[Amps] Russian HV Supply Capacitors

Jim Thomson jim.thom at telus.net
Sat Jan 11 03:15:46 EST 2014

Date: Fri, 10 Jan 2014 11:16:32 +0100
From: peter chadwick <g8on at fsmail.net>
To: km1h at jeremy.mv.com, amps at contesting.com
Subject: Re: [Amps] Russian HV Supply Capacitors

##  I concur.  I once used  4 x  30uf at 3500 v OIL caps...rated for discharge use in a 4-1000 amp back in the late 70s.  Wired series parallel with careful eq across the caps.  caps were wired  series-parallel.
IE:  30 uf at 7 kv.  B+  supply put out  4400 vdc no load.    Worked for 18 months...then  3 of em leaked oil badly.    4400 / 7000 =  63% of max V rating.  max plate current on the 4-1000 amp at the time was 600 ma. Loaded B+ was  4400 vdc. :

##  The problem with that russian cap is....its missing the two most important specs.   ESR....and   CCS ripple current rating.  My  B+K 875B  measures esr at 1 khz.    Some esr measuring devices will measure at freqs like
100 hz, 300, 1 khz, 10 khz etc.   Watch out.  On modern design lytics, the ESR will drop as test freq increases.   This is due to the lower internal  XL   from wider conductors being used.   Switching supplies operate at high freqs. On the old style caps, it was the reverse.  Old style caps had low esr at low freqs.....which got worse at freqs increased.  On old switching designs in the ARRL books, they used several caps in parallel  to handle the  ripple current at the higher freqs.  

##  If we knew the ESR at 120 hz.......and also CCS  ripple current rating at 120 hz....... one could then properly evaluate the Russian oil cap.  Carl is no doubt correct. Don’t operate discharge caps at any more than 50% of their V rating. 

## Years ago, Far electronics was selling high ESR lytics, designed for   photo flash use.  Most reported that their 8 caps in series would overheat, spew crap out the vent holes, etc... when used in the typ 1200-1500w  pep out SSB amp.  

Jim  VE7RF 

I agree with Carl here. I had a string of 220mFd 500 volt electrolytics meant for photoflash work: even in a choke input filter, they didn't last very long before squirting stuff out of the vent holes. The Sprague 36D computer grade electrolytics I replaced them with lasted for years, and have only been taken out of service because there's an Acom 1500 due to arrive on Monday!

Capacitors meant for SCR commutation are another matter - they are designed for continuous high currents


Peter G3RZP

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