Re: making hv caps

From: 	Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: 	bert.hickman-at-aquila-dot-com
Sent: 	Saturday, January 10, 1998 9:35 AM
To: 	Tesla List
Subject: 	Re: making hv caps

Tesla List wrote:
> From:   Homer Lea[SMTP:HomerLea-at-aol-dot-com]
> Sent:   Friday, January 09, 1998 11:36 PM
> To:     tesla-at-pupman-dot-com
> Subject:        making hv caps
> has anyone tried to take apart large hv caps like mine (60 kv etc.) , separate
> the smaller segments and partly unwind them to make say 20 or 30 kv caps with
> less capacitance so they could be used for tesla coils???????
> jim heagy


Richard Hull has a videotape where he did this with a utility
power-factor correction capacitor. I looked at doing this with a surplus
54 uF 15 KV polypropylene-kraft paper pulse cap, but it turned out that
the cap was actually internally constructed as 28 identical ~2 uF
modules connected in parallel, with none in series! Each element was
constructed to run at 15 KVDC - not a typical pulse cap at all!
Reconnecting these modules in series would have resulted in a 0.07 uF
"bulletproof" cap. It depends to a large extent upon how the capacitors
are internally constructed. 

Usually, high voltage consist of combinations of identical modules
connected in series (for sharing the high voltage and reducing field
stresses within each module so that the risk of developing destructive
corona is reduced). Identical groups of these modules are then connected
in parallel to get to the desired total capacitance. By disconnecting
the paralleled groups and reconnecting them is series, one can often get
the much higher breakdown voltage and lower capacitance desired for
Tesla Coil usage.

However, if you already are starting with a high voltage pulse cap, the
strategy will really depend on how many groups of identical series
chains are connected in parallel. You would then use either a single
series group, or reconnect some number of groups in series to get into
the right capacitance range. With large caps a picnic it's not...

Safe cappin' to you!

-- Bert --