Darwin award: How to kill yourself with a 9V battery

[Sigmoid]

I recently found this (old) Darwin award, where a young soldier managed to get himself killed using little more than a 9V battery.
I think it teaches a very important lesson in work safety, so I think all beginners should read it. There are lots of stories around about the dangers of high voltage - it's important to remember that low voltage can kill you just as well, if you're reckless.

http://www.darwinawards.com/darwin/darwin1999-50.html

[Phaedrus]

I manage to work around 400V off-line power supplies with not even a burn mark, and this duff goes and offs himself with a 9V battery. I'm not even mad. That's impressive.

[jeremy0203]

I am in the Navy. This is nothing but an urban legend passed along in the schools where electronics or electrical things are taught.

[Len]

Yeah, note how this Darwin Award (like many others) is listed as "unconfirmed". As a rule, if there's no name & date attached to it, it never happened.

[mcinque]

Yeah, note how this Darwin Award (like many others) is listed as "unconfirmed". As a rule, if there's no name & date attached to it, it never happened.

Agree, I don't believe is happened. First, I hardly believe that from a 9V battery 30mA could reach the heart running thru the blood. At second, noone without mental disorders would pierce his thumbs with a couple of multimeter probes.

[zapta]

Assuming 300v body voltage, 150ma body current, 10sec time to death,  500mah 9v battery capacity, and 50% efficiency, by my calculation a single battery can kill 20 people or so.

[jimmc]

I'm surprised that this is still listed as unproven when it's obviously false.
For a start the short circuit current of the Simpson 260 is less than 100uA on the 'Ohms x 10,000' range where the 9v battery is used!
(For details see my post here https://www.eevblog.com/forum/blog/eevblog-64-fluke-28-series-ii-multimeter-review-teardown/msg2417/#msg2417)

Jim

[G0HZU]

At second, noone without mental disorders would pierce his thumbs with a couple of multimeter probes.

It doesn't work on dogs with a 9V battery... 

I'm going to test it on my neighbours cat next but they are harder to catch and hold down... :O)

[G0HZU]

Seriously though, it's supposed to take several hundred milliamps of dc current to give a fatal shock.

So you would have more success if you tried to eat/digest the contents of the 9V battery or if you dropped it on your head from a great height.

[Tinkerer]

The reason you cant kill yourself with a 9v is because there simply isnt enough voltage, even if the battery can output enough amperage. If you manage to boost that voltage up some, then yes, I could see someone killing themselves with just a 9v where the end result isnt 9 volts anymore.

[Psi]

At second, noone without mental disorders would pierce his thumbs with a couple of multimeter probes.

It doesn't work on dogs with a 9V battery... 

I'm going to test it on my neighbours cat next but they are harder to catch and hold down... :O)

You shouldn't joke about animal torture, people have no way to know if you're serious or not.
There's a lot of real dickheads out there.

[Fraser]

This takes me back to my childhood when I used to check the state of PP3 9v batteries in my toys by placing my tongue across the terminals.....nasty sting = good, little or no sting = bad 
It is still a useable 'field test' test to see if the battery is flat but likely not a great idea all the same 

It tingles a little but no other harm done as far as I am aware 

[G0HZU]

Apparently there's a band called "Killed by 9V Batteries" in Austria

[vk6zgo]

Yeah, note how this Darwin Award (like many others) is listed as "unconfirmed". As a rule, if there's no name & date attached to it, it never happened.

There's a lot of such stuff on what I call the "Lie Net"!

One of which is an inflammatory speech which has been accredited to three Australian Prime Ministers & one French PM.

Dr Goebbels is alive & well,& having fun on the Internet!

[zapta]

This takes me back to my childhood when I used to check the state of PP3 9v batteries in my toys by placing my tongue across the terminals.....

Is there another way to test a 9V battery?

[c4757p]

This takes me back to my childhood when I used to check the state of PP3 9v batteries in my toys by placing my tongue across the terminals.....

Is there another way to test a 9V battery?

Does this actually work? I'd suspect that an almost dead 9V battery might still be able to pump out a couple mA to tingle your tongue.

[cwalex]

This takes me back to my childhood when I used to check the state of PP3 9v batteries in my toys by placing my tongue across the terminals.....

Is there another way to test a 9V battery?

Does this actually work? I'd suspect that an almost dead 9V battery might still be able to pump out a couple mA to tingle your tongue.

yeah it works, the difference between a dead and full battery is easy to tell.

[vk6zgo]

Back in the day when I was a "Storeman" at an Electronics shop,we got some special 67.5v batteries in.
They were used in some sort of gear used by a Govt.Department.
This customer (& a few others) used a fair number of them,so the Boss decided to keep them in stock.

