Lightning and modems

  • Thread starter Thread starter KenK
  • Start date Start date
Buffalo said:
"Buffalo" wrote in message news:[email protected]...

But, once the air is ionized, then it might only take the low amt of
voltage to continue the arc. Perhaps that is what he was talking about.
Click to expand...

Let's say the breakdown voltage of dry air was 50,000 volts per inch.
If we had 100,000,000 volts to work with, that's 2000 inches or 167 feet.
That means we can't get a good discharge, without some other
mechanism at work.

That's where ionization and eventual plasma formation come in. Which
aren't discussed in enough detail here, for my liking.

http://science.howstuffworks.com/nature/natural-disasters/lightning2.htm

The lightning bolt can go "up and down" several times, when
a bolt hits. So the process is pretty complicated.

And as that page points out, everything involving lightning
involves the "assignment of probabilities". Using lightning
protection structures, does not guarantee where the bolt
will hit. It improves the probability a bit, that you
are in control of where it goes, but the lightning can still
surprise you, shoot through the side of the house, and so on.
When they tell you to stand in a certain place to be
safe, it's not really a guarantee of your safety (the so-called
"cone of protection"). Things that are safe bets, would be
standing tangentially versus radially, to an object affording
protection. As the electric field when the bolt strikes the
ground, makes "circular rings of potential difference" at ground zero point.
If you're standing radially with respect to where the bolt
hits, a potential is placed between your two feet, and your
balls get burned :-) If you're standing tangentially
to the rings of potential difference, there is no
potential difference between your feet. Maybe the best
advice, is to stand with your feet... really close
together :-) Just in case you're a bit too flustered
at the time, figuring out what is radial and what is
tangential. And why did this tree just fall on me.

Paul
 
"Paul" wrote in message news:[email protected]...
Let's say the breakdown voltage of dry air was 50,000 volts per inch.
If we had 100,000,000 volts to work with, that's 2000 inches or 167 feet.
That means we can't get a good discharge, without some other
mechanism at work.

That's where ionization and eventual plasma formation come in. Which
aren't discussed in enough detail here, for my liking.

http://science.howstuffworks.com/nature/natural-disasters/lightning2.htm

The lightning bolt can go "up and down" several times, when
a bolt hits. So the process is pretty complicated.

And as that page points out, everything involving lightning
involves the "assignment of probabilities". Using lightning
protection structures, does not guarantee where the bolt
will hit. It improves the probability a bit, that you
are in control of where it goes, but the lightning can still
surprise you, shoot through the side of the house, and so on.
When they tell you to stand in a certain place to be
safe, it's not really a guarantee of your safety (the so-called
"cone of protection"). Things that are safe bets, would be
standing tangentially versus radially, to an object affording
protection. As the electric field when the bolt strikes the
ground, makes "circular rings of potential difference" at ground zero
point.
If you're standing radially with respect to where the bolt
hits, a potential is placed between your two feet, and your
balls get burned :-) If you're standing tangentially
to the rings of potential difference, there is no
potential difference between your feet. Maybe the best
advice, is to stand with your feet... really close
together :-) Just in case you're a bit too flustered
at the time, figuring out what is radial and what is
tangential. And why did this tree just fall on me.

Paul
Click to expand...
If you stand with your feet apart and are perpendicular to the rings, then
most likely you heart will suffer more than your balls. :)
But, by saying a spark will jump the gap of an automobile spark plug with as
low as 15volts, is total nonsense.
Standing, or better yet squatting with your feet together (if your balance
is good enough) or sitting on the ground with your feet together and
touching your butt 'may' even be better.
Sitting in a bar and having a drink would even be safer. :)
 
"Bill in Co" wrote in message
Yeah, I'd say! :-) So, so much for that link!
Next thing I expect to hear is about people getting electrocuted off of a
12V car battery! Uh-huh!
Click to expand...
Depends if you are standing with your feet apart and parallel to the battery
posts or perpendicular to the line of the battery posts.
That link does have a lot of useful and accurate info, AFAIK.
 
