Killer capacitors - what's the true
Marion D. Kitchens
While most people normally don't think about it, there have been numbers of
people killed by as little as 25 volts -- that under the right (wrong?)
conditions. So do be careful of any high voltage, even a 100 or so. Yes, I
too have survived several higher voltages "accidents" but still.......
There are many variables, so it is not possible to simply state a voltage
and or charge on a cap that can do you in. I stay away from them all if
they are charged with 100 or more volts!
Rolf Roubs wrote:
> Killer capacitors - what's the true
>
> In electronic plans/circuits (manly strobe, laser, tesla -circuits)you
> often see notes regarding safety.
> In there they always warn you about the potential a capacitor has, even
> when it is disconnected. They talk about that if you are not careful it
> could kill you instantly!?
> Is that really possible ? (if I, for example, touched a loaded
> 440uF/350V ???)
> Yes - there is a violent sounding spark if I short it - but is that
> really enough energy to kill a normal person in good condition?
> I remember touching a live wire (220V/50Hz) when I was a child and I
> survived it !?
> Or - Why do they use 10'000 volts and 2 amps over quite a time for the
> death penalty (and they can still not be sure that the victim is death
> after the first shock)!
> Well - Now I want to know it for sure and in a understandable way : From
> what load on is a capacitor dangerous !!!!!!!??????????????
> Please don't talk about Joules or Watt ! Better tell me about
>
> xxxMicroFarad/yyyVolts - throws you back to the next wall
> xxxMicroFarad/yyyVolts - is quite dangerous
> xxxMicroFarad/yyyVolts - is very dangerous
> xxxMicroFarad/yyyVolts - probably kills you
> xxxMicroFarad/yyyVolts - kills you for sure
> xxxMicroFarad/yyyVolts - is enough to roast an elephant
> etc.
>
> I hope my questions does not sound too stupid - but I am really
> concerned about and don't find an answer in the books I have access to.
>
> Any help very appreciated !!! :) - Thanks
>
> Please also email me to : xy...@iname.com
Geoff S. Drayson
A most important factor is the path the current takes.
The most DANGEROUS path is one that passes the current on a path near to the
heart. This typically occurs when you touch a HV point, while your other hand
is a earth. (hence the idea that you keep one hand "in your pocket" !!!)
I know a person who got a HV shock from a Radar Transmitter.... it threw him
across the room, and opened up a wound down his arm, clean to the bone... you
could see the bone... but he survived. If his other hand has been grounded,
he would most likely have been killed.
Geoff
Cam McCrackin
I can't believe people are playing around with electricity and don't even
know the safety rules. VOLTAGE DOES NOT KILL!!! AMPERAGE DOES!!!!!
Anything over about 25 mA is considered lethal. Remember, that is 25mA
through your heart. ANY shock at ANY voltage can be lethal under the right
conditions. Even a 1.5V dry cell is enough to send a heart into convulsions
if connected directly to the cardial nerves.
The voltage only increases the potential (pressure) for Amperage (flow) to
kill. For instance, if the resistance of your body is reduced by a special
(conductive) medicinal cream, a defibrolator can start or stop a heart at
will. Also, if water were placed on the skin, the same result would occur.
In short, (no pun intended!), If you don't know what you're doing with
electricity, maybe you should find some safety literature on the suject
before continuing.
By the way, to answer the capacitor question.......
The more uF a capacitor has, the higher the potential over time it can
store. All it does with more capacity is lenthen the duration of the shock.
The longer the duration, the better the chance of making the skin conduct,
therefore the more chance of getting killed. JUST BE CAREFUL!
C. McCrackin
mccr...@vaxxine.com
Steven Leffler
[Newsgroups line trimmed.]
Rolf Roubs wrote:
>
> Killer capacitors - what's the true
>
> In electronic plans/circuits (manly strobe, laser, tesla -circuits)you
> often see notes regarding safety.
> In there they always warn you about the potential a capacitor has, even
> when it is disconnected. They talk about that if you are not careful it
> could kill you instantly!?
> Is that really possible ?
Yes, very.
...
> Yes - there is a violent sounding spark if I short it - but is that
> really enough energy to kill a normal person in good condition?
...
> Well - Now I want to know it for sure and in a understandable way : From
> what load on is a capacitor dangerous !!!!!!!??????????????
> Please don't talk about Joules or Watt ! Better tell me about
>
> xxxMicroFarad/yyyVolts
It's not quite that simple, because the total energy or the voltage
is NOT what determines whether the capacitor kills you. In most cases,
it is the current that determines the effect of the electricity on your
body, as well as the path the current takes through you. Here's a table
giving the effect as a function of current (approximate, of course).
I've taken this from a local workplace safety manual. The effects are
for continuous current, but they give some idea of the type of effect
that's likely from a brief shock.
Current Effect
======= ======
< 1 mA You probably won't even feel it.
1-8 mA Shock felt, not painful. No loss of muscular control.
8-15 mA Painful shock. No loss of muscular control.
15-20 mA Painful shock. Muscular control lost--you may not be able to
let go.
20-50 mA Painful. Severe muscular contractions. Breathing difficult.
50-200 mA Possible ventricular fibrillation -> death. Muscular
contraction and
nerve damage.
>200 mA Severe burns and muscular contractions. Heart stops for the
duration
of the shock.
In regards to your question, it's the last two categories that are
most significant for a brief shock. If the current is over 200 mA, you
will be badly burned but will probably survive, even if the current
passes through your heart. (The heart restarts itself after the shock
is over.) Ironically, it's LOWER current that's fatal. If the current
is between 50 and 200 mA and passes through your heart the heart may go
into ventricular fibrillation. This is fatal. CPR will not help. A
ventricular defibrillator would save you, but only if administered
within a few minutes. By the time the paramedics get there, you're
dead.
Now, the current that passes through you depends on two things: the
voltage and the resistance of your body. The latter varies tremendously
depending on the circumstances. Dry skin has a resistance of 100,000 to
600,000 Ohms. Wet skin can have a resistance as low as 1000 Ohms. Once
past the skin the resistance through the rest of your body is a few
hundred Ohms. If your hands are wet and you grab a grounded surface with
one hand and a charged capacitor with the other, 100 to 400 volts falls
nicely within the lethal range. Higher voltages are more likely to give
you a nasty burn but not kill you. There have been rare cases of
extremely unlucky people being killed by a 50 V shock.
Now, the size of the capacitor determines how long the shock lasts.
Crunching a few numbers, I get that the minimum *likely* lethal
combination is about 0.4 microfarad, 100 V, assuming it takes around a
millisecond to produce ventricular fibrillation (This is a total
guess). If you want to be on the safe side, avoid contact with ANY
capacitor that's charged to more than 50 V.
Note that the effects depend tremendously on how wet your skin is and
where you're grounded (ie. what path the current takes through your
body.) Lots of people have survived 120V or 220V shocks. Lots of people
have been killed by them. Just ask yourself: "Do I feel lucky?"
> Or - Why do they use 10'000 volts and 2 amps over quite a time for the
> death penalty (and they can still not be sure that the victim is death
> after the first shock)!
I think that it's because they don't want to depend on the
ventricular fibrillation effect, especially since it takes several
minutes to kill the person, during which time the individual may be
conscious and in agony. The high voltage and current passing through
the brain probably guarantees that the person is unconscious
immediately, and will more reliably kill the individual than
fibrillation, since the damage is done by simple burning of tissue,
rather than upsetting the heart.
--
--------------------------------------------------------------------------
Steven Leffler | Department of Physics & Astronomy
| University of British Columbia
lef...@physics.ubc.ca | Vancouver, BC V6T 1Z1 CANADA
http://www.physics.ubc.ca/~leffler | (604)822-2894 FAX: (604)822-5324
--------------------------------------------------------------------------
W Letendre
Marion D. Kitchens wrote:
>
> While most people normally don't think about it, there have been numbers of
> people killed by as little as 25 volts -- that under the right (wrong?)
> conditions. So do be careful of any high voltage, even a 100 or so. Yes, I
> too have survived several higher voltages "accidents" but still.......
> There are many variables, so it is not possible to simply state a voltage
> and or charge on a cap that can do you in. I stay away from them all if
> they are charged with 100 or more volts!
>
Knew of one unfortunate kid, an Engineerin' student, who electrocuted
himself with a D cell. Kid was takin' an intro electronics project lab,
doin' exercise on use of VOM (old fashioned DMM...). Exercise had
student measure skin resistance, holding one probe in each hand, then
asked, as rhetorical question, what fraction of this resistance might be
attributed to contact resistance versus body's internal resistance.
Kid decided to find out. Stuck a pin into index finger on each hand,
wired himself up on low resitance scale.
