Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!mgm.mit.edu!wolfgang
From: wolfgang@mgm.mit.edu (Wolfgang Rupprecht)
Newsgroups: sci.electronics
Subject: Re: Powering PC from +12
Message-ID: <9065@bloom-beacon.MIT.EDU>
Date: 3 Feb 89 03:13:34 GMT
References: <00112@m5.UUCP>
Sender: daemon@bloom-beacon.MIT.EDU
Reply-To: wolfgang@mgm.mit.edu.UUCP (Wolfgang Rupprecht)
Organization: Freelance Software Consultant, Boston, Ma.
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In article <00112@m5.UUCP> keith@m5.UUCP (Keith J. McQueen) writes:
>Does anyone out there have a circuit for producing the
>necessary +12, -12, +5, -5 for powering an IBM PC from
>a single lead acid battery?  The supply should provide
>enough current to run a loaded PC with a hard disk drive,
>and a 12 volt monitor.

You can certainly design yourself a set of DC-DC converters but that
is honestly a *lot* of work.  Toroidal power-transformer selection and
design will probably take you quite a while the first time around.
Then you have to get the regulator to react *quickly* to current
transients yet still be stable. Using a *single* 12V cell is lots of
work.

Why not take the fast way out?  You already have a 150-watt to
250-watt DC to DC converter sitting right in that PC of yours!  All
you really need to do is make sure that it gets its uninterrupted
source of DC.  This is relatively simple to do.  All you really need
is a bunch of batteries in series.  About 170 volts of batteries to be
exact.
	    		    |------|
	--| )---------------|	 + |------o-------<
	  |  )		    |~     |	  |
	--| )---------------|	 - |--o---)-------<
			    |------|  |   |
       	120 VAC in.		      |   |        To IBM-PC
				      |	  _
				      |	  ^ DIODE
				      |	  |
				      |	  |
				      |	 ___ + 170 V
				      |   -
				      |  ___
				      |   -
				      |  ___
				      |   -
				      |  ___
				      |   -
				      |  ___
				      |   -
				      |  ___
				      |   -  0 V
				      |   |
				      ----|


Now this circuit can be trickle charged with the addition of a
resistor across the battery's diode.  (And perhaps a small
transformer, or a capacitor to boost the voltage slightly.)

The basic assumption of this circuit is that nothing in the PC really
needs AC.  You may have to replace the fan with a 12v unit, and run it
from the +12 line to fulfill this assumption.

Now for the disclaimers:

This circuit is dangerous as all hell.  170VDC is very lethal.  If you
grab both voltage extremes, you will probably be very sorry, if not
dead.  Use lots of common sense, generous interlocks etc.  If I were
*actually* crazy enough to build this thing, I would put a switch
between every few batteries, so that one wouldn't see more than, say,
24 volts in series when the case was open.  If you play with High
Voltage DC, please be extremely careful.

-wolfgang
Wolfgang Rupprecht	ARPA:  wolfgang@mgm.mit.edu (IP 18.82.0.114)
TEL: (617) 267-4365	UUCP:  mit-eddie!mgm.mit.edu!wolfgang