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Topic: Bigger power supply (Read 1 time) previous topic - next topic

ma_hty

Hi,

Finally, I moved on to a power supply with bigger capacity, i.e. 12V 30A .  I'm just wondering.  How far the damage would be if I accidentally shock myself with the 12V 30A output?  ( Sorry for asking newbie questions )

Thanks.
Gary

cjdelphi

none at all...

the worst that could happen is you short out the terminals which would cause a huge amount of heat build up, the result being a burnt finger or hand

AlxDroidDev


Hi,

Finally, I moved on to a power supply with bigger capacity, i.e. 12V 30A .  I'm just wondering.  How far the damage would be if I accidentally shock myself with the 12V 30A output?  ( Sorry for asking newbie questions )

Thanks.
Gary


It is the current that kills, not the voltage. 30A is much more than enough to kill a person, specially given the proper conditions.

One proper condition would be your hands wet and each hand grabbing one of the poles of the PSU. That current would go from one hand to the other, passing through your heart and killing you.
Learn to live: Live to learn.
Showing off my work: http://arduino.cc/forum/index.php/topic,126197.0.html

ma_hty

:smiley-roll-sweat: ... different opinions... which one is more likely?

cjdelphi

no, not conflicting data.

You're safe to touch the 12v terminals, if you were not "safe" there would be a LOT more dead mechanics
and warnings all over 12v power sources.

If you took that 12v supply, and then prodded yourself with it, penetrating your skin, then it's likely current will flow enough to kill you.

(Go ahead, grab the terminals, 1 hand touching + and the other the -, you wont die) up to about 50v is "safe" unless you're intentionally
trying to kill yourself.

Coding Badly


ISBN 0-8493-1889-0 pp. 2317-2324 (obtained via Wikipedia) appears to be an excellent resource on the matter; Google books has it available.  The lowest skin resistance (which varies dramatically) mentioned in the book is 5 K?.  At 12 V the current is 2.4 mA.  According to the author (at 60 Hz AC)...

1 mA --> Sensation that shock is occurring
5 mA --> Upper limit of safe or harmless range

(Which agrees well with my personal experience with low-voltage AC.  For what that's worth.)

300 mA to 500 mA is where ventricular fibrillation occurs for DC.

The fact that the power supply is 12 V is important and the fact that the power supply can provide more than 300 mA is important but the actual current rating of the power supply is irrelevant.  The most important factor is skin condition (versus voltage).  But you would be very hard pressed to get a resistance less than 5 K?.  I guess the best advice is to keep the power supply terminals away from the left side of your bare chest after you've run a marathon.

fungus



Finally, I moved on to a power supply with bigger capacity, i.e. 12V 30A .  I'm just wondering.  How far the damage would be if I accidentally shock myself with the 12V 30A output?  ( Sorry for asking newbie questions )


What is it about Ohm's law that bothers you? Why do you refuse to accept it?

The thing that determines how much current will pass though you is the 12V, not the power supply's theoretical capacity.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

fungus


It is the current that kills, not the voltage. 30A is much more than enough to kill a person, specially given the proper conditions.


Of course...but the conditions would have to be very special for a 12V 30A power supply to put more current though him than a 12V 1A power supply.

Hint: The important number is "12"

Ohm's law. It's not just somebody's opinion.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

cjdelphi

Fungus, do you grow on trees?  or just humans?

fungus

#9
May 25, 2013, 12:24 pm Last Edit: May 25, 2013, 12:33 pm by fungus Reason: 1

Fungus, do you grow on trees?  or just humans?


I don't recall growing on any humans... :)

The general lack of trust in Ohm's law disturbs me.

The evidence all around suggests it's at least as reliable as gravity but nobody seems to believe in it.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

majenko

#10
May 25, 2013, 12:48 pm Last Edit: May 25, 2013, 12:54 pm by majenko Reason: 1


Fungus, do you grow on trees?  or just humans?


I don't recall growing on any humans... :)

The general lack of trust in Ohm's law disturbs me.

The evidence all around suggests it's at least as reliable as gravity but nobody seems to believe in it.


"Gravity is a myth - the earth sucks."

If Ohm's law was wrong you wouldn't be reading this right now.  Your computer wouldn't be working.  It is the most fundamental of the fundamental laws of electronics.

If you don't believe us, get yourself a battery, some resistors (a variety in the 470? - 10K? range for instance - don't go too low or you may burn your fingers), and a DMM.  Measure the resistance of a resistor (don't go by the "rated" value), then connect it across the battery.  Measure the voltage across the battery with the resistor attached.  Insert the DMM between one of the leads of the resistor and the battery terminal and measure the current at that point.  Then do the simple sum I=V/R and you'll see that the current you measured is the same as the value you just calculated.  Change the resistor for a different value and repeat the experiment.  You'll see that every time the sum works out right.  Not just some times, but EVERY TIME.  That is one of the most fundamental experiments you do in the first week of your electronics course.

Once you have done that, print out this formula wheel and stick it to your wall.



Also, a good tutorial:
http://youtu.be/dQcHMsKCCCg
Get 10% off all 4D Systems TFT screens this month: use discount code MAJENKO10

karl_eller

If you grab some probes, connect them to the battery and jam them into your chest across your heart, you'll probably kill yourself. If you just grab the battery terminals, you might get a small shock if your hands are wet, otherwise nothing happens.


It is the current that kills, not the voltage. 30A is much more than enough to kill a person, specially given the proper conditions.

V=I*R. You can have a power supply that can supply lots of current but doesn't have enough voltage to do push the current through your body's resistance, and you can have a power supply that has huge voltage but very little current flow (eg electric fence). It's never as simple as "voltage kills" or "it's the current, not the voltage".

cjdelphi

Fungus, do you grow on trees?  or just humans?
[/quote]

The general lack of trust in Ohm's law disturbs me.

The evidence all around suggests it's at least as reliable as gravity but nobody seems to believe in it.
[/quote]


You should hear what this guy has to say about Volts/Amps killing you.

https://www.youtube.com/watch?v=8xONZcBJh5A

retrolefty

The biggest safety risk of high current lower voltage power sources (like a 12 volt car battery) is if you happen to short out the supply output across a ring or watch band as the resulting high temperature of the metal would severely burn you. We had written safety rules at work about removing all such personal articles before working on live electrical systems regardless of their voltage ratings.
Lefty

ma_hty

#14
May 25, 2013, 08:20 pm Last Edit: May 25, 2013, 08:27 pm by ma_hty Reason: 1

...
You should hear what this guy has to say about Volts/Amps killing you.

https://www.youtube.com/watch?v=8xONZcBJh5A



In the video at 6:00, the author actually connects himself to a car battery at 30V to measure the current flow through his body.  I guess I should be safe with 12V, provided that my hands are dry and I didn't wear anything metal.  Am I correct?  ( I swear I won't try it on purpose.  I just want to know where the bottom line is. )

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