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Re: Polyethylene Capacitors
>From: Skip Greiner <sgreiner-at-mail.wwnet-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: Polyethylene Capacitors
>
>
>Richard and all
>
>I have a very basic question about placing all of these rolled caps in
>series. These caps very definitely have inductance. Inductance ADDS when
>placed in series. Inductance also retards the rate of discharge of the
>total cap. It seems to me that we are defeating our purposes when we put
>a bunch of caps in series which have inductance. Wouldn't it make more
>sense to use flat plate caps with end foil terminations in all cases????
>
Skip,
Yes, inductances in series add. Now what are you discharging
this capacitor, with several hundred nanohenries of series inductance
(I'm guessing here, I've not taken the time to run the numbers for an
8' by 1' sheet conductor's inductance; I hope to be guessing high),
into? A 100uH+- inductor. The primary inductance is the current
limiting factor here. Even given a shorted secondary, the coupling
factor (K=~0.2) only decreases this inductance by 20%; say to 80uH.
You could also view it as 0.1uh/100uh = 0.001% of off axis inductance
by treating you capacitor as a perfect cap and a 100nH series inductor
driving a 100uH coil. To a first order approximation: this can be
viewed/treated as a capacitor driving a 100.1uH inductor.
cheers,
jim