Bill said:
Yeah, I'd say! :-) So, so much for that link!
Next thing I expect to hear is about people getting electrocuted off of a
12V car battery! Uh-huh!
Click to expand...

You can be electrocuted from as little as 1.5V.
It's a matter of making a good connection, and
getting the current flow to go through your heart.

It's the level of current flow that counts. High
voltage just makes it easier to get the necessary
current level (V/R = I, large V gives large I).

Holding two paddles in your hands, with 1.5V applied,
will not do it. However, using needles penetrating the
skin of your body, can arrange the necessary conditions.

A certain level of resistance to electrical flow is
expected, for "contact with palms" type events. We have
certain expectations of our ability to resist the
effects of electricity, based on an assumption of
"dry palms". Some people's hands are a lot damper than
others, which makes a difference to their perception
of what is dangerous.

http://en.wikipedia.org/wiki/Electric_shock

"If an electrical circuit is established by electrodes
introduced in the body, bypassing the skin, then the
potential for lethality is much higher if a circuit
through the heart is established. This is known as a
microshock. Currents of only 10 µA can be sufficient
to cause fibrillation in this case. [citation needed]"

And with no citation, the comment is not worth much to us.

I had a professor in university, who was a biomedical engineer,
and he used to regale us with stories of electrical accidents
at the hospital he worked at. It's easy to damage people who
are naked, and have all sorts of monitors connected, then
use equipment which cauterizes (like during surgery). Any
electrical wiring mistakes or bad assumptions, can cause
real misery. He told us stories of various body parts
getting burned, while a patient is unconscious and some
electricity is flowing where it should not. So talk to
a biomedical engineer about the kind of mistakes
that happen with electricity.

Paul
 
"Paul" wrote in message news:[email protected]...
You can be electrocuted from as little as 1.5V.
It's a matter of making a good connection, and
getting the current flow to go through your heart.
Click to expand...
Total bs.
You are ultra sharp with computers, but I'm afraid you are out of your
expertise here.
Perhaps 1.5v fed directly to a naked heart could cause a problem, but an
electrocution on a person by 1.5v is not possible.
Shit, sometimes they have a difficult time killing someone in an Electric
Chair.
Ever stick your tongue on a 9 v battery to see if it is still potent?
Chances of getting electrocuted by doing that is nil.
Heard many stories of people getting electrocuted by an electric welding
machine? Very high amperage and low voltage.
 
Buffalo said:
"Paul" wrote in message news:[email protected]...
Total bs.
You are ultra sharp with computers, but I'm afraid you are out of your
expertise here.
Perhaps 1.5v fed directly to a naked heart could cause a problem, but
an electrocution on a person by 1.5v is not possible.
Shit, sometimes they have a difficult time killing someone in an
Electric Chair.
Ever stick your tongue on a 9 v battery to see if it is still potent?
Chances of getting electrocuted by doing that is nil.
Heard many stories of people getting electrocuted by an electric welding
machine? Very high amperage and low voltage.
Click to expand...

I didn't give instructions on how to do it with 1.5V.

Obvious it requires a connection pretty close to the
heart muscle.

It was purely to indicate the limit is pretty low,
if the conditions are just right.

At some point, the voltage is low enough, that conduction
might not have any impact. Presumably the activation
voltage of nerves and muscles has some lower limit. And then
your attempts at setting a new low record, would fail.

Applying a battery to your tongue, doesn't go across your
heart. I'm sure a physiologist could explain why there aren't
major contractions when you apply a battery to your tongue,
but I can't.

What kind of welding machine ? There are differences in
circuit behavior, depending on power source. Whether it's
a generator, alternator, transformer connected to line,
or whatever. Some power sources have high open-terminal
voltage. Take my bicycle generator as an example. With
no load, the terminal voltage can rise as high as 50 to
100VAC. Once even a little bit of load is applied to the
thing, the voltage comes down to reasonable levels again.
The generator on the bicycle is speed sensitive - whereas
the alternator on your car, the field winding is adjusted
to give the desired output, so it's a feedback system. The
bicycle generator doesn't have any feedback system, and if
you run it open circuit, be careful what you touch. And no,
I have no desire to verify this by touching the bicycle generator
while going 20 miles an hour (no load), to see what
kind of kick its got.

