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chen
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[*] posted on 23-12-2010 at 17:47
can a computer power supply kill you?


I am going to make a electrolysis machine with a computer power supply and want to know if I will die if I touch the (stripped) wires accidentally. I believe most people die at .5A so I'm leaning towards yes.

The input rating is 100-120V and 3A
OR
200-240V and 1.5A

The outputs for various wires are:

RED +5V 10A
YELLOW +12V 2A
BLUE -12V .3A
ORANGE +3.3V 6A
PURPLE +5VSB 0.8A
BLACK GROUND
GRAY POWER GOOD

I'm wondering what "gray= power good" means.

Maximum continuous output power is 100W.

[Edited on 24-12-2010 by chen]
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bfesser
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[*] posted on 23-12-2010 at 17:48


Why touch the wires?
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not_important
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[*] posted on 23-12-2010 at 17:57


If you get a good connect, such as a firm grip on a bare wire or even a moderate grip on wet wires, 12 V can kill you. The path is important, right hand to left foot is likely to be bad for instance, as the flow goes through the chest region.
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DDTea
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[*] posted on 23-12-2010 at 18:04


When you fight the power, the power will fight back. :cool:



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entropy51
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[*] posted on 23-12-2010 at 18:24


Quote: Originally posted by chen  
I am going to make a electrolysis machine with a computer power supply and want to know if I will die if I touch the (stripped) wires accidentally. I believe most people die at .5A so I'm leaning towards yes.

The power supply can deliver 0.5 amps through an appropriate resistance, but it won't if you touch the wires because the resistance of the body (through the skin of the hands) is too large to permit that much current.

Look up Ohm's Law and the resistance of the human body and calculate the current that will flow.
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bbartlog
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[*] posted on 23-12-2010 at 18:33


People have died from 12V, but I think it really takes some doing (dip both hands in electrolyte gel and then seize the leads firmly, or something). Even then, the mechanism is disruption of the heart's electrical rhythm rather than gross physical damage such as burns or hyperthermia.
I've done manual repairs on a 16V power supply while the wires were live, and with dry skin you can barely feel it when you complete the circuit with your body. A bigger hazard IMO when working with low-voltage high-current power supplies is that a short through something with a really low resistance will cause a spark or explosion that might burn you.
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smuv
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[*] posted on 23-12-2010 at 19:33


Don't worry about it. I use 12v power supplies all the time, and have never felt so much as a shock from one (except on my tongue...next time I will use a voltmeter). But then again, the voltage to feel a shock is highly dependent upon the area of the body and also how conductive it is. As long as you are handling 12v with dry hands, you will never feel a shock.
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[*] posted on 23-12-2010 at 19:41


" 12 volts can kill you " seriously ?
A medical citation for this assertion is warranted I think.

I have spliced and twisted bare telephone hookup wire while live,
at 50 volts DC one can just start to feel a tingling in the fingers ,
others who do this can't discern any sensation.

Granted that if you are hogtied so you cannot disconnect yourself
and for the purpose of torture are subjected to a current across
the chest , cardiac arrhythmia might be induced. A high applied current
at low voltage can burn nerves but requires a large contact area
for needed conduction as well as a prolonged more than transitory
exposure. Car batteries will put out 90 plus amperes and are for
this reason connected observing basic electrical ground safety.

Sensibly if there is doubt about what can pose a risk heed that
instinct. Electricity beyond the power of a few flashlight batteries
if you don't know much about what you 're doing , is not something
one can be safely careless with.

.
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[*] posted on 23-12-2010 at 19:49


I have been shocked on many occasions by welders and im still alive they were set at very high amps 100+ and 20ish volts, didn't kill me.



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[*] posted on 23-12-2010 at 19:52


Yeah, I know ohm's law by heart, I just don't know how actual electronics work. Good to know to look at the voltage and not the current.

I looked up a story online about a naval officer who killed himself with 9V by puncturing his skin with both leads. I'm not going to do this.
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[*] posted on 23-12-2010 at 21:15


Almost every single post in this thread has totally missed the point and everyone is talking about volts this and volts that, I use to daily touch well over 100k volts and not even get a little tingle this is because of a couple factors, mainly the fact that there was almost zero current comming from the air cored transformer. Its the amps that kill not the voltage.




