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BIG Capacitors




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From:  Bert Pool [SMTP:bertpool-at-ticnet-dot-com]
Sent:  Friday, February 20, 1998 12:33 AM
To:  Tesla List
Subject:  Re: BIG Capacitors


> From:  Bill Lemieux [SMTP:gomez-at-netherworld-dot-com]
> Sent:  Wednesday, February 18, 1998 4:57 PM
> To:  Tesla List
> Subject:  Re: BIG Capacitors
> 
> Edward V. Phillips wrote:
> 
> >         Any idea how big a 100 uF 18 kV capacitor would be?
> 
> Good point.  I just required a very nicely-designed, massive pulser
> which contains 6ea 63uF / 10kV caps.  Each unit is about 8x12x24" and
> weighs over 100lbs.  The whole machine weighs nearly 1000 pounds, and
> was an iron-clad galloping bitch to transport.
> 
> Which reminds me, does anyone have a good source for surplus ignitrons?
> I prefer the National 7703H so as to match the originals.  I may have
> damaged the tubes by moving the machine- National's literature says
> that in crowbar and cap-discharge applications, moving the tubes may
> damage the ignitor and shorten the life of the tube.  I am hoping that
> proper re-conditioning the tubes will alleviate this...
> 
> 
> > You can get 4800 ufd 450 volt electrolytic capacitors pretty
> > cheaply at swap meets (less than a buck around here). 
> 
> Ed- eletrolytics are really lousy for fast pulse-discharge work.
> 
> 1. they have high-self-inductance, which slows down their discharge time
> too much for 1uS pulse times.  Most pulse-discharge research is looking
> for very high peak power, and the narrower you can get your pulse, the
> higher the peak power for a given stored energy.
> 
> 2. they have high effective series resistance, limiting their discharge
> current and thus, discharge time.
> 
> > 40 of
> > those in series would be 120 ufd at 18 kV, if you could
> > equalize the voltages with shunt resistors across each
> > capacitor.  Since typical leakage is of the order of 2 ma,
> > that wouldn't take too much power.  I have used one of these
> > very successfully in a magnet charger, and think the series
> > resistance isn't more than a couple of ohms.  Have looked at
> > the can crusher page, but can't remember how many turns on
> > the primary, so hard to judge what peak current is.  This
> > may or may not be a foolish idea, but I'm sure discharging
> > such a bank would be pretty spectacular.
> 
> It's less than you would expect.  I built a 1.4 kJ bank out of Aerovox
> high voltage filter caps, and could not get discharge times faster than
> some hundreds of milliseconds.  It was loud, but dangerously so.
> 
> Later, I found a single pulse-dischage cap beautifully designed for
> low-inductance, fast-pulse work, of about 1.5 kJ at roughly the same 
> voltage.  Its discharge times were on the order of less than 1uS with
> a rather lousy switch and transmission design, and the noise was
> stunning.
> 
> -G
> 

People, you should know Greg well enough by now to know that he 
loves to use words literally, so when he says the noise was stunning, 
it was literally so.  OK Greg, how many people did you stun, and how 
many of them were able to get up off the ground and walk away 
unassisted? <grin>

Bert Pool
TCBFW
bertpool-at-flash-dot-net