Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!lll-winken!uunet!iscuva!jimc
From: jimc@iscuva.ISCS.COM (Jim Cathey)
Newsgroups: sci.electronics
Subject: Re: Running a Mac/SE from batteries and inverter
Keywords: Mac, batteries, inverter
Message-ID: <2452@iscuva.ISCS.COM>
Date: 11 Apr 89 01:37:10 GMT
References: <13671@jumbo.dec.com> <2446@iscuva.ISCS.COM> <4224@midas.STS.TEK.COM>
Organization: ISC Systems Corporation, Spokane WA
Lines: 34

In article <4224@midas.STS.TEK.COM> jeffw@midas.STS.TEK.COM (Jeff Winslow) writes:
>First of all, if you really mean inrush current as in what you get when you
>first turn the switch on: Since switching supplies don't try to synchronize

Bad choice of words on my part.  I meant to refer to the peak current through
the diode during each cycle.  This will be worse for the squarish wave because
if the capacitors sag during the dead part of the input cycle the voltage
differential across the diode will be much higher (or at least it'll try to
be).  This can result in hot spots in the diode, leading to premature failure.


>Secondly, rms running current will be lower for a square wave, since the
>conduction angle is much greater than for a sine wave, even the chopped-off
>version. The rectifiers will run cooler, last longer. The capacitors will,
>too - lower rms current -> lower core temperature, and the single most telling
>variable affecting electrolytic capacitor life (in normal use :-)) is
>temperature.

I disagree, the conduction angle may well be larger, but the _peak_ current
will be very high in the early part of the cycle.  Thus higher RMS current,
and the exact opposite results.

Or maybe the math says otherwise.  I'm just quoting what the data sponge in
my head says it saw several years ago.  Original source was a power supply
design article (quoth the sponge).  Any real experts care to comment?

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