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Re: trigger


Hi Dave, all,
The current rating of a capacitor for pulse discharge service
is usually specified in the manufacturers data sheet or
catalog as a ratio of the number of shots to current
above design value.  Too much current such as from
a direct short across the terminals of the capacitor
can cause several undesirable effects such as:
1.  Dielectric dissipation can become so great that
     the dielectric heats up and ruptures.  The oil
     then vaporizes and forms a gas that forces
     the can or porcelain insulator apart explosively.
2.  The foil that comprises the plates of the capacitor
      can melt, open up, and arc internally.  This will
      have the same affect as above.
3.  The internal connections can melt, break, and
      arc with the above result.
4.  The electroacoustic shock wave from the
     capacitor discharging can cause things such as
     connection leads and foil to break.  It can also
     overcompress the dielectric causing it to abrade,
     wrinkle, and rupture.  The ringing waveform
     multiplies this stress N times.
If your capacitors are for high voltage filtration
then their lifetime will be limited by how much
the discharge current exceeds the design ripple
current.  And then there are manufacturing
defects the effect of which everyone on
this list is well aware from the CP incident!
You can seldom tell when a capacitor
whishes to die catastrophically but if it is
well shielded then it can't take you with
it!
Barry


 ----------
From: "tesla"-at-poodle.pupman-dot-com-at-PMDF-at-PAXMB1
To: Benson Barry; "Tesla-list-subscribers"-at-poodle.pupman-dot-com-at-PMDF-at-PAXMB1
Subject: Re: trigger
Date: Saturday, January 18, 1997 3:19AM

<<File Attachment: 00000000.TXT>>
Subscriber: dbell-at-baygate.bayarea-dot-net Fri Jan 17 22:38:33 1997
Date: Fri, 17 Jan 1997 07:21:23 -0800 (PST)
From: Dave Bell <dbell-at-baygate.bayarea-dot-net>
To: Tesla List <tesla-at-poodle.pupman-dot-com>
Subject: Re: trigger

Barry:

  Thanks for putting your "off-topic" post up on the
Tesla coil list.  This capacitor discharge topic is one
I've been wanting to work on for a long time. I appreciate
your safety notes and circuit suggestions!

What exactly did you mean by the following?

> Your load should not exceed the current rating of the capacitors.

What *is* the current rating of a capacitor??

  I have available a set of eight caps from a high voltage
pulse forming network, that I've been dying (no pun intended!!)
to put into this application. They are each rated at 248 uF/5 kV.
That's a LOT of energy...

Dave