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A really (I'm guessing) simple voltage question...

I've often wondered why a 9 volt battery can be so harmless, yet a 12
volt car battery can (I've heard) kill you. Can't you put two 9 volt
batteries in series and get an 18 volt "battery pack"?

Please, enlighten me... someone.
 
A

Alan B

Jan 1, 1970
0
I've often wondered why a 9 volt battery can be so harmless, yet a 12
volt car battery can (I've heard) kill you. Can't you put two 9 volt
batteries in series and get an 18 volt "battery pack"?

Please, enlighten me... someone.

The magic word is "capacity." It's easy to get hung up on the question of
voltage, but electricity is mostly about power. How many horses can the
source deliver?

Now, you'd have to really pull something crazy in order to get a car
battery to kill you; you'd almost have to have open sores on both hands and
short out the terminals with a crowbar while holding onto the crowbar with
a death-grip with both hands, and then you might only get burned fingers.
You might scare yourself silly with the big spark that would result from
shorting the positive terminal to chassis, and cause the hood of the car to
crash down upon your head. You might cause the battery to blow up by
hooking up jumper cables backwards. Something like that.

But I digress. The car battery has an "amp-hour" capacity that allows it
to pump an enormous amount of current for a short period of time.
Mishandled, that current can be very dangerous. The 9V battery will have
its capacity rated in "milli-amp hours," which is a rating less than the
car battery by a factor of one thousand. Et don' haf da joos ta hoit ya.
 
J

John Larkin

Jan 1, 1970
0
I've often wondered why a 9 volt battery can be so harmless, yet a 12
volt car battery can (I've heard) kill you. Can't you put two 9 volt
batteries in series and get an 18 volt "battery pack"?

Please, enlighten me... someone.

Neither is dangerous. And yes, two 9 volt batteries in series gives
18, but that's not dangerous either.

John
 
J

jasen

Jan 1, 1970
0
I've often wondered why a 9 volt battery can be so harmless, yet a 12
volt car battery can (I've heard) kill you.

dropped from a second-floor window, maybe.

there's not enough voltage in a car battery to kill by electrocution.
it can however explode or start a fire if mis-handled

However most car-batterry caused fatalities result from it being used to
start a car ant the car killing.

Can't you put two 9 volt
batteries in series and get an 18 volt "battery pack"?

you can even can do 4 and get 36v, and I once read, on a bad day
that was enough to kill.

Bye.
Jasen
 
Ok, well now that we've determined that I fell victim to a bit of an
urban legend, I'm still curious why a 9 volt battery is so tiny, yet a
12 volt battery is the size of a concrete block.

Also, something I read indicated a car battery has a sufficient CURRENT
to really hurt you, but too low a voltage. But I fail to see how that's
a true statement given Ohm's Law.
 
P

PeteS

Jan 1, 1970
0
Ok, well now that we've determined that I fell victim to a bit of an
urban legend, I'm still curious why a 9 volt battery is so tiny, yet a
12 volt battery is the size of a concrete block.

Also, something I read indicated a car battery has a sufficient CURRENT
to really hurt you, but too low a voltage. But I fail to see how that's
a true statement given Ohm's Law.

A battery is not a pure voltage source (there aren't any, but some can
approach it).

A battery is generally modelled as a pure voltage source (an output
with zero resistance) in series with it's internal resistance.

A car battery has a low internal resistance (although as with all
batteries, it increases as the battery discharges) and a high capacity.
A 9V battery pack has a higher internal resistance and relatively low
capacity.

Due to chemical effects, the effective internal resistance of some
types of battery varies (increasing) with increasing current. For that
reason, we usually specify the maximum load current of a battery
(either absolute or in terms of it's capacity).

A car battery, due to it's low internal resistance and high capacity
can provide literally hundreds of amps (although to kill a person
requires of the order of 100 milliamp) during cranking, although the
terminal voltage will drop significantly. A 9V powerpack would quickly
discharge (with the associated increase in internal resistance).

