RE: 2500 VAC mot into 4x voltage multiplier = 20000 volt capacitor arc-over?

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Original poster: "Philip Chalk" <phil-at-apsecurity-dot-com.au> 



-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Friday, 27 February 2004 2:01 PM
To: tesla-at-pupman-dot-com
Subject: 2500 VAC mot into 4x voltage multiplier = 20000 volt capacitor
arc-over?

Original poster: "Hydrogen18" <hydrogen18-at-hydrogen18-dot-com>

		>>>  Snip  <<<

Anyhow I was charging 2 strings of 10
kilavolt 500 pf by 2 for a 20 kilavolt 250 pF capacitor.


 > Hi Eric,

 > Huh ? You mean 2 strings in parallel, of 2 series caps each string (4
caps total)? That would be 500pF at 20kV. 2 strings of 4 caps, 8 in
total would be 250pF at 40 kV. Anyway, what do you want a 250pF 20kV cap
for ?

For some reason the
2nd string is starting to arc-over(again, these caps are cursed).

 > What type of caps are they ?

 > How exactly are they arcing over? 1 cap at a time? Same cap always?
When, what circumstances? Can you describe just what they're doing.

Is it
possible that the caps need some sort of equalizing resistors or
something?

 > It's a good idea anyway, even if it's not the root of this problem. If
it's 10kV rms, & you wanted 0.1mA thru the resistors, you'd use a total
of 100M ohm across the supply, divided by the no. of series caps for
each resistor; i.e. 2 caps-2x 50M, 4 caps-4x25M etc. They'd dissipate 1W
in total, but it's good to overrate the resistors by at least 2x, better
5x or 10x, so they don't run stinking hot (& have shorter life).

I may soon replace them with some doorknobs I have if this
persists.Thanks
for any help you can provide.

---Eric

 > Phil Chalk.