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Teen electrocuted by power supply while building computer - Page 3

post #21 of 60
Quote:
Originally Posted by Art Vanelay View Post

Actually that's because it has special resistors designed to prevent lethal current. That is something that you won't find when you are sticking your fingers in a power supply.If your resistance is high enough, you will survive. If your hands are damp or you create a circuit with both of your hands, you will be more likely to die, due to the decreased resistance.


That was my point, Volts are not what kill you, That why they have resistors on tasers to prevent lethal current, i.e Amps.

I know they PSU don't have resisters, My theory was that he was messing around the psu while it was on, because if it was off it might not have the amps to kill you, because there is no current, Now like Phardrus said, the PSU will hold a charge for a little while even after its unplugged, but since there is no current going through the PSU the amps should start to dissipate.

I just don't believe the kid could have dismantled the PSU fast enough and expose a part that had the amps to kill and touch it in enough time before it dissipated, unless it was a really crappy PSU or he was doing something he shouldn't have, Like tweaking it while it was on, Or had all the parts exposed while on, unplugged it, then made contact shortly after. Either or is negligence.
post #22 of 60
Quote:
Originally Posted by Philliesfan View Post

I know they PSU don't have resisters, My theory was that he was messing around the psu while it was on, because if it was off it might not have the amps to kill you, because there is no current, Now like Phardrus said, the PSU will hold a charge for a little while even after its unplugged, but since there is no current going through the PSU the amps should start to dissipate.
The amps won't dissipate, as an ampere is a rate of current (coulombs per second), but the amount of stored energy will dissipate, which will probably cause the voltage to decrease, but I have no idea how fast that happens.

Here's an article on capacitor self discharge:
http://www.robotroom.com/Capacitor-Self-Discharge-1.html
post #23 of 60
Quote:
Originally Posted by Sh4dowH4ze View Post

P=U*I, meaning P as in watts is U in volts times I in amps,
soooo......
the wattage is the amount of energy (watt or joule/second) that the "current" carries
amperes is the amount of electrons the current exists of (a "current " is electons that switch atoms sort of)
and volt is the driver or engine that pushes the electrons around in the current, that's why it's called a current.
so:
if we take I=P/U we see that the amount of amperage is depending of P (energy in watts) and U (in volts) meaning, that if i have 110000 volt current with 2 watt I get: I=2/110000, I=0.0000181 ampere
but, if i take a 1000 watt and divide by 240 volt:
1000/240= 4.16 ampere
Actually trying to teach something so please don't take this as a insult. thumb.gif



No insult taken, I know and fully understand how electricity works, I wasn't trying to get into a in depth conversation about, I didn't even want to mention Wattage. I was only busting out the basics.
but in this situation where the supposed device is off watts really don't play into fact as much as the amps and ohms does, the kid could have wet hands for all we know.

But really do any google search, about death on electricity, It the amps that kill you and that does not change.
Why do you think they wet the sponge when they fry some one up? To help increase the current (amps) and not to literally fry the sucker up. More "Humane" that way.
Edited by Philliesfan - 10/13/12 at 2:16pm
post #24 of 60
Quote:
Originally Posted by Phaedrus2129 View Post

Voltage determines how far the electricity will go through a high-impedance medium. There is a minimum voltage required to penetrate flesh. Once that threshold is exceeded, the amps are what determine what kill you. 0.2A will stop your heart. Above that your heart won't be instantly stopped, but you will receive worse and worse burns as the current increases.
A power supply contains voltages between microvolts and ~450V. The maximum is typically 250V to 450V depending on design. The primary capacitors, when partially discharged (as in being unplugged for a few seconds) can generate maybe a hundred volts and between .05 and .50 amps of current. It's all very variable and hard to determine.

I was only using the information the PSU expert gave us, I was under the impression that once the current was killed that it wouldn't retain any amps either, but Phaedrus knows more about PSU then I do so maybe they do?
post #25 of 60
double post
post #26 of 60
We do agree that the power supply that powers that high voltage lead on the back of the CRT in the picture (finger under here dead) is not the same as the power supply for your computer,or perhaps we do not agree? I consider the capacitor that provides the high voltage for the CRT to be part of the power supply.There is no need for this value of capacitor in a computer power supply