Those old Simpson 260's used a D cell as the voltage source for
resistance measurements, all of a volt and a half. Turned out, though,
kid's internal body resistance was low enough (musta been only an ohm or
so) to allow that D cell to push enough current through his chest to
cause cardiac fib. He was doin' the lab exercise at night, no one else
in lab. Janitors found him the next mornin'...
So, mind your P's & Q's, keep one hand in pocket when probin' HV
circuits. Warning labels are not put on (entirely) to keep folks in
Legal Department happy!
W Letendre
Dir Eng
NEAT
狂人
In <6hrdm9$ok9$1...@news.vaxxine.com>, on 04/24/98
>I can't believe people are playing around with electricity and don't even
>know the safety rules. VOLTAGE DOES NOT KILL!!! AMPERAGE DOES!!!!!
Agreed, static electricity only give you a nasty jump, but no more, and
those often reach the tens of thousands of volts easily...
>Anything over about 25 mA is considered lethal. Remember, that is 25mA
>through your heart. ANY shock at ANY voltage can be lethal under the right
>conditions. Even a 1.5V dry cell is enough to send a heart into
>convulsions if connected directly to the cardial nerves.
It is kind of like shorting out the CPU of your computer... however, a 1+
amp shock delivered from the skin can sometimes shut down the heart instead
of sending it into a state of confusion... which would sometimes surprise
people that more amperage might not always kill faster or better... (okay,
maybe better is not the word, but I'm not sure which other one that I can
really use there).
>The voltage only increases the potential (pressure) for Amperage (flow) to
>kill. For instance, if the resistance of your body is reduced by a special
>(conductive) medicinal cream, a defibrolator can start or stop a heart at
>will. Also, if water were placed on the skin, the same result would occur.
There are salts and stuff on your skin, which would turn into electrolytes
with the addition of water... thus making it very easy to hurt people...
>In short, (no pun intended!), If you don't know what you're doing with
>electricity, maybe you should find some safety literature on the suject
>before continuing.
Agreed... AFAIK, it takes about 10 thousand volts for electricity to travel
on cm in air, is this right?
--
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Rolf Roubs
Killer capacitors - what's the true
In electronic plans/circuits (manly strobe, laser, tesla -circuits)you
often see notes regarding safety.
In there they always warn you about the potential a capacitor has, even
when it is disconnected. They talk about that if you are not careful it
could kill you instantly!?
Is that really possible ? (if I, for example, touched a loaded
440uF/350V ???)
Yes - there is a violent sounding spark if I short it - but is that
really enough energy to kill a normal person in good condition?
I remember touching a live wire (220V/50Hz) when I was a child and I
survived it !?
Or - Why do they use 10'000 volts and 2 amps over quite a time for the
death penalty (and they can still not be sure that the victim is death
after the first shock)!
Well - Now I want to know it for sure and in a understandable way : From
what load on is a capacitor dangerous !!!!!!!??????????????
Please don't talk about Joules or Watt ! Better tell me about
xxxMicroFarad/yyyVolts - throws you back to the next wall
Don Klipstein
Steven Leffler (lef...@physics.ubc.ca) wrote, in part:
: Current Effect
: ======= ======
: < 1 mA You probably won't even feel it.
Depends on contact area. Half a milliamp 60 Hz AC through a small area
of skin is easily felt.
: 1-8 mA Shock felt, not painful. No loss of muscular control.
I had about 5 mA 60 Hz AC once - it hurts.
: 8-15 mA Painful shock. No loss of muscular control.
Depends on how the current is distributed through the body, and your
mileage may vary.
: 15-20 mA Painful shock. Muscular control lost--you may not be able to
: let go.
: 20-50 mA Painful. Severe muscular contractions. Breathing difficult.
People sometimes die from this.
: 50-200 mA Possible ventricular fibrillation -> death. Muscular
: contraction and nerve damage.
Probably true on an average, but response can vary widely.
This varies with frequency, etc. and 50/60 Hz AC is particularly bad.
Pulsating DC and capacitor discharges are bad. Steady DC is not as bad,
and the higher survival rate (but under 100%) leads to horror stories
spread by horribly burned survivors.
: >200 mA Severe burns and muscular contractions. Heart stops for the
: duration of the shock.
: If the current is over 200 mA, you
: will be badly burned but will probably survive, even if the current
: passes through your heart. (The heart restarts itself after the shock
: is over.) Ironically, it's LOWER current that's fatal.
I have heard elsewhere that the current most likely to cause heart
fibrillation (for an arm-to-arm shock) is a broad range from 100 mA to a
whole amp, and there is a lesser but significant chance of fibrillation
well outside this range (up to 5 amps or more on the high end). And with
high current shocks you have to worry about cardiac arrest as well as
fibrillation. Even a properly applied defibrilator does not always
affect the heart as planned with the first jolt.
Results may vary with the timing in the heartbeat cycle at which the
shock is applied.
The hazard is significant well outside the .1 to 1 amp range on the low
end also - I have heard as little as 5 mA not guaranteed safe, and 13 mA
having a significant danger (although probably survivable).
- Don Klipstein (d...@misty.com)
David VanHorn
>Please don't talk about Joules or Watt ! Better tell me about
>
>xxxMicroFarad/yyyVolts - throws you back to the next wall
>xxxMicroFarad/yyyVolts - is quite dangerous
>xxxMicroFarad/yyyVolts - is very dangerous
>xxxMicroFarad/yyyVolts - probably kills you
>xxxMicroFarad/yyyVolts - kills you for sure
>xxxMicroFarad/yyyVolts - is enough to roast an elephant
>etc.
V * V * (C/2) = Joules.. What you're asking for above is ratings in Joules.
Steven Leffler
> : 15-20 mA Painful shock. Muscular control lost--you may not be able to
> : let go.
> : 20-50 mA Painful. Severe muscular contractions. Breathing difficult.
>
> People sometimes die from this.
Yes, directly or indirectly. One example given in the safety workshop
where I got much of this info, was an electrician who was doing wiring
on an aluminum ladder set on a relatively fresh concrete floor (still
damp). He got a shock in this range, fell off the ladder, and was
killed. Another hazard is that the muscular contractions can cause you
to contact ground with another part of your body, possibly increasing
the current through your heart.
> And with
> high current shocks you have to worry about cardiac arrest as well as
> fibrillation.
This is true. I certainly didn't mean to imply that higher currents
were harmless. They are less likely to cause fibrillation, but they
have their own hazards.
John Woodgate
In article <35411453...@iname.com>, Rolf Roubs <xy...@iname.com>
writes
>Well - Now I want to know it for sure and in a understandable way : From
>what load on is a capacitor dangerous !!!!!!!??????????????
>
>xxxMicroFarad/yyyVolts - throws you back to the next wall
>xxxMicroFarad/yyyVolts - is quite dangerous
>xxxMicroFarad/yyyVolts - is very dangerous
>xxxMicroFarad/yyyVolts - probably kills you
>xxxMicroFarad/yyyVolts - kills you for sure
>xxxMicroFarad/yyyVolts - is enough to roast an elephant
>etc.
The problem is that it depends on YOUR state of health and WHERE the
discharge current flows, even whether your hands are wet or not.
Anything below 100 V PROBABLY will only be unpleasant. Anything above
100 V/10 uF COULD be lethal.
The charge energy in joules is just 0.5CV^2 - not so difficult. But
there is no definite relationship between charge energy and biological
effect.
--
Regards, John Woodgate, Phone +44 (0)1268 747839 Fax +44 (0)1268 777124.
OOO - Own Opinions Only. You can fool all of the people some of the time, but
you can't please some of the people any of the time.
Lasse Langwadt Christensen
In article <6hrdm9$ok9$1...@news.vaxxine.com>,
"Cam McCrackin" <mccr...@vaxxine.com> writes:
> I can't believe people are playing around with electricity and don't even
> know the safety rules. VOLTAGE DOES NOT KILL!!! AMPERAGE DOES!!!!!
>
> through your heart. ANY shock at ANY voltage can be lethal under the right
> conditions. Even a 1.5V dry cell is enough to send a heart into convulsions
> if connected directly to the cardial nerves.
>
> kill. For instance, if the resistance of your body is reduced by a special
> (conductive) medicinal cream, a defibrolator can start or stop a heart at
> will. Also, if water were placed on the skin, the same result would occur.
>
> electricity, maybe you should find some safety literature on the suject
> before continuing.
>
>
> The more uF a capacitor has, the higher the potential over time it can
> store. All it does with more capacity is lenthen the duration of the shock.
> The longer the duration, the better the chance of making the skin conduct,
> therefore the more chance of getting killed. JUST BE CAREFUL!