The more common version was a small rectangular unit,but these looked like a very large version of modern 9v batteries,complete with "press stud" connectors on one end.

The proportions were different,though,as they just fitted into the stock shelves.
As the shelves were metal,we put them with the "press studs" facing outward.

All was well,until one sweaty Summer day,when a colleague asked me about something on an Order Sheet.

Leaning against the shelves (as you do! ),I placed my arm across about four of these batteries.

Ouchhh!

I was quite surprised by this and yelled "Golly Gosh,Gee Whiz!" or something of that nature.

Luckily the Boss was elsewhere,so I didn't get chewed out for swearing just outside the Office.

[IanB]

special 67.5v batteries

When I was a child around 1970 I remember the local radio shop used to stock 90 V batteries, as I suppose people still had portable battery powered valve radios and wanted to buy the batteries for them. I was fascinated by those batteries, as the voltage was so exotic compared to the ordinary low voltage batteries I would buy for torches and bicycle lamps. At the time I had no clue what they were used for. I do remember that the terminals were covered by a paper seal that you had to tear off before use, so that you didn't accidentally get a shock from them.

[vk6zgo]

Yeah,the standard filament batteries,at least in Oz,were 9v for some radios with series filaments,& 1.5v for others.

The HT batteries were 45v,67.5v & 90v.

Some radios used two 45v in series for 90v,others used them on their own.

The bigger & older valve portables used  the midsized 45v ones & usually a 9v.

Smaller radios often used one 67.5v.or or 90v batteries,as they came in smaller packages.
These also often used "D" cells for filaments,usually two in parallel,or in series,depending on the filament string.

There were still ( early to mid '60s) a lot of large radios outside  the  Mains Electricity supply which used "Farm Packs",which,if I remember correctly,were very two very big 45v batteries & an even larger 9v one.

Other "Country Radios" used 6v car batteries & a mechanical "vibrator" supply.

Others,yet,were designed to run off 32vdc--a common supply voltage from wind or diese/petrol generators
in  isolated farms & Cattle Stations.

[ice595]

its pretty hard to kill your self with a 9v battery
unless its lodged in your head or by eating the chemicals in there.

[Psi]

A 9V battery and a small DC/DC boost reg however, is a totally different story...

[ice595]

A 9V battery and a small DC/DC boost reg however, is a totally different story...

heck, even a camera flash circuit can give a REAL NASTY shock if the capacitor is charged
and they're usually just powered by a single 1.5v alkaline cell 

[peter.mitchell]

cmon, if you get a mains  -> 18~6v transformer and put the primaries on your finger then tap the secondaries on a 9v battery you get a fairly nasty feeling zap.

[Phaedrus]

cmon, if you get a mains  -> 18~6v transformer and put the primaries on your finger then tap the secondaries on a 9v battery you get a fairly nasty feeling zap.

Why do you know this?

[staxquad]

And that's exactly the problem with TASERS, if the probes enter the skin, the victim is dead.  But they won't ever admit to that, too much profit, too much police psychopathy.  So, they explain away the deaths (over 550) that the victims were weakened by whatever excuse available.

[Fraser]

@staxquad,

I totally agree that TASERS are only partially effective..........in cases where a TASER is justified, I far prefer that the Police use a 7.62mm caliber bullet. Nice and reliable.   

Too dangerous ? Oh.... OK, I will be pragmatic and let the Police use a TASER, as that at least gives the target a fighting chance.

What exactly is the reason for raising TASERS and kill rates in a killer 9V battery folk lore thread ? They are somewhat different.


Edit: I have struck out my commnets.......I was feeling grumpy when I read your message and should not have been so sarcastic in my response. Apologies.

[Biff383]

The probes do enter the skin in some of ours. Never tried to get them to hit both thumbs.

[electronics man]

yes there are a few ways you can put it undeload and test the voltage.

[jc101]

A few years ago now someone I know thought it would be an idea to jam 9v battery, terminals down, onto a brillo pad.  Quite impressive, if somewhat hot and damaging to nearby surfaces.  They only tried that the once.

[N2IXK]

The 90 and 135V "B" batteries would give you a little tingle, but for real fun you want one of these guys:

http://www.batteriesinaflash.com/special-application/eveready-493-carbon-zinc-300v-batteries-neda-722-replacement-3pk

Used mainly (in sets of 3 in series)  to power Geiger tubes back in the days before transistorized inverters were practical.

Early electronic photoflash units used a 510V battery to charge the storage capacitor. Have never actually seen one of those puppies, though.

[Galaxyrise]

A few years ago now someone I know thought it would be an idea to jam 9v battery, terminals down, onto a brillo pad.  Quite impressive, if somewhat hot and damaging to nearby surfaces.  They only tried that the once.

