Cap setup suggestions needed

From: 	Micheal Huff[SMTP:msnock-at-theonramp-dot-net]
Sent: 	Thursday, June 19, 1997 1:20 PM
To: 	Tesla List
Subject: 	Re: Cap setup suggestions needed

Tesla List wrote:
> From:   Brandon Doughan[SMTP:fiveht-at-well-dot-com]
> Sent:   Wednesday, June 18, 1997 9:48 AM
> To:     tesla-at-pupman-dot-com
> Subject:        Cap setup suggestions needed
> Hey you HV freaks-
>         I was lucky enough to get ahold of 20 or so doorknob caps rated
> at 30KV and 3600 pF (.0036MFD).  I'm wondering about a few things:
>         Firstly, they are paired and incased in rubber blocks with three HV
> leads, coming of each end and in the middle. [they are from a HV
> multiplier device].  On one end of the cap pairs (I've scrapped the
> rubber off a few) there is a resistor.  I don't know the value.  My
> question is, if I use several pair in a coil powered by a 15KV NST, how
> will these resistors affect my capacitance?  

The resistors won't affect the capacitance at all.   They should be
removed though, since they will hinder the coils output.

> It would be nice to keep
> the added insulation of the rubber (and not have to scrap all of it
> off!), but if the resistance is negatively affecting my coil output, as I
> suspect, then I'm gonna have to do it.

No, just toss the rubber.  The caps should have plenty of insulation.
You might want to save the resistors though for an HV probe.
>         Second question-  I know you want to have your caps rated 3
> times your primary voltage, but I want to get away with just have my 30KV
> caps with my 15 KV NST.  Anyone have experience with doorknob cap
> failure?  Think I can do it?

Well, since you say you have about 20 hook several series/parallel
stacks up for 90kVDC.  You will want about 5000pF if you are using a
15kV -at- 30mA neon.  Be aware that these caps will run hot because they
are very high loss, RF wise.  I wouldn't run the coil for long periods.
A large cooling fan my be of some use here.
>         Last question-  I cracked one of these caps open and found that
> it consists of just two plates each no more than 3 sq. ins. and about an
> inch of that strange ceramic dielectric.  How do these get .0036MFD??
> This must be because of the K value of that stuff.  This amazes me.

It's probably barium titanate.  This stuff has an extremely high 'K'.
> Thanks for your help_  Brandon
> PS-  Visit the High Voltage Camp at Burningman '97!


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