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DaveC
Guest
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 Posted:
Sun May 29, 2005 1:47 pm Post subject:
Re: electrocution by car battery |
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| Quote: | 120 or 240 is not very high. You would get shocked, but probably
wouldn't die.
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What news source are you reading? People are electrocuted every year from
those "not very high" voltages.
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.
DaveC
me@privacy.net
This is an invalid return address
Please reply in the news group
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Bill Bowden
Guest
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| Posted:
Mon May 30, 2005 12:35 am Post subject:
Re: electrocution by car battery |
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| Quote: | 120 or 240 is not very high. You would get shocked, but probably
wouldn't die.
What news source are you reading? People are electrocuted
every year from those "not very high" voltages.
|
I'm not reading a news source, just stating experience.
I've been shocked many times from line voltages with
no ill effects. Once, I was shocked by 10KV from
an aviation radar system, and it threw me across the room,
but I got up and went back to work.
120VAC is low voltage. Why do you think it's used instead
of 880 or higher, which would be much more efficient?
-Bill |
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Guest
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| Posted:
Mon May 30, 2005 4:35 pm Post subject:
Re: electrocution by car battery |
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i thought it's the current that kills not the voltage. the voltage is
just to get past the skin resistance to your heart. I read somewhere if
the current at about 0.030 amp would even stop your heart.
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Don Klipstein
Guest
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| Posted:
Mon May 30, 2005 8:46 pm Post subject:
Re: electrocution by car battery |
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| Quote: | Fibrillation (which is what kills you) is perfectly possible with a 12V
battery in the 'right' conditions.
What it takes is 100mA through the heart (an acquaintance of mine got
killed this way doing a charging check on the 28VDC system in a
helicopter many years ago)
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Most references say fibrillation is generally a problem at 100 mA to an
amp, with one or two saying this starts at 50 mA.
I do not believe the risk of fibrillation drops to zero when the current
decreases to 99 or 49 mA. I have heard of someone getting killed by a 30
mA neon sign transformer.
As for 12 volts being enough to push enough current through you to cause
electrocution? Not impossible, but very rare - requiring broken skin
or large skin contact area with wet skin.
I think a greater hazard is shorts causing those burning hot wedding
rings, also burning wires causing fires, and burning wires or sparks (and
flying droplets of molten metal from sparks) igniting explosive gases that
lead acid batteries sometimes produce.
Other hazards to watch out for: Ignition voltage - usually not lethal,
but I don't feel certain. Also shocks could jolt you into dropping a
wrench onto a +12V point and a ground point, or getting
fingers/hands/clothing caught in moving fans or belts.
- Don Klipstein (don@misty.com) |
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Don Klipstein
Guest
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| Posted:
Mon May 30, 2005 8:50 pm Post subject:
Re: electrocution by car battery |
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One problem with 120V is its perceived safety. People get more
careless, and as a result despite a small percentage of shocks from that
voltage being fatal, that voltage has a high body count.
US Navy warships have most of their power circuits being 440V, and most
of their electrocution deaths from the 110V that also exists there.
- Don Klipstein (don@misty.com) |
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John Fields
Guest
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| Posted:
Tue May 31, 2005 12:35 am Post subject:
Re: electrocution by car battery |
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On Mon, 30 May 2005 17:21:37 -0400, John Popelish <jpopelish@rica.net>
wrote:
| Quote: | Don Klipstein wrote:
(snip)
I do not believe the risk of fibrillation drops to zero when the current
decreases to 99 or 49 mA. I have heard of someone getting killed by a 30
mA neon sign transformer.
(snip)
Which puts out about twice that on into a low impedance load, like the
human body.
|
---
It can't, since it's designed to saturate at 30mA, but looking at its
load line it'll put out, say, 15kV at 0A into an open, and 0V at 30mA
into a dead short.
That means that with an initial 500kohm human load across it its
output voltage will drop to 7500VRMS and it'll be forcing 15mA through
the load, and the load will be dissipating about 113 watts. OUCH!!!
--
John Fields
Professional Circuit Designer |
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John Popelish
Guest
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| Posted:
Tue May 31, 2005 12:35 am Post subject:
Re: electrocution by car battery |
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John Fields wrote:
| Quote: | On Mon, 30 May 2005 17:21:37 -0400, John Popelish <jpopelish@rica.net
wrote:
Don Klipstein wrote:
(snip)
I do not believe the risk of fibrillation drops to zero when the current
decreases to 99 or 49 mA. I have heard of someone getting killed by a 30
mA neon sign transformer.
(snip)
Which puts out about twice that on into a low impedance load, like the
human body.
---
It can't, since it's designed to saturate at 30mA, but looking at its
load line it'll put out, say, 15kV at 0A into an open, and 0V at 30mA
into a dead short.
