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Hi.
I am building a coilgun with some capacitors, and I would like to use a PIC handle the charging process. I read that gigh voltage capacitors are dangeroud, but what is it that makes electricity dangerous? If you were to pu 10 or 15 9-volt-batteries in series, and touch the contacts, would it shock you? Is it safe to build a capacitor bank (about 47000uf) at 25vdc?
What is the difference (speaking about dangers) betweeb DC and AC?
Thanks in advance!!!!
Manuel
Hi Manuel,Electricity thru people, is a strange acting phenomenon. It is difficult to predict what dangers or problems someone might run into making a coil-gun. It is a subject you should research in full before you start your project. There are better places to find out about general electric safety.Quote:
Originally Posted by manumenzella
Capacitors have a “bad rap” because they can store a charge and catch unsuspecting victims days after the power has been removed. Proper circuit design and proper respect can keep them from surprising you. The coil can also give a nasty surprise as well.
10 to 15 9V batteries wired in series, would be slightly more than 90 to 135 Volts. Most professionals in “hands on” electronics, work around that amount of voltage on a regular basis. With nominal conventional precautions, this is considered a normal workday. Note that they do not touch the conductors barehanded (so I guess, “hands on”, may be just an expression). Wikipedia states “...death has occurred from supplies as low as 32 volts...”!
There is some beginning information and references to information you should learn. Wikipedia has a good start. http://en.wikipedia.org/wiki/Electric_shock There is some discussion on AC / DC comparisons too.
This should not be read as an all doom and gloom reply. It’s just your post sound like you may not have had much “hands on” experience. Do your homework and then you will be launching things on the coil-gun.
I am sure others will be adding to the discussion.
-Adam-
Here is something to think about.
Go to your local fire department and talk to the paramedics about the battery powered defibrillator's that they use.
Anything above 48 volts is considered dangerous. I can not say exactly how it effects the muscular system, but having had close calls with DC and AC it seems like DC is more dangerous at a lower voltage than AC. DC as the name implies is constant and would not allow me to let go at 90 volts. ( co worker had to throw a switch). AC swinging through Zero must be the reason I was able to break away from 240 volts.
I have heard some say it is the amps and others say voltage is what you should be concerned with. Personally I think it is watts.
Is there a DOCTOR in the house.:)
History has never been a strong suit for me. But as I recall, back in the late 1800's there was a fierce battle between Edison and Westinghouse.
Edison had a DC electrical system wired up to an entire street full of electric lights. And his competition (Westinghouse) wanted to use an AC system because it could transmit the power over longer distances than DC could.
Well, Edison wanted no part of an AC system, so he set out to prove to everyone that AC voltages were too dangerous, and designed an "Electric Chair" using AC power, to show how easy it was to kill something if it wasn't DC.
Obviously, the ploy didn't work. The need for long distance transmission outweighed the potential for death. But the chair stuck around, and was used for both people and animals for many decades to come.
The standard rule for death by electrocution, is that 100 MA thru the heart, will stop the heart from beating. Actually causing death by asphyxia (lack of oxygen) rather than killing you outright with the voltage. It doesn't really matter if it's DC or AC. 100 MA will do it. But since alot of how voltage travels through the body depends on the capacitance of the body (among other things) AC gets through a lot easier.
If it doesn't go directly through the heart, you can withstand many AMPS and still survive. It'll hurt like hell, but it probably won't kill you.
Personally, I've been hit with 8,000V DC from the anode of a klystron amplifier.
Knocked me on my butt, and threw me backwards about 10-15 feet.
After regaining my senses and thinking I was lucky to be alive, everyone around me just laughed, and said ... That power supply may have 8,000V, but it only puts out 100ma, so you were never going to die, ya wimp.
I've also been locked in a "death grip" from a 90VAC telephone ringer voltage. Somebody dialed in while I was installing a phone jack. Fortunately, phones don't ring continuously. But that one rang too long for my comfort.
So I guess the moral here is, ... You must treat ALL electricity as if it's going to kill you. If you don't, some day you'll grab a wire you thought was low voltage, and it'll be the last thing you do. Cause it was really 220VAC.
