Date: Sun, 11 Apr 2010 09:59:15 -0700
From: "Bill, W6WRT" <dezrat1242@yahoo.com>
Subject: Re: [Amps] HV lytic max V ratings..some notes.
>
>Yeah, that's what I was always lead to believe. I was told that it is
>better to run your caps very close to their voltage rating. Dunno if
>its a wives tale or not.
REPLY:
I was told that too, but never heard any real proof. The idea was that
an electrolytic is not a static (pun intended) component. The
electrolyte is chemically active and will gradually deteriorate if not
run near it's rated working voltage.
Possibly just an old wive's tale. If anyone has any authoritative
source, please post it.
73, Bill W6WRT
## Well, I don't see any [ new and old] tech notes from any of the cap makers
on this topic. I think a quick email to CD, etc.. would be in order at this
point.
## bring up old caps, or old B+ supplies, or caps that have been used at
no more than 75% of their ratings, etc... on a variac, in staged intervals,
appears to work good. I still would not suggest running em at more
than 90% of their ratings..esp in a series string.
## I could see where firing up an old B+ supply, where caps were run at
>90% of their V rating could cause problems. You could end up with a
scenario where the leakage current is initially sky high, and the ratio of
bleeder current to leakage current is really low, too low. That, plus EQ
resistor's that are not matched up... could easily lead to individual caps in
the
string, being well over their V rating. Instead, bring em up slowly on a
variac. If the caps are real antiques, like > 25 yrs old, imo, you are better
off to
just re-cap the entire supply, put in new eq resistors, [100k-3 watt mof] ,
safety
rvs diode across each cap... and new 1N5408/6A10's in the FWB/FWDoubler.
Add some hv fuses.. and a Glitch R... and be done with it.
## all these old 200 uf caps were too small in value to begin with. The 560+
uf
variety can easily be retrofitted in place. Carl is correct. get rid of the
old 25-30k
eq resistors. They just cook the caps.. and the resistors will have drifted
anyway.
## EQ resistor's that are all over the place in value... will have V drops
that are all
over the map. The highest value eq resistors in the string will have the
highest V drops.
Jim VE7RF
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