That means that with an initial 500kohm human load across it its
output voltage will drop to 7500VRMS and it'll be forcing 15mA through
the load, and the load will be dissipating about 113 watts. OUCH!!!
|
You may be right, but that is not what I understand to be the case. I
thought they are rated for normal load current over the voltage range
expected when driving a gas tube. And that they have a very nonlinear
current limit, much like Sola ferro resonant constant voltage
transformers. Those hold specified voltage regulation at rated
current but the current increases only to about double rated under a
short circuit. I don't think most neon sign transformers are just a
tightly coupled step up transformer in series with a big resistor. |
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John Popelish
Guest
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| Posted:
Tue May 31, 2005 12:35 am Post subject:
Re: electrocution by car battery |
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Don Klipstein wrote:
(snip)
| Quote: | I do not believe the risk of fibrillation drops to zero when the current
decreases to 99 or 49 mA. I have heard of someone getting killed by a 30
mA neon sign transformer.
(snip) |
Which puts out about twice that on into a low impedance load, like the
human body. |
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Bill Bowden
Guest
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| Posted:
Tue May 31, 2005 6:26 am Post subject:
Re: electrocution by car battery |
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| Quote: | i thought it's the current that kills not the voltage.
the voltage is just to get past the skin resistance to
your heart. I read somewhere if the current at about 0.030 amp
would even stop your heart.
|
No, it's the power that kills, which is the
voltage squared divided by the resistance.
So, if your skin resistance is a Megohm,
you only get 120^2/1 Meg = 14 milliwatts which is not much.
But, if your hands are wet and the skin resistance is only 50K or so,
you get E^2/R =120^2/50K = 288 milliwatts, which might be dangerous.
-Bill |
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Larry Brasfield
Guest
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| Posted:
Tue May 31, 2005 6:40 am Post subject:
Re: electrocution by car battery |
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It's not power that does people in, except in the
sense that, without power, there is no effect.
What kills most electrocuted people is interference
with their heart's operation due to disruption of its
"electrical" control system.
Something people seem to be missing in this
discussion is that AC is much more dangerous
than DC, due to its ability to disrupt normal
heart operation at lower current levels. (This is
why defibrillators, which pass a large unipolar
current pulse thru the chest, a curative rather
than lethal.)
Of course raw power can kill, too. But not often.
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me. |
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John Fields
Guest
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| Posted:
Wed Jun 01, 2005 12:09 am Post subject:
Re: electrocution by car battery |
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AIUI, they're designed to be ballasts. That is, to start off with a
high enough voltage to strike the arc through the tube and then to
provide the proper current (30 or 60 mA) to run the tube when the gas
ionizes and provides a more or less constant low-resistance load
through the plasma.
Using a Transco T1512, which is a 15kV 30mA NST, like this:
Iout->
120VAC>----+ +---------+ <-----+
)||( | |
)|| >-GND [R] Eout
)||( | |
120VAC>----+ +---------+ <-----+
I get the following data:
R Eout Iout
M kV pk mA RMS
-----+-------+--------
0.00 0.000 17.3
0.05 0.662 17.3
0.09 1.647 17.1
0.13 2.586 16.8
0.17 3.456 16.3
0.21 4.270 15.9
0.25 5.02 15.5
0.29 5.744 15.1
0.33 6.37 14.7
0.37 6.971 14.3
0.41 7.511 13.8
2.0 10.0 6.6
4.0 10.8 5.5
5.0 11.0 5.3
10.0 11.37 5.2
20.0 11.55 5.1
INF 15.0 0.0
Which shows there's no voltage regulation at all, but only a 3.5mA
change in current for a 7500V change in voltage across the load from
410kohms to a dead short.
The reason the short-circuit current is 17.3 mA instead of 30 is
because I loaded the entire secondary, and it's wired so you can only
get 15mA or so that way. If you take current from either end of the
secondary to the center tap you can get 15mA out of each half of the
secondary for a total of about 30mA.
--
John Fields
Professional Circuit Designer |
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John Larkin
Guest
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| Posted:
Wed Jun 01, 2005 12:14 am Post subject:
Re: electrocution by car battery |
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What's the DCR of the secondary?
John |
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John Fields
Guest
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| Posted:
Wed Jun 01, 2005 12:35 am Post subject:
Re: electrocution by car battery |
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---
+-----S1
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7K1
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+----CT
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7K1
| __
+-----S2
--
John Fields
Professional Circuit Designer |
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John Larkin
Guest
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| Posted:
Wed Jun 01, 2005 12:35 am Post subject:
Re: electrocution by car battery |
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So it must be leakage inductance that limits the current.
John |
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Don Klipstein
Guest
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| Posted:
Wed Jun 01, 2005 4:41 am Post subject:
Re: electrocution by car battery |
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I failed to track who said this, but a 30 mA neon sign transformer
pushes only a little more than 30 mA into a short circuit in my
experience.
- Don Klipstein (don@misty.com) |
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