Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ukma!xanth!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: <2446@iscuva.ISCS.COM>
Date: 6 Apr 89 02:20:55 GMT
References: <13671@jumbo.dec.com>
Organization: ISC Systems Corporation, Spokane WA
Lines: 28

In article <13671@jumbo.dec.com> murray@jumbo.dec.com (Hal Murray) writes:
>I'd assume that the vanilla line => bridge => big caps power supply front
>end would be happy with a squarish wave as long as it didn't brown out.

Switching power supplies might very well object to square(ish) waves as input.
The problem is inrush current through the diodes and into the capacitors.
This can cause premature failure on both components.  If you do need to feed
the supply this nasty current, you could probably put some sort of series 
resistor in the power feed to tame the waveshape a little.  Unfortunately
this beastie will waste some power.

If you're into hacking, what the Mac supply really wants is 180 VDC (a guess, 
easy enough to measure it) at its internal power supply point.  The switcher
runs off of this.  In fact, you might be able to feed the Mac DC directly.
I can't remember all the details, although I did trace out the supply once.

If this is so, all you need to do is think up a rectifier scheme that _will_
survive the square waves, and save your poor Mac the trouble!  Peripherals
are another question.

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