Re: flashing vs. whatever

To: "'Tesla List'" <tesla-at-poodle.pupman-dot-com>
Subject: Re: flashing vs. whatever
From: Tesla List <tesla-at-stic-dot-net>
Date: Tue, 25 Nov 1997 20:49:33 -0600
Approved: tesla-at-stic-dot-net

From: 	Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: 	bert.hickman-at-aquila-dot-com
Sent: 	Tuesday, November 25, 1997 8:41 AM
To: 	Tesla List
Subject: 	Re: flashing vs. whatever

Tesla List wrote:
> 
> From:   Barton B. Anderson[SMTP:mopar-at-mn.uswest-dot-net]
> Sent:   Sunday, November 23, 1997 7:11 AM
> To:     Tesla List
> Subject:        flashing vs. whatever
> 
> To all, a question for rolled polyethylene caps.
> I'm getting ready to begin plans for building these caps. My transformer
> matched cap value is .256uF. I'm planning on building three .083uF caps
> to achieve the (near) value. The plate area required is 2592 sq. inches
> (18" x 144"). I also plan on using four 4 mil sheets each side of plate
> for total of 8 between plates. In transformer oil the caps should prove
> durable assuming I get the air out.
> 
> It seems those of you who have built this type of cap have used roof
> flashing. I'm not real familiar with roof flashing, but isn't it a bit
> thick for the purpose? At least the pulse caps I've seen have an
> extremely thin aluminum sheet. What advantage wood roof flashing give
> over say aluminum wrap bought at a grocery store?
> 
> Just curious,
> Bart Anderson

Bart,

Flat plate caps work very well with heavy duty aluminum foil - flashing
is not necessary. However, I do question the dielectric thickness and
capacitance value, especially if you're using the cap with a rotary gap.
32 mils of dielectric is pretty thin, especially if you're planning on
"sizing" the cap to the transformer. When you "size" the tank cap to
your power transformer, you're actually "tuning" the pair to resonate at
line frequency. For excessively long gap settings, this can
significantly increase the voltage stress on the cap and transformer by
a factor of 3-5X (or more!) over the nominal transformer output voltage!
Connecting the caps in parallel will NOT increase their voltage handling
capability, only the effective capacitance. Also, with a tank cap this
large, you'll need to have a fairly large secondary and toroid so that
you can bring this system in tune with a reasonable number of primary
turns. 

How big were you planning on making your secondary and toroid, and what
voltage/current is your power source??

Safe cappin' to you!

-- Bert --