Newbie - Voltage - shock of 9v battery vs. 12v car battery

[Anthony Fremont]

I Can't I can feel ring voltage but not battery voltage, unless you are
putting it in your mouth. Which I suppose would be uncomfortable with a
12VDC Car battery

Given that a good 9V battery can tingle the tongue pretty well, I'm sure
that 12V, with a closer spacing than the 9V terminals, could be quite
uncomfortable. Putting the phone line (RJ11) in your mouth will
certainly burn your tongue. With wet fingers you should easily feel the
phone line if you bare off a 1/2 inch of wire or so.

I never considered that... Now I wish you hadden't

We are talking about torture here, right? ;-)

Perhaps a full sweat lather, Licking my index fing fingers and applying an
Ohm Meter I can't below 90K

I can't even get mine close to that low, must be something to do with
age. Interestingly enough though, I get virtually the same results
using two hands as I do when using one finger. It appears that skin
resistance is major factor. Inner body resistance must be fairly low.

 

[Jasen Betts]

Hi, I'm just starting out self learning electronics and have a
question regarding voltage. If a volt is a volt is a volt, that is 1
volt can push 1 coulomb of electron flow (1 amp) through 1 ohm of
resistance,

one coulomb per second is one amp, but otherwise that's correct.

than all volts are the same pressure, hence why is a unit
of measurement. So why is it if I take a new small 9v battery from any
convenience store and shock myself with it, the shock of this 9v
battery is MUCH smaller then a shock from a 12v car battery ? It
can't be the 3v difference.

there's nearly twice the energy disipated when a 12V battery is connected
to a resistor than then a 9V is used, Watts = volts x amps

with a 100 ohm resistor 9V x 0.09 mA = 0.81 W
12V x 0.12 mA = 1.44 W

but it gets worse the body isn't a pure resistor and with higher voltages
its effective resistance actually decreases.

Is it the amount of current ? But then
since there is not resistance between myself and the battery, the 9v
would produce 9 amps and the car battery 12 amps again, not that much
difference but the shock is a huge difference.

And no, I'm not into shocking myself but it happens...

you need to dry your hands more. With very dry hands it's extremely hard
to get a shock from less than 20V

Bye.
Jasen

 

[Jasen Betts]

1 amp is one coulomb per second.


They aren't that different. You won't feel either one with dry skin.
You have to do something like lick the two poles of the battery to
feel it.


What can't? I have not gotten a shock from either a 9 volt battery or
a 12 volt car battery, though I have handled both extensively.

You have resistance. Hold the leads of an ohm meter to find out how
much. That resistance is what limits the current from either battery
that will pass through you.

different meters will givee different answers depending on what voltage they
use to proble the resistance. right now my pinch-to-pinch resistance measures
about 1.2M at 1.5V and about 310K at 9V

Please explain the situation that caused you to be shocked by a 12
volt battery.

I've been shocked by as little as 4.5V (but I was trying very hard, grasping
metal rods with wet hands....)

A few years ago my cousin who always had damp hands got shocked by my dodgy
RS232 breakout box unit. I wired that thing up when it was "live" and never
felt a thing.

Bye.
Jasen

 

[Jasen Betts]

I have worked on my car and have, though my own carelessness forgotten
to disconnect one of the terminals and have been shocked. I have also
taken a new 9v battery and have touched it to my tongue. I can tell
you first hand there is a big difference. I guess that is why we've
all heard stories of prisoners being tortured using 12v car batteries
and not 9v toy batteries. Why is the intensity so different ?

for a start use your upper lip (after licking it) to test 9v batteries,
the sensation is much milder.

the intensity is different mainly because of the quality of the contact if
you've just washed your hands and are gripping a metal tool with one hand
and supporting yourself with the other and happen to touch a live wire with
the tool there's a large are of contact at both ends.
Also with the cross-body current there's more nerves in the path of the
current and that makes a big difference in the perceived strenght of the
shock alone

when the shock only passes through a small part of the body (like one hand
or one finger) it doesn;t seem as strong.

that 4.5V shock left almost as strong an impression as a 250V shock that was
localised to my hand,

but the 4.5V shock was over as soon as the current stopped,
the 250V I was still feeling 15 minutes later.