That was actually taught to me as a survival fire starting technique in the Boy Scouts. 

[mrkev]

And that's exactly the problem with TASERS, if the probes enter the skin, the victim is dead.  But they won't ever admit to that, too much profit, too much police psychopathy.  So, they explain away the deaths (over 550) that the victims were weakened by whatever excuse available.

Nah. It doesn't matter if the probes pierce the skin. They use charged cap, that doesn't (shouldn't have) enough charge to cause you a serious damage (I would say that healthy person could survive "zap" almost directly to heart). Those deaths are caused usually by shock, fall itself or hiden illness/weakness of heart...

[Redcat]

When I was a little kid we also used the "toung technique" to test 4.5V batteries  . We sometimes did this just for fun  . But I agree, with a boost circuit you could have success. We had to open single-use cameras (1.5V batt) in the lab to get the film out many years ago and I was not the only one who got shocked by the flash circuit  (you normally learn this after 1 or 2 zaps  ). Problem is not so much the 9V battery but the cap and the transformer.

[electronics man]

It the same with CCFL invertors for old fashioned backlights for lcds but the shock isn't that bad if you haven't felt the shock then the smell of burned flesh will soon tell you but it has never done too,ucl harm to me.

[Rigby]

Tasers are why I always wear a chain mail undershirt.  I suppose I should get into some trouble at some point and test it.

I'm joking; I never wear a chain mail undershirt and I get tasered daily because I'm on the lam.

I'm joking; I'm not on the lam, I'm running from authority.

I'm joking; I always keep library books one day past the due date, so I can stick it to The Man.

[leppie]

cmon, if you get a mains  -> 18~6v transformer and put the primaries on your finger then tap the secondaries on a 9v battery you get a fairly nasty feeling zap.

We used to do this is school   It also worked well chaining up several people and let the end guy zap someone.

In hindsight, it was probably not so safe, but the pulse is so short, I doubt it could do any real damage.

[G7PSK]

I remember 15 and  33 volt batteries as well as the 67.5 75.5 80 and 90 volts being sold at the local post office and hardware shops in the 60's.
the 15 and 33 were a little smaller than a pp3 and had a stud each end apart from some radios they were mostly used in hearing aids. There were also big 7.5 volt batteries with plug tapping points used for grid bias and filament power in radios some of the high voltage batteries also had low volt taping for grid bias also some radios used a battery that had a 4 pin socket and supplied filament and HT in one unit, all available now which is a pity as I have a few radios that used them.

[G7PSK]

Been thinking about this (killing yourself with a multimeter ) I have just checked the voltages used in my DMM for resistance the UNI-T 61E voltages vary between 0.3 volts on the M ohm range to 2.9 volts on the K ohm range, why the higher  ranges use lower voltages I don't know. The amprobe meter I have uses around .5 volts. I have not checked my other meters but the old AVO I have states it uses 9 volts on the meg ohm range but as that is used in a resistance bridge the effective voltage is likely a lot lower on the probes. So I think that story about the sailor is most likely a lot of bull.

[Sigmoid]

And that's exactly the problem with TASERS, if the probes enter the skin, the victim is dead.  But they won't ever admit to that, too much profit, too much police psychopathy.  So, they explain away the deaths (over 550) that the victims were weakened by whatever excuse available.

While the incident described in the Darwin award is highly improbable (and apparently debunked by several people on this thread), what you state about tasers is purely ludicrous. A taser has two electrodes separated by an inch or so. The circuit does not close through the heart. (Also, afaik taser electrodes are made to penetrate skin. That's how the thing works 99% of the time.)

Yes, there are fatalities from taser use, mostly people with pre-existing heart conditions. That said, would you prefer that police got back to using live ammo whenever they got scared? I think tasers are a huge improvement.

[hgg]

heck, even a camera flash circuit can give a REAL NASTY shock if the capacitor is charged
and they're usually just powered by a single 1.5v alkaline cell 

I have been zapped by mains in the past, but I will not forget the day I was almost
electrocuted by a camera flash!...      The thing I remember very well is that the shock
from the flash was much worse than the one from the 220V mains. 

DC is way more dangerous than AC.

[Rigby]

DC is way more dangerous than AC.

Eh.  In terms of how much it hurts, I believe it has a lot more to do with the current, voltage, and how exactly it's finding its way into and out of your body than it does AC vs. DC.

[IanB]

DC is way more dangerous than AC.

No, that's an unjustified conclusion. The shock you got from the camera flash was more painful than the previous shocks you have had from the mains. That's as much as you can say.

[ejeffrey]

There is one other physics part of this story that doesn't follow, and which anyone can easily test at home.

