Pain from shock when getting out of car ...

The pointy end of the key acts as a "corona discharge point". Charges on your body are also present on the pointy end of the key (a pin works better). The charge density in the point becomes so high that charged particles actually are forced away from the point into the surrounding space. This is known as a corona. Corona discharge is a slow, steady discharge of electrical charges streaming off of a point or edge of an object into the surrounding space in the presence of high opposing electrical charge. Corona discharge is usually visible as a small, slightly glowing 'spray' extending out into the air.As the key nears the metal car frame (oppositely charged) the corona charges tends to flow towards the car frame and neutralize the difference in charge potential between the key (and your body) and the frame. Devices that use this principle are sometimes called static dissipaters. They are used on aircraft, boats, antennae, and may other places where the reduction of electrostatic discharge intensity is desired.

On a small scale such as the level you are talking about (vs. lightning), corona discharge can actually equalize the opposing electrostatic charges before full electrical breakdown occurs and a spark jumps. You feel this as a greatly reduced "shock" sensation or no shock at all as opposed to that when no such charge dissipation has occurred. You may want to search for "corona discharge points" and "static dissipaters" for moor info.

Perion

Pain is a function is where energy exists. The electricity is flowing through the entire body. But energy is only where the spark occurs - and painfully.

BTW, another poster discussed corona discharge. However that is also the myth promoted by the Early Streamer Emission industry. ESE claims to discharge the air, thereby avoiding CG lightning. They offer no proof. Their devices have even been blown off air traffic control towers by direct lightning strikes - in one case during the same month it was installed. Why would they be struck if they had discharged the air around them?

ESE promoters demanded that NFPA (the National Electrical Code) list their device. The NFPA refused. So ESE promoters tried to sue the NFPA to bankrupt this non-profit organization

- a sort of blackmail. Still they offer no proof that ESE concepts are valid. There is not indication that ESE devices discharge the air.

Many IEEE papers accuse the ESE industry of not proving a 'corona discharge to avoid lightning' claim. One particularly strong advocate of science (opposed to ESE) is Dr Abdul Mousa.

The key simply puts discharge energy at a po> Why is it that, when I get out of my car on a dry day when wearing the

"aphexcoil" wrote on Thursday (11/12/2003) :

It seems to be for the most part the size of the area of contact. Put a finger to the car as you get out and you receive a shock. Use the entire flat of your hand and you feel nothing. Take a good grip of the keys and it will produce a similar result, but the spark will also be moved to the metal tip of the key.

What I find rather odd, is that I get a regular shock from some cars, but not others. My previous car was exactly the same model as my present one, but I never received a shock from my older car. I can guarantee I will get one from my latest one no matter what the weather.

I was thinking something along those lines. Nerves are sensitive to the current flow. Something like a set of keys spreads the current over your entire palm so the current-density is low enough not to register. I don't think the actual *spark* causes the pain, just the extremely localized current density where it contacts the finger.

This *could* be a function of the type of tires on the car and the shoes one wears. When you open the door from inside, you're probably at the same potential as the door. Put your feet on the ground and now you're at ground potential. If the car was above ground potential due to tire material and movement, then you get a shock.

Another obvious way to avoid it is hold onto the door as you get out and put your feet on the ground. Broad sole of shoe would lessen the current density and the shoe material would act like a 'bleeder' resistor to lesson the total current as you 'ground' yourself and the car.

IIRC, old style gasoline delivery trucks and such had chains and/or lether straps that dragged from the rear axle so the truck would always be well grounded. Maybe newer tires have more carbon or something to reduce static build up??

daestrom

I can't speak for the old ones, but certainly newer gasoline delivery trucks (and all sorts of other petrochemical delivery trucks) go to seemingly extraordinary lengths to ensure the truck is properly grounded before loading or unloading is possible. Did the old straps (seen hanging from extremely-untrendy cars as well) actually work?

Maybe newer tyres do have more carbon in the rubber or something, but if you are getting a spark stepping out of the car due to static buildup, I'd be making sure you discharge the static before opening your fuel cap and sticking the bowser fuel hose into your tank - the only ground connection there is the metal rim of your fuel tank pipe..

Cameron:-)

I'm assuming based on the 1/4" sparks I can produce from the door, that the voltage must be at least a few kilovolts up to possibly 10k. The amperage must be in the microamps range, though. The spark probably only lasts for a few thousands of a second.

What I find amazing is how strong I can get nailed from just this if I happen to touch the door with my finger instead of my keys.

Doesn't a Van De Graaff generator produce 100's of kv's? What's a shock from one of these things like?

Thanks for the replies!

Fun. You should try it some time.. ;-)

Cameron:-)

What's interesting is that at the Baltimore Science museum, a guy was demonstrating a Van De Graaff generator and standing on the ground. He put his elbow out and approach the sphere and a good 6 inch spark hit his elbow / upper arm.