So we're not violating ohm's law at all - one just has to take into
account all the facts about batteries.

Cheers

PeteS
 
M

Mark Fortune

Jan 1, 1970
0
John said:
Neither is dangerous. And yes, two 9 volt batteries in series gives
18, but that's not dangerous either.

John

there's a similar thread running on sci.electronics.design entitled "60V
DC dangerous?" that goes a long way to answering your question. its a
long thread though. in a nut shell some seem to think that its not the
12v from the battery that is likely to kill you, moreso this is an urban
legend stemming from people being killed by not respecting the output
from the ignition coil on early car designs which reached upwards of
40,000 volts (ouch!). car batteries can give a lot of amperage though,
which can cause fires if a short develops on an unfused system and/or
faulty wiring.

9v PP3 batteries do however pose more of a choking hazard than car
batteries.
 
J

James Thompson

Jan 1, 1970
0
I've often wondered why a 9 volt battery can be so harmless, yet a 12
volt car battery can (I've heard) kill you. Can't you put two 9 volt
batteries in series and get an 18 volt "battery pack"?

Please, enlighten me... someone.
A 1.5 volt flashlight cell can kill you if you are intent on doing so.
You would need to stick pins into your fingers to break the skin resistance
and touch from both hands to the battery terminals.
An Industrial electric teacher of mine once told us that story that happend
at a prison he worked at, and an inmate did that.
But both the 12 volt car battery or 9 volt transistor battery is considered
safe by there self due to the high skin resistance of your body.
The difference in the batteries is not so much of there voltage, but there
amp capacity.
Which usually go by the size of the battery, not its voltage.
 
T

Tim Williams

Jan 1, 1970
0
James Thompson said:
A 1.5 volt flashlight cell can kill you if you are intent on doing so.

Actually, 1.5V isn't really enough to do anything inside the body. I mean
maybe if you put it directly across the nerves that supply the heartbeat,
but really, they are in fact safe to eat and poop out because 1.5V isn't
enough!

Tim
 
B

Bob

Jan 1, 1970
0
Actually, 1.5V isn't really enough to do anything inside the body. I mean
maybe if you put it directly across the nerves that supply the heartbeat,
but really, they are in fact safe to eat and poop out because 1.5V isn't
enough!

Tim


I'm not sure if the table at this website is completely accurate, but it
seems to jibe with what I've heard -- that 20mA, through the heart, can
kill.

http://www.mpoweruk.com/shock.htm

Assuming this is true, then the subdermal resistance, from the left arm to
the right arm, would only have to be 75ohms in order for a 1.5V source to
deliver 20mA (yes, I had to use a calculator). Even a AAA battery can
deliver this type of current while still developing close to 1.5V at its
terminals.

So, could the arm-to-arm subdermal resistance be as low as 75ohms? I would
think so (we're full of salty water), but I'm not going to do any
experiments on myself, and I don't recommend anyone try it.

Bob
 
W

Warren Weber

Jan 1, 1970
0
I've often wondered why a 9 volt battery can be so harmless, yet a 12
volt car battery can (I've heard) kill you. Can't you put two 9 volt
batteries in series and get an 18 volt "battery pack"?

Please, enlighten me... someone.

Life is strange. When working at a electric utility company one of our
troublemen was working on 25000 volt under ground line. It was fused at both
in and out of what he was working on. He thought he opened the IN line. No,
he opened the out line. As he started work and contacted the circuit he was
blown out of the hole and only suffered some burns and a change of shorts.
About 65 years ago I took a jolt hand to hand with 1000 volts DC. Only
results were a momentary blackout and very sore painful elbows for several
days. Both of us were very lucky. W W
 
J

Jamie

Jan 1, 1970
0
I've often wondered why a 9 volt battery can be so harmless, yet a 12
volt car battery can (I've heard) kill you. Can't you put two 9 volt
batteries in series and get an 18 volt "battery pack"?

