RE: Tank Cicuit Capacitor (discharging)

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

Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-compaq-dot-com>

The way that a Tesla coil is wired, you have a loop consisting of the NST
secondary, the tank cap, and the Tesla primary coil.  When power is shut
off, the spark gap is out of the picture, and the primary coil is
essentially just a piece of heavy wire, so the tank cap ends up being
connected in parallel with the NST secondary.  The resistance of the NST
secondary will discharge any remaining charge in the cap in a few
milliseconds after power is turned off.

HOWEVER - should the primary tap connection or NST secondary or NST
protection network connections come loose, you'll loose this built-in
discharge mechanism.  This happened to me once and I got "bit".

Also, if you have two or more caps wired in series rather than a single cap,
the NST secondary will be unable to discharge them.

Shorting out the cap with a piece of wire is a bad idea since it generates
potentially damaging high current pulses and makes a mess out of your cap
terminals.  It also won't work with series-wired caps.  And it's an easy
thing to "forget".

A permanently wired bleeder resistor on the capacitor is a much safer
approach.  For series caps or MMC's, a resistor across each individual cap
is needed.  For a single cap, you can make a suitable bleeder resistor out
of many (~15) series-wired resistors, aka MMR.

Gary Lau
MA, USA



> Original poster: "Stolz, Mark by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Mark.Stolz-at-st-systems-dot-com>
>
> Hi All!
>
> Does the capacitor in the tank circuit hold a charge once power is turned
> off?  I've heard some say yes and some say no.  Isn't that by definition
> what a capacitor does?
>
> Mark Stolz
> Houston, TX
>
>
>