Take a jar and fill it with salt water.  This will approximate blood.  Now dip the tips of a multimeter in a few cm apart and measure the resistance.  You will measure a very high resistance -- probably 100s of kohms.  The reason is that there isn't enough surface area in the probe tip to make contact with the relatively poor conductor that is salt water (or blood).  The bulk resistance of a jar of salt water is low, but the point-to-point resistance is dominated by the small area in the neighborhood of the probe tips.

Now get aligator clip leads and a couple of sections of copper braid.  Clip the copper braid to the test leads and immerse them in the salt water.  Presto -- the resistance is probably only a few ohms.

Make sure to wash and thoroughly rinse your probe tips after this experiment to prevent corrosion.

9V can't put a fatal (or even detectable) current through you from a pair of test leads, even if you pierce the skin. At a minimum you would need a much bigger contact area to get dangerous currents.

[mariush]

I touched AC wires with 220v 50 Hz when I was a kid for about 10 seconds, there was supposed to be a light switch behind a fence pole but the owners planned to repaint the fence and the wires were uninsulated without me knowing...
I remember it actually didn't hurt at all, just felt some sort of buzzing in my fingers and the two fingers involved got numb and stayed numb for about 20 minutes.

I did get zapped by a flash camera once, I did touch a power supply mains capacitor once... both times the instant reaction/reflex was to throw away the thing and it mostly hurt my feelings.. can't say that it hurt physically (well, for more than the actual moment)

I also inserted a faulty testing pen in the mains socket and it flew out of my hand all the way to the other wall about 3 meters away. That was a bit scary.

[linux-works]

my scary 9v battery story:

this is the aftermath:



I had left that battery pointing up and sitting in the bedroom on the night table.  I was using it for a headphones amp, iirc.

removed the battery once I was done and left it on the table.  went into another room for a while.

I heard a loud BANG! and came back to find that battery broken open and sitting on its side.  the 'nail' had launched upwards and hit the ceiling!

this only happened once to me in my 50+ yrs of living.  I never saw the insides of a 9v battery before and to be honest, I hope I never do again.

from now on, I will not leave batteries around on tables like that  anymore.  with the chinese making total shit quality and supplying us with all our gear (and power), more and more stuff like this is going to happen ;(

[electronics man]

Batteries (as far as I know) don't just explode something must have happened to it for that to happen

[linux-works]

Batteries (as far as I know) don't just explode something must have happened to it for that to happen

I used the battery, removed it and placed it on the table.

that's ALL I did.  I did not short it out or push it beyond its limits.

they don't usually explode; but this one sure did, I assure you!  it was not even IN USE at the time, which is even stranger!

[electronics man]

Weird

[IanB]

Batteries (as far as I know) don't just explode something must have happened to it for that to happen

It's rare for it to happen, but alkaline batteries do have the possibility of exploding. During operation, and especially when they are depleted, batteries generate bubbles of hydrogen gas that can build up pressure inside the cell. There are two protection mechanisms against this. The first is chemical: there is a catalyst inside the cell that converts hydrogen bubbles back to water. The second is physical: there is a pressure vent in the cell to let any excess pressure out (this looks like a rubber seal at the negative end).

So, if the cell is badly made and excess hydrogen gas builds up inside the cell without being chemically absorbed, and if there is a fault in the pressure seal so that the pressure cannot escape, then the cell could burst with a significant pop.

(By the way, when alkaline batteries leak and spew their contents all over the battery compartment, it is the same gas bubbles that are responsible. The gas pressure builds up inside the cell and forces the cell contents out through the pressure vent.)

[cybermaus]

DC is way more dangerous than AC.

Eh.  In terms of how much it hurts, I believe it has a lot more to do with the current, voltage, and how exactly it's finding its way into and out of your body than it does AC vs. DC.

I once read that DC is sometimes more dangerous, but not because of the bigger 'bite' or potential heart problems. Its because of potential electrolysis in your body. With AC, once they got your heart defibrillized, you are OK (maybe a few burns and a bit of skin graft needed afterward). But DC you may not at all have had heart issues, and a day later die due to internal poisoning.

The article I read said that a proper burn ward knows to ask if it was DC or AC for that reason, especially nowadays with large scale solar panel deployment which often have up to 600V DC in a string.

[electronics man]

DC is way more dangerous than AC.

Eh.  In terms of how much it hurts, I believe it has a lot more to do with the current, voltage, and how exactly it's finding its way into and out of your body than it does AC vs. DC.

I once read that DC is sometimes more dangerous, but not because of the bigger 'bite' or potential heart problems. Its because of potential electrolysis in your body. With AC, once they got your heart defibrillized, you are OK (maybe a few burns and a bit of skin graft needed afterward). But DC you may not at all have had heart issues, and a day later die due to internal poisoning.

