[GreenKeys] Eico EC 700 - Re: Loop supply, or are we still beating out wifes and kicking the dog

[drlegendre .]

@Doug

"The standard electrician's test screwdriver has an NE2 bulb inside plus a
10 or so megohm resistor."

Then obviously, the tiny currents passing the 3M3 parts must be sufficient
to keep the circuit operating - I didn't realize that any functional level
of current would flow under those conditions.

Thanks for the comments.



On Tue, May 31, 2016 at 9:19 PM, Jones, Douglas W <douglas-w-jones at uiowa.edu
> wrote:

> From: drlegendre . [drlegendre at gmail.com]  Tuesday, May 31, 2016 7:21 PM
> > Simply put, I don't see why this circuit should work. If you notice,
> both leads of +all+ caps are connected to what should be the same voltage
> potential. Both leads connect to B- with a 3M3 resistor in series with each
> lead. No functional level of current should flow into any capacitor, at any
> point.
>
> The standard NE-2 implementation of an astable multivibrator uses 2 NE-2
> lamps, with one lead of each lamp tied directly to the supply, and the
> other lead of each lamp tied to the opposite side of the supply through a
> high resistance, with a single non-polar capacitor bridging the two points
> where lamp ties to resistor.  That is, with fewer lamps, exactly what the
> circuit in question does.
>
> With just two lamps and one capacitor, the two lamps alternate.
> Initially, one or the other lamp will light first.  As it lights, the
> voltage across an NE-2 lamp drops abruptly from about 60 volts (the strike
> voltage) to about 40 volts (the forward voltage).  Whichever lamp lights
> first will drag down the voltage across the other lamp through the
> capacitor.  The RC circuit on the off-lamp then recharges until that lamp
> turns on, at which point it pulls the voltage across the other lamp down to
> 20 or so volts, turning it off.  The process then repeats with the roles of
> the two lamps reversed.
>
> NE2 lamps light with pathetically small forward currents.  The standard
> electrician's test screwdriver has an NE2 bulb inside plus a 10 or so
> megohm resistor.  Stick it in a lamp socket with the electrician in the
> circuit, and the bulb will light.  That's the way it's intended to be used
> to see if the circuit is energized.  I have one and use it on and off when
> I need to see if a 110V line is hot.
>
> So, I see no reason why the circuit for the do-nothing-box shouldn't work
> just fine.
>
>           Doug Jones
>           jones at cs.uiowa.edu
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