>
> C. McCrackin
> mccr...@vaxxine.com
>
while repairing it, it didn't kill him :-), but he was put in hospital for
24 hours for observation, not because there was anything wrong with him but
that was a standard procedure after such accidents. The stress on the heart
from the shock, could apparently cause it to stop later.
-- Lasse
----------------------------------------------------------
Lasse Langwadt Christensen, M.Sc. EE (to be in 1999)
Aalborg University, Department of communication technology
Applied Signal Processing and Implementation (ASPI)
e-mail: F...@control.auc.dk, http://www.control.auc.dk/~fuz
snail-mail: Lobovej 20 - 9230 Svenstrup - Denmark
Phone: +45 4026 5572
Bertho Boman
First, it depends on if the energy source is AC or DC. In the case of a
capacitor, it is obviously DC but I will mention both.
Voltage is only indirectly important here. The critical factor is
current. That is why people sometimes get killed by very low voltages.
The resistance in the circuit was very low and therefore the current
become high.
AC is in general much more dangerous because if you by accident grab a
"hot" object, if the resulting current is above about 20 mA you can not
let go because of muscle contraction. Interestingly, if the voltage is
a lot higher than the normal household voltages, the initial contact
muscle contraction is so violent that sometimes the person is jerked
away and newer get stuck.
The getting stuck is the bad part, because now the current flows through
your body for an extended time.
DC generally generates one shock/jerk motion but usually not extended
contact periods. Often the damage is not electrical in nature. Cuts
and falls are common results.
Body Damage: there are at least four different modes:
1. The first one is not really electrical at all. When very high power
levels are involved as in power station and industrial areas, a short
or flash-over creates such intense power release that it is literally an
explosion and the person get hurt/killed by the resulting shock wave.
At the same time, an very intense flash is generated that causes
non-electrical burn damages.
2. Next in the list is a very short but high current pulse. It can
often cause nerve damage.
3. If the current last for longer time the actual power dissipated in
the body literally cooks the flesh. (Remember cooking hot dogs with 120
AC and two forks?)
4. The last one is relating to the heart. If the hearts rhythm is
interrupted or disturbed by an electrical current in the vicinity of the
heart we have problems. There are basically two sub-modes here:
a. The current confuses the hearts trigger mechanism and it starts to
violently "vibrate" without pumping blood (fibrillate). After about 10
seconds or so with out blood to the brain the person gets unconscious
and shortly dies.
b. The current causes the heart to stop. If it does not restart the
result is the same as above.
Usually, if the current is very high, the heart stops but restarts after
the shock is over. This again explain explains why sometimes apparently
higher shocks are survived and weaker ones are not. The weaker ones
often trigger fibrillation.
That is why the de-fibrillator works. One massive contractions which
stops the heart completely and then it can restart normally.
I know, it did not answer your elephant roasting question but hopefully
it has aided you understanding of electrocution.
Bertho Boman
Vinland Corporation
===============================================
25 Apr 1998 00:38:11 +0100, Rolf Roubs <xy...@iname.com> wrote:
> Killer capacitors - what's the true
>
>In electronic plans/circuits (manly strobe, laser, tesla -circuits)you
>often see notes regarding safety.
>In there they always warn you about the potential a capacitor has, even
>when it is disconnected. They talk about that if you are not careful it
>could kill you instantly!?
>Is that really possible ? (if I, for example, touched a loaded
>440uF/350V ???)
>Yes - there is a violent sounding spark if I short it - but is that
>really enough energy to kill a normal person in good condition?
>I remember touching a live wire (220V/50Hz) when I was a child and I
>survived it !?
>Or - Why do they use 10'000 volts and 2 amps over quite a time for the
>death penalty (and they can still not be sure that the victim is death
>after the first shock)!
>Well - Now I want to know it for sure and in a understandable way : From
>what load on is a capacitor dangerous !!!!!!!??????????????
>Please don't talk about Joules or Watt ! Better tell me about
>
>xxxMicroFarad/yyyVolts - throws you back to the next wall
>xxxMicroFarad/yyyVolts - is quite dangerous
>xxxMicroFarad/yyyVolts - is very dangerous
>xxxMicroFarad/yyyVolts - probably kills you
>xxxMicroFarad/yyyVolts - kills you for sure
>xxxMicroFarad/yyyVolts - is enough to roast an elephant
>etc.
>
Mike Dodd
>
>Agreed... AFAIK, it takes about 10 thousand volts for electricity to travel
>on cm in air, is this right?
>
As far as I can remember it's around 3kV/mm for "dry" air (can`t remember
the definition of "dry" air)
--
Mike
Sam Goldwasser
> Killer capacitors - what's the true
> In electronic plans/circuits (manly strobe, laser, tesla -circuits)you
> often see notes regarding safety.
The time to worry is if you DON'T see those warnings as most of these devices
are easily lethal under the wrong conditions :-(.
Where warnings are NOT present, one must assuem that either the device isn't
powerful enough to be a risk or (more likely) that the author/designer
doesn't know enough to be aware of the risks themselves since. If for no
other reason, they would put the warnings in there to somewhat protect them
from legal action should an accident occur!
--- sam : Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Usually latest: http://www.pacwest.net/byron13/sam/sammenu.htm
Lasers: http://www.misty.com/~don/lasersam.html
James Meyer
>Those old Simpson 260's used a D cell as the voltage source for
>resistance measurements, all of a volt and a half. Turned out, though,
>kid's internal body resistance was low enough (musta been only an ohm or
>so) to allow that D cell to push enough current through his chest to
>cause cardiac fib. He was doin' the lab exercise at night, no one else
>in lab. Janitors found him the next mornin'...
I sincerely doubt the veracity of that story.
I don't doubt that *you* believe that it's true.
Jim
狂人
Jim Lagerkvist
Rolf Roubs wrote:
>
> Killer capacitors - what's the true
Well, here's my two bad & different experiences with high voltage:
I was a kid and wanted to pry off the rosebud (2nd anode) from a very
large television CRT. It was the equivalent of a major capacitor. I
knew better than to use a metal screwdriver so I grabbed a wooden
pencil, forgetting there was graphite inside. It threw me clear across
the room and I could hardly catch my breath.
Several years later I got interested in ham radio and fired up a
transmitter with no load. Thousands of volts from an out-of-resonance
tank circuit arced into my fingernail and I never felt it.... only
smelled something really bad. It took many weeks for that RF burn to
heal.
William L. Bahn
Not necessarily, RF currents tend to flow on or near the skin and muscles.
The inductance along the path into the chest cavity attenuates the current
making it to the organs.
Geoff S. Drayson wrote in message ...
Tom MacIntyre
According to Introduction to Electric Circuits/Jackson/4th Edition,
the dielectric strength of air is 3kv per mm. No standard is specified
for temperature, pressure, humidity, etc.
"狂人" <nos...@canadawired.com> wrote:
>Agreed... AFAIK, it takes about 10 thousand volts for electricity to travel
>on cm in air, is this right?
>
Bloody Viking
Marion D. Kitchens (jkit...@erols.com) wrote:
: While most people normally don't think about it, there have been numbers of
: people killed by as little as 25 volts -- that under the right (wrong?)
: conditions. So do be careful of any high voltage, even a 100 or so. Yes, I
: too have survived several higher voltages "accidents" but still.......
: There are many variables, so it is not possible to simply state a voltage
: and or charge on a cap that can do you in. I stay away from them all if
: they are charged with 100 or more volts!
I once used to have a 720uF or so cap that could hold 120V and a home-made
charger cord for it. Dangerous, but great fun for showing people the power
held in a good size capacitor. Discharging it with a screwdriver made for
a nice popping sound and spark. Of course, I was careful when charging my
little toy. :)
--
CAUTION: Email Spam Killer in use. Leave this line in your reply! 152680
A cult founder's rustbucket freighter is his battleship.
2406069 bytes of spam mail deleted. http://www.wwa.com/~nospam/
Sam Goldwasser
In article <35424c0c...@nr1.ottawa.istar.net> tmac...@highlander.cbnet.ns.ca (Tom MacIntyre) writes:
> According to Introduction to Electric Circuits/Jackson/4th Edition,
> the dielectric strength of air is 3kv per mm. No standard is specified
> for temperature, pressure, humidity, etc.
This may be under ideal conditions with super smooth large electrodes.
The typical figure given for dry air (without elaboration) is around
1 KV/mm (25 KV/inch).
狂人
In <SAM.98Ap...@colossus.stdavids.picker.com>, on 04/25/98
>In article <35424c0c...@nr1.ottawa.istar.net>
>tmac...@highlander.cbnet.ns.ca (Tom MacIntyre) writes:
>> According to Introduction to Electric Circuits/Jackson/4th Edition,
>> the dielectric strength of air is 3kv per mm. No standard is specified
>> for temperature, pressure, humidity, etc.
