Touching pos & neg of battery

[srah1953]

In recent posts there were comments on spanners frying, etc. My question is, which may seem stupid having regard to spanners, etc, if I touch both positive and negative poles of a battery how big a shock will I get? Will it kill me?

 

[john_morris_uk]

If you touch there positive and negative terminals of a standard 12 volt battery with dry hands you won't feel a thing.

I've never tried it with wet salty hands but even then I'd be surprised if you felt anything at all. You might feel a tingling sensation? The real danger with DC is the grab effect - you can't let go! At least AC tries to throw you off if you haven't fried first.

 

[SAMYL]

You can get one hell of a shock from a 12 volt car battery if you touch both terminals with wet hands.

Don't ask me how I know..................

 

[RichardS]

You can get one hell of a shock from a 12 volt car battery if you touch both terminals with wet hands.

Don't ask me how I know..................

That surprises me. You certainly couldn't be killed or injured by a car battery because 12V across the resistance of human skin and the body in between would never generate enough current to cause death.

It would seem from your experience that having wet hands lowers the resistance sufficiently to be able to feel the effects but I'm surprised it's that noticeable.

Richard

 

[elton]

The biggest danger with a 12v lead/acid battery is a short circuit between the terminals. If it's a heavy duty conductor such as a spanner, the battery will boil very quickly, and probably explode, showering everything nearby in sulphuric acid. You can't hurt yourself by touching the terminals.

 

[oldharry]

That surprises me. You certainly couldn't be killed or injured by a car battery because 12V across the resistance of human skin and the body in between would never generate enough current to cause death.

It would seem from your experience that having wet hands lowers the resistance sufficiently to be able to feel the effects but I'm surprised it's that noticeable.

Richard

Oh yes, you can feel it all right...... Better still with 24 volts. Enough to make you swear!

But the OP asked about shorts with metal tools such as a spanner. No its unlikely to be lethal, but a big starter battery can kick quite a few Kws of power in dead short through a thick bit of metal which will flash the temprature up to several 100's degrees C very rapidly, and you will receive serious burns before you can let go.

A particularly unpleasant accident I heard reported was a tool pusher wearing his wedding ring. He touched a live terminal with the ring while working with a spanner which unfortunately was also in contact with the ring. There was one hell of a bang, and the ring burned through his flesh right down to the bone almost instantly.

So no, not fatal, but easily enough damage to join the queue in A&E and do permanent damage.

 

[PaulRainbow]

If you touch there positive and negative terminals of a standard 12 volt battery with dry hands you won't feel a thing.

I've never tried it with wet salty hands but even then I'd be surprised if you felt anything at all. You might feel a tingling sensation? The real danger with DC is the grab effect - you can't let go! At least AC tries to throw you off if you haven't fried first.

AC will grab you too, so if you get hold of something that is live and it grounds (baring in mind Negative and ground are bonded here) through your body you can't easily let go of it.

 

[penberth3]

There's a well known "party trick" of dropping a big lump of wire wool across the top of a battery. Once you've seen that you'll always make sure batteries are properly covered or boxed.

 

[Dan Tribe]

I learnt that it is not a good idea to try to measure a battery with a steel tape. That definitely gets your attention.

 

[John the kiwi]

I am astonished that you can feel 12 volts even with wet hands. You didn't touch an ignition circuit by chance where the voltage is many thousands?
To the OP:
Its the volts that jolt but the amps that kill. So an electric fence designed to keep cattle in place will zap you with thousands of volts potential difference, but almost zero current, so while you get a jolt that will wake you up it won't kill you.
At the other end is the humble torch battery which has low voltage and has such high internal resistance that even a dead short wont allow much current flow.

Then there is the 12 volt battery, which i maintain you will never feel cos the resistance of the human body is too high, but it does have the capability of producing large amperage(current).
Thus if you short a 12 volt battery with a good conductor such as a spanner it is capable of heating it to melting point!
As a young engineer i worked near a motor vehicle mechanic who had an expanding metal wristwatch strap. Every day he arrived at work and took it off and sat it on his toolbox and after days end wash up would put it back on. One day someone came in with a car just after George had washed up and put his watch back on. It was a simple problem and being an obliging sort he stuck his hand behind the dash to fix it. As you will have guessed, he shorted 12 volts through his watch strap! Literally months off work and multiple skin grafts later he bought a fabric watch strap.
Equally, a short circuit on an unfused cable can easily start a fire, so never take 12 Volts for granted.

