Re: Blown Cap

Tesla List wrote:
> >From jim.fosse-at-bdt-dot-comSun Jun  2 21:52:12 1996
> Date: Sun, 02 Jun 1996 23:43:25 GMT
> From: Jim Fosse <jim.fosse-at-bdt-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Blown Cap
> >
> >NWL engineers, (my cap maker of choice), have had long engineer to
> >engineer discussions with me and they say, unequivocally, that duty
> >cycles drop to near zero on even the most high end pulse caps once the
> >rep rate against AC power input exceeds 1000 BPS.  This is especially
> >true if real large impulse RF currents are involved (as they always are
> >in our kind of work).
> >
> Did they give any reason for this drop off? So many presentations at
> low voltage portions of the 60Hz cycle?
>         Regards,
>         jim


The capacitor disappates energy based on duty cycle and time 
rate of discharge (impedance seen by the discharging cap)  For low 
impedance shorted loads and fast rep rates.  The dielectric takes a 
beating.  If we measure the tank current correctly (250 amps in our 
case), we can see that our lowly .0125 ufd cap, in high end magnifier 
circuit service, might be expected to provide a peak impulse power per 
pulse of about 5 million watts and this might be expected 120 times per 
second!!  Add a few "also rans" as lower voltage pulses occur on the up 
and down side of the sine wave and you see we really "put it to" our 
caps.  They need a rest!  Even a few hundred microseconds will relieve 
the burden on the dielectric.

You must not look at the 1000 bps as a drop off.  It is a limitation of 
our ability to recharge the cap fast enough using current dielectric 

Richard Hull, TCBOR