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
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.
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.
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 ( snipped-for-privacy@misty.com)
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 ( snipped-for-privacy@misty.com)
What's the DCR of the secondary?
John
current
So it must be leakage inductance that limits the current.
John
--
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>----+ +---------+
--
+-----S1
|
7K1
|
+----CT
|
7K1
| __
+-----S2
On Sun, 29 May 2005 16:45:33 -0700, Bill Bowden wrote (in article ):
Your experience notwithstanding, people die from 110 vac. You're healthy and lucky. Not everybody is.
-- 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
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 ( snipped-for-privacy@misty.com)
What I expect:
15 mA has minimal (but not zero) electrocution risk, although by many (but not all) accounts is able to cause humans to latch onto shocking conductors, and become unable to let go and may die from fibrillation resulting from prolonged shock or may die from breathing muscles being impaired by the shock.Main result that I expect from 113 watts of power dissipation into a human body is burns.
With initial contact resistance of 500K ohms (highish side but fairly typical of human contact with wires), I expect most of this resistance tio be in small volumes of skin, that get burned through quickly with 113 watts. That means the victim of such a neon sign transformer shock quickly gets to dissipate a small fraction of the above-mentioned 113 watts, while conducting a current close to 30 mA - which has a non-zero chance of being fatal.
Another thing: The output impedance of neon sign transformers is mostly inductive reactance rather than resistance. Put a 500K-ohm load across the output of a 15KV 30mA neon sign transformer, and you get more than
7.5 KV at 15 mA, as in closer to 10 KV at 20 mA, ideally 10.3 KV at 20.6 mA.- Don Klipstein ( snipped-for-privacy@misty.com)
In article , John Fields wrote: (in part)
This is much less current than I have found from a few neon sign transformers and "oil burner" transformers. In my experience, the short-circuit current using the entire secondary is close to the "label" current or slightly higher, and with a load whose impedance is the ratio of rated voltage to rated current I find voltage and current typically around 60-66% of the "label" values.
- Don Klipstein ( snipped-for-privacy@misty.com)
Facts are so much better than assumptions. Thanks for going to this trouble for all of us. I dug a bit deeper, and my assumptions fell through. I was thinking of the effect of the resonant circuit in a ferroresonant transformer, and apparently, neon sign transformers have only leakage inductance (more like the character of a microwave oven transformer or welder), which would agree well with your measurements. But I wonder how they get it to act as nonlinear as it does. It seems strange that the short circuit current is only about 1.25 times as high as the current that pulls the output voltage down by half. That surely looks like an attempt at current regulation. On a graph of this data, there is a bit of a kink.
--- Yes, at the high voltage end I used a bunch of 20 megohm metal oxide resistors for the load, but I'm pretty sure they aren't rated for
10-15kV, so that may be where the kink came from. Or, measurement error :-(There's another problem I'm trying to solve, though, and that's why the output current is so low. I had thought that 15mA out of each secondary to the center tap would result in 30mA total, but that's not right. I called the manufacturer and their tech guy said that I ought to get 30mA RMS out of the entire shorted secondary, just like Don said. Well, he didn't say RMS, but...
The strange part is I've got a 9kV and a 15kV transformer, and I get the same short circuit current out of both of them, making several measurements with different meters.
I've got a friend who owns a sign shop, so I guess the next thing I'll do is take a meter over there and see what a known good transformer puts out.
-- John Fields Professional Circuit Designer
The data posted shows 78.8% of short-circuit current with a load that loads down the output voltage to half the open circuit voltage.
Ideally, inductive reactance such as leakage reactance would result in
86.6% of short circuit current to a load that loads down the output voltage to half the open circuit voltage.I believe the data above show resistance being part of the output impedance, and/or the leakage inductance being nonlinear (less at higher current).
One thing I have experienced: Output impedance (ratio of open circuit voltage to short circuit current at least) of an oil burner transformer being higher when the input voltage is decreased.
- Don Klipstein ( snipped-for-privacy@misty.com)
John Fields wrote: (snip)
Excellent. I love experimental science.
-- John Popelish
Actually, I'm not healthy, but I am lucky. I have coranary heart disease and luckily had a triple bypass operation last year that brought me back to normal. I had angina pains when walking uphill, so I went to a cardiologist, who gave me a treadmill test, and then told me to go to the hospital. I was lucky again to have insurance that paid $85,000 for the angiogram and surgery. Otherwise, I would be bankrupt today.
But I feel pretty good now. I can walk uphill for long distances and climb 4 flights of stairs with no pain.
Haven't tried the 120VAC shock test yet, but I'm really more afraid of falling down than getting shocked.
Last month, I fell down and hit my head on a open tool box and needed 5 stitches. I would have much prefered being shocked from 120VAC than smashing my head on a open tool box.
-Bill
When I was a kid my older brother had an "Electric Lab", the lab contained a device that was a coil with contacts. The Idea was to connect a small battery 1.5v to it and adjust the contacts to "resonate" ( switch on/of continuosly ) . It had also 2 wires ending in 2 separate pieces of pipe that I will hold and feel the electricity. I was used to connect it to an old train toy AC adapter and set it up full blast. I had to grab the pipes carefully ( more than letting them rest in the palms of my hands and slowly grab them. I could feel the electricity moving all the muscles of my hands and arms. So much that sometimes it was difficult to open my hands to let go.
I also played with a neon sign transformer that make an arch 2 inches long , and thru wood. When I turned off the light to do it I coud see the cable and my fingers with a light blue color, I think it was 15000 volts. I got a shock once with it but the electricity whent in and out in my hand , so nothing happened to me.
At school there was a cold water founta>> Your experience notwithstanding, people die from 110 vac.
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