_
I'm going to underscore what Darrel has already stated--always treat electricity with respect!
My knowledge of history isn't all that great, either, but I believe the AC versus DC issue began with Edison versus Nikola Tesla; Westinghouse came in a little later.
On one hand, I routinely test 9-volt batteries by touching the terminals to the end of my tongue. In high school, I knew a TV repairman who could tell whether the AC line voltage was right by touching two bare wires with one hand, and he died of cancer at age 81. And a former co-worker of mine, about four years ago, survived 28,000 volts DC (television transmitter) but had some nasty burns and many skin grafts after. He's also suffered some subsequent neurological problems. (If you think I mean, "He's not as sharp as he used to be," you're right.)
When I was a kid, I learned the "one hand in your pocket" rule, and I still use it. (When you're working with a live circuit, keep one hand in your pocket.) All my close encounters with electricity have been with one hand--including about 1000 watts of RF across the palm of my right hand (and a burn). The scariest shock I ever got was from 90 volts of AC telephone ringer--again, just my right hand, but it wanted to grab and hold on.
And, of course, whenever possible, work on the circuit or equipment with the power off!
My understanding has always been that current kills, not voltage--otherwise we'd all keel over and croak when we get that static shock from a doorknob on a really dry day. The big difference, supposedly, is that low-frequency AC disrupts the electrical rhythm of the human heart, so it is much more dangerous at comparatively lower voltages; high-voltage DC just cooks you.
Don't be a resistor! (Very bad pun . . . )
Hi,
FOR ALUMINUM ELECTROLYTIC CAPACITORS, CAUTION:
Personnel injury or property damage may result from a capacitor explosion or the expulsion
of electrolyte due to mechanical or electrical disruption of the capacitor. Contact with
liquid or vapor is to be avoided. In the event of contact with the skin or eyes, or accidental
oral ingestion, action may be taken as follows:
Emergency treatment is as follows:
Skin Contact: May result in irritation.
Flush and wash thoroughly with soap and water immediately.
Eye Contact: Contact lenses must be removed at once.
Immediately flush the open eye(s) with large amounts of water and seek immediate medical attention.
Oral Ingestion: As an interim emergency measure, administer warm water or milk, induce vomiting and
seek immediate medical attention.
Vapors: Avoid inhalation of vapors. Ventilate area thoroughly and go to fresh air.
* * * * *
Often risk takers are not aware of the danger they put themselves in:
http://www.youtube.com/watch?v=50YaOt_C2n0
Best regards,
Luciano
Good old YouTube.
Blowing up capacitors.
Seems to be one of the favorite pass times there. :)
http://www.youtube.com/results?searc...plod+capacitor
_
Like all others said before its always wise to be carefull and if possible work without power applied .
However you will have to test you're projects so there will always be moments you will work under voltage .
Battery's (and capacitors) store energy which can take hours to charge but depending on what type of battery it is can discharge in seconds .
Don't let youreself be fooled by a nickel cadnium penlight for instance ,you might not expect it .
But we measured peaks over 200 Ampere from a AA Nicad battery .
Since that day i got a lot more carefull with throwing walkman battery's in my pockets .
What i mean to say is this low voltage doesnt mean no danger ,the danger just lies more in the burnwounds .
With battery's in series however 120 volts & up battery's can be very dangerous .
Like before the peakcurrents delivered can be very very high .
Simple car battery's are well capable of delivering 200 Ampere or more (you will have a voltage drop though) .
10 carbattery's in series delivering 120 (138) volt imagine youreself dropping a screwdriver .
I would put my money on the battery that screwdriver goes up in smoke .
Long ago at work i once made a wiring error with 12 gel battery's in series (12 volt 7Ah) a 6mm wire just dissapeared partly ,i was lucky black hands, black face wire & accu destroyed but i wasnt hurted .
Just be carefull with batterypowered projects .
Use fuses were possible and if unfused is needed switch on remotely (saves youre eyebrows).
Goodluck :)
I usually sense 100 volts floating in air with my oscilloscope, it amps what dangerous not volts
Hi,
The current flowing through your body is determined by
the electrical resistance of the body and the voltage
applied.