>This may be under ideal conditions with super smooth large electrodes.
>The typical figure given for dry air (without elaboration) is around 1
>KV/mm (25 KV/inch).
So again, we come back to 10KV for 1 cm... :)
Scott Stevens
It sounds like an "urban legend" but I know it's possible to stop a
person's heart (fibrilation) with very small currents. I work in the Medical
device industry designing neurological stimulators for pain relief and
physical therapy, and our class of devices always(!) stimulates through
surface electrodes attached to the skin. Once the barrier of the skin has
been penetrated the blood circulatory system provides quite a low impedance
path. In the hospital there are two classes of electrical shock risk, and two
sets of leakage current limits for instrumentation. For the average patient
it's in the milliampere range. A higher risk class is established for
catheterized patients, that is, where there's a more direct path to the heart
exposed. In the past, there have been cases where a catheterized patient has
been killed by the doctor or nurse just walking up and touching the wrong
spot, and the static discharge in the room causing fibrillation. This doesn't
happen much anymore, because it's a characterised risk and proper grounding is
provided in critical areas of the hospital.
The path the current travels in is also important. You aren't going to kill
yourself by passing current through pins pressed through the skin if both pins
are on the same arm, for instance. The Chinese use a device called an
Acupunctoscope (sp?) where an electric current is applied by aligator clipping
the stimulator leads to a pair of acupuncture needles in the patient (I
evaluated one of these units in the lab about ten years ago). But a
thumb-to-thumb connection is about the worst case possible, as the current
path will pass through the heart in making a complete circuit. All it takes
then is a small amount of current (one would have to measure the resistance to
determine 1.5 volts were enough to force enough current to fibrilate, but bear
in mind that several microamperes is enough to fibrilate in some cases).
It's possible that in the case of the "killer Simpson 260" that the
instrument was set on one of the higher resistance ranges. The 260 contains a
B battery (I believe 67-1/2 volts?) that provides the current for the ohms
function on the highest range(s?).
holograf
>It sounds like an "urban legend" but I know it's possible to stop a
>person's heart (fibrilation) with very small currents.
Well, here's where I embarrass myself, but hopefully save a life...
I've worked on medium and large frame lasers (168's, 171's, innova 90's,
100 and 200's) since about 1980. Never in all that time did I ever get hurt
other than getting a few retinal burns (that's bad enough, but at least I
never fell across a tube or ignitor at startup). Anyway, the one laser that
almost did kill me was also the smallest that I ever worked on..
I was doing some testing of AO devices along with some small cyl HeNe
tubes from Siemans. These little coax tubes had clips for attaching the anode
and cathode connections. Well, I was going through a few boxes of these things
a day doing tests, etc. Just slap them on the bench, fire them up, discharge
the supplies and then disconnect and try another one. They ran off a 9v DC
power supply. Well, at the end of one long day, I called it quits early and
just shut the laser supply off and left the tube in place as I was just going
to put on a new tube in the morning. Well, that next morning, I came and
incorrectely assumed that the power supply would have discharged on it own
overnight. So, with each hand I stupidly grab one clip each on the laser to
disconnect it. YeeHaaaaaaaaa!!!!. I felt like I had been hid across my temples
with a two by four. It felt like I swallowed my tongue and then I kinda
blacked out. One of the guys came and helped me up, but I was weak in the
knees, and very disoriented. I stumbled around for about 15 minutes and then
out of nowhere it was just like I got another shock! This cycle of stuff went
on for about 3 hours, then stopped once I got to the hospital. I can't even
remember what they did to me there. Anyway, how embarrassing to almost get
killed by a HeNe after all that other high power stuff that I did.
I think that's called "irony"
Doug
Ed Price
Scott Stevens wrote:
> In article <6ht41o$l...@bgtnsc03.worldnet.att.net>, notj...@worldnet.att.net (James Meyer) wrote:
> >On Fri, 24 Apr 1998 21:26:54 -0400, W Letendre
> ><WJLS...@worldnet.att.net> wrote:
> >>Those old Simpson 260's used a D cell as the voltage source for
> >>resistance measurements, all of a volt and a half. Turned out, though,
> >>kid's internal body resistance was low enough (musta been only an ohm or
> >>so) to allow that D cell to push enough current through his chest to
> >>cause cardiac fib.
> It sounds like an "urban legend" but I know it's possible to stop a
> person's heart (fibrilation) with very small currents.
> It's possible that in the case of the "killer Simpson 260" that the
> instrument was set on one of the higher resistance ranges. The 260 contains a
> B battery (I believe 67-1/2 volts?) that provides the current for the ohms
> function on the highest range(s?).
>
> stev...@freenet.msp.mn.us
No, Scott, maximum current is available on the lowest Ohm range in a
classic VOM circuit. And most VOM's use a single D or C or AA cell.
Also, my 2 cents says this is a legend.
Now, let me add my own tale of knowledge gained through stupid
experimentation. In 1961, right after I built my Knight Kit VTVM, I was
measuring the voltage and resistance of everything I could find. I
eventually found an old "Press" style flashbulb, about an inch in
diameter. I started out on a high Ohms range, and worked my way down to
the 1x range. The lessons I learned involved design of experiments,
resistance testing, chemical reaction of magnesium, optical transfer of
energy and emergency room procedure. Did you know that those old bulbs
had a plastic outer layer which could very effectively fuse to charred
skin?
Dirty Harry Callahan was right; "...when properly used, you can REMOVE
the fingerprints."
Next time (if somebody asks politely), I'll tell you how I got radiation
burns from a pencil.
Sam Goldwasser
The highest voltage in my 260 is I believe 6 V.
Supposedly, 5 uA is enough to take control of the heart AT the heart. To
get that from a 1.5 V supply arm-arm does seem unlikely.
--- sam : Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Usually latest: http://www.pacwest.net/byron13/sam/sammenu.htm
Lasers: http://www.misty.com/~don/lasersam.html
In article <35429...@aedes.isd.net> stev...@freenet.msp.mn.us (Scott Stevens) writes:
It sounds like an "urban legend" but I know it's possible to stop a
It's possible that in the case of the "killer Simpson 260" that the
Richard E. Wagner
I worked I a electric motor repair place 30 years ago (before OSHA) and we
had a simple light bulb in series with a set of probes for testing for
shorts and continuity. One day I got both my hands connected to both the
electrodes and I could not let go! What saved me was I back backwards and
finally the distance was great enough so I broke the connection. Thats why I
am here today. Just though I would pass it on if anyone is still using such
a devise.
James Meyer
>It's possible that in the case of the "killer Simpson 260" that the
>instrument was set on one of the higher resistance ranges. The 260 contains a
>B battery (I believe 67-1/2 volts?) that provides the current for the ohms
>function on the highest range(s?).
The Simpson 260 has a meter movement with 50 microamp
sensitivity. The ohms function uses resistors in series with the
battery and the meter movement to limit the current in the circuit so
that when the meter is indicating zero ohms that the meter movement is
seeing 50 microamps. On the higher ranges more voltage is needed to
generate that 50 microamps of current. My 260 uses a 9 volt "B"
battery.
Measurements on my meter indicate....
Resistance Short Circuit Open Circuit
Scale Current Voltage
Rx1 100 mA 1.5 V
Rx10 1.5 mA 1.5 V
Rx10,000 0.09 mA 9.0 V
It's common knowledge that the Rx1 scale produces enough
current to damage very sensitive transistor and diode junctions. That
was a real possibility with early germanium devices, but I've never
had a failure with any silicon junctions.
The human body is mostly water with a little salt dissolved in
it. Sea water is more salty than body fluids. Stick two pins into
some sea water about 5 feet apart and measure the resistance. You
will find that it's considerably higher than the one ohm figure that
was supposed in the "killer 260" message. That means that the current
the dead guy got was considerably less than 100 mA.
Jim
Stefan Huebner
> >It sounds like an "urban legend" but I know it's possible to stop a
> >person's heart (fibrilation) with very small currents.
> Well, here's where I embarrass myself, but hopefully save a life...
Nice, the guys are telling their famous experiences :-)
Someone asked how many volts and uF one will need to roast an
elephant. Well, I have never roasted one, actually, I never saw
a good reason for doing so. I don't like meat very much...
I think almost everyone knows the constructions that TV manufacturers
provide to put the TV PCBs into service position ? I had a set on the
bench in which the board was supposed to stand upright for service.
