Licking Batteries?

[jast]

Continuing the discussion from Beware the Nitrogen Laser Capacitor:

Beware the Nitrogen Laser Capacitor

Beware the Nitrogen Laser Capacitor

… meaning that less than a millisecond after using the discharge probe, the capacitors should be discharged.

I strongly encourage that you maintain physical contact between the grounded discharge probe and the capacitor for at least a full minute, and longer if measurements indicate otherwise.

The estimates that the formulas you used are basically fine; however, there are a number of assumptions embedded in them. Most notably that the resistance will remain constant over the discharge period. The problem is that with real world components, particularly when you putting hundreds of watts of power through them they heat up. Resistance in components change with temperature.

It is better to be safe, and keep contact for at least a full minute.

BTW, the resistance through your body was likely MUCH higher then 50K, because the resistance between your body and earth ground is in series. And if you were wearing shoes, it should have been quite a bit higher. The latter is why standing in water and getting shocked is so much worse. You only have your bodies resistance to deal with at that point.

So this reminds me of a topic of discussion during a college class at which I was in attendance. The discussion started when one student pulled a 9v battery out of an electronic device and licked the electrodes “to see if it’s any good”. Several others had never heard of such a thing, or thought it would really hurt, so discussions ensued. Then came the “if you had a tongue that long, can you lick a car battery?” question. All but 1 person in the room asserted that it would almost surely kill you, since car batteries are so much bigger than the little 9v which “produces a tingle on the tongue”. Which side would you be on, and why?

(Yeah, this IS pretty elementary, but for non-electronically inclined folks, I wonder if your ellucidation might be helpful. No matter what is asserted or postulated here, please don’t actually DO any of this at home! Get your friends to do it, and be sure to video and post back. (that’s sarcasm, folks. Really, don’t anyone attempt any of this at home) )

[wandrson]

The crux of what kills you generally is the current that flows across your heart. Much like a defibrillator in reverse.

Have never put my tongue across the terminals of a car battery, but have seen a safety video where a ‘mechanic’ wearing a dangling necklace had the necklace make contact with both terminals. Weld itself to those terminals and proceed to discharge through said mechanic. Didn’t end well.

That said, we could always do a Mythbusters, and get a dummy made from balistics gel and some electrodes and do some empirical measurements. Sounds like an activity for the Science committee…

[jast]

Some folks in the class had seen similar videos. It appears they learned “car batteries are dangerous” instead of the actual lesson (assuming it was an educational video) which is generally INTENDED to be “Do NOT wear jewellery while working with electricity, including car batteries”.

I got no funds, but I’m all in favor of the proposal…

[wandrson]

Car batteries ARE dangerous, most useful things are.

[Opcode]

All but 1 person in the room asserted that it would almost surely kill you, since car batteries are so much bigger than the little 9v which “produces a tingle on the tongue”.

A 9 Volt battery discharging across a wet tongue probably produces about 10 mA of current

I = V/R = 9 / 1k ~ 10 mA

and so P = IV = 10 mA * 9 V = 90 mW

A 12 V car battery would produce a little more current and a little more power, but I doubt it would kill you. Your tongue probably would hurt a lot, though.

I’d be more worried about the sulfuric acid, lead and other nasty chemicals on the battery.

[wandrson]

A 9v battery has an extremely high ESR, which drastically reduces the amount of current it can deliver. On the other hand, a car batter has very little ESR, so can deliver extremely large ammounts of current.

Your ‘estimates’ of bodily resistance is flawed. For instance, if you would put two jumper cables across your tongue you would be creating essentially a dead short, since you have a conductive liquid on the surface. With enough current to cook your tongue.

Easy to determine how correct your expectation of resistance of the tongue would be. Just use hookup wire, a 9v battery, and a meter. Might make a good demonstration for the open house.

[coloneldan]

A lot depends upon the conductivity of the circuit. Your tongue is more conductive and sensitive than other parts of your anatomy such as your hand so the current flow is more through your tongue. Put a much more conductive solution in your mouth like salt water then put your tongue out and try it.

Ever see those shows where a battery bank and jumper cables are used to torture a poor soul who has been doused with water? Can’t say it would kill you but the pain would be intense.

Lastly, my wife has a TENS unit for medical reasons and it uses a little ole 9V battery, but due to the amplification circuitry can inflict some serious pain on the highest setting. So can a cattle prod for that matter, so the size of the battery isn’t the real issue.

Walter is right it is the current across the heart that kills you. Either that or your organs, limbs etc being cooked due to the high current and voltage, like on a power line. They were probably dead before they cooked, but still the cooking wasn’t good for them either.

