60V DC dangerous?

I was talking to a doctor friend of mine a few nights ago, and he told me that the mechanical frequency response of human muscle tissue is not too dis-similar from 50/60Hz, exacerbating the "gripping" problem.

Cheers Terry

I was concerned about the danger from accidently touching live 60V DC circuit (mainly batteries). ESD is another matter that I didn't include in original post. Components can be replaced, people can't.

There are actions that have such obvious and unnecessary high risks one just don't do them.

Enough conjecture.

I have a nice little HP power supply. So I connected two banana leads, ended in bare alligator clips, grabbed one firmly in each hand, slightly sweaty, and cranked it up. No sensation to 65 volts, increasing tingling above there, gets uncomfortable at about 85-90.

John

How many milliamperes did the little power supply show?

Now try touching your tongue. How much voltage does it take?

And how many millamperes?

Regards,

Mike Monett

Don't be a jerk. Nobody likes a jerk.

John

No one takes you for an idiot, John. Not intended that way at all.

Obviously you would start with a very low voltage and work your way up until you start to feel the current. Did I have to point that out, and risk having you complain because I implied you were sub-par?

According to the recent postings, the current should be hard to detect below 1 mA. This should correlate with the value you detected through your fingers.

If the thought of sticking rosin-encrusted alligator clips in your mouth is unpalatable, you can use them to clip to coffee spoons instead.

Since the same person is taking the data in both cases, subjective bias should be reduced. This is a competely scientific and totally harmless experiment that should add more insight to the problem and is as worth doing as the first part was.

Regards,

Mike Monett

Oh, did I mention that nobody likes a jerk?

One can test a 9-volt battery by applying it to the tongue, and it's about as unpleasant as one would voluntarily undertake. So there's another data point.

So much talk, so little experiment.

John

When our kid was a toddler he was sitting on the floor by my office chair one time and he started crying suddenly. I looked down and there was no obvious reason. A minute or so later, the same thing. Turned out he was putting an (energized) 2mm adapter plug into his mouth. It was for an EPROM eraser and rated at 24VDC @ 100mA (a little over 30V unloaded). I tried it at the time just to see how bad it was... definitely *very* unpleasant. In contrast, licking a 9V battery is a time tested technique for checking the condition, and just a bit unpleasant.

So, there's another data point. Of course the distance on the tongue is short and there's no danger of electrocution (just fried tongue), but probably higher current than you'd get most other ways.

Best regards, Spehro Pefhany

A while back I felt a burning sensation on my leg. At first I ignored it, but it kept getting worse. It was a 9-volt alkaline battery, shorted by coins. Thermal, of course, not electrical.

One of the cats, Ajax [1], keeps chewing through the DC power cord to Mo's Sony Vaio laptop computer. She musn't get zapped much, because she keeps at it.

John

Not much use without knowing the current. The point was to find the minimum detectable current level.

I make a small silver ion generator for friends. It runs off 160VDC from the line for simplicity. There are two 220k resistors to the outside leads to limit the current. One NE-2 bulb indicates when power is applied, and another shows when the leads don't make proper connection to the silver electrodes.

The short-circuit current is around 360uA. Nobody can feel it, but the second NE-2 bulb goes out when you touch the leads with your fingers.

A badly designed experiment is of little value. We need numbers, John. 9V across the tongue is useless, except to tell if the battery is completely dead.

Regards,

Mike Monett

OK, I have bravely taken the challenge, and stuck my tongue out.

A 1.5V watch battery barely tastes a bit salty.

So based on my now-calibrated tongue, a 1.5V watch battery gives perhaps less than half the sensation of 340uA. So the resistance of a wet tongue is approximately

R = 1.5 / (340e-6 / 2) = 8,823 ohms

and unlike skin, is independent of pressure.

This compares with data indicating megohms or more for dry skin, and perhaps 100k for damp skin.

It is interesting to note the tongue is quite a bit more sensitive than current applied to the fingers.

Regards,

Mike Monett

It was not. I was responding to the original post, and that was about voltage.

John

John

Once, when I was a strapping young teenager, there was an arcade at a local abusement[sic] park, and one of the attractions was a little console, with two chrome knobs like doorknobs that you could grasp while standing there. You'd put in your coin, and it would start an electric current from one knob to the other, i.e., through both arms and the customer's chest. There was also a meter, which increased as you cranked the right-hand knob up, (like a "volume control") and the current _did_ increase - I remember my forearms cramping up, but wanting to beat the record and all that (being an idiot teenager), but it got to a point where it hurt too much.

Evidently it didn't kill me. ;-P

Cheers! Rich

Yabbut. you're in San Francisco, second-humid city in the country right after Seattle, IIUC. ;-)

Thanks, Rich

On Wed, 05 Jul 2006 11:14:42 -0700, John Larkin Gave us:

On Wed, 05 Jul 2006 13:43:31 -0700, John Larkin Gave us:

I suppose that means that it is too late for you.

Show of hands... How many engineers feel that ESD concerns are not a risk to electronic circuitry?

On Wed, 05 Jul 2006 14:50:30 -0700, John Larkin Gave us:

Examine the lead spacing on a nine volt battery.

Examine the lead spacing between a spoon in your mouth, and a clip in one hand. No comparison.

Did somebody shit in your corn flakes today?

On Thu, 06 Jul 2006 02:47:50 GMT, Rich Grise Gave us:

Took your brain out though.