Well, it indeed stood there, even after switching the set on. But in the
moment I tried to check a signal with a scope probe the board fell right
onto my hand. Of course it was the power supply area which hit me. This
is most likely the first and hopefully the last case that I was happy
about not having used an isolation transformer, the GFI did its job, but
the main filter cap - 220uF at about 300 volts - bit me and burned two
holes into the skin of my hand. This is now about 6 1/2 years ago, the
holes became two almost invisible spots. The other "accident" I had
involved a charged glass-vacuum-capacitor - some people call them color
TV picture tubes. While lifting the anode cup the HV bit my finger from
about one inch or so, looked very spectacular, but it didn't actually hurt
more than grabbing both contacts of one of these old doorbells. But don't
try this at home, kids !
bye
Stefan!
Scott Stevens
In article <354304...@pacbell.net>, edp...@pacbell.net wrote:
>Scott Stevens wrote:
>
>> In article <6ht41o$l...@bgtnsc03.worldnet.att.net>, notj...@worldnet.att.net
> (James Meyer) wrote:
>> >On Fri, 24 Apr 1998 21:26:54 -0400, W Letendre
>> ><WJLS...@worldnet.att.net> wrote:
>
>> >>Those old Simpson 260's used a D cell as the voltage source for
>> >>resistance measurements, all of a volt and a half. Turned out, though,
>> >>kid's internal body resistance was low enough (musta been only an ohm or
>> >>so) to allow that D cell to push enough current through his chest to
>> >>cause cardiac fib.
>
>> person's heart (fibrilation) with very small currents.
>
>> instrument was set on one of the higher resistance ranges. The 260 contains
> a
>> B battery (I believe 67-1/2 volts?) that provides the current for the ohms
>> function on the highest range(s?).
>>
>
>No, Scott, maximum current is available on the lowest Ohm range in a
>classic VOM circuit. And most VOM's use a single D or C or AA cell.
>Also, my 2 cents says this is a legend.
Well, now you prompted me to crack open the case on my Triplett 630 VOM.
Inside I find a single D cell, and a 30 volt "B" battery, used to get enough
current on the high resistance ranges. The "maximum current" in the lower
resistance ranges would be at a voltage less hazardous to the human body. The
reason a B battery exists in the meter is to provide a higher potential, to
get enough current to deflect the meter movement, with higher resistances. I
am confident that a Simpson 260, which is a design of the same vintage as a
Triplett 630, has the higher voltage B battery in it. Newer analog meters,
which might have more sensitive meter movements, or an amplification stage to
boost the sensitivity of the meter, might only have only the cell battery.
Remember that there are no gain components whatsoever in a 'classic' VOM.
The original story does still sound like legend, though.
Petercoe
I think different people, under different conditions can stand more or less
voltage. I know now that my physics teacher back in 1950 was foolish. He had
a static electricity generator. We had one female student who could hold the
probes in each hand while the generator was producing 100v.
Pete...@aol.com
35 year tv repair
Oldguyteck
Pete! I wounder if it altered her perm at all heheh :) Shocking news
LOL.
Ed.............................(Oldguyteck)
--
Old tecks never die - They just SPARK AWAY !
Petercoe <pete...@aol.com> wrote in article
<199804270212...@ladder01.news.aol.com>...
Sam Goldwasser
Foolish, perhaps. However, by holding the probes, any serious buildup of
charge was prevented since her body was essentially a short circuit as far
as the generator was concerned. I would assume he discharged any caps in
the generator before letting her touch it :-).
--- sam : Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Usually latest: http://www.pacwest.net/byron13/sam/sammenu.htm
Lasers: http://www.misty.com/~don/lasersam.html
Walter Gray
In article <SAM.98Ap...@colossus.stdavids.picker.com>, s...@stdavids.picker.com (Sam Goldwasser) writes:
:In article <35411453...@iname.com> Rolf Roubs <xy...@iname.com> writes:
:
:> Killer capacitors - what's the true
:
:> In electronic plans/circuits (manly strobe, laser, tesla -circuits)you
:> often see notes regarding safety.
:
:The time to worry is if you DON'T see those warnings as most of these devices
:are easily lethal under the wrong conditions :-(.
:
:Where warnings are NOT present, one must assuem that either the device isn't
:powerful enough to be a risk or (more likely) that the author/designer
:doesn't know enough to be aware of the risks themselves since. If for no
:other reason, they would put the warnings in there to somewhat protect them
:from legal action should an accident occur!
Or else the equipment dated back to the era before lawyers took over
the world and when coffee was _supposed_ to be hot.
Walter
Disclaimer: My employer is not responsible for this stuff.
Please reply to: wag...@dra.hmg.gb as the address given above
sometimes doesn't work.
Walter Gray
In article <6ht41o$l...@bgtnsc03.worldnet.att.net>, notj...@worldnet.att.net (James Meyer) writes:
:On Fri, 24 Apr 1998 21:26:54 -0400, W Letendre
:<WJLS...@worldnet.att.net> wrote:
:
:
:>Those old Simpson 260's used a D cell as the voltage source for
:>resistance measurements, all of a volt and a half. Turned out, though,
:>kid's internal body resistance was low enough (musta been only an ohm or
:>so) to allow that D cell to push enough current through his chest to
:>in lab. Janitors found him the next mornin'...
:
: I sincerely doubt the veracity of that story.
:
: I don't doubt that *you* believe that it's true.
I believe the kid actually _swallowed_ the D cell and choked to death.
Roy McCammon
Here's what UL standard 1244 (July 1980) lists as unacceptable for
accessible charged capacitance
1. voltage between 42.4V and 450V: capacitance greater than 0.1uF
2. voltage between 450V and 15KV: charge greater than 45uC
3. voltage greater than 15KV: energy greater than 350mJ
disclaimer: don't make designs based on this info. Get the latest
edition on the relevant UL or other spec and read it carefully.
Requirements may be more stringent in some circumstances.
Rolf Roubs wrote:
>
> Killer capacitors - what's the true
>
> In electronic plans/circuits (manly strobe, laser, tesla -circuits)you
> often see notes regarding safety.
Opinions expressed herein are my own and may not represent those of my employer.
'Pistol' Pete Haduch
Scott Stevens wrote:
>
> In article <6ht41o$l...@bgtnsc03.worldnet.att.net>, notj...@worldnet.att.net (James Meyer) wrote:
> >On Fri, 24 Apr 1998 21:26:54 -0400, W Letendre
> ><WJLS...@worldnet.att.net> wrote:
> >
> >
> >>Those old Simpson 260's used a D cell as the voltage source for
> >>resistance measurements, all of a volt and a half. Turned out, though,
> >>kid's internal body resistance was low enough (musta been only an ohm or
> >>so) to allow that D cell to push enough current through his chest to
> >>cause cardiac fib. He was doin' the lab exercise at night, no one else
> >>in lab. Janitors found him the next mornin'...
> >
> > I sincerely doubt the veracity of that story.
> >
> > I don't doubt that *you* believe that it's true.
> >
> >
> >
>
> It sounds like an "urban legend" but I know it's possible to stop a
> instrument was set on one of the higher resistance ranges. The 260 contains a
> B battery (I believe 67-1/2 volts?) that provides the current for the ohms
> function on the highest range(s?).
>
> stev...@freenet.msp.mn.us
A "B" battery vs. a "D" battery. That could do it!
--
'Pistol' Pete Haduch
Visit my web site at http://members.tripod.com/~Pistol_Petes
For sales and service in the Baltimore/Metropolitan area, log
onto the AVP web site at
http://members.tripod.com/~Pistol_Petes/amusvdpn.htm
Ed Price
Scott Stevens wrote:
> >> In article <6ht41o$l...@bgtnsc03.worldnet.att.net>, notj...@worldnet.att.net
> >> ><WJLS...@worldnet.att.net> wrote:
> >> >>Those old Simpson 260's used a D cell as the voltage source for
> >> >>resistance measurements, all of a volt and a half.
> >> It's possible that in the case of the "killer Simpson 260" that the
> >> instrument was set on one of the higher resistance ranges.
> >No, Scott, maximum current is available on the lowest Ohm range in a
> >classic VOM circuit. And most VOM's use a single D or C or AA cell.
> >Also, my 2 cents says this is a legend.
> Well, now you prompted me to crack open the case on my Triplett 630 VOM.
> Inside I find a single D cell, and a 30 volt "B" battery, used to get enough
> current on the high resistance ranges. The "maximum current" in the lower
> resistance ranges would be at a voltage less hazardous to the human body. The
> reason a B battery exists in the meter is to provide a higher potential, to
> get enough current to deflect the meter movement, with higher resistances. I
> am confident that a Simpson 260, which is a design of the same vintage as a
> Triplett 630, has the higher voltage B battery in it. Newer analog meters,
> which might have more sensitive meter movements, or an amplification stage to
> boost the sensitivity of the meter, might only have only the cell battery.
> Remember that there are no gain components whatsoever in a 'classic' VOM.
> The original story does still sound like legend, though.
