occurred to you that the reason the "numbers" are not forthcoming may have nothing to do with lack of data, but rather, the likelihood of its being absorbed?

Prove your point. Provide the numbers. Stop with spin politics about number absorption. Explain why all those nearby radios - especially AM radios - are not damaged by nearby fields. Stop wasting good bandwidth with excuses. Put up those numbers and facts.

I know one reason why those numbers are never posted. Those who claim 'induction and RF transmission' cause damage never even repaired lightning damaged equipment by traceing the direct strike path let alone take two semesters of Electromagnetic Fields class. Too many newsgroup posters just know because previous posters said so. Junk science reasoning promotes these myths. Nearby lightning causing destructive fields is promoted by the same logic that promoted Geritol and Listerene.

Prove me wr> w_tom wrote:

I have heard that sound and always assumed that it was arcing in the electrical outlet boxes. Never heard it outside. Do you have a source of information on this?

I can state with some authority that if a EE PhD told you in general terms about induction and RF transmission, you wouldn't belive it. So I'm not going to bother. Perhaps someone else will.

John's response breaks down into the classic "he just knows that induction and RF transmission causes damage"; without any scientific knowledge. He cannot provide numbers and probably does not even know what numbers would be required.

John Miller demonstrates how so many claim that damage happens. He just knows that the electromagnetic fields from a nearby strike all but destroys life. Clearly those undamaged nearby radios must be an anomaly. He needs no numbers, no professional citations, and no classes in basic electrical engineering. He is above all that. He just knows, which is why he will not provide numbers.

In the meantime, those nearby radios, et al are damaged when the nearby lightning strike actually is a direct strike to electronics. When a current flows into and out of the electronics. Knowing this, then commercial buildings, cell phone towers, etc are all easily hardened from lightning damage. The heart of a protective system is the essential single point earth ground.

Cited earlier was an example where a nearby strike harmed sleeping campers. Lightning induced fields caused harm? Of course not. Some campers were sleeping so that they became electrical conductors. The nearby strike actually conducted electricity through their bodies. They suffered a direct strike.

How to protect yourself from a nearby strike? Wrap yourself > I can state with some authority that if a EE PhD told you in

I thought the original post claimed that the computer was interfered with, not damaged.

My own computer often malfunctions and locks up from static discharges that only cause a "pop" sound in radios, TV, and audio equipment.

I have also heard of Tesla coils locking up and rebooting computers several feet away, and radios, TV, and audio equipment normally have interference effects. Usually, none of the above suffers any damage.

- Don Klipstein ( snipped-for-privacy@misty.com)

Plastic is nonconductive, and I doubt wood is conductive enough for this. I suspect inductive coupling or a pulse of RF.

- Don Klipstein ( snipped-for-privacy@misty.com)

I have heard it. I have only heard it when outdoors or at an open window. Having a windowscreen between me and the lightning does not change this sound much, but having glass in between does. I thought it was from a very slight but very sudden pressure change in the air from the air absorbing shortwave UV radiation from the lightning. What I thought this was is definitely what happens with quartz xenon flashtubes that make really noticeable snap/pop sounds.

I have heard of radar pulses causing audible effects, believed to be from sudden but extremely slight pressure rises in the heads of people being exposed.

- Don Klipstein ( snipped-for-privacy@misty.com)

When talking about these types of voltages and currents, then wood, some plastics, concrete, wall paints, and linoleum all become good conductors. Some better than others.

Rather > Plastic is nonconductive, and I doubt wood is conductive enough