Re: Old Capacitors

From: 	Jim Fosse[SMTP:jim.fosse-at-bjt-dot-net]
Reply To: 	jim.fosse-at-bjt-dot-net
Sent: 	Wednesday, December 03, 1997 1:06 PM
To: 	Tesla List
Subject: 	Re: 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

>These sound like they're Mylar, made for DC filtering applications.
>Assuming that you're running at a gap firing voltage of, say, 9 KV, and
>matching it with a primary inductance of about 9.5 uH to get 200 kHz
>operation, your maximum tank current will be about 750 Amps, shared
>between the two paralleled groups, ot about 375 Amps/cap. While this is
>nothing for a properly constructed pulse cap, these caps don't sound
>like they're pulse caps! 

>I believe they were designed for single shot high speed photographic 
Alan, Bert, Malcolm;

	The clue to these units is the specification of  +8% ripple
50Hz. This implies that while the DC rating is 10kV, the applied AC
may not exceed 800V (long term) without over heating the cap.
Likewise, this 8% rating implies that these caps have a very high
effective series resistance which limits their ripple current to
800*2*pi*50*0.1e-6 = 25mA!