Bye.
Jasen

 

[DBLEXPOSURE]

I can't even get mine close to that low, must be something to do with

age. Interestingly enough though, I get virtually the same results
using two hands as I do when using one finger. It appears that skin
resistance is major factor. Inner body resistance must be fairly low.

Seems we are all just a bunch of parallel resistors.
1/r=1/r+1/r+1/r+1/r......

Or maybe it has something to do with the skin effect :^)

 

[Big Mouth Billy Bass]

lol, they just kept coming to me... Curios to know your other two...


I'll be firing up the bench supply in the morning to see if I can feel
28VDC, I doubt I can let alone be tortured by it.

Get good and wet. You'll feel it, and it can be torture.

90V "DC" based on 90-100K Ohms..


Sniped from Wikipedia

Wikipedia, IIRC, is written by whomever might want to contribute an
anecdotal reference. Hence, easily infiltrated with old wives tales.

'Let go' current
With alternating currents there can be a muscular spasm which causes the
affected person to grip and be unable to release from the current source.
The maximum current that can cause the flexors of the arm to contract but
that allows a person to release his hand from the current's source is termed
the let-go current. For DC, the let-go current is about 75 mA for a 70-kg
man. For alternating current, the let go current is about 15 mA, dependent
on muscle mass.



I can only assume the same would hold true for initial sensation

It might hold true, if it were true. Try to find a scientific
reference, as opposed to urban legend.

Penlight cell, A small vibrating interrupter, and a coil.. the old gadget
invented a hundred years ago, a box promising goodies inside, you,
unknowingly place your finger tips on the electrodes to slide open the box.
doing so you release the vibrator to start the oscillation and you get a
nice little zap across your hand.

You missed the sarcasm there.

 

[DBLEXPOSURE]

Get good and wet. You'll feel it, and it can be torture.

30VDC No sensation. Supply leads 1/2 inch apart on my palm in a puddle of
saliva

You missed the sarcasm there.

No, I ignored it. A single cell battery is commonly referred to as, "a
battery".

Wikipedia, IIRC, is written by whomever might want to contribute an
anecdotal reference. Hence, easily infiltrated with old wives tales.

Okay, How about Ohio State Univ. ?

(2) AC is said to be four to five times more dangerous than DC. For one
thing, AC causes more severe muscular contractions. For another, it
stimulates sweating that lowers the skin resistance. Along that line, it is
important to note that resistance goes down rapidly with continued contact.
The sweating and the burning away of the skin oils and even the skin itself
account for this. That is why it's extremely important to free the victim
from contact with the current as quickly as possible before the climbing
current reaches the fibrillation-inducing level.

The frequency of the AC has lots to do with the effect on the human body.
Unfortunately, 60 cycles is in the most harmful range. At the house voltage
frequency, as little as 25 volts can kill. On the other hand, people have
withstood 40,000 volts at a frequency of a million cycles or so without
fatal effects.

A very little current can produce a lethal electric shock. Any current over
10 ma. will result in serious shock.

Summary

Voltage is not a reliable indication of danger because the body's resistance
varies so widely it is impossible to predict how much current will be made
to flow through the body by a given voltage.

The current range of 100- to 200-ma, is particularly dangerous because it is
almost certain to result in lethal ventricular fibrillation. Victims of
high-voltage shock usually respond better to artificial respiration than do
victims of low-voltage shock, probably because the higher voltage and
current clamps the heart and hence prevents fibrillation.

AC is more dangerous than DC, and 60-cycle current is more dangerous than
high-frequency current.





Look, I have been bit enough times to know from first hand experience that
AC feels different than DC. I prefer DC.... They don't call it "Hertz"
for nothing



If you don't believe it, try it for yourself. Use your variac 90VDC Vs.
90VAC @ 60Hz. Please, have a trusted friend handy to flip the switch on
and off, quickly, for you. go across the palm of your hand...

Report back what felt worse...

 

[Big Mouth Billy Bass]

30VDC No sensation. Supply leads 1/2 inch apart on my palm in a puddle of
saliva

Perhaps the experiment needs refinement [1].

No, I ignored it. A single cell battery is commonly referred to as, "a
battery".

Dang, you missed it again!

Okay, How about Ohio State Univ. ?