These are rather morbid thoughts, but honestly the most effective safety videos I ever showed in the Air Force were of guys getting hurt, maimed or killed while doing something they shouldn’t have been doing according to the USAF Tech Orders. We should continually focus on safety and help our fellow members when we see them doing something unsafe.

[jast]

care to share your sources for R?

[coloneldan]

Actually, I don’t have a source, but by reducing R you get more current (I) so anything such as additional salinity should increase the current right? The more ions the better the conductivity right?

[jast]

Thank you. You’ll get no argument from me on that front. But my query was actually directed to @Opcode …

[Opcode]

care to share your sources for R?

Several sources state that human body electrical resistance varies from about 1k-ohm to 100k-ohm. I’m using the lowest value as an estimate, for a starting point. Feel free to use whatever value you feel is reasonable. I’m certain that no part of the natural human body has an electrical resistance as low as a 12-gauge copper wire, or a piece of metal jewelry.

[TBJK]

Hell, I will still do the 9 volt battery to the tongue. I did that as recent as Tuesday when I was checking to be sure it was a good battery. Anyone care to be a guinea pig with a megger to test the resistance? lol

[wandrson]

I’m certain that no part of the natural human body has an electrical resistance as low as a 12-gauge copper wire, or a piece of metal jewelry.

I am fairly certain that you are mistaken. Our blood has a very similar conductivity as a salt solution of similar concentration. Which is a VERY low resistance. It is why currents introduced below the skin (which provides a great deal of electrical insulation) is so much more dangerous.

Your tongue is bathed in a similar electrolyte solution, which further increases it’s conductivity. I would guess well little more than 0.01 siemens.

The OP described procedure is largely safe because the high ESR of 9V batteries significantly limits the current those sources can provide.

Further, it is important to recognize the path the current flows through. So for instance, when you shocked yourself with the capacitor, the path was through your body, then your socks, then your shoes, and finally through the concrete to an earth ground.

The 9V path (or presumably the 12V car batteries path) would be across an inch or two of your highly conductive tongue, since the ‘ground return’ would be the negative terminal of the battery and not an earth ground. This low resistance would allow a lot of current to flow in a source that is capable of delivering it (which a 9V battery is not). That current would then produce a lot of heat dissipation.

A reasonable mockup of what might happen could be demonstrated with a moderately moist host dog and two nails, and a pair of jumper cables.

[Opcode]

A reasonable mockup of what might happen could be demonstrated with a moderately moist host dog and two nails, and a pair of jumper cables.

We could get an actual tongue from a butcher shop and see. Of course, that isn’t the same as a live tongue, but maybe close enough.

[wandrson]

Of course, that isn’t the same as a live tongue, but maybe close enough.

As long as you inject it with saline and coat it just before the test then I agree it would make a good test.

The advantage to the hot dog, is that someone might actually be willing to eat it after we cook it with electricity.

[Lampy]

sounds like an open house demo to me. Ahhh, electrocuted hot dogs.

[rolbrey]

As a kid I had a electric hot dog cooker, which was basically two electrodes that you stuck each end of a hotdog into, put on the lid, and it ran 120vac through the dog and cooked it in about a minute. So I don’t thing these things are too conductive to spontaneously combust at 12v.

http://www.neighborhoodvalues.com/nv/kitchen/misc/35kc.htm

The issue with the necklace on the 12v battery is heating not electrocution. It is the fact that a car battery can conduct thousands of amps shorted.

[wandrson]

As a kid I had a electric hot dog cooker, which was basically two electrodes that you stuck each end of a hotdog into, put on the lid, and it ran 120vac through the dog and cooked it in about a minute. So I don’t thing these things are too conductive to spontaneously combust at 12v.

No one has claimed they will combust. But you can cook a hot dog with a 12V battery, I have seen it… You can’t cook a hot dog with a 9V battery…

The issue with the necklace on the 12v battery is heating not electrocution. It is the fact that a car battery can conduct thousands of amps shorted.

I believe I said the same thing in a post above; " With enough current to cook your tongue. "

[jast]

Here’s some elementary school level science on licking a 9v.
According to Ohm’s law, I=V/R, so using their numbers, change V from 9 to 12 and there ya go…
Thoughts?

The Science of Licking a 9V Battery - News - SparkFun Electronics

For those of you with no patience for reading, here’s the accompanying video. It does not address the whole article, but…

[jast]

sounds like an open house demo to me. Ahhh, electrocuted hot dogs

I take it the weenie roast did not happen?
Too bad. I was ready for it…