[Amps] Computer Grade Electrolytic Capacitors vs. Radial

Michael J. Tubby B.Sc (Hons) G8TIC mike.tubby@thorcom.co.uk
Wed, 4 Sep 2002 21:11:18 +0100

----- Original Message -----
From: "Steve Thompson" <g8gsq@qsl.net>
To: <amps@contesting.com>
Sent: Wednesday, September 04, 2002 8:10 PM
Subject: Re: [Amps] Computer Grade Electrolytic Capacitors vs. Radial

> -----Original Message-----
> From: Bill Smith <ko4nrbs@yahoo.com>
> To: amps@contesting.com <amps@contesting.com>
> Date: 04 September 2002 19:53
> Subject: [Amps] Computer Grade Electrolytic Capacitors vs. Radial
> >I was give 12 radial 450 vdc 220uf capacitors and was
> >wondering if they were ok to use in a HV power supply.
> > What would I gain if I spent the extra money for the
> >computer grade?  Are the radial types ok even though
> >they are much smaller?
> I'd suggest using the Duncan PSU designer prog. to model your PSU and get
> figure for the rms (=heating) current in the caps. Then use a low voltage
> transformer and variac to get that much current through the caps and see
> much they heat up.
> Steve
> PS There's an updated version of the prog as of yesterday changed so that
> the prefix for kilo is now correctly lower case.

Whether they're so-called "computer grade" or not probably isn't the
issue... its the ripple current rating and temprature rating that are
as Steve implies.

Assuming traditional full-wave bridge configuration, and you know the
transformer voltage and likey DC voltage you'll acheive then if you use
all 12 in series you're going to have about 18uF of C which is okay-ish.

If the caps are the snap-in types for switched mode PSUs then they're
probably good for around 1.5-2.5A RMS ripple - check manufacturer
data sheets. You'll probably be fine if you use them in a power supply
where your Idc(max) out is about 0.5 times the ripply current rating.

I use 12 x 470uF 450V DC snap-in types rated at 2.7A ripple @ 85
deg C in my 8877 and 4CX1000A amp PSUs and they've been fine
for years. The "trick" is to run the caps well within their voltage, current
and temprature ratings - 2/3 to 3/4 voltage and current and below half
max temp and they'll last forever.

My big PSUs are seperate boxes and have fan cooling which is a good idea.