 

[sailor211]

There's a well known "party trick" of dropping a big lump of wire wool across the top of a battery. Once you've seen that you'll always make sure batteries are properly covered or boxed.

I recall doing that at the age of 8?, I guess if old batteries in garages were fully changed it could have been much more interesting. I may have learnt something as I did not make a habit of shorting batteries

 

[macd]

The real danger with DC is the grab effect - you can't let go! At least AC tries to throw you off if you haven't fried first.

I think that should be the other way round. AC ratchets up the grab effect through successive cycles, whilst DC also needs significantly more current to induce grab.

But the OP asked about shorts with metal tools such as a spanner.

I don't think he did, although his post wasn't especially clear.

 

[Praxinoscope]

Years ago I drove an ex MOD Land Rover around, it was the 24v version, one day I had the two 12v batteries exposed whilst testing a circuit and managed to short them out, there was a massive bang and I was showered in sulphuric acid, fortunately the garden hose was close by and turnec on o I soaked myself in water, but still had a couple of minor burns on my hands but my overalls were ‘rather holey’.
As for getting an electric shock from 12v batteries, I’ve touched both terminals with fingers hands etc, dozens of times and never felt anything, but years ago for architectural photography we often used what were known ad PF100 flash bulbs, these were the size of normal household light bulbs which we used to fire using a 12v motor cycle battery, to test the circuit we used to touch the wire ends with our tongue and you could certainly feel a ‘zing’ that way.

 

[rogerthebodger]

You can get one hell of a shock from a 12 volt car battery if you touch both terminals with wet hands.

Don't ask me how I know..................

I agree I also have had a shock from 12V when my feet were wet which connecting up 12V wiring in the bilge pumps

 

[JumbleDuck]

Those of you who have had significant 12V shocks with wet hands ... were they wet with seawater, by any chance? Not only does it conduct much better than fresh water, it contains lots of Na⁺ sodium ions, and since sodium (and potassium) ions moving from cell to cell are how nerve signals propagate, having some on the skin greatly increases the "feelability" of electricity. In fact you can give yourself an unpleasant shock from 1.5V if you immerse each hand in a bowl of brine containing an electrode. It won't kill you, but by golly you'll feel it.

 

[rogerthebodger]

Mine was in the bilge so most likely sea water.

 

[steadyeddy]

Many years ago I worked as a aa patrol man .I was sent to a member on the motor way who had broken down on the hard shoulder i,was asked to pick up a set plug leads on the way .It was dark when I arrived and had to use a torch, when he first broke down he thought it was the plug leads it was light so he cut through the leads and could not find any copper wire inside only black string inside ie carbon,he advised as it was dark he had no torch he knew he had plenty of water in his battery as he put his fingers in to check and they was burning on the ends fingers.

 

[UK-WOOZY]

when i was wiring up the new mast lights this year before restepping i tested them with a leisure battery, without thinking i just held the +/- on each terminal with my finders. felt nothing. When i was adding my solar panel too the negative wire caught the positive while the positive was already connected and sparks and dead solar controller

 

[Daydream believer]

When in my early teens my father sent me to his shed to collect a battery that was on charge. As i leaned over it to pick it up I knocked over a steel ladle that fell & shorted across the terminals. The battery exploded in my face showering my eyes.
I ran from the shed screaming & my mother grabbed me & shoved my face in the washing up bowl of water in the sink. She then turned me round & ran the cold tap into my eyes. She caught my forehead with the tap causing a big bruise & bump.

Following a trip to casualty I spent 3 days with my eyes bandaged, so I now have the greatest sympathy with the blind.

On day 3 she marched me into the Nuffield hospital. At the entrance there was a pair of glass doors. She had my arm & I was complaining as she was rushing me & she marched me up some steps calling me a big girl's blouse.

She then walked through the open door of the double doors & forgot to tell me that the other door was closed. I walked smack into it & as well as sore eyes had an almighty nose bleed.!!! To make matters worse, all she did was tell me off for making a mess.:ambivalence:

Never again will I lean over a battery without wearing glasses or making sure that I have nothing to short across it.

 

[davidej]

I used to puzzle why the professional advice is to disconnect negative first and reconnect last. It seemed to be counterintuitive.

However i found out why when disconnecting the positive , my metal watch bracelet brushed against some metalwork which was earthed. No serious harm done but a lesson learnt!

Apart from now following that rule, I always take my watch off before starting work on electrics