Please, enlighten me... someone.
think of voltage as speed of movement and
current as mass of movement.
now think of a 9 volt battery going
9 feet per second and a 12 volt battery
doing 12 feet per second.
now one has a little more speed than the
other and isn't really that much of a difference.
now think of this, the 9 volt is coming out a
brook (current), and the 12 Volt is coming out
of a River! (lots of current).
which one is going to be stopped the easiest ?
and still. think of the 12 volt (speed) moving
down a little brook verses the 9 Volt moving down
a river! ,. think of the mass of water ...

you need current to cause damage and of course to
get current, there will always be voltage involved!
because a lake sitting still has lots of mass (current)
but no movement(voltage)! so of course nothing is going
to happen here, it is the combination of the 2..
the same can be applied in water wheels., wider rivers
allow for wider paddles to be used, thus the current is stronger
but the speed of movement remains the same (Voltage).
this enables them to connect more generators on the shaft to
build up the amp supply..
 
J

John Larkin

Jan 1, 1970
0
9v PP3 batteries do however pose more of a choking hazard than car
batteries.

But car betteries are much more dangerous when dropped from a height.

John
 
A

Alan B

Jan 1, 1970
0
Ok, well now that we've determined that I fell victim to a bit of an
urban legend, I'm still curious why a 9 volt battery is so tiny, yet a
12 volt battery is the size of a concrete block.

Also, something I read indicated a car battery has a sufficient CURRENT
to really hurt you, but too low a voltage. But I fail to see how that's
a true statement given Ohm's Law.

Ah, you might try re-reading my first post in the thread. :-(

Message-ID: <[email protected]>
 
A

Alan B

Jan 1, 1970
0
http://www.mpoweruk.com/shock.htm

Assuming this is true, then the subdermal resistance, from the left arm to
the right arm, would only have to be 75ohms in order for a 1.5V source to
deliver 20mA (yes, I had to use a calculator). Even a AAA battery can
deliver this type of current while still developing close to 1.5V at its
terminals.

Well, one would also have to assume that *all* the current that passes from
the left arm to the right arm will go straight through the heart, and that
none of it will diffuse throughout the rather massive muscle, bone and
tissue mass contained within the arms and chest cavity. Tall order, there.
 
P

Puckdropper

Jan 1, 1970
0
But car betteries are much more dangerous when dropped from a height.

John

Yeah, but they're easier to hear dropping. Just listen for the grunt
from the guy with the battery, then look up. ;-)

Puckdropper
 
J

jasen

Jan 1, 1970
0
Ok, well now that we've determined that I fell victim to a bit of an
urban legend, I'm still curious why a 9 volt battery is so tiny, yet a
12 volt battery is the size of a concrete block.

because volts aren't the only size parameter
Also, something I read indicated a car battery has a sufficient CURRENT
to really hurt you, but too low a voltage. But I fail to see how that's
a true statement given Ohm's Law.

ever short-circit a 9V battery?

nothing specacular happens if it's a short duration...

Try that with a car battery and the wire will melt instantly.

(don't use thick wire it could do expensive damage)

Bye.
Jasen
 
J

jasen

Jan 1, 1970
0
Actually, 1.5V isn't really enough to do anything inside the body. I mean
maybe if you put it directly across the nerves that supply the heartbeat,
but really, they are in fact safe to eat and poop out because 1.5V isn't
enough!

wouldn't the zinc give you (hydrogen) gas?

Bye.
Jasen
 
M

Michael A. Terrell

Jan 1, 1970
0
John said:
But car betteries are much more dangerous when dropped from a height.

John


Especially if it is still in the car. ;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
R

Rich Grise

Jan 1, 1970
0
But car betteries are much more dangerous when dropped from a height.

And if you overcharge them, they outgas hydrogen and oxygem, which can
be explosive if they're confined together.

Thanks,
Rich
 
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