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PICList Thread
'Safety of 12V dc to 110v ac using D cells'
2005\11\14@141845 by olin piclist

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John Waters wrote:
> It is hard to imagine 8 D cells could kill someone, right?

Wrong.  It doesn't take long at much of a current accross the heart or thru
the brain to kill a human.  In other words, the total energy to kill a human
by electrocution isn't that high.  I'm sure 8 D cells contain way more than
that amount of energy.  Of course it has to be converted to the appropriate
voltage/current, but that's exactly what your inverter is doing.

Do the math.  I'm not up on the amp-hour rating of D cells, but 2 AH for a
primary AA cell is quite conservative.  Therefore 10 AH for a D cell must at
least be in the ball park.  10A x 3600 seconds x 1.5V = 54KJoules, so let's
say we've got about 50Kj to start with, and 40Kj after conversion to a
different form.  And that's just one D cell.

So let's look at some examples of 40Kj.  40Kj = 40000 N-m = 4082Kg-m at 1g.
That's about 1 ton (2000 pounds) lifted 4.5 meters or about 15 feet up.
Imagine that crashing down on you.  Or let's say you weigh 100Kg.  40Kj is
how much energy gets dissipated when you fall 41 meters.  In other words,
40Kj is about the splat you'd make after jumping out a 13th floor window.

But back to an electrical form of the energy.  40000 joules is 1000V and 1A
for 40 seconds.  A D cell couldn't release all its energy that fast, so this
is only meaningful if it were stored then quickly released.  But let's say
each cell can deliver 3A for long enough to kill a person.  3A x 1.5V x 8
cells = 36 watts.  That's 300mA at 120V.  Even if it's 200mA to account for
conversion losses, that means the D cells can sustain a 400 ohm load at
120V.  Without special electrodes that make good contact, you're body is
going to present a lot more than 400ohms, so the D cells will have no
problem maintaining the 120V.  And, this is using rather conservative
numbers.  In reality a 8x D cell to 120VAC converter should be able to
sustain a considerably lower resistance load for long enough to kill you.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2005\11\14@175220 by Russell McMahon

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>> It is hard to imagine 8 D cells could kill someone, right?

Hard to imagine, yes.
Entirely possible though.

And

> .... Of course it has to be converted to the appropriate
> voltage/current, but that's exactly what your inverter is doing.

Certainly an inverter will easily allow it to be lethal,

*** BUT ***

it is possible to die with the voltage and current provided by 8 D
cells in series alone - ie a 12 volt supply. This is most unusual, but
in unusual circumstances people HAVE died from a 12 V supply! The
voltage would probably have to be applied more or less to the chest
surface, and having low resistance body contact would 'help', but it
has happened.

Always treat with care.


           RM


2005\11\14@184536 by Richard Prosser

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I was working on some 48V systems in Malaysia a year or so ago. Due to
the nature of the system (telecom) we had to work on them live.
It was hot, sweaty work mostly and I got a noticable, unpleasent shock
when touching both live & common, even though the actual voltage was
only about 53V.

RP

On 15/11/05, Russell McMahon <spam_OUTapptechTakeThisOuTspamparadise.net.nz> wrote:
{Quote hidden}

> -

2005\11\14@191857 by Steph Smith

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you wont get any joy using D cells,they dont have the capacity to drive an
inverter for more than a few minutes,thats why things like electric fences
use sealed lead acid batteries...besides which; imagine the cost of
replacement!
{Original Message removed}

2005\11\14@193524 by Steph Smith

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On the subject of batteries and safety; i recently accidentally shorted out
a 6v (4xAA cells) battery pack when a screwdriver in my bits box slipped
across the contacts,the resulting smoke,noise,heat,and stained underwear
where something else...
{Original Message removed}

2005\11\14@195450 by Russell McMahon

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> On the subject of batteries and safety; i recently accidentally
> shorted out
> a 6v (4xAA cells) battery pack

A single AA NimH battery carried in a pocket with coins keys et al can
(and has)(on several occasions that I am personally aware of :-) )
become so hot that the outer plastic peels off and the battery is too
hot to be picked up (100C plus) - certainly hot enough to burn skin.
As the battery will (or should) be venting under such conditions other
adjacent items may be chemically affected.

