Re: Old Capacitors

From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Tuesday, December 02, 1997 4:34 PM
To: 	Tesla List
Subject: 	Re: Old Capacitors

Aha!  I can help here :)
                         A friend in England sent me a couple of 
50nF, 25kVDC caps made by Hivolt and they sound like the same type....

> From:   Alan Sharp[SMTP:100624.504-at-compuserve-dot-com]
> Sent:   Monday, December 01, 1997 4:46 AM
> To:     INTERNET:tesla-at-pupman-dot-com
> Subject:    Old Capacitors
> Greetings all,
> I've just aquired six 0.1uf 10kv DC capacitors.
> They are 7" long, 1" diameter brown cylinders with stud terminals
> marked Hivoltage Capacitors Limited
> Londonderry N.Ireland
> +8% ripple 50Hz
> TPM 100-114
> I was going to put 3 of these in series,
> then 2 series in //  for my 7.5KV AC 550mA supply - to give 0.066uf 30kV DC
> but I'm wondering if they will take the current at 200kHz -
> would I be better to use 4 or 5 in series and get the other 0.04uF from
> my other capacitors? Or reduce the voltage to 5kV AC.
> It also occurs to me that moving to a lower frequency - bigger coil
> will ease the load on the capacitors.
> Any thoughts.

They are lossy at coil-type frequencies. In fact, they are 
demonstrably lossier than my homerolled dry-fired poly caps.
I believe they were designed for single shot high speed photographic 
apps.  They would be excellent for voltage multipliers (-at- mains F),
D.C. filter caps etc. They do last in TC service but I wouldn't run 
them up to the ratings and I wouldn't fire them for long either. They 
get warm to touch.