I'll bow to your direct investigatory evidence, Scott. OTOH, I am now
gonna find my old 260 and have at it. (Maybe it time, after about 15
years, oops, to check the battery anyway!)
jncmciver
You seem to have set off quite a storm here! Most of the people involved
in electronics and electricity have acquired a healthy respect for
electricity, myself included, and there is nothing like a healthy dose of
fear learned from past mistakes to make one wary.
I have been tingled by electricity as well as had my chest slammed by a
dose of unknown current, from five volts to five hundred. No fun at all,
as you ponder your heart restarting while you hope your legs don't give out
under you. That means I was incredibly lucky to even be able to think
about it! Oh yes, and after that I started wearing the rubber boots my
employer provided me. No amount of discomfort was worth what I felt in
just one millisecond!!!
What I am trying to say in too many words is don't take for granted that
any circuit is dead, even if that TV has been sitting out in the rain for
weeks, or you know that the circuit breaker is off. Check it with a meter!
In the case of capacitors, do not discharge them with a scredriver!! You
might at least ruin a screwdriver and at the worst have a surgeon dig it
out of your chest! Know what you are looking at, know what the potential
is, and always keep one hand behind you (in your pocket is NOT a safe
place!) and never, never, and I mean NEVER!! put your hand around something
that in the remotest possibility could be hot!
Please, take the advice of someone who is too young to die, but has been
bit so many times I feel like an old man when I talk about it!
Rolf Roubs <xy...@iname.com> wrote in article
<35411453...@iname.com>...
Sam Goldwasser
> Here's what UL standard 1244 (July 1980) lists as unacceptable for
> accessible charged capacitance
> 1. voltage between 42.4V and 450V: capacitance greater than 0.1uF
> 2. voltage between 450V and 15KV: charge greater than 45uC
> 3. voltage greater than 15KV: energy greater than 350mJ
Not sure what significance this really has. The stored energy of a CRT with
a 1000 pF capacitance at 15 KV is about 112 mJ. I wouldn't want to come in
contact with THAT!
--- sam : Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Usually latest: http://www.pacwest.net/byron13/sam/sammenu.htm
Lasers: http://www.misty.com/~don/lasersam.html
> disclaimer: don't make designs based on this info. Get the latest
Roy McCammon
Sam Goldwasser wrote:
>
> In article <354493A9...@mmm.com> rbmcc...@mmm.com (Roy McCammon) writes:
>
> > Here's what UL standard 1244 (July 1980) lists as unacceptable for
> > accessible charged capacitance
> > 1. voltage between 42.4V and 450V: capacitance greater than 0.1uF
> > 2. voltage between 450V and 15KV: charge greater than 45uC
> > 3. voltage greater than 15KV: energy greater than 350mJ
>
> Not sure what significance this really has. The stored energy of a CRT with
> a 1000 pF capacitance at 15 KV is about 112 mJ. I wouldn't want to come in
> contact with THAT!
I think that we might agree that exceeding these
limits is a bad idea.
Eric Y. Chang
Hi. Watch out about those high energy pulse type shocks. They can be
quite dangerous. We had a neighbor who disconnected one of the boots
on his spark plugs. He received a minor shock, but lost 3 fingers in
the fan. All the kids were looking around for his fingers, but one
could not be found. Finally, one of the guys found one in a nearby
tree, but by this time it was all dried up, and it could not be
reattached. Another neighbor received a high energy pulse through
his thigh to ground (he was standing in a puddle of water). He
suffered no ill effects from the shock, but the resulting muscular
contraction cut cleanly through the ball joint of his knee, permanently
crippling him. So, according to these two silly stories, these kinds
of shocks are not too dangerous as long as you can keep still. Eric
No#Spam
Sam Goldwasser (s...@stdavids.picker.com) wrote:
: In article <354493A9...@mmm.com> rbmcc...@mmm.com (Roy McCammon) writes:
: > Here's what UL standard 1244 (July 1980) lists as unacceptable for
: > accessible charged capacitance
: > 1. voltage between 42.4V and 450V: capacitance greater than 0.1uF
: > 2. voltage between 450V and 15KV: charge greater than 45uC
: > 3. voltage greater than 15KV: energy greater than 350mJ
: Not sure what significance this really has. The stored energy of a CRT with
: a 1000 pF capacitance at 15 KV is about 112 mJ. I wouldn't want to come in
: contact with THAT!
Also, it may take some time to discharge CRT's -- a quick short to the
chassis or ground may be insufficient. I did learn that when I was
replacing the CRT in my TV when I was a teenager. I knew the dangers,
so I did short the CRT and the big caps momentarily to the chassis with
a piece of insulated wire (attached to a plastic rod when shorting the
CRT) , then proceeded to remove the CRT -- and a couple of minutes later
-- OUCH, a shocking experience.
---
#include <Standard.Disclaimer> about this post being a personal opinion
#define <From: and Reply-To:> being bogus to avoid unwanted junk EMail
Sam Goldwasser
I recommend that anode cap be jumpered to the coating on the outside of the
CRT whenever they are handled. It isn't that they take more than an instant
to discharge but rather that a variety of effects can result in picking up
some charge again.
--- sam : Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Usually latest: http://www.pacwest.net/byron13/sam/sammenu.htm
Lasers: http://www.misty.com/~don/lasersam.html
Gareth Jones
In article <6hrrph$j7p$1...@news.iquest.net>, David VanHorn
<dvan...@cedar.net> writes
>
>
>>Please don't talk about Joules or Watt ! Better tell me about
>>
>>xxxMicroFarad/yyyVolts - throws you back to the next wall
>>xxxMicroFarad/yyyVolts - is quite dangerous
>>xxxMicroFarad/yyyVolts - is very dangerous
>>xxxMicroFarad/yyyVolts - probably kills you
>>xxxMicroFarad/yyyVolts - kills you for sure
>>xxxMicroFarad/yyyVolts - is enough to roast an elephant
>>etc.
>
>
>
>V * V * (C/2) = Joules.. What you're asking for above is ratings in Joules.
>
>
>
err.. isnt it 2*uJ/V^3?
(sorry to be a smart-ass)
--
Gar...@lsas.demon.co.uk
Bob Weiss
I thought it was:
E=(C*V^2)/2
Sam Goldwasser
In article <3547954A...@carroll.com> Bob Weiss <bwe...@carroll.com> writes:
> E=(C*V^2)/2
Yes, in Joules = w-s.
Winfield Hill
Sam Goldwasser at s...@stdavids.picker.com says...
>
> I recommend that anode cap be jumpered to the coating on the outside of
> the CRT whenever they are handled. It isn't that they take more than an
> instant to discharge but rather that a variety of effects can result in
> picking up some charge again.
>
->
-> Also, it may take some time to discharge CRT's -- a quick short to the
-> chassis or ground may be insufficient. I did learn that when I was
-> replacing the CRT in my TV when I was a teenager. I knew the dangers,
-> so I did short the CRT and the big caps momentarily to the chassis
-> with a piece of insulated wire (attached to a plastic rod when shorting
-> the CRT) , then proceeded to remove the CRT -- and a couple of minutes
-> later -- OUCH, a shocking experience.
We know that a capacitor's dielectric absorption will restore some of the
charge after a shorted discharge (I've seen as much as 15% a few minutes
after removing the short); I wonder how large this effect is with typical
CRT supplies...
--
Winfield Hill hi...@rowland.org
Rowland Institute for Science
Cambridge, MA 02142
David VanHorn
>E=(C*V^2)/2
>> >V * V * (C/2) = Joules.. What you're asking for above is ratings in
Joules. (Mine)
Mine evaluates to point 5 V squared C which is stored energy in Joules, and
so does the one above.
>> err.. isnt it 2*uJ/V^3?
This one... I'm not sure what it makes.
Ascii is not good for formulae :(
Gareth Jones
In article <3547954A...@carroll.com>, Bob Weiss
<bwe...@carroll.com> writes
>I thought it was:
>
>E=(C*V^2)/2
E=(C*V^2)/2
2E=C*V^2
2E/V^2=C
2E*10^-6/V^2=C*10^-6
2E*10^-6/V^3=C*10^-6/V (uF/V)
(do I lead a sad life or what)
>
>Gareth Jones wrote:
>
>> In article <6hrrph$j7p$1...@news.iquest.net>, David VanHorn
>> <dvan...@cedar.net> writes
>>
>> >
>> >
>> >>Please don't talk about Joules or Watt ! Better tell me about
>> >>
>> >>xxxMicroFarad/yyyVolts - throws you back to the next wall
>> >>xxxMicroFarad/yyyVolts - is quite dangerous
>> >>xxxMicroFarad/yyyVolts - is very dangerous
>> >>xxxMicroFarad/yyyVolts - probably kills you
>> >>xxxMicroFarad/yyyVolts - kills you for sure
>> >>xxxMicroFarad/yyyVolts - is enough to roast an elephant
>> >>etc.