Even a good Alkaline AAA cell will deliver over 5 Amp short circuit.


       RM



2005\11\14@233035 by William Chops Westfield

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>> On the subject of batteries and safety;

I'm a little surprised that there haven't been more "accidents" with
old circuits and new batteries.  The hobbyist books used to be full
of "tickler" circuits and such that claimed "This circuit is made safe
by low power delivered by a typical dry cell.  Do NOT connect to an
AC power supply."  That was then; these days a typical battery can
deliver a lot more power...

BillW

2005\11\15@035924 by Vasile Surducan

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On 11/15/05, Russell McMahon <.....apptechKILLspamspam@spam@paradise.net.nz> wrote:
> >> It is hard to imagine 8 D cells could kill someone, right?
>
> Hard to imagine, yes.
> Entirely possible though.

In many ways. Swallowing. Applying potential directly on the hard
muscle or brain tissue. By pushing them in the eyes. By crashing them
in the nose. And so on.

Vasile

{Quote hidden}

> -

2005\11\15@070503 by Russell McMahon

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> On 11/15/05, Russell McMahon <apptechspamKILLspamparadise.net.nz> wrote:
>> >> It is hard to imagine 8 D cells could kill someone, right?
>>
>> Hard to imagine, yes.
>> Entirely possible though.
>
> In many ways. Swallowing. Applying potential directly on the hard
> muscle or brain tissue. By pushing them in the eyes. By crashing
> them
> in the nose. And so on.

Humour has its place - but don't let it distract you from the fact
that they can also kill simply by having their 12 or so volts applied
to the body in an inopportune manner :-(


       RM

2005\11\15@080309 by Josh

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I used to work on 9volt powered devices that had a 2000 volt stage in
the circuit.  If you touched it, it would give you a good jolt that hurt
but it could not maintain current at that voltage so it really wasnt
dangerous.  Painful, yes.  Not deadly.  Maybe that part of the circuit
in combination with a really large and high voltage capacitor could kill
somebody.  Would make a great murder weapon, a cap, 9volt and a handfull
of components.  Forget the 9volt and components, you could just hit
someone over the head with your 2000 volt cap.

Russell McMahon wrote:

{Quote hidden}

2005\11\15@094204 by John Ferrell

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No, it is not guaranteed safe.
This is one of the very first things I learned about electricity. Dad
brought 4 th grade son an old car battery and broken car radio home to play
with. These were 6 volt days. Safe, right? It lead to my getting the
vibrator power supply running and some very nasty burns between my thumb and
finger on my right hand. I learned a lot in a couple of seconds there
including the smell of burning flesh. Still have the scars. It may have been
the most important thing I ever learned. No, I did not tell Dad!

John Ferrell
http://DixieNC.US

{Original Message removed}

2005\11\15@115123 by William Chops Westfield

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On Nov 15, 2005, at 5:00 AM, Josh wrote:

> I used to work on 9volt powered devices that had a 2000 volt stage in
> the circuit.  If you touched it, it would give you a good jolt that
> hurt but it could not maintain current at that voltage so it really
> wasnt dangerous.  Painful, yes.  Not deadly.  Maybe that part of the
> circuit in combination with a really large and high voltage capacitor
> could kill somebody.

Consider the typical disposable camera electronic flash.  1.5V AA cell
driving an in inverter to generate about 300V, which is then used to
charge an approx 100uF cap.  100uF at 300V is 4.5J; in the realm of
high voltage (and this probably doesn't qualify, but it's close),
one measures possible danger in Joules of discharge, and a 10J discharge
is generally recognized as being potentially fatal (Moore,
"Electrostatics")
So merely tripling the output capacitance gives you a device that is
rather likely to have the potential to be fatal.