(2) AC is said to be four to five times more dangerous than DC. For one
thing, AC causes more severe muscular contractions. For another, it
stimulates sweating that lowers the skin resistance. Along that line, it is
important to note that resistance goes down rapidly with continued contact.
The sweating and the burning away of the skin oils and even the skin itself
account for this. That is why it's extremely important to free the victim
from contact with the current as quickly as possible before the climbing
current reaches the fibrillation-inducing level.

The frequency of the AC has lots to do with the effect on the human body.
Unfortunately, 60 cycles is in the most harmful range. At the house voltage
frequency, as little as 25 volts can kill. On the other hand, people have
withstood 40,000 volts at a frequency of a million cycles or so without
fatal effects.

A very little current can produce a lethal electric shock. Any current over
10 ma. will result in serious shock.

Much better; the second paragraph you quote is the reference I was
hoping you'd find. Keep up the good work! BTW, do you know why 60Hz
is so particularly dangerous?

[1] I've been shocked by both 28VDC and 15,000VDC. The 15K was barely
as bad as a static shock from a doorknob, the 28V shocks, sustained in
very wet weather, were intensely uncomfortable. The differences were
the magnitude of sustainable current from the source supplying the
shock, the resistance of my skin, and the paths the sources managed to
find to return.

 

[DBLEXPOSURE]

Perhaps the experiment needs refinement [1].


More sodium in my diet... I am 90K That's it. A fit 40 year old 90K
Ohms...

I have been hit by a 27" TV Anode cap (TV Off) Knocked me on my but. I
wouldn't call it a shock(even though it was) but felt more like a hit.

120VAC Count less times.. Always the worst.

Collector voltage on a 17" Video Monitor 15Khz Don't know what the voltage
was but sure it was in KV range. I smelled it before I felt it. Tip of my
index finger.

Sever RF hits working at Transmitter tech for a Chnl 5 station.. Feels like
tiny needles..

Telephone Ring voltage, Just for fun...

Never low voltage DC.... Well, the 9V alkaline on the tongue...

Much better; the second paragraph you quote is the reference I was
hoping you'd find. Keep up the good work! BTW, do you know why 60Hz
is so particularly dangerous?

RICE.EDU

Shock Sensitivity. Because of a person's highly developed nervous system,
they are sensitive to very small currents. For example, the tongue will give
a sensation of taste at currents as low as 45 microamperes. The threshold of
feeling on the hand is found to be on the order of 5 mA DC and 1 mA at 60
Hz. The shocks due to currents at this threshold are usually considered
annoying rather than dangerous. However, they are startling when not
anticipated, and may cause involuntary movement that sometimes results in
serious injury. As the value of current increases above the threshold, one
becomes aware of sensations of heat and contraction of the muscles.
Sensations of pain develop and voluntary control of the muscles in the path
of the current becomes increasingly difficult. Finally a value of current is
reached where the victim "freezes" to the circuit. The value of current at
which a victim can just release the electrode is referred to as "let-go"
current. The average let-go current for healthy people is about 16 mA rms
(60 Hz). It is important to note that let-go currents of as low as 5 mA have
been measured. Experience has shown that an individual can withstand, with
no ill aftereffect except for possible sore muscles, repeated exposure to
their let-go current for at least the time required for them to release the
conductor

30VDC No sensation. Supply leads 1/2 inch apart on my palm in a puddle of
saliva

Perhaps the experiment needs refinement [1].

No, I ignored it. A single cell battery is commonly referred to as, "a
battery".

Dang, you missed it again!

Okay, How about Ohio State Univ. ?

(2) AC is said to be four to five times more dangerous than DC. For one
thing, AC causes more severe muscular contractions. For another, it
stimulates sweating that lowers the skin resistance. Along that line, it
is
important to note that resistance goes down rapidly with continued
contact.
The sweating and the burning away of the skin oils and even the skin
itself
account for this. That is why it's extremely important to free the victim
from contact with the current as quickly as possible before the climbing
current reaches the fibrillation-inducing level.

The frequency of the AC has lots to do with the effect on the human body.
Unfortunately, 60 cycles is in the most harmful range. At the house
voltage
frequency, as little as 25 volts can kill. On the other hand, people have
withstood 40,000 volts at a frequency of a million cycles or so without
fatal effects.