The article I read said that a proper burn ward knows to ask if it was DC or AC for that reason, especially nowadays with large scale solar panel deployment which often have up to 600V DC in a string.

What does it do to your electrolytes

[cybermaus]

Maybe I used the wrong word. The DC electric current splits molecules into component molecules.

Is that not Electrolysis?

From what I read, even though AC is just DC alternating, with AC this poisoning problem does not occur. I would assume because the components are put back together as quickly as they get split.

[electronics man]

Yeah it's like charging and discharging a battery the electrons are removed from molecules on the positive peek and the. Put back in on the negative trough

[G7PSK]

DC is more dangerous simply due to muscle contraction, if the muscles contract such that you hold onto the live source there is no relaxation whereas with AC there is a zero point which can leave enough time to be thrown clear, Dc also contracts the heart and holds it contracted again no let up.
I have just measured the amperage from my DMM ohms range varies between 4.5 u amps and 1.5 milli amps depending on rage. I cant see that doing anything to the heart unless you make direct contact with the probes and that act alone will quite likely kill you without the current. Electrolysis will take place just as well with AC as DC you just dont get a pure product, put wires into some saline solution and connect to an AC source you still get gas bubbles at both leads but mixed oxygen and hydrogen.

[cybermaus]

Yes, but do you get the same amount? Or is some of it reacted back?

I also seem to remember a myth-buster episode where they tried to 'rust' their way through some metal bars in a fake jail escape, and found the AC current corroded the iron much less then the AC+diode current. Extra significant as the half-wave rectification means 50% duty cycle only. This would match the body internal poisoning thing.

And indeed, muscle contraction is also an often quoted problem with DC

[Nerull]

I cannot find a single source, credible or otherwise, to back up the claim that DC "poisons" your body. I think you misheard.

[IanB]

Prolonged contact with DC will cause chemical burns at the contact points due to electrolysis. This is one of the dangers of swallowing coin cells. They can cause ulceration of the intestines.

[rjk5378]

I remember it actually didn't hurt at all, just felt some sort of buzzing in my fingers ...

My experience too, the few times I've been "bitten" by mains current. An intense vibration of the muscles, and scary as hell, but not particularly painful. Felt a similar zap once when I was a kid, I assume from surrounding static buildup and not a directly from lightning ... I was walking down our driveway to the mailbox, in the rain, and holding an umbrella. Part of my hand was above the plastic handle and touching the metal rod part of the umbrella. Suddenly I felt the zap, that same buzzing, vibrating feeling. Not painful, but startling.

Bob, KY3R

[cybermaus]

I cannot find a single source, credible or otherwise, to back up the claim that DC "poisons" your body. I think you misheard.

I admit, after searching, neither can I. (I did find references to poisoning and reno failure, but none of them seemed to care or indicate if DC was worse then the AC, or indicate it was a significant problem)

I am pretty sure I did not mishear or misremember. The info came to me in the period I was figuring out what solar panels to install, about a year ago. Maybe it is an urban legend repeated on solar forums. Or maybe it is true, but just too obscure to be found, but known to Solar folk because they primarily work with DC at high voltages.

[Rigby]

Lots of things that are "known" by old-timers turn out to be wrong.  Every old sailor knows that a taught cable snapping under load will cut you in half if it hits you.  Turns out that's not true. 

There are lots of examples of this, and it always seems to be the things that everyone "knows" which are wrong, because no one ever questions them.

[cybermaus]

Convenient that you bring up that specific example. I know the myth-buster episode you probably saw, with the pig.

And while he was not snapped in half, my brother in law last summer did use a too weak chain to pull some device out of the mud with his tractor. It did snap, and the chain did break his femur into 3 parts (two parts and a large shard). And that was a small tractor compared with ocean-liners. Maybe Mythbuster is not the final authority in these matters?

Not that I re-argue the DC current thing. But "old-timers" experiences may sometimes be right, even when going against reason? At the very least any exaggerated myth with a kernel of fact has a useful teaching function: Snapping cables may not cut you in half movie style, but they can cause serious harm, probably right up to terminal if you are really unlucky.

[mrkev]

...And while he was not snapped in half, my brother in law last summer did use a too weak chain to pull some device out of the mud with his tractor. It did snap, and the chain did break his femur into 3 parts (two parts and a large shard). And that was a small tractor compared with ocean-liners. Maybe Mythbuster is not the final authority in these matters?

Big difference between chain and steel rope.... First one has much more mass and can do serious damage, second one is not that heavy and therefore doesn't have that much energy...