>> >
>> >
>> >
>> >
>> >
>> >
--
Gareth Jones
17 Chalky Road, Great Abington, Cambridgeshire. CB1 6AT. UK
Tel/Fax/Data: +44 (0)1223 893 791
GSM: +44 (0)802 783 503
e-mail: gar...@lsas.demon.co.uk
Tom Sedlemyer
Not the subject of this group but your post brought it to mind.
Several years ago my brother was in college taking a beginners algebra
course. He asked my assistance because his homework was marked "wrong"
by his instructor. When I looked at his work sheets they consisted of
just answers with none of the steps written out that were used to derive
the answers. Had to argue an hour or so to convince him to at least keep
his scratck paper and write his derivations plainly so he could show
them to his instructor and find out where he made his mistake. Turned
out the ones that were correct were arrived at by faulty logic too.
I've seen the same sloppy teaching methods twice since with other people
taking algebra. When I took algebra and higher maths, the answer was
never as important as how you got to it.
Done right, learning algebra teaches more than math, it teaches logical
problem solving and rational thought. (THEN WHAT AM I DOING IN THIS
BUSINESS!)
Tom MacIntyre wrote:
>
> Just think of the sad lives led by people who can't derive the
> equations which you have just presented!!
Walter Gray
In article <35491f2d...@nr1.ottawa.istar.net>, tmac...@highlander.cbnet.ns.ca (Tom MacIntyre) writes:
:
:Just think of the sad lives led by people who can't derive the
:equations which you have just presented!!
ummm, lawyers, doctors, presidents, CEOs, film stars...
So sad we should all be.
:
:
:Gareth Jones <gar...@lsas.demon.co.uk> wrote:
:
:>In article <3547954A...@carroll.com>, Bob Weiss
:><bwe...@carroll.com> writes
:>>I thought it was:
:>>
:>>E=(C*V^2)/2
:>I had to go and work it out again...
:>E=(C*V^2)/2
:>2E=C*V^2
:>2E/V^2=C
:>2E*10^-6/V^2=C*10^-6
:>2E*10^-6/V^3=C*10^-6/V (uF/V)
:>(do I lead a sad life or what)
:>>
:>>Gareth Jones wrote:
:>>
:
Tom MacIntyre
I wouldn't be happy in any of those activities. However, as for the
money................Oh, yeah!!!!!!!!!!!
Junius
jncmciver wrote:
> You seem to have set off quite a storm here! Most of the people involved
> in electronics and electricity have acquired a healthy respect for
> electricity, myself included, and there is nothing like a healthy dose of
> fear learned from past mistakes to make one wary.
> I have been tingled by electricity as well as had my chest slammed by a
> dose of unknown current, from five volts to five hundred. No fun at all,
> as you ponder your heart restarting while you hope your legs don't give out
> under you. That means I was incredibly lucky to even be able to think
> about it! Oh yes, and after that I started wearing the rubber boots my
> employer provided me. No amount of discomfort was worth what I felt in
> just one millisecond!!!
I can't agree more with your sentiment. Like a number of people who have
responded, I've been lucky with surviving high voltage capacitor shocks from
being careless. My experience was with a Coherent 325 CO2 laser about
15 years ago. The 25KV discharge went across my chest and pitched me
about three feet through the air, and muscle movement was impossible for a
few minutes. After that, my afternoon activities were pretty much wrapped
up.
David Sherman
Tom MacIntyre
You'll have to follow it back to the branch in the road.
Eric Houg
> What does this thread of discussion have to do with capacitors?
Attack of the killer capacitors!
Coming soon to a theater near you.
Equivalent series resistance is futile!
Tracey Levin
HELP!
I need help designing a very very simple two transistor FM
transmitter that uses any crystal between 30 and 108 mhz.
Tank circuits are easy to make to control the frequency, but that
is all I have had luck with so far.
I am currently using an electret microphone plus a few caps,
resistors to tie it to the mixer transistor that is connected to the
tank circuit. HOW ON EARTH do I replace the tank with a simple crystal?
This must be the most simple thing on earth to do, but I have no
idea how to connect a crystal to the collector of the PN2222A in place
of the variable tank circuit! Actually, it musts be so easy and I feel
kind of strange asking this question, but this has been bugging me for
some time now and I know that someone out there knows the simple answer.
This is a very simple baby monitor and its not unlike the millions
of FM transmitters in kits and lots of lit out there in radio land. Im
saying this so youll know what basic design Im using.
I would prefer to use a crystal that my FM radio could pick up,
but any portion of the band will do. So, Im going to ask you one last
thing....please respond via email to me so that my sister can use save
it for me since this is her account. Thanks very much to all who
respond. This project has kept me at the breadboard for many hours and
is yet unresolved. Thanks!
Checkout these sites:
Steve & Catherine Rogers + kids
John Lundgren
Tracey Levin wrote:
> HELP!
> I need help designing a very very simple two transistor FM
> transmitter that uses any crystal between 30 and 108 mhz.
> Tank circuits are easy to make to control the frequency, but that
> is all I have had luck with so far.
[snip]
You say FM, but you're using a crystal. That means that you have to
pull the frequency of the cystal, and that can't be done easily or
cheaply. What little you can pull it will not be enough modulation.
The usual procedure is to start with a low frequency crystal, and FM it
with a varicap or variable reactrance modulator. Then multiply it by
about 24 times up to the freqency of the transmitter. This is not
simple and takes more than a couple transistors.
>
--
Please remove NO and SPAM from my email addr to reply.
--
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Read what the FTC has to say about Junk Email at URL
http://www.ftc.gov/bcp/conline/pubs/online/inbox.htm
John/Lori
In June '92 Radio Electronics in the "Hardware Hacker" column,
Don Lancaster describes a crystal pulling fm modulator as
implimented in a Pioneer dingus for playing your portable CD
through an fm radio (in an automobile).
There was also a follow up describing some of the trickyer bits
involved (but I don't remember which issue).
Pete
From my knowledge you cant use crystal in FM transmitter because
it's"frequency modulation" and crystals have fixed frequency.
--
Pete
newm...@ihug.co.nz
Tracey Levin wrote in message <355687...@swbell.net>...
>HELP!
>
> I need help designing a very very simple two transistor FM
>transmitter that uses any crystal between 30 and 108 mhz.
> Tank circuits are easy to make to control the frequency, but that
>is all I have had luck with so far.
>
Tamarack Greenman
If memory serves you can......use xtal for oscillator then use reactance type
modulation
(Use audio to change the fq... hence FM)
btw the cheap 49 mhz kiddie walkie talkies use fm (and xtal control <g>)
I got the kids a set for $5.00
Tom AA1ID/5
Pete wrote:
> From my knowledge you cant use crystal in FM transmitter because
> it's"frequency modulation" and crystals have fixed frequency.
>
> --
> Pete
> newm...@ihug.co.nz
> Tracey Levin wrote in message <355687...@swbell.net>...
> >HELP!
> >
> > I need help designing a very very simple two transistor FM
> >transmitter that uses any crystal between 30 and 108 mhz.
> > Tank circuits are easy to make to control the frequency, but that
> >is all I have had luck with so far.
((((the rest clipped))))
--
"Is it boasting to say that I don't need Viagra?"
Larry King
Timothy Jacobs
"Pete" <newm...@ihug.co.nz> wrote:
>From my knowledge you cant use crystal in FM transmitter because
>it's"frequency modulation" and crystals have fixed frequency.
<snip>
You can swing them a bit. Enough multiplication afterwards and you get
decent deviation.
--
Tim Jacobs timothy...@gecm.com
Driving a boat is 90% mental. The other 10% is in your head
These are my views, not GEC's.
John Lundgren
John/Lori wrote:
ANd in a recent issue of Nuts & Volts or R-E, he described the Radio
Shack transmitter that is also xtal controlled, but it uses a special
xtal that can be FMed more than the usual.
For most xtals, you can't even FM them to a narrow band FM channel.
Maybe only 500 or 1000 Hz.
John Lundgren
Tamarack Greenman wrote:
> What???? that's going to come as a shock to a few people.
> If memory serves you can......use xtal for oscillator then use reactance type
> modulation
> (Use audio to change the fq... hence FM)
> btw the cheap 49 mhz kiddie walkie talkies use fm (and xtal control <g>)
> I got the kids a set for $5.00
The bandwidth is less than 1/10 the bandwidth of a FM broadcast
channel. FMing a xtal on the BCB would be almost too weak to hear.
That's why the TXes start out FMing a xtal at some low freq and
multiplying it up to the FM band, multiplying the modulation in the
process.
It's cehaper to go with PLL nowadays.
