[AMPS] Electrolytics

[Paul Hewitt]

Hello Steve
I've been running capacitor banks made of 330uf
@450v 85c snap-ins with a fwb for over 18 months
now with fine results in two 4KV 1A supplies.  I
deliberately pull cooling air over the bank and
diode strings.  All the newer caps I've researched
use working voltage for their rating.  There
should be no concern on their mounting position as
the cans are insulated from their interior unlike
the older electrolytics.
Paul

Paul Hewitt
WD7S PRODUCTIONS
QRO HOMEBREW COMPONENTS
http://wd7s.home.att.net


> -----Original Message-----
> From: owner-amps@contesting.com
> [mailto:owner-amps@contesting.com]On
> Behalf Of Steve Thompson
> Sent: Thursday, May 24, 2001 6:13 AM
> To: amps@contesting.com
> Subject: [AMPS] Electrolytics
>
>
>
>
> -----Original Message-----
> From: nospam4me@juno.com <nospam4me@juno.com>
> To: amps@contesting.com <amps@contesting.com>
> Date: 24 May 2001 06:48
> Subject: [AMPS] re: Dayton and Emtron
>
> >The capacitors were also mounted right
> next to each other.
> >Cap cooling is something less than
> desired. In my opinion,
> >an issue that should be looked at.
> Although I wasn't able
> >to check the values, the capacitor
> bank looked "rather light
> >duty" for the power supply level so
> these close spaced caps
> >will get at least very warm with
> significant ripple current.
>
>
> This got me thinking, and I wonder if
> we are overly pessimistic about
> electrolytics, maybe based on the poor
> quality components of the past.
>
> Based on a 3kV supply with a stack of
> 10 x 330u 450V ordinary (not special
> computer grade) 85C caps, rms ripple
> current rating is 1.5-2A (depending on
> brand) with dissipation about 2W at
> maximum ripple. 2W doesn't seem a huge
> amount for the size of can to dissipate.
>
> Roughly, rms ripple is around 2xdc for
> a bridge, and 2.5xdc for a doubler,
> so these caps would be inside rating
> for, say, 7-800mA dc in a typical psu.
>
> The Siemens version I looked at quotes
> 10,000 hours life at full ripple at
> 85C ambient. If we work on 65C ambient,
> 50% tx duty and 50% loading for
> ssb/cw use, then the lifetime
> prediction is 160,000 hours (18 years)
> continuous operation.
>
> Steve
>
>
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