One should also remember all those "20,000V stun gun" devices being
sold that operate off of a single 9V battery.  They're not supposed to
be fatal either, but I don't doubt that they could be if optimized
slightly differently.

> I want to use it to drive a small device that uses 110v and
> consumes power less than 3 Watts.

Put another way, the current through the body generally thought of
as "fatal" is 20mA.  Assuming that 110V is enough to push that through
the body (so that the current is limitted by the supply rather than
the body), that's only about 2.2W.  So a 3W inverter is well within
the realm of "possibly fatal", and your 8 pieces of D cells are
capable of providing much more than 2.2W via an inverter.

BillW

2005\11\16@075328 by Vasile Surducan

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On 11/15/05, Russell McMahon <EraseMEapptechspam_OUTspamTakeThisOuTparadise.net.nz> wrote:
> > On 11/15/05, Russell McMahon <apptechspamspam_OUTparadise.net.nz> wrote:
> >> >> It is hard to imagine 8 D cells could kill someone, right?
> >>
> >> Hard to imagine, yes.
> >> Entirely possible though.
> >
> > In many ways. Swallowing. Applying potential directly on the hard
> > muscle or brain tissue. By pushing them in the eyes. By crashing
> > them
> > in the nose. And so on.
>
> Humour has its place - but don't let it distract you from the fact
> that they can also kill simply by having their 12 or so volts applied
> to the body in an inopportune manner :-(

Absolutely ! But the people must have a very low skin resistance.
Usualy the minimum voltage which may produce a death current is bigger
than 48V.
At least in romanian standards.

cheers,
Vasile
A surviver of a 220V DC from acid battery electrocution. Who knows
what means no zero crossing on his hands.

>
>
>        RM
>
> -

2005\11\16@120132 by Steph Smith

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yep.. i once(foolishly) tried out a wet-from-rain laser torch,the flash and
smoke made it look like my car had just been blown up!very impressive for
the kids standing nearby! OH the shame...
{Original Message removed}

2005\11\16@154359 by Peter

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On Wed, 16 Nov 2005, Steph Smith wrote:

> yep.. i once(foolishly) tried out a wet-from-rain laser torch,the flash and
> smoke made it look like my car had just been blown up!very impressive for
> the kids standing nearby! OH the shame...

You don't really want to know what a professional photographer flash
does if charged and fired when wet (about 50 Joules in it).

But the nastiest experience I had was with 12V dc in sweet water. I was
very very wet and I held bare wires to contacts at 12V. If it had been
24V I would likely gotten stuck like that. Now I know exactly what those
frog legs Volta used for his experiments felt.

Peter

2005\11\16@160018 by David Van Horn

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> You don't really want to know what a professional photographer flash
> does if charged and fired when wet (about 50 Joules in it).


Some of the older flashes used belt battery packs, with a bunch of these
batteries:
www.bhphotovideo.com/bnh/controller/home?A=details&Q=&is=REG&O=pr
oductlist&sku=19185



2005\11\16@164346 by Russell McMahon

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> But the nastiest experience I had was with 12V dc in sweet water. I
> was very very wet and I held bare wires to contacts at 12V. If it
> had been 24V I would likely gotten stuck like that. Now I know
> exactly what those frog legs Volta used for his experiments felt.

This was exactly the point I was making that caused so much
opportunity for hilarity that the point was at risk of being lost.

12 volts HAS killed people. It's very rare, but it's possible. One
need not be paranoid about the risk, but awareness of the risk is
useful.


       RM

2005\11\17@130226 by Juan Cubillo

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About a couple moths ago I was playing with a camera flash transformer and
it´s corresponing capacitor (180uF 330V).
To keep the story short, when the cap was fully charged I somehow got
shocked with it. I was extremely scared and when I tried to feel my heart it
was pumping very fast. I dont know if it was because of the electric shock
or íf I was scared. The worst thing was that I was completely alone in my
house.
I haven´t touched that camera PCB since then... :)

Juan Cubillo

{Original Message removed}

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