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[*] posted on 24-12-2010 at 05:48


Quote:
Almost every single post in this thread has totally missed the point and everyone is talking about volts this and volts that


On the contrary. You can't deliver amps without volts, so in the context of this discussion (a reasonably high current power source) it makes perfect sense to talk voltage. Of course, if the source is severely current limited, then high voltage is not a problem. Static electricity runs into five figure voltages and doesn't kill people.
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[*] posted on 24-12-2010 at 06:12


Daft analogy, but voltage is the motor and amperage the weight of the vehicle - I've had accidental bangs off electric fences, mains power (standing on wood) and an NST!
10kV *will* make one roar, but so will a fence . . .
People's resistance varies, I think, and what might kill in one instance, in another the recipient might just be jellied for a day.
If in *any* doubt, don't touch it!

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[*] posted on 24-12-2010 at 07:06


Quote: Originally posted by bbartlog  
People have died from 12V

Quote: Originally posted by chen  
I looked up a story online about a naval officer who killed himself with 9V by puncturing his skin with both leads. I'm not going to do this.
Sorry fellas, but neither of these scenarios is even remotely possible.

Chen, measure the resistance of your body by gripping the two leads of an ohm meter (or google for it) and then use Ohm's law to calculate the current resulting from 12 volts. Then google for the lethal current and compare the two. Learn how to answer these questions for yourself.
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[*] posted on 24-12-2010 at 07:21


I routinely take 12 volts, 24 volts and 5 volts with my bare hands, from computer supplies and all kinds of other supplies. These low voltaes cannot kill. You may get some funny tingling feeling when your hands are wet and salty with 24 volts, but that's all. So, no need to worry shock or electrocution.




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[*] posted on 24-12-2010 at 10:50


With wet hands then you will feel serious tingling with 12v, if you apply 12v to the wrong places (near the heart especially) you could get bad effects. With normally dry skin you should have no ill effects from the voltage. HOWEVER inside a computer psu there is clearly a mains input so presence of certainly dangerous voltages. If the PSU can deliver serious current then heating could be a problem with the associated burns.
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[*] posted on 24-12-2010 at 11:10


Of course, INSIDE a power supply there are parts which carry 230 V AC or 110 V AC and these ARE dangerous. But as long as the case is not opened and you do not spill liquids or metal objects inside the power supply through the ventilation openings, then I see no real risk. No one would put the two electrodes with 12 V just near his heart while the body is wet or sweaty.



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[*] posted on 24-12-2010 at 13:36


I agree with Woelen. Unless you plan on stabbing your heart with electrodes that is. 1 Ma you can just feel. 100 Ma across your heart will stop it. 150 Ma across your heart will more often than not stop it so hard they cannot bring you back. DC burns more than AC yet AC makes it harder to let go. Volts push amps. Volts = acceleration potential for each electron and amps = number of electrons. Virtually all electrocution deaths are from AC but we are most often exposed to AC whenever we encounter dangerous voltages. Anyone surviving a bolt of lightning will attest DC is a killer as well. Around 80 volts you can not let go from the current flow between two hands across your heart with dry skin. Been there, done that. This could be as low as 24 volts when current potential exists and you are wet. I was locked up unable to let go and my co worker stood there looking at me with the most stupid expression watching me fry. Knowing the trouble I was in I willed myself to violently thrust myself away from the machine. Had it been up to the moron I worked with I would not be writing this. I have been hit by many voltages and currents many times and the 80 volts was actually the closest I came to being done for. It would not let me let go. If you work in the industry then you know 480 VAC is the most dangerous voltage in the panels as it loves to cause explosions. A guy I know after years of grafts from a 480 VAC panel exploding still looks more reptilian than human. When an arc occurs at 480 volts the plastic insulation turns into a ball of rapidly expanding plasma in a runaway reaction. The greater heating effect of DC makes this worse as anyone working in a submarine can tell you.