I've worked with high voltage in home experiments, and
only received one significant shock. And that was while
playing with an ignition coil, and leaning on the wrong thing
on my bench. I've been a lot more careful since then.

Paul
 
Bill said:
Paul said:
Bill said:
Yeah, I'd say! :-) So, so much for that link!
Next thing I expect to hear is about people getting electrocuted off of a
12V car battery! Uh-huh!
Click to expand...
You can be electrocuted from as little as 1.5V.
It's a matter of making a good connection, and
getting the current flow to go through your heart.

It's the level of current flow that counts. High
voltage just makes it easier to get the necessary
current level (V/R = I, large V gives large I).

Holding two paddles in your hands, with 1.5V applied,
will not do it. However, using needles penetrating the
skin of your body, can arrange the necessary conditions.

A certain level of resistance to electrical flow is
expected, for "contact with palms" type events. We have
certain expectations of our ability to resist the
effects of electricity, based on an assumption of
"dry palms". Some people's hands are a lot damper than
others, which makes a difference to their perception
of what is dangerous.

http://en.wikipedia.org/wiki/Electric_shock

"If an electrical circuit is established by electrodes
introduced in the body, bypassing the skin, then the
potential for lethality is much higher if a circuit
through the heart is established. This is known as a
microshock. Currents of only 10 µA can be sufficient
to cause fibrillation in this case. [citation needed]"

And with no citation, the comment is not worth much to us.

I had a professor in university, who was a biomedical engineer,
and he used to regale us with stories of electrical accidents
at the hospital he worked at. It's easy to damage people who
are naked, and have all sorts of monitors connected, then
use equipment which cauterizes (like during surgery). Any
electrical wiring mistakes or bad assumptions, can cause
real misery. He told us stories of various body parts
getting burned, while a patient is unconscious and some
electricity is flowing where it should not. So talk to
a biomedical engineer about the kind of mistakes
that happen with electricity.

Paul
Click to expand...

When I mean by "getting electrocuted", I don't count such things as sticking
electrodes into your heart (or even brain for that matter) and attaching a
car battery. :-) As that's never going to happen in practice. :-)
Click to expand...

In my line of business, SELV (safe extra low voltage) was defined
as 48VDC. So that's an example of a pretty high value, that I'm sure
you would not enjoy if you touched it.

Whether it is AC or DC makes a difference. If AC, and the frequency
is high enough, the skin effect takes over. The high voltage supply
I've got, most of the effect from it would travel over the skin surface,
and not below. So the physical effects would be burning rather
than shock.

One of the experiments they do in high school class, is connect
thirty students to a hand cranked generator (the one with three
or four horseshoe magnets). The frequency is pretty low when you
slowly turn the handle... and that thing is as effective as hell :-)
I'm sure you guys must have had a teacher who wanted to try that.
I guess no reports headed home, to get parents excited. I certainly
didn't feel the need to red flag the experiment. The generator makes
something like 90V, across 30 students, and if there was just 3V across
each student, it didn't feel like 3V. It felt like a lot more.
Very effective.

Paul
 
"Paul" wrote in message news:[email protected]...
I didn't give instructions on how to do it with 1.5V.

Obvious it requires a connection pretty close to the
heart muscle.

It was purely to indicate the limit is pretty low,
if the conditions are just right.

At some point, the voltage is low enough, that conduction
might not have any impact. Presumably the activation
voltage of nerves and muscles has some lower limit. And then
your attempts at setting a new low record, would fail.

Applying a battery to your tongue, doesn't go across your
heart. I'm sure a physiologist could explain why there aren't
major contractions when you apply a battery to your tongue,
but I can't.