Best regards,
Luciano
* * * *
Amount of Body Resistance.
Your body resistance varies greatly in different parts of your body.
A value of 1500 ohms is commonly used as the resistance between major
extremities of an average human body: hand to hand, or hand to foot.
Let’s use Ohm’s Law to figure how much current would flow through
your body if you accidentally grabbed a wire carrying 120 volts
alternating current (vac).
Ohm’s Law for figuring current is I = E/R.
Let E = 120 VAC— The voltage you grabbed
Let R = 1500 Ohms—Your (average) body resistance
Now let’s compute it:
I = 120/1500 = .080 amperes (80 milliamperes).
I = 80 milliamperes. So if you grabbed a 120-vac wire, 80 milliamperes
of current would flow through your body.
=============================================
Human reaction (at 60Hz)
1.1 milliamperes: PERCEPTION - A slight tingling sensation.
10 milliamperes: CAN'T LET GO - Arm and hand muscles close involuntarily. (120 lb. person).
16 milliamperes: CAN'T LET GO (175 lb. person).
18 milliamperes: CAN'T BREATHE - Paralysis of the chest muscles.
65 milliamperes: HEART FIBRILLATION - Rapid irregular contractions of the heart muscles. (Could be fatal).
=============================================
Now use the above table to determine the effect of 80 milliamperes
of electric shock. You can see that you may not be around long enough
to grab any more wires. You grabbed 80 milliamps of current!
That’s 15 milliamps beyond what could be fatal. It’s also 70 milliamps
beyond the can’t- let-go threshold, and 62 milliamps beyond what
is needed to cause you to stop breathing. It’s important to remember that
the 1500 ohms is just an average value. Body resistance varies from
person to person and may often be LESS than 1500 ohms. When your
skin is moist, your body resistance could be as low as 300 ohms. Also, breaks
in your skin at the point of contact reduce your skin resistance to nearly
zero. Skin resistance is only important when you’re handling voltages of
less than 240 volts. If you get shocked by more than 240 volts, the voltage
arc will burn through your skin and leave deep third-degree bums where it
enters your body.
Time of Current Flow.
The longer you’re being shocked, the more chance there is for your heart to
begin fibrillation. Fibrillation is the shocking of your heart into a useless
flutter. Most people who die from electric shock die from fibrillation.
Fibrillation in a normal adult is unlikely if the current in milliamperes is
less than 116/t, where t is the shock duration in seconds. The longer you
are shocked, the less current is needed to cause heart fibrillation. Here are
some examples of shock current levels and durations that would cause fibrillation:
21 milliamperes for 30 seconds
44 milliamperes for 7 seconds
* * *
How much electricity will kill me?
This is an often asked question. How many Volts? How many Amps? To answer this we need to look at kinds of damage an electric current can cause.
The first and least likely one is tissue damage as a result of burning. Ignoring other electrical effects such as microwave cooking and high frequency transmitter outputs, and looking just at direct electrical contact, burning damage is only likely from very high voltage sources in excess of 1000V for example Eskom power lines and Transnet overhead rail power systems, and as we are not likely to come into contact with these, we will just look at mains borne 220V/380V systems.
This leaves us the most likely cause of death which is the failure of the heart muscle through fibrillation and this will occur when a (generally accepted) current of between 60mA and 1A passes through the heart. The heart's electrical system gets disrupted and it stops pumping. So you might say it's the current that kills you, but wait, to get such a current to pass through the heart we have to satisfy Ohm's law which tells us that to get a current through a resistance (the body and skin resistance) we need a certain voltage. (current = voltage ÷ resistance).
This leads us to the source of the variability: What is the resistance of the body?
If you were to stick a drip needle in each arm and measure the resistance between them, you could get a resistance of as little as 500Ω. To get a current of 60mA to pass through this you would need only 30V! This is why electro-medical equipment has to be so carefully designed. Your skin resistance varies greatly with the dampness, sweat and salinity, and can vary from 1000Ω to 30,000 Ω.
