Re: sec coil zap ouch!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>


>I ran my coil last night in the foundry at Mass-art.

>What a great show.
         ...
>2.
>When I was breaking down the coil at the end of the night

>I was zapped by my sec coil twice.

         Not uncommon.  cf the list archives.
         Titles like 'strange shocks', etc.

>It was obviously residual capacitance.

         What is 'residual capacitance'?

>Why did this happen?

         cf the archives, also electret and electrophorus.
         OK:
         If a DC field (stay with me) be applied to some
         insulators, those insulators can be permanently
         (welllll) modified to hold a charge.  Sometimes
         called 'electret', sometimes 'electrophorus'.
         (roughly:
         The charges inside get yanked out of position and
         then 'stuck' there'.  Effect is improved by heating
         the 'electret', then cooling with field applied.
         Can happen at other times.)
         The analogy to making a permanent magnet is very
         close.


         Whence cometh the DC field?
         Two things:
                 gases (air) result in stray rectification
                 due to different 'mobility' of positive
                 and negative charge carriers.

                 Shapes, especially pointy shapes, have
                 different 'breakout' voltages for each
                 polarity.  This results in rectification.

         The whole subject is covered under 'field ion
         rectifiers', or close to that, and used to have
         practical application.  The usual Tesla System
         incidentally rectifies, inefficiently, a portion
         of its AC output.  (roughly: AC keeps things
         discharged, but the 'last shot' leaves a residual
         several KV DC.)

         The effect is seen more in some coils than others,
         part of this is some people observe/experience it
         and some don't, part of it may be differing coil
         form materials.

>When I turn the coil off the stray capacitance should flow

         'capacitance' generally does not flow.
         CHARGE from capacitance does flow...

>to ground.

         If its in a capacitance and if there is a conductive
         path.  If the charge is trapped 'internal' to an
         insulator, it takes a while to get out.

>Shouldn't it?

         IF it can.  cf above.

>I hate getting whacked!
         Try:

         Discharge the coil _form_ several times, say with
         a wad of Al foil, or steel wool, which is connected
         to ground.

         (The same ;stored charge' effect IS observed in
         capacitors, can be a nuisance.  Takes some 'looking'
         to see it.)

-- 
         best
         dwp

...the net of a million lies...
         Vernor Vinge
There are Many Web Sites which Say Many Things.
         -me