[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: safety gaps on capacitors



Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Bart,
          I would use a resistance which limited peak discharge 
current to the cap rating. That should easily produce a damped 
response. Simple Vpk/R = Ipk. 

Regards,
malcolm

On 5 Aug 01, at 12:20, Tesla list wrote:

> Original poster: "Barton B. Anderson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>
> 
> Hi Rob, All,
> 
> I understand that a safety gap is needed to protect the tank cap from an
> overvolt condition, and that simply throwing
> a simple gap can also damage the cap. The use of a series impedance is
> recommended to extend the discharge time
> reducing the overvolt stress of the safety gap occurance. You mention, to
> reduce the Blumlein effect, a carefully
> matched series impedance is needed. Could you elaborate on how to design in
> the correct impedance?
> 
> Thanks,
> Bart
> 
> Tesla list wrote:
> 
> > Original poster: "Area31 Research Facility by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <rwstephens-at-hurontario-dot-net>
> >
> > All,
> >
> > Simple safety gaps (not impedance current limited) placed across your tank
> > capacitor can cause the capacitor to fail due to a mechanism known as
> Blumlein
> > Inversion Generator.  The capacitor is usually a long pair of foil strips
> with
> > a dielectric between.  The fact that it is rolled up is not important.
This
> > structure is a form of parallel wire transmission line. If you fully
> charge the
> > line to some voltage X, then if you place a low impedance short circuit
> across
> > one end of this line (the safety gap firing) you will create a pulse of
> reverse
> > polarity which will travel down the transmission line, adding to the
original
> > charge and appearing as 2X voltage at the other end.  You have just
subjected
> > your capacitors innards to the highest possible discharge current it can
> > possibly produce with all the associated hydrodynamic stresses, and you
have
> > doubled whatever overvoltage condition you normally subject the capacitor
> to in
> > Tesla use.  This is a proven formula for capacitor failure!
> >
> > Safe use of a capacitor safety gap requires carefully matched series
> impedance
> > to neutralize the Blumlein effect.
msnip...