At 1000Ω you would need a voltage of only 60V to be lethal, on the other hand with very dry clean skin at 30,000Ω a voltage of 220V would only produce a tingling 7mA and this is why many folks have had shocks which did them no harm. So at 220V you need a body resistance less than 3700Ω to kill you. Of more concern at higher voltages greater than 500V, skin puncturing can occur, causing a now much lower resistance and potential fatalities.
So we can now answer the question "Is it the current or is it the voltage that kills you?"
Certainly it is the current, but for it to reach a lethal level we need the voltage to drive it. To be safe, treat anything over 24V with caution, and anything over 50V with a great deal of respect. Anything over 100V is certainly able to kill you.
Graham Lambert
Dont forget that electrons ALWAYS travel by least resistive path, if you touch hight voltage most electrons will not go deeper than you skin and travel from one point to another by skin, so you heart will not sense a tenth % of current you skin experience, So use this property when working with hight voltage use just 1 hand and in worst situation you will bun you hand not heart.
Dont forget that (current = voltage ÷ resistance) is ideal but dont apply to real world, all powersuply have limited amount of amps it can supply and usually it less than few amps, TV flyback transformer output 20,000 ~ 100,000 Volts but limited to only few miliamps of current, and I accidentally shock myself many times, it painful especially arm to arm but not dangerous.
but be careful with capacitors (current = voltage ÷ resistance) apply almost as ideal to them , it can give so many amps for a millisecond, that it will literally trow you into sealing
And there is one more issue, in real world usually it not voltage or ampers that do damage, it you muscle, shocking yourself will contract them really fast and just imagine stand near glass window, you can break it and cut youself badly.
@therian
You wrote:
Dont forget that electrons ALWAYS travel by least resistive path, if you touch hight voltage
most electrons will not go deeper than you skin and travel from one point to another by skin, so
you heart will not sense a tenth % of current you skin experience, So use this property when
working with hight voltage use just 1 hand and in worst situation you will bun you hand not heart.
And then you also wrote:
And there is one more issue, in real world usually it not voltage or ampers that do damage,
it you muscle, shocking yourself will contract them really fast and just imagine stand near
glass window, you can break it and cut youself badly.
* * *
What about if you are wearing leather sole shoes and your feet and soles are humid and the floor
is conductive? Will your one hand method work? I don't think so.
What about if while your are working with your one hand method you get shocked and an uncontrolled
muscle contraction makes your other hand touch the rest of the circuit?
The skin is not electrically insulated from the rest of the body!
(See sweat glands and sweat pores, see sebaceous glands).
http://www.sun-togs.co.uk/images/sce/skin1.jpg
* * *
There are young people reading this thread so please do not post information that could be dangerous.
Best regards,
Luciano
What about if you are wearing leather sole shoes and your feet and soles are humid and the floor
is conductive? Will your one hand method work? I don't think so.
Will the 2 hands method work better ? =)
What about if while your are working with your one hand method you get shocked and an uncontrolled
muscle contraction makes your other hand touch the rest of the circuit?
What about if while your are working with your 2 hands method you get shocked and an uncontrolled
muscle contraction makes your head touch the rest of the circuit? =)
The skin is not electrically insulated from the rest of the body!
it not but it usually salty enough to be good conductor
I knew someone will say about floor contact but I believe people sane enough not to touch main power staying in a salty water. I told one hand method it safer not total safe, but chance of dying reduce greatly so why not to use this opportunity.
The only safe way to work around anything above 40 volts is to follow lock out / tag out procedures.Quote:
I knew someone will say about floor contact but I believe people sane enough not to touch main power staying in a salty water. I told one hand method it safer not total safe, but chance of dying reduce greatly so why not to use this opportunity.
I am the operations manager for a large chemical company and electricity is but one of the many hazards my crew and myself have to contend with. We have set safety standards so that everyone goes home to their family at the end of the day.
You check as many times as needed to make sure the system is "dead" and that there is no way the system can become "live". This goes for computers that control the systems also. Do you really want to put your life in the hands of a faulty relay?
There is ABSOLUTELY no reason to work on a "live" system.
I have heard the "one hand method" more times than I care to count. When I do hear it the person who said it is off the job.
Ma'am, I am sorry to tell you this... you husband is dead. It could have been worse though. He could have been using both hands.