On 8/1/2014 2:47 PM, amdx wrote:
On 7/31/2014 4:17 PM, rangerssuck wrote:
On Thursday, July 31, 2014 4:44:14 PM UTC-4, amdx wrote:
On 7/31/2014 2:23 PM, wrote:

On Thursday, July 31, 2014 1:57:33 PM UTC-4, rangerssuck wrote:



I don't know how you can discuss voltage and current without also

including impedance (resistance) in the same discussion. They

are all directly related and inseparable in this context.









How would discussing impedance in any way alter the specific high
voltages advertised for the taser and stun-gun that I told Lloyd
about as an example?





Very good question! The answer should lead to understanding.



A power supply or voltage source is modeled as a voltage source with

ZERO internal resistance (impedance) in series with some resistance.



I will pick numbers that I saw for Tasers to use in an example.

My example is not perfect, I hope I can explain why.

50,000 volts and 2 milliamps. In order for a 50,000 volt source to

only deliver 2 milliamps the internal resistance (impedance) has to be

2.5 million ohms.



What that means is, if you short the output pins, 2 milliamps will

flow from one to the other. But with a short on the output the voltage

between the pins will be 0 volts.



Now if we assumed the combined resistance happened to be 1,000 ohms

the voltage would rise to 1.9999 volts and 0.001999 milliamps would
flow.

*the 1,000 ohms consists of the combination pin to skin resistance, the

resistance of the skin between the pins, and the another skin to pin

resistance.



If we assume 100,000* ohms between the two pins then the voltage

will increase to 199.2 volts with 0.001992 milliamps flowing.



If the combined resistance happened to be 1 million ohms

the voltage would rise to 1923 volts and 0.001923 milliamps would flow.



Where my example may fall short, I don't know how the measure to get

their specifications. I assumed 50,000 volts open circuit and 2

milliamps short circuit current.



As you may see from that, The output voltage is not 50,000 when

the pins are put against the skin. Also the current is limited to

2 milliamps or less because of the internal impedance of the stun gun.

Mikek

Oh CRAP. 50E3/2E-3 = 25E6 NOT 2.5E6. While the reasoning in your
explanation is fine, a decimal place has been dropped. I didn't check
the rest of it (left as an exercise for the reader).

But the point is the same: The stun gun CAN'T put out more than 2mA
because of the generated voltage and the internal resistance
(impedance if you prefer, but I'll bet most of it is resistance). If
it was a lower voltage with the same resistance, the max current would
be lower.

Anyone who wants to argue with that is simply not worth arguing.

Would you care to comment on the lethality of this DIY stun gun in
this video. When he connects it to the light bulb it lights, it is
possible the filament is open, but if you watch closely, it looks like
the filament is slow to warm and cool (relatively) not like an arc.
https://www.youtube.com/watch?v=7HM4oiJNGJs
I think it might be deadly. I don't think 4 ma will light that bulb.

Mike


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The Arc is so hot - more than 4 ma any day. Likely 40ma The light bulb
wasn't drawing current like normal.
The resistance is high enough that arcing across the turns of the
tungsten occurred and the arc was inside of the glass tube.

And if you look closely the bulb has a dark spot on the side - might
be a burned out bulb just arcing away across the open.

Remember a cold light bulb is 1/10 of the resistance when hot. Thus 10x
current flows for an instant. (reason so many bulbs go bad then)
and why I put shunt resistors across controls in designs to keep the
filaments Warm but not glowing as it extends the lamps for years. I
have a design done in high school (at home) and the lamps (Christmas
tree) are still burning upon command. The tungsten is spongy and
brittle once heated to full temp. Flexing it causes fractures.
Dimmers are the modern home best friend. Slight different current
and a slow start keeps the bulbs burning.



Martin