As he was doing this, he was saying, "I've done this so many times, that I'm used to the feeling the shock but don't try this at home!"

I could see the muscles in his upper arm contract each time he got hit with a huge spark.

Quite amazing.

Yeah. We had a small Van De Graaff generator in the science lab at school and have tried the same trick many times. Because there is no real current flow, if you can tolerate the initial shock, you're home already. (Rubber-soled school shoes are reasonable insulators).

The best trick is to put your hand on the thing and watch your hair stand on end... and then use one finger of your other hand to zap your friends nearby!! It's all very cute, really.

Cameron:-)

Actually I got the notion from a couple physics books. See my reply to DarkMatter, above. I'm not sure I buy the physics books' analysis anymore after hearing some of the other replies. Kinda weird though - the one physics text is VERY reputable - but old - 1970.

Regards, Perion

The concepts of corona discharge are not in error. Just that corona discharge has nothing to do with this scenario. For example, a major loss of power on highest voltage transmission lines is corona discharge. It does exist. Corona discharge is one reason why males typically charge only up to

18K and females up to something like 20 Kv. But corona discharge does not reduce charges so much that static spark does not occur. Using the key to discharge a human body still results in a spark. But the painful point of high energy is no longer on a little point of skin. As Dark Matter notes, energy leaves the body over a wide area into the key meaning that minimal energy concentrates on skin - and much energy (relatively) concentrated at the end of the key.

BTW, it is current that def> Actually I got the notion from a couple physics books. See my reply

Yes - I think you and DarkMatter are right. The key idea (yuk yuk) is the location of the actual spark in reference to the nerves in the skin. Makes sense.

Perion

I remember having equipment problems on a machine that had sensitive cmos switches. It turned out that one of the operators had some Kmart shoes with some sort of plastic material in the soles. When I suggested another pair of shoes the problem disappeared......This has actually occured more than once through the years.....So the moral to the story might be...Try another brand of shoes.... Have a great holiday!.....Ross

I think it has something to do with the type of carpets and/or seatcovers in the car. It's like the old rub your feet on the carpet and touch your friend school-trick, it worked really good on some carpets and not so good on others.

I found it a problem trying to locate a good earth point fro the drivers seat. Everything metal was already well painted. :(

On Fri, 12 Dec 2003 11:47:09 -0500, "Perion" Gave us:

Which describes how attractors and fields work. As well as air ionization principles. The discussion here was about how to discharge one's self without sensing pain at the exit/entry site from what the header states.

The answer is to distribute the charge inrush/egress to a larger area.

A plastic key with a wire running down to the tip would present quite a gradient. Doesn't matter. If one touches the other end of the wire it will still hurt a bit as the surface area is again reduced to a small area. The charge travels right up the wire (or down it). All of the current of the entire discharge is again on a small spot, as opposed to the entire thumb and forefinger.

The amount of pressure (read pain)on any given nerve in the fully metallic key with the point on the end is negligible if felt at all.

The amount of pressure on the set of nerves involved with all of that energy entering or leaving one area smaller than a square millimeter as in direct "jump to finger" or "plastic key with a pointy wire" scenarios would exhibit would be felt quite a bit. "Hurt" even.

In other words.. It ain't about the point, it's about distribution of a short term event over a large area in such a way as to be not "felt".

Wet fingers, works even better. No pain... Till that charge level starts gettin' up in another realm anyway.

LOL. yeah, when aroused, I only charge up to 5 kv.

You'll find the amperage quite a bit more than you think! If you know the voltage, capacitance, resistance and the time of the discharge you can calculate the current. John

Actually the guy was doing something important. He was demonstrating a defect in that machine design. By replacing his shoes, you only cured the symptom.

Switches are typically rated for 20,000 volts. But they don't mention why. That switch must make a connection to chassis ground. Like in all high voltage transient protection, one does not stop, block, or "dam" the transient. One shunts, diverts, or "dikes" the transient. But that transient still requires someplace to discharge - a "downriver" channel.

This is also why the chassis ground is separated from electronics ground. For example, in a properly constructed computer, motherboard only makes a single point connection to the chassis - typically in the area of IO peripheral cards and power supply connection. This to eliminate any ground loops between chassis ground and motherboard ground. This eliminates failure due to 20,000 volt static electric shock.

In short, a good designer puts his design on a glass (wood is too conductive) table, puts on a pair of leather slippers, and static electric shocks every corner of that system. The painful static electric shocks will never interrupt a properly built system.

Encountered the same problem on my design. Hole where a keyswitch was mounted was not conductive due to epoxy paint. Therefore a static shock was interrupting (crashing) the computer. Solution. A large internal tooth lock washer was installed with teeth to cut through the epoxy paint. Switch body made electrical contact with chassis. No more static electric problems because switch was grounded to the right ground (chassis; not electronic ground).

How to f> I remember having equipment problems on a machine that had sensitive