> Tom AA1ID/5
> Pete wrote:
> > From my knowledge you cant use crystal in FM transmitter because
> > it's"frequency modulation" and crystals have fixed frequency.
> >
> > --
> > Pete
> > newm...@ihug.co.nz
> > Tracey Levin wrote in message <355687...@swbell.net>...
> > >HELP!
> > >
> > > I need help designing a very very simple two transistor FM
> > >transmitter that uses any crystal between 30 and 108 mhz.
> > > Tank circuits are easy to make to control the frequency, but that
> > >is all I have had luck with so far.
>
> ((((the rest clipped))))
--
John Lundgren
Timothy Jacobs wrote:
> "Pete" <newm...@ihug.co.nz> wrote:
> >From my knowledge you cant use crystal in FM transmitter because
> >it's"frequency modulation" and crystals have fixed frequency.
> You can swing them a bit. Enough multiplication afterwards and you get
> decent deviation.
Well, this thread started out looking for a cheap xtal controlled TX,
and those terms are, essentially, mutually exclusive.
> --
>
> Tim Jacobs timothy...@gecm.com
Dwayne McCoy
Try looking at shematics of old "rock rig" (crystal) transmitters, I built a
heathkit hand held transmitter 146Mhz that used a X9 crystal multiplier and
a Varactor parallel to a "trimming" capacitor to vary the frequency. You
might check the Ham-radio NGs for schematics of old crystal gear.
DMc (N5BPF)
Pete wrote in message <6jb5j6$c5k$1...@newsource.ihug.co.nz>...
>From my knowledge you cant use crystal in FM transmitter because
>it's"frequency modulation" and crystals have fixed frequency.
>
>
>--
>Pete
>newm...@ihug.co.nz
>Tracey Levin wrote in message <355687...@swbell.net>...
>>HELP!
>>
>> I need help designing a very very simple two transistor FM
>>transmitter that uses any crystal between 30 and 108 mhz.
>> Tank circuits are easy to make to control the frequency, but that
>>is all I have had luck with so far.
>>
Kevin White
Even cheap 49MHz NBFM band devices usually have the crystal at 1/3 of
the transmit frequency and multiply by three.
kevin white
John Lundgren wrote:
> Tamarack Greenman wrote:
>
> > What???? that's going to come as a shock to a few people.
> > If memory serves you can......use xtal for oscillator then use
> reactance type
> > modulation
> > (Use audio to change the fq... hence FM)
>
> > btw the cheap 49 mhz kiddie walkie talkies use fm (and xtal control
> <g>)
> > I got the kids a set for $5.00
>
> The bandwidth is less than 1/10 the bandwidth of a FM broadcast
> channel. FMing a xtal on the BCB would be almost too weak to hear.
> That's why the TXes start out FMing a xtal at some low freq and
> multiplying it up to the FM band, multiplying the modulation in the
> process.
>
> It's cehaper to go with PLL nowadays.
>
> > Tom AA1ID/5
>
> > Pete wrote:
>
> > > From my knowledge you cant use crystal in FM transmitter because
> > > it's"frequency modulation" and crystals have fixed frequency.
> > >
> > > --
> > > Pete
> > > newm...@ihug.co.nz
> > > Tracey Levin wrote in message <355687...@swbell.net>...
> > > >HELP!
> > > >
> > > > I need help designing a very very simple two transistor FM
> > > >transmitter that uses any crystal between 30 and 108 mhz.
> > > > Tank circuits are easy to make to control the frequency, but
> that
> > > >is all I have had luck with so far.
> >
> > ((((the rest clipped))))
Reverend Tweek
Dwayne McCoy <dmc...@laol.net> wrote:
>Pete wrote in message <6jb5j6$c5k$1...@newsource.ihug.co.nz>...
>>
>>it's"frequency modulation" and crystals have fixed frequency.
From your knowledge, you might not. On the other hand, prior to 20 years
ago and PLL technology, just about every FM Broadcast station used a
crystal for its operating frequency. My personal experience was with
a Gates FM Exciter... rock was in a case which included a heater to
keep the crystal stable over a wide range of ambient temperatures, but
yet there was also a variable cap right next to crystal which let us
shift the oscilator frequency within a range of AT LEAST 2000 hz (at
the output of the final stage)... IIRC, that exciter had about eight
or so multipliers, some x3 and some x4... The crystal was cut for
somewhere around 118 khz, but the final product came out of the exciter
at 89.5 mhz.
Of course, the above exciter was in an old GE amplifier cabinet in the
place of the original GE exciter sitting in the corner which used a
completely different method to produce an FM receivable signal... the
method used was Phase Modulation.
>Try looking at shematics of old "rock rig" (crystal) transmitters, I built a
>heathkit hand held transmitter 146Mhz that used a X9 crystal multiplier and
>a Varactor parallel to a "trimming" capacitor to vary the frequency. You
>might check the Ham-radio NGs for schematics of old crystal gear.
Or the GE Phasatron... which changes the phase of the carrier by using
a tube to retard or advance the carrier in its cycle.
--
-------------------------------------------------------------------------
| Had your share of stoopid(tm) people? | |
| View the "Contra Costa Whines" at | [This space for lease] |
| http://www.io.com/~tweek/cocowhine/ | |
j...@southwind.net
That was the reason the GE exciter was retired,the Phasetron tube died
and no one would make any more.That's about the only piece of tube gear
that really _had_ to be retired because the tube was no longer
available.
Douglas Dwyer
In article <355BA9...@southwind.net>, j...@southwind.net writes
In about 1947 the BBC broadcast FM transmissions started, at least some
of the transmitters used direct FM on the crystal.
The key to this was careful crystal design by Mortley at Marconi at
approx 6? MHz he was the first to knowingly employ energy trappping in
his design. His work (published in Marconi review) was re-discovered in
the 60s? in the US and used to break energy trap patents which had been
filed for monolithic crystal filters.
Douglas Dwyer Frequency Precision Ltd. I design/advise on Xtal osc TCXO OCXO
SAWc etc Reply via demon or 10150...@compuserve.com phone/fax:
+44(0)1837810590 http://ourworld.compuserve.com/homepages/Frequency_Precision/
Mike McCarty
Most of the "really" old stuff used <forget the term, but means
simulated> FM. The actual modulation was PHASE modulation done with a
tube or FET in series with a capacitor. Integrate the modulating
signal before applying to the PM.
And then there were Reactance Tubes.
Mike
In article <EszB2...@moraga.ness.com>,
Reverend Tweek <tw...@netcom-NO.SPAM-com> wrote:
)Dwayne McCoy <dmc...@laol.net> wrote:
)>Pete wrote in message <6jb5j6$c5k$1...@newsource.ihug.co.nz>...
)>>
)>>From my knowledge you cant use crystal in FM transmitter because
)>>it's"frequency modulation" and crystals have fixed frequency.
)
)From your knowledge, you might not. On the other hand, prior to 20 years
)ago and PLL technology, just about every FM Broadcast station used a
)crystal for its operating frequency. My personal experience was with
)a Gates FM Exciter... rock was in a case which included a heater to
)keep the crystal stable over a wide range of ambient temperatures, but
)yet there was also a variable cap right next to crystal which let us
)shift the oscilator frequency within a range of AT LEAST 2000 hz (at
)the output of the final stage)... IIRC, that exciter had about eight
)or so multipliers, some x3 and some x4... The crystal was cut for
)somewhere around 118 khz, but the final product came out of the exciter
)at 89.5 mhz.
)
)Of course, the above exciter was in an old GE amplifier cabinet in the
)place of the original GE exciter sitting in the corner which used a
)completely different method to produce an FM receivable signal... the
)method used was Phase Modulation.
)
)>Try looking at shematics of old "rock rig" (crystal) transmitters, I built a
)>heathkit hand held transmitter 146Mhz that used a X9 crystal multiplier and
)>a Varactor parallel to a "trimming" capacitor to vary the frequency. You
)>might check the Ham-radio NGs for schematics of old crystal gear.
)
)Or the GE Phasatron... which changes the phase of the carrier by using
)a tube to retard or advance the carrier in its cycle.
)
)
)
)
)--
) -------------------------------------------------------------------------
)| Had your share of stoopid(tm) people? | |
)| View the "Contra Costa Whines" at | [This space for lease] |
)| http://www.io.com/~tweek/cocowhine/ | |
--
----
char *p="char *p=%c%s%c;main(){printf(p,34,p,34);}";main(){printf(p,34,p,34);}
This message made from 100% recycled bits.
I don't speak for DSC. <- They make me say that.
widget
Ever try using a ba1404 as it is mean't to broadcast in fm stereo. Havn't
tried it my self but there is plenty of info on the web about them. They
also have a few plans for transmitters.