Re: pulse cap

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

It probabably depends...

Some pulse discharge caps are "self healing" to a certain extent, esp the
ones with polypropylene dielectric and the "plates" printed on the plastic
and connected by little "fuses" to a bus bar. Over time, the dielectric
will fail, all the energy gets dumped, blowing the (deliberately) tiny
conductor to that section of the plate, and causing a gradual degradation
in the capacitor.

On the other hand, the larger castor oil/paper units (Type C for Maxwell)
that store more than a kiloJoule tend to fail pretty catastrophically.
Internally, they are a bunch of smaller caps in series parallel to get the
necessary rating.  Particularly for the lower voltage units, if a breakdown
occurs, all the energy stored goes into that one failed sub-capacitor,
causing a fair amount of mayhem. In the older (70s and 80s vintage) units
(say in the 3-5 kJ/can area), the steel casing contains the damage.  In the
newer 50kJ/can units, the case might rupture (violently).

Just to keep things in perspective.. your little plastic bricks don't store
all that much energy.

0.03 uF -at- 30 kV is only 13-14 Joules... Like dropping a 10 pound weight on
it from a foot.

50 kJ, on the other hand, is like dropping a car (call it 1000 kg) off the
top of your house (5 meters)...  Lots of damage potential there...



Tesla list wrote:
> 
> Original poster: "Rick Williams by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <richardwwilliams-at-earthlink-dot-net>
> 
> Hi all,
> About that pulse life spec. Does the cap simply die (if so, how?) or is that
> how long it will perform "within spec" before performance begins to degrade?
> 
> Rick W.
> Salt Lake City
>