[Rigby]

Plenty of energy in both, and I haven't seen the Mythbusters episode in question.  Find one, just one death report in any year of anyone dying by a cable severed under load.  Then, find out if that person was cut in half.

Another example that I have seen on Mythbusters was the "driving with the tailgate down on a truck improves mileage" myth.  MANY people I know KNEW this to be a FACT before Mythbusters proved it wrong.  Many still don't believe the Mythbusters result and continue to drive with their tailgate down or off in the belief that they get better mileage this way.  I tested it at the time and proved that with my truck, the fact that everyone "knew" was, in fact, wrong.

My point isn't that Mythbusters is right or that I'm right; my point is that when you hear something that sounds true and that makes sense to a lot of people, you're not going to find a lot of people that will actively question that something, whatever it is, and simply accept it as fact.  This is how urban legends and myths are created.

Lots of us KNOW that 90 degree traces on PCBs are bad design.  Fact is that they're not bad design, and unless you're into 10s of GHz, the stray capacitance caused by the extra trace area of a 90 degree bend isn't going to do anything.

Just beware of word-of-mouth knowledge that hasn't been proven.  It's often incorrect.

[mariush]

Lots of us KNOW that 90 degree traces on PCBs are bad design.  Fact is that they're not bad design, and unless you're into 10s of GHz, the stray capacitance caused by the extra trace area of a 90 degree bend isn't going to do anything.

I knew about the capacitance (or the lack of importance for simple designs) but I remember 90 degrees traces were also not recommended because it's more difficult to manufacture (traces lifting or something like that) and something about trapping the silkscreen paint and that chemical liquid used to cover the traces into those 90 degrees angles.

[G7PSK]

I have seen steel ropes snap first hand when winching, very nasty indeed, on one occasion the rope cut into the back of the vehicle the winch was mounted on. You never stand next to a wire rope under winching conditions and it is also good idea to put a sack or blanket on the rope as this slows down the recoil if it breaks.

[mrkev]

Plenty of energy in both, and I haven't seen the Mythbusters episode in question.  Find one, just one death report in any year of anyone dying by a cable severed under load.  Then, find out if that person was cut in half.

I was just saying that they are not the same... I almost agree on the rest.

Lots of us KNOW that 90 degree traces on PCBs are bad design.  Fact is that they're not bad design, and unless you're into 10s of GHz, the stray capacitance caused by the extra trace area of a 90 degree bend isn't going to do anything.

Well actually they are bad design, even when you have signals with couple of MHz (f.e. almost any uC)... And it's not about capacitance at all, pointy routes can make antenna so couple of 90 degree bends can increase EMC noise from your design. I don't really remember the actual numbers, but i remember doing the measurment and it's result... Also, even when you generate like 1kHz square from an uC, the time to change the output is usually less than some fraction of internal clock freq, so very high harmonics are present.

[Rigby]

Plenty of energy in both, and I haven't seen the Mythbusters episode in question.  Find one, just one death report in any year of anyone dying by a cable severed under load.  Then, find out if that person was cut in half.

I was just saying that they are not the same... I almost agree on the rest.

Lots of us KNOW that 90 degree traces on PCBs are bad design.  Fact is that they're not bad design, and unless you're into 10s of GHz, the stray capacitance caused by the extra trace area of a 90 degree bend isn't going to do anything.

Well actually they are bad design, even when you have signals with couple of MHz (f.e. almost any uC)... And it's not about capacitance at all, pointy routes can make antenna so couple of 90 degree bends can increase EMC noise from your design. I don't really remember the actual numbers, but i remember doing the measurment and it's result... Also, even when you generate like 1kHz square from an uC, the time to change the output is usually less than some fraction of internal clock freq, so very high harmonics are present.

If that were true, all vias would exhibit this behavior.  Vias are two 90 degree bends adjacent to each other.

[EvilGeniusSkis]

I did the measurements and math.
0.22V 1M? are the output voltage of my DMM and the thumb to thumb resistance of me. Using Ohms law we get 220nA. Not lethal. Even using my dad's old analog multi-meter with 7.7v (5 AAs) output voltage we get 7.7?A, again not lethal. Can anybody find the minimum voltage required to kill someone

[vk6zgo]

What's a "?A"  ?

[BravoV]

Can anybody find the minimum voltage required to kill someone

Sorry ... not very interested, especially its for free.

[EvilGeniusSkis]

What's a "?A"  ?

?A= micro amps, I copied the funny "u" from somewhere else. Up near the top of my fist post on this topic the ? Means ohms as I copied the omega symbol from somewhere else.

Can anybody find the minimum voltage required to kill someone

Sorry ... not very interested, especially its for free.

Look I don't want to kill anyone, I just want to know for the sake of knowing.