What kind of welding machine ? There are differences in
circuit behavior, depending on power source. Whether it's
a generator, alternator, transformer connected to line,
or whatever. Some power sources have high open-terminal
voltage. Take my bicycle generator as an example. With
no load, the terminal voltage can rise as high as 50 to
100VAC. Once even a little bit of load is applied to the
thing, the voltage comes down to reasonable levels again.
The generator on the bicycle is speed sensitive - whereas
the alternator on your car, the field winding is adjusted
to give the desired output, so it's a feedback system. The
bicycle generator doesn't have any feedback system, and if
you run it open circuit, be careful what you touch. And no,
I have no desire to verify this by touching the bicycle generator
while going 20 miles an hour (no load), to see what
kind of kick its got.

I've worked with high voltage in home experiments, and
only received one significant shock. And that was while
playing with an ignition coil, and leaning on the wrong thing
on my bench. I've been a lot more careful since then.

Paul
Click to expand...
Hope your weren't leaning your crotch against a metal table when you got
shocked from the ignition coil or taking a leak !! :) (Yes I know it would
have to be grounded to the ground as the coil.)
Sticking your tongue on a 9 v battery only has the current going from the -
across the tongue to the + of the battery.
Haven't heard of anyone dying from electrocution from getting a shock from
an automobile ignition coil which probably sends out well over 20k v at that
time either, so when you spout that you can get electrocuted with 1.5v, I
have to laugh, just like you probably did yourself.
Van de Graaff generators also put out extremely high voltage, even upwards
of 100k v and they make your hair do strange things at that voltage.
I doubt your bicycle generator will kill you unless it causes you to crash
into something, :)
So, pushing the envelope by saying " You can be electrocuted from as little
as 1.5V" is outright misleading. Almost sounds like the tv news' facts and
figures.
How many people have been electrocuted from a door bell transformer on the
low voltage side (around 40v)?
Enjoy .
 
Buffalo said:
"Paul" wrote in message news:[email protected]...
Hope your weren't leaning your crotch against a metal table when you got
shocked from the ignition coil or taking a leak !! :) (Yes I know it
would have to be grounded to the ground as the coil.)
Sticking your tongue on a 9 v battery only has the current going from
the - across the tongue to the + of the battery.
Haven't heard of anyone dying from electrocution from getting a shock
from an automobile ignition coil which probably sends out well over 20k
v at that time either, so when you spout that you can get electrocuted
with 1.5v, I have to laugh, just like you probably did yourself.
Van de Graaff generators also put out extremely high voltage, even
upwards of 100k v and they make your hair do strange things at that
voltage.
I doubt your bicycle generator will kill you unless it causes you to
crash into something, :)
So, pushing the envelope by saying " You can be electrocuted from as
little as 1.5V" is outright misleading. Almost sounds like the tv news'
facts and figures.
How many people have been electrocuted from a door bell transformer on
the low voltage side (around 40v)?
Enjoy .
Click to expand...

The 1.5V thing came up in a thread on one of these groups,
and I didn't bring it up. Someone else did. That with needles
inserted into the skin, and current flow through the heart
muscle, 1.5V would be enough to cause the heart to stop pumping.
And this is something a biomedical engineer would know
as well, when making instruments safe to connect to people.

It's also one of the reasons a lot of electronics datasheets
have a disclaimer the component is not intended for
medical instruments. As a CYA in case someone is hurt by
the mis-application of one of their products.

It's a different set of assumptions when the
electricity is presented to the skin surface.
So at that point you can take more voltage.
With some people able to take a bit more, because
their skin may be drier.

With an AC shock, you have slightly more opportunity
to let go. With DC, your muscles stay clenched. If you
see someone in distress from that, kick them with your
foot, don't grab them with your two hands. Or you'll become
part of the circuit too.

The last lab I worked in, had 800 VDC circuits they were
working on. And I had my foot all warmed up, to give
someone a kick :-) For their own good, of course.

Paul
 
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