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Re: need capacitor information
Subject: Re: need capacitor information
Date: Sun, 25 May 1997 23:19:09 -0700
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
Organization: Stoneridge Engineering
To: Tesla List <tesla-at-pupman-dot-com>
References: 1
Tesla List wrote:
>
> Subject: need capacitor information
> Date: Sat, 24 May 1997 10:52:51 -0700
> From: Mark Mackinnon <mmackinnon03-at-sprynet-dot-com>
> To: tesla-at-pupman-dot-com
>
> I recently found a 12kv 60ma sign transformer and I have been designing
> the tesla coil on paper.
>
> I have designed the primery and secondary but I need some information
> about the primary capacitor.
>
> I need to know the dielectric constants and voltage resistance per mil
> of polypropelene, polyethelyne, polystyrene. etc. so I can use the
> capacitance formula to design the cap.
>
> If someone has a table with this information of can help in any other
> way it would be much appreciated.
>
> Sincerely
>
> MSM
Mark,
A rough rule of thumb is that a 12 KV source should use at least 60 mils
(0.060") of polyethylene (LDPE or HDPE) or polypropylene (PP), while a
15 KV source will require 90 mils in order to run reliably.
Multiple-thicknesses of thinner dielectric material will give you higher
breakdown capability as long as you can exclude entrapped air - use at
least 2 thicknesses of dielectric between plates.
The dielectric constant (k) for these materials is about 2.2, although,
you'll find that after assembly the "effective" k for these materials
will be about 2.0 if you immerse the cap in mineral oil (k ~ 2). This is
because of the gaps that form between the capacitor plates and the
dielectric material. Make sure you get most of the entrapped air out of
the cap - if you don't, the ionization and heat build-up will destroy
your cap under extended operation.
Safe cappin' to you!
-- Bert H --