[sci.electronics] Powering PC from +12

keith@m5.UUCP (Keith J. McQueen) (01/31/89)

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.

The application is to run a packet radio Bulletin Board
System entirely from a single DC supply.  (We are using
low power trancievers... < 5 watts).

Ideally, the circuit should be fairly efficient, and 
handle low voltage (ie. less than +12 input) as the
battery runs down.

If possible, I would like to have the battery float
charging all of the time, with current draw only happening
when the power goes out.

I realize that I could probably get a UPS to do this,
but that is quite expensive, and not near as much fun.
I also believe that, since the computer runs on DC
anyway, a more efficient way can be found.

Any Ideas?


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wolfgang@mgm.mit.edu (Wolfgang Rupprecht) (02/03/89)

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

payne@batcomputer.tn.cornell.edu (Andrew Payne) (02/04/89)

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.

	My experience with computers/digital electronics has been that
90% of a given circuit runs from +5.  The other voltages are required for
a very small portion of the sytem (the most common being +12/-12 for the
serial RS-232 drivers).  Most hard drives/floppy drives want +5 and +12.
	If you could isolate any sections that use -5/-12 (like a RS232 
board), and work around such sections (like using the MAX232 chip for
RS232, which has an on board voltage doubler/inverter, and runs from a 
single +5 supply), you might be able to run the computer from a single 
12V battery and +5/+12 regulators.

	In this day of generic PCs with little or no tech documentation, 
this may be more trouble than it's worth....

-- 
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Andrew C. Payne               UUCP:  ...!cornell!batcomputer!payne
                          INTERNET:  payne@tcgould.tn.cornell.edu
PHONE: +1 607 253 2776      USMAIL:  5428 Cls '26-UHall 5   Ithaca, NY  14853

sukenick@ccnysci.UUCP (SYG) (02/07/89)

>>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.
>RS232, which has an on board voltage doubler/inverter, and runs from a 
>single +5 supply), you might be able to run the computer from a single 
>12V battery and +5/+12 regulators.

If the -5, -12 sections don't draw much current, then why not wire
in a -12 & -5 volt inverter (either the integrated circuit or forreal
fun, the diode/capacitor combos ;-)) to the power bus ?

PC's are pretty  modular; to get it to work off of straight DC,
just remove the connector from the power supply and plug into your
DC supply.  There are some ~5 amp single chip regulators (with proper heat
sinking..)  one difficulty might be the 12 volt supply (as
well as current capacity for the negative supplies - you might want to
put an ammeter in with the PC loaded and accessing different accesories
to find the draw, and decide if you will need another battery- maybe a smaller
one will be all that is needed). Many regulators need  ~ 2 volts  over the
regulated   voltage - a lead   acid 12v is ~13.5 voltages when fully charged
so it might be sufficient.  National Semiconductor has a data book on
regulators which might be useful.
it  is to regulate 

markz@ssc.UUCP (Mark Zenier) (02/09/89)

In article <1233@ccnysci.UUCP>, sukenick@ccnysci.UUCP (SYG) 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.
> 
> If the -5, -12 sections don't draw much current, then why not wire
> in a -12 & -5 volt inverter (either the integrated circuit or forreal
> fun, the diode/capacitor combos ;-)) to the power bus ?
> 
> PC's are pretty  modular; to get it to work off of straight DC,
> just remove the connector from the power supply and plug into your
> DC supply.  

A cleaner more modular method is to get a DC input open frame switching
power supply.  There are switching power supplies that input low voltage
DC and output the regulated voltages.  See the EEM or similar 
buyers guides.  If you want to run a monitor and floppy disks, you'll
need at least 2 amps at 12 volts.  Your battery isn't going  to last
very long.

This is request that shows on the net with great regularity.
Here is an excerpt from a posting that showed up last time this came up.
(I tried to mail this but you know how that goes)

--------------------------------------------------------
:From: sgt@dukeac.UUCP (Stephen G. Tell)
:Newsgroups: sci.electronics
:Subject: Re: DC to DC powersupplys
:Summary: Commercial unit; not cheap but good
:Message-ID: <1113@dukeac.UUCP>
:Date: 20 Nov 88 07:39:16 GMT
:
:
:I have used some switching power supplies from Converter Concepts, Inc.,
:and noticed that they have some that run on a DC input of 10-40 volts.
:(I used the models that ran on 100-380VDC or 90-265VAC, and liked them.)
:
:Their VT/VX-50 (50-watt) series has one that can take 10 to 40 volts
:DC input and produce that following outputs:
:+5 @ 1.2 to 6 amps
:+12 @ 0.05 to 1 amps
:-12 @ 0.05 to 1 amps
:
:as for input current; the requirements
:you specified of 5(5)+1(12)+.1(12) = 38.2 watts; call it 40.
:They specify efficiency of typicaly 70%, so input power is 57 watts, or just
:under 5 amps at 12 volts.  The other 17 watts comes out as heat, which
:doesn't look too bad.
:
:...
:I would caution against connecting too directly to the vehicle's battery
:(say using that 13.8 as the +12 supply directly.)  The regulation
:won't be good enough, and automotive electrical systems have lots of
:noise of all kinds.  A switching regulator of this sort will help
:insulate you from a lot of that.
:
:My only connection with these guys is as a satisfied customer:
:Converter Concepts Inc.
:Industrial Parkway, Pardeeville WI, 53954
:800-253-5227  or  608-429-2144
:-- 


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