EDIT: Here is a quote about how the "finger under here equals dead" comment is not always true.
The high voltage to the CRT, while 200 times greater than the line input, is not nearly as dangerous for several reasons. First, it is present in a very limited area of the TV or monitor - from the output of the flyback to the CRT anode via the fat HV wire and suction cup connector. If you don't need to remove the mainboard or replace the flyback or CRT, then leave it alone and it should not bite. Furthermore, while the shock from the HV can be quite painful due to the capacitance of the CRT envelope, it is not nearly as likely to be lethal since the current available from the line connected power supply is much greater

Second edit: what sections of the computer power suppy have 250-450V present? I would think it would be on the AC side,but not sure where.certainly not on the output.Now the power supply for a plasma screen TV does have some output voltages around 180V that you could come in contact with.
Edited by PCCstudent - 10/13/12 at 2:33pm
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post #27 of 60
To those going off topic and trying to say volts dont kill you or volts do, even that video posted states(without saying) that the amperes are what cause the damage. With that in mind, in real world applications, higher voltages almost always come with higher amp capabilities. Hence, the general rules of thumb, don't' mess with high voltage applications unless you have the proper safety gear and know what you are doing.
An electrical rating is typically in watts (watts = amps x volts) the most basic of power supply units are, lets use 250 watts as the norm. Even if it is running on a 240v circuit, that's just over 1 amp of power. .2 amps of current at the heart(most commonly through the arms) will kill you. So, figure you will get atleast 1/3 the actual shock hitting you, that's still above the lethal level.
Lesson to be learned here.. DO NOT MESS WITH ELECTRONICS IF YOU DO NOT KNOW EXACTLY WHAT YOU ARE DOING!
Sorry if it seems I am bashing anyone, not trying to. Just want to make sure the lesson here is very sound, since a lot of people seem a bit confused on this matter.
Off topic, I can tell you first hand messing with electronics of many kinds, bull fences(electric fences for large cattle) put out about as much as a taser but don't have as many safeties and they hurt. because of the lack of those safeties, I have had burn marks on my hands from messing with them, but they never did more than that, and that was standing on the ground in very wet grass up to my knees. Then there's been times I've been shocked while working on home electrical getting very good contacts between wires and metal air ducts.. It isn't pleasant. I made it off very lucky but the lesson is, always use safety. Why will you trust luck to keep you safe, especially since luck is hard to come by lately..
Be safe all, and be smart about what you do with your electronic items.
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post #28 of 60
I have read some medical reports that the odds of your heart stopping due to an "mishap" with electricity are increased if two things happen.One is if the path of the current (on its journey in and out of your body) passed through your heart (like in one hand and out the other) and if the current is the AC 60 cycle varitey common in the US.The reason is 60 cycles is very close to the normal human resting heartbeat,a bad match.
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post #29 of 60
Quote:
Originally Posted by PCCstudent View Post

We do agree that the power supply that powers that high voltage lead on the back of the CRT in the picture (finger under here dead) is not the same as the power supply for your computer,or perhaps we do not agree? I consider the capacitor that provides the high voltage for the CRT to be part of the power supply.There is no need for this value of capacitor in a computer power supply
EDIT: Here is a quote about how the "finger under here equals dead" comment is not always true.
The high voltage to the CRT, while 200 times greater than the line input, is not nearly as dangerous for several reasons. First, it is present in a very limited area of the TV or monitor - from the output of the flyback to the CRT anode via the fat HV wire and suction cup connector. If you don't need to remove the mainboard or replace the flyback or CRT, then leave it alone and it should not bite. Furthermore, while the shock from the HV can be quite painful due to the capacitance of the CRT envelope, it is not nearly as likely to be lethal since the current available from the line connected power supply is much greater
Second edit: what sections of the computer power suppy have 250-450V present? I would think it would be on the AC side,but not sure where.certainly not on the output.Now the power supply for a plasma screen TV does have some output voltages around 180V that you could come in contact with.

In designs with PFC: 400 - 450V exists between the PFC chopper, through the primary switches, through to the transformer primary winding. Prior to the PFC section you will have either 115VAC or 230VAC depending on the mains input.

In designs without PFC, 220-250V exists between either the voltage doubler or the mains (depending on if 115VAC or 230VAC input), through the primary switches and into the primary winding of the transformer.

Everything from the transformer secondary winding on is generally <20V.
post #30 of 60
PFC=Power Factor Correction.It seems to be a way to clean up the input.I am working my way through this article.
http://ijrte.academypublisher.com/vol01/no04/ijrte0104075078.pdf
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