A very little current can produce a lethal electric shock. Any current
over
10 ma. will result in serious shock.

Much better; the second paragraph you quote is the reference I was
hoping you'd find. Keep up the good work! BTW, do you know why 60Hz
is so particularly dangerous?

[1] I've been shocked by both 28VDC and 15,000VDC. The 15K was barely
as bad as a static shock from a doorknob, the 28V shocks, sustained in
very wet weather, were intensely uncomfortable. The differences were
the magnitude of sustainable current from the source supplying the
shock, the resistance of my skin, and the paths the sources managed to
find to return.

 

[Dr. Anton T. Squeegee]

I guess I still don't see where the big difference is. Voltage is
pressure (or potential pressure) or the amount of EMF. The more force,
the more electrons will flow so the more current or amps there will be.
The resistance of the human body will be the same for both batteries.
So why is it, one can be literally tortured with a 12v battery but not
with a 9v ? The amount of current difference due to the 3v difference
can't be enough to make one battery a torture device and one a toy.

Hmmm... Methinks you've been watching one too many old
'Pretender' episodes. ;-)

The reason Hollywood likes to use car batteries in their phony
"torture" scenes is because they look big and impressive, and because,
when the ends of whatever cable they're using are brushed together, it
makes a very impressive (to the untrained eye) spark.

The human body presents a typical skin resistance, hand-to-hand,
of over 250,000 ohms. I suppose this might drop down to a few thousand
ohms if you're soaked to the skin with salt water.

Just for the sake of argument, let's say your skin resistance
drops to, say, 2500 ohms hand-to-hand if you're soaking wet (which is a
drop of two orders of magnitude in this context).

Using Ohm's Law, and taking 12V over 2500 ohms, I come up with a
total current flow of 0.0048 amps, or 4.8 milliamps. Under normal
conditions, with dry skin and assuming 250k ohms, the max current
possible with 12V is about 48 microamps.

Considering that the "danger" threshold across the chest is at
least 20 milliamps, I don't see how a 12V car battery could possibly be
harmful, or even felt, at either amount of current. According to some
further number-crunching, you'd need to up the voltage to between 48-50
to get anywhere close to dangerous.

So, in summary: If you just got out of the ocean, and you
immediately go work on things in a telephone central office (where the
standard voltage is around -52VDC), yes, you could be setting yourself
up for some problems.

Outside of that, it's just Hollywood messing with your gray
matter.

Keep the peace(es).


--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute.
(Known to some as Bruce Lane, ARS KC7GR,
kyrrin (a/t) bluefeathertech[d=o=t]calm -- www.bluefeathertech.com
"If Salvador Dali had owned a computer, would it have been equipped
with surreal ports?"

 

[Rich Grise]

The human body presents a typical skin resistance, hand-to-hand,
of over 250,000 ohms. I suppose this might drop down to a few thousand
ohms if you're soaked to the skin with salt water.

Just for the sake of argument, let's say your skin resistance
drops to, say, 2500 ohms hand-to-hand if you're soaking wet (which is a
drop of two orders of magnitude in this context).

Well, I've just done the experiment. Washed my hands, dried them
thoroughly, and grabbed the leads of my DVM on KOhms between thumbs
and forefingers, and came up 700K +/- 50K. Dissolved about a teaspoon
of table salt in about three tablespoons of water in a little plastic
"medicine cup", and it went down to 40K +/- 10K, even with my fingers
(and thumbs, and probes) dipped into the salt water solution. The
salty water itself measures even less - crap - my fingers must have
been insulating the probes from the water.

There must be some kind of breakdown voltage to the skin interface
or something, because these are pretty significant resistances. I'm
too lazy to do the arithmetic, but what's 120 divided by 30,000?

Thanks!
Rich

 

[Big Mouth Billy Bass]

Never low voltage DC.... Well, the 9V alkaline on the tongue...

Showing that sensation is completely dependent upon skin resistance.
I'll grant you a concession; the voltage I felt *might* have been
115Vrms 400Hz. But probably not.

