Re: Danger, and I don't understand why.

Hi Richie,
             Here is the evidence that a transformer core stores 

> Original Poster: "R.E.Burnett" <R.E.Burnett-at-newcastle.ac.uk> 
> Hi all,
> Today something a little scary and even more strange happened
> during what I thought was a fairly routine test.
> I hooked up a simple static gap across a neon transformer,  with a
> view to later examining the RF behaviour of the gap with my
> oscilloscope.
> A real simple circuit as show below:
>       Power switch
>          /
>   O-----o  o-----D  C----------------!
> 240VAC           D  C                O
> Supply           D  C--- Ground         2mm air gap (bare wire ends)
>                  D  C                O
>   O--------------D  C----------------!
> I tried the circuit without the scope connected first.  Sure enough a
> tiny flame like arc leapt across the gap between the two pieces of bare
> HV wire.  No surprises there.
> Now here is the weird bit.  After a few seconds of buzzing and fizzing
> one of the wires moved a little and the gap closed up (shorted.)  I
> turned off the power switch, unplugged the supply cord,  walked over
> to the gap, and pushed the wires apart with a plastic rod.  To my
> surprise a 4mm white spark snapped across the gap.
> This caught me by surprise.  I thought the circuit would be dead once
> the power was switched off, as there are NO CAPACITORs etc. in circuit.
> I could easily have grabbed hold of the wires with my hands, because I
> expected no danger !

I do the same trick with a *large* 1:1 transformer and a DC power 
supply.  First, the supply gets connected across one of the coils 
with the other remaining circuit. Then, when the current has built up 
to a maximum, I short the previously open coil and then disconnect 
the supply from the first coil. On opening the short across the 
second coil, I am greeted with an arc.
    I am impressed by the amount of time the energy stays in the core 
of your transformer without getting lost in the circuit resistances.
All the time the coil is shorted, there is a current flow maintained 
by the core magnetism trying to collapse.