[cybermaus]

I came across a few references of that while searching for the poison thing:

http://www.patient.co.uk/doctor/Electrical-Injuries-and-Lightning-Strikes.htm

1 mA = threshold of perception resulting in tingling sensation.
>7-9 mA = muscular tetany preventing release of grip from current source (this is lower for children and women).
20-50 mA = pain and severe breathing difficulties leading to respiratory arrest.
50-100 mA = VF.
>2 A = asystole.

http://www.uic.edu/labs/lightninginjury/treatment.html

[pickle9000]

This is a very interesting read.

[electronics man]

I came across a few references of that while searching for the poison thing:

http://www.patient.co.uk/doctor/Electrical-Injuries-and-Lightning-Strikes.htm

1 mA = threshold of perception resulting in tingling sensation.
>7-9 mA = muscular tetany preventing release of grip from current source (this is lower for children and women).
20-50 mA = pain and severe breathing difficulties leading to respiratory arrest.
50-100 mA = VF.
>2 A = asystole.

http://www.uic.edu/labs/lightninginjury/treatment.html

what I don't understand is that that website says AC is more dangerous than DC

[mrkev]

Plenty of energy in both, and I haven't seen the Mythbusters episode in question.  Find one, just one death report in any year of anyone dying by a cable severed under load.  Then, find out if that person was cut in half.

I was just saying that they are not the same... I almost agree on the rest.

Lots of us KNOW that 90 degree traces on PCBs are bad design.  Fact is that they're not bad design, and unless you're into 10s of GHz, the stray capacitance caused by the extra trace area of a 90 degree bend isn't going to do anything.

Well actually they are bad design, even when you have signals with couple of MHz (f.e. almost any uC)... And it's not about capacitance at all, pointy routes can make antenna so couple of 90 degree bends can increase EMC noise from your design. I don't really remember the actual numbers, but i remember doing the measurment and it's result... Also, even when you generate like 1kHz square from an uC, the time to change the output is usually less than some fraction of internal clock freq, so very high harmonics are present.

If that were true, all vias would exhibit this behavior.  Vias are two 90 degree bends adjacent to each other.

No. Pointy edges can make antenae, vias are not pointy, but 90 degree bends on routes are. The irony is that more precise pcb manufacture is, the more pointy the edge. Btw that's why hi RF layouts don't use bends at all, just curves.

[Rigby]

No. Pointy edges can make antenae, vias are not pointy, but 90 degree bends on routes are. The irony is that more precise pcb manufacture is, the more pointy the edge. Btw that's why hi RF layouts don't use bends at all, just curves.

Pointy traces don't make antennae any more than straight traces do.  If a 90 degree bend makes an antenna, so does a 45 degree bend, it's just a lesser one, and you need two to make a 90 degree turn.  The traces themselves make better antennae than the point on a bend would.  I won't even get into the shape of a trace, when you look at a cross section.  Two long, sharp edges all along the entire trace...  It's all pointy, somehow, and it's much more the frequency of the oscillation and the length of the trace matching the wavelength of the oscillation (or 1/2, 1/4, 1/8, etc) that produces EMI than any pointy trace corner.  This is how intentional emitters such as PCB traces work.  It isn't the 90 degree bends on those, it's the length of the trace being carefully matched to the frequency being emitted.

You're going to have to show some proper evidence if you want me to believe this.  I've heard EMI folks go on and on about how this is a myth and how it's untrue, yet I hear it repeated over and over as if it were known fact.  It's a perpetuated thing that makes sense on the surface but that is never meaningfully tested by hobbyists.

[BravoV]

Bla..bla.. sharp angle PCB trace is bad .... read here -> NO ! You don't need to worry about 90 degrees corner at PCB trace

... or if you feel you have better qualification than Dr. Howard Johnson (His -> Bio), then bring on the proof, meanwhile suggesting to read this too here -> Who's Afraid of the Big Bad Bend? 

Favorite quote from Dr. Howard Johnson : 

Might the electric-field concentration at a sharp, pointy corner create a lot of radiation? Hogwash !

Your average electron smacks into something and changes directions billions of times in a length of 10 mils. Electrons don't have any trouble banging around a corner.

[mrkev]

No. Pointy edges can make antenae, vias are not pointy, but 90 degree bends on routes are. The irony is that more precise pcb manufacture is, the more pointy the edge. Btw that's why hi RF layouts don't use bends at all, just curves.