 

[ngdbud]

How on Earth do you get shocked by a twelve volt car battery? My shop
teacher gave us a week long uit on how car batteries work and had two
in front of the class (we were required to jump them for the test that
friday, nobody touched red to black , dang it) but anyways, once he
told us they capeable of giving out over 400 amps I asked if it would
hurt to touch them. he said no, so I did, I felt nothing. One student
licked his fingers and and touched the two terminals, he wasn't
schocked either, trust me, I know his face when he's got current
running through him. 1 school play + 6 nine volt batteries for the mics
each night + 4 nights = equals alot of fun. Don't worry, we were
running it at under 1 hundered volts for all of our experimentation. by
now each of those batteries is giving out between 5 and 7 volts.

 

[Doug McLaren]

| How on Earth do you get shocked by a twelve volt car battery?

Under normal conditions, you don't.

However, you could touch it to your tongue -- that would shock.

You could run it to two needles and pierce your skin -- that would
shock.

There are other places in your body that are likely to be extra
sensitive to electricity, besides your tongue. We'll leave them to
your imagination.

Also, if you were to connect a coil (an electromagnet) to the battery
and then disconnect it, the back EMF created by the collapsing
magnetic field could be several thousand volts, and that certainly
COULD shock you, though you're not being shocked directly by the
battery. You might get the same effect if you try to run the starter
while you're holding the contacts, though I'm going to assume that
that sort of thing is filtered out (or otherwise it could damage your
radio and similar things.)

As for people getting tortured in the movies with 12 volt car
batteries, well, 1) it _looks_ impressive, and 2) it probably helps
make their legal department happy when their torture methods aren't
actually effective, just in case some moron decides to copy them.

If you're a mechanic, a more real danger is being burned by a short
circuit involving a car battery than being shocked by it. This is why
you don't wear jewelry when working on anything electrical -- if your
ring ends up completing a short circuit, it may suddenly end up so
incredibly hot that it starts to melt, at which point it will be
impossible to remove, and the end results won't be pretty.

(Un-pretty pictures and some more discussion can be found at
http://www.medbc.com/annals/review/vol_5/num_1/text/vol5n1p33.htm .)

| trust me, I know his face when he's got current running through him.

Now now, what you do with consenting adults (or at least peers) is not
our concern

 

[ngdbud]

"Also, if you were to connect a coil (an electromagnet) to the battery
and then disconnect it, the back EMF created by the collapsing
magnetic field could be several thousand volts,..."

Let me see if I have my terminology right... counter elctromotive
force, CEMF, right?

 

[Jamie]

"Also, if you were to connect a coil (an electromagnet) to the battery
and then disconnect it, the back EMF created by the collapsing
magnetic field could be several thousand volts,..."

Let me see if I have my terminology right... counter elctromotive
force, CEMF, right?

hmm, what ever happen to
flyback ?

 

[Doug McLaren]

| "Also, if you were to connect a coil (an electromagnet) to the battery
| and then disconnect it, the back EMF created by the collapsing
| magnetic field could be several thousand volts,..."
|
| Let me see if I have my terminology right... counter elctromotive
| force, CEMF, right?

I'm not sure if you're being sarcastic, or really just trying to get
your terminology right, or what.

Certainly, `back emf' is not a term that I invented. Google has
115,000 hits on that term, and apparantly it's also called `counter
emf' so I guess your version is used as well, though a google fight of
"back emf" vs. "counter emf" finds "back emf" winning 115,000 to 916.
(Though CEMF has 47,700 hits, but they're mostly not related to
electicity.)

 

[Paul Burridge]

If you're a mechanic, a more real danger is being burned by a short
circuit involving a car battery than being shocked by it. This is why
you don't wear jewelry when working on anything electrical -- if your
ring ends up completing a short circuit, it may suddenly end up so
incredibly hot that it starts to melt, at which point it will be
impossible to remove, and the end results won't be pretty.

I personally can't feel anything below about 80V dc. And even that's
just a slight tingle. But you're right to point out the overwhelming
danger with car batteries: their current supplying capability. And by
the time you feel the heat from that current circulating through your
watch or ring, it's probably already well-welded together and you're
in deep sh*t.

 

[ngdbud]

I'm a newbie, 14 years old. Still very sensative I guess. My personal
test say i can start feeling the tingle at 45 volts.