Bottom line is unless you open the supply you are fairly safe but survival dictates you always treat things safely and never fail to consider a possible heart path for current flow whenever you work with electricity. Your computer power supply is not isolated from the mains meaning a fault internally can possibly be hazardous with a potential existing between your output leads and earth ground. If you put your body in this path who knows. Do not stand in water holding one of the electrodes even if it is 5 volts referenced to the power output common. The chance of a common mode voltage between the power supply negative or positive leads and earth ground does exist. Isolation consists of the windings in the ferrite transformers in the supply, and these windings can short together under the right circumstances.

In short treat all power with respect no matter how benign you think it is. Do this always until it is second nature. Meaning until you do it without thinking about it. You never know when these habits will someday actually save you when things do go wrong.


"When you fight the power, the power will fight back."

Resistance is Futile



[Edited on 12-25-2010 by IrC]




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[*] posted on 25-12-2010 at 00:04


Just don't give it a gun.



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[*] posted on 25-12-2010 at 01:40


Current varies inversely with resistance, so as the resistance goes down then the current goes up. One example of this that I discovered accidentaly is my aquarium pump, I use it to circulate water through my condensors. I noticed that when barefooted or with socks on the concrete that when I touched the water in the pump resevoir nothing happens, but on a rainy day or when the concrete is wet if you touch the water you end up getting quite a jolt.

So as long as you are careful you should have no trouble at all.
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[*] posted on 25-12-2010 at 11:50


V=I/R not to hard realy



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[*] posted on 25-12-2010 at 12:29


Quote: Originally posted by Ephoton  
V=I/R not to hard realy


Are you sure it is easy if you post E=I/R instead of E=I*R? I prefer E instead of V for volts.



Ohmslaw.jpg - 37kB




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[*] posted on 25-12-2010 at 13:08


I have never had a shock or a tingle from a 12V supply eg car batteries and they pack quite a punch being capable of delivering tens of amps.
I know quite a few people who have survived a 240V AC shock.
The capacitors inside a computer power supply are quite nasty and can give you quite a poke even when it is not plugged in if they have not fully discharged and you touch their terminals.
Similar shocks but a lot less unpleasant can be had from Coleman lamp igniters and electronic flashes.
Old fashioned cathode ray tube displays carry a big voltage and can hold it for a long time after switch off.
Naive poking can result in a Darwin Award, for you not the tube!
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[*] posted on 25-12-2010 at 14:11


Assuring that all powered devices maintain the same polarity to ground
eliminates the principal risk of being shocked. One conductor of the house
service power line is isolated , the other is connected to ground typically
to the water pipes and even gas lines , which provide parallel conductive
paths the same as the grounded conductor. By bridging a point of contact
to the isolated side of a powered device with ground , even a damp concrete
floor , creates a ground fault. In other words your nose lights up just like
Rudolph the reindeer.
High voltage utility lines in some areas have just one conductor and use
ground instead of the second conductor. The transformer provides isolation
in this case. See further explaination below. #
http://en.wikipedia.org/wiki/Single-wire_earth_return

Equipment will in almost all cases further isolate the electrical parts at
ground from the units enclosure. Devices which have a chassis ground to
the metal case of the unit pose a risk if powered with the case connected
to the isolated power line conductor. An electrocution hazard then exists
for touching that case and anything else that is grounded.

# An added layer of safety is provided by an isolation transformer because
it has only inductive coupling with the service power line and the supply side
has no physical connection to the isolated conductor of the service
power line.

A risk that can occur is if more than one device powered from the supply side
of the isolation transformer sharing common ground one has reversed polarity
as described before. Touching both in such event you will receive a shock.

Explained in some detail here , See Figure 83-2
http://web.squ.edu.om/med-Lib/MED_CD/E_CDs/anesthesia/site/c...

The images should enlarge by clicking on each , but if they don't as for me
they are attached below. *NOTE the circuit as shown gives the
impression that a ground fault occurs within the isolation transformer unit
itself. A FAULT CAN OCCUR ANYWHERE in the circuit , the connecting power
cords and the connected equipment.
Ground fault.gif - 19kB

[Edited on 26-12-2010 by franklyn]
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Ephoton
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[*] posted on 25-12-2010 at 22:20


ye typo V=I*R

no more iphone for me.




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