Pointy traces don't make antennae any more than straight traces do.  If a 90 degree bend makes an antenna, so does a 45 degree bend, it's just a lesser one, and you need two to make a 90 degree turn.  The traces themselves make better antennae than the point on a bend would.  I won't even get into the shape of a trace, when you look at a cross section.  Two long, sharp edges all along the entire trace...  It's all pointy, somehow, and it's much more the frequency of the oscillation and the length of the trace matching the wavelength of the oscillation (or 1/2, 1/4, 1/8, etc) that produces EMI than any pointy trace corner.  This is how intentional emitters such as PCB traces work.  It isn't the 90 degree bends on those, it's the length of the trace being carefully matched to the frequency being emitted.

You're going to have to show some proper evidence if you want me to believe this.  I've heard EMI folks go on and on about how this is a myth and how it's untrue, yet I hear it repeated over and over as if it were known fact.  It's a perpetuated thing that makes sense on the surface but that is never meaningfully tested by hobbyists.

As I wrote, I based this claim on result of measurment. We did that measurment at university in our RF class in EMC chamber... It wasn't significant, but it was above the background. And yes, I may used wrong word, instead of pointy would be better something like "sharp angle".

[gotwood]

Couple of pastes to why in SOME instances AC worse


Direct current (DC), because it moves with continuous motion through a conductor, has the tendency to induce muscular tetanus quite readily. Alternating current (AC), because it alternately reverses direction of motion, provides brief moments of opportunity for an afflicted muscle to relax between alternations. Thus, from the concern of becoming "froze on the circuit," DC is more dangerous than AC.

However, AC's alternating nature has a greater tendency to throw the heart's pacemaker neurons into a condition of fibrillation, whereas DC tends to just make the heart stand still. Once the shock current is halted, a "frozen" heart has a better chance of regaining a normal beat pattern than a fibrillating heart. This is why "defibrillating" equipment used by emergency medics works: the jolt of current supplied by the defibrillator unit is DC, which halts fibrillation and gives the heart a chance to recover.

A domestic power supply voltage (110 or 230 V), 50 or 60 Hz alternating current (AC) through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 30 mA.[4] With direct current (DC), 300 to 500 mA is required

[gotwood]

Another thing ....if I remember correctly the lowest voltage that caused a death was somewhere between 19 and 30 volts...I'd have to ask my instructor again.

The 9V just doesn't have the pressure to push through the body's resistance

[moemoe]

This is why "defibrillating" equipment used by emergency medics works: the jolt of current supplied by the defibrillator unit is DC, which halts fibrillation and gives the heart a chance to recover.

That's neither totally right nor totally wrong: Todays defibrillator are all biphasic units, which means they provide one shock in either polarity. This is mainly because of lower energy needed in comparison to a monophasic defibrillator to achieve the same result.

You find many marketing blahblah here, but http://www.resuscitationcentral.com/defibrillation/biphasic-waveform/ seems to be a rather good short summary.

[Rigby]

As I wrote, I based this claim on result of measurment. We did that measurment at university in our RF class in EMC chamber... It wasn't significant, but it was above the background. And yes, I may used wrong word, instead of pointy would be better something like "sharp angle".

Ok, I won't argue that EMI is produced.  I won't argue that at all.  At what point does this EMI become a problem, though?  What power levels and what frequencies did you test at?  Do you have the data?  I'd absolutely love to see it.  edit: I say this from a genuine position of curiosity, not one of challenge or disbelief.

One needs to be at a high power and very high frequencies in order for the points that 90 degree traces make to become a problem, and even then the problem is not likely to be RF, but lots of stray capacitance.  A hobbyist is very unlikely to ever encounter this, and if a hobbyist is doing something where a 90 degree trace would affect the outcome, they wouldn't be using an FR4 PCB at all, because at those frequencies FR4 isn't that great of a dielectric.  There is absolutely zero point in worrying about it if it is not sufficient to cause a problem somewhere down the line. 

I don't understand why, but many people feel that they should worry about lots of things that have far too low of a "return on investment" instead of the more important things.  This is discussed on The Amp Hour occasionally when they discuss doing something very dangerous, and no one argues, but people will fight endlessly about what color to paint the bathroom.  That's not the exact analogy, I can't remember the exact analogy, but it's something like that.  My participation in this thread is coming to mind as another example...

I categorize worrying about 90 degree traces as "premature optimization."  Worrying about something that doesn't matter or worrying about it before it is appropriate to worry about it.

[G7PSK]

I thought the thing about sharp bends in pcb traces at RF is due to the same reason it is not a good idea to have sharp bends in aerials/antennas.
The signal sees the sharp bend as the end of the line.

[BravoV]

I thought the thing about sharp bends in pcb traces at RF is due to the same reason it is not a good idea to have sharp bends in aerials/antennas.
The signal sees the sharp bend as the end of the line.

Hear what Dr. Howard Johnson said about that -> #77 – An Interview with Dr. Howard Johnson – Winsome Waveform Wizardry