In article , amdx
wrote:

On 8/1/2014 6:01 PM, Joe Gwinn wrote:
In article , Lloyd
E. Sponenburgh wrote:

amdx fired this volley in news:lrgv8c$1fe$1@dont-
email.me:

I just got to thinking, the output voltage must be well below 120
volts, otherwise the bulb would glow a lot brighter.
Mikek


Yep, you're right. But the point is, if it can deliver the half-amp or
so necessary to 'glow' that bulb (at, say, 10V), think how high the
voltage would be at only 5ma (1/100th of that)... if you were doing the
math, AND the output impedance/resistance were linear, that would be
1000V; although there's not enough information there to say that
conclusively. On would have to test a bulb to see how much current it
took to make it glow like that, then measure the voltage across it.

My guess is that it's sparking over the filament. Incandescent bulbs
these days are filled with low pressure xenon or argon, and that is
probably the path of least resistance. Arcs in gas can have negative
resistance.

Nor is the battery powering the homebrew stun gun all that large.

Joe Gwinn


I don't know but, I doesn't seem like it would arc when there is a
say 20 ohm wire for it to flow thru. Once it sees the 20 ohm load the
voltage has dropped way way down at least across the light bulb. Note
the 20 ohms is in series with the arc on the base of the bulb, he can't
quite make connections to both electrodes to the bulb.

We don't know the full details of the inverter used, but it will be
high frequency square waves, so the rate of rise is quite fast. The
filament is coiled or even supercoiled, and so has some inductance.
And at RF, the stray capacitance allows significant current to flow.
As others have mentioned, this is how many welders strike their arc.


Something has me puzzled, once you get an arc across the electrodes of
the stun gun, the plasma is very low ohms. That would drop the output
voltage.
So the question;
Once you have an arc started can you sustain it with low voltage?

Absolutely. Typical neon sign transformer puts 7,500 or 15,000 volts
across the tube to strike the arc, but is impedance limited so it is
happy working into a short circuit.

...http://en.wikipedia.org/wiki/Neon-sign_transformer


Joe Gwinn