From: fhl@milton.u.washington.edu (Dean Pentcheff)
Subject: Battery-powering a PC expansion chassis [SUMMARY]
Followup-To: sci.comp-aided
Summary: Yes, it can be done.
Reply-To: dean2@tbone.biol.scarolina.edu (Dean Pentcheff) 
Organization: Department of Biology, University of South Carolina, Columbia
Date: Sat, 12 Sep 1992 23:04:09 GMT

Some time ago I asked if anyone had suggestions regarding battery
powering the expansion chassis for a laptop/notebook.  We're trying to
set up a field-portable data acquisition system based on a portable
PC.  It turns out that no one makes laptops with ISA-bus (AT-type)
slots for an A/D card (with the exception of Toshiba's very
top-of-the-line models).  So... it occurred to me that we might be able
to use an "expansion chassis" with a generic laptop/notebook, if such
an expansion chassis could be battery powered.

Ask and ye shall receive.  Following is a summary of the replies I
received, slightly edited for brevity.  They are in a format that will
work with "mail -f", if you want to view individual messages.

Thanks to all who answered!

-Dean
--
Dean Pentcheff  (Internet: dean2@tbone.biol.scarolina.edu) (803) 777-8998
Department of Biology, University of South Carolina, Columbia SC 29205

==========================================================================

From jar@banach.ece.wisc.edu Wed Aug 12 14:03:54 1992
Date: Wed, 12 Aug 1992 13:02:26 -0500
From: "James A. Rose" <jar@banach.ece.wisc.edu>
Subject: Re: Battery powering a PC expansion chassis?

....
There are off the shelf "generic" A/D boards which can be driven by the 
serial channel on a PC.  They take and send out ASCII sequences to initiate
sampling and receive data.  In some ways, they are a lot like hooking up
a modem.

How portable (i.e., weight, size, etc.), how long do you have to keep 
running, and how much are you willing to spend?  If you don't want to do 
any wiring you could use an UPS (though not as efficient power wise as 
the solution you suggest).  There are also IBM PC style power supplies 
with built in batteries and charging circuitry.  

The alternative you are suggesting requires some sort of voltage 
regulation and a charging circuit.  You could simply use rechargeable 
'D' type cells which you can buy at your local WalMart.  1.5 volts per 
cell -> at least 12 batteries (to give you 18 volts to be regulated 
down to 12 volts and 5 volts).  For longer active time you could use 
a car battery (and add a lot more weight).  If you can afford them, 
DC to DC converters are more efficient than regulation (75 to 85 % 
efficient).  Also, they can be more stable over wide input voltage 
ranges and do not require as high an input voltage (e.g., +5V in 
gives +12V out). I would be glad to offer further suggestions if you 
have more details.  

+------------------------+-------------------------------------------+
| Jim Rose               | Class of '92                              |
| Post Doctorate         | Looking for job opportunities in          |
| jar@boole.ece.wisc.edu | Computer Architecture & Engineering.      |
+------------------------+-------------------------------------------+

From rkh@wpi.wpi.edu Wed Aug 12 19:36:41 1992
From: rkh@wpi.wpi.edu (R Kurt Heinzmann)
Date: Wed, 12 Aug 1992 19:35:09 -0400
Subject: Re: Battery powering a PC expansion chassis?

....
>2) What sort of batteries might be appropriate for this?
NiCds or sealed lead acid.  I prefer NiCds.

>3) What magical little bits of circuitry would be needed?
a) Simple, inefficient, cheap way:
   A 6-cell NiCd and a 5V linear regulator plus an 11 or 12-cell NiCd
   plus a 12V linear regulator

b) Simple, efficient, moderate cost ($100 more) way:
   A DC-DC converter that puts out both 5V and 12V plus a battery with
   a voltage in the range required by the converter (probably a 12-cell
   would be best, but you may be able to use a much lower voltage battery).

>4) Is this a totally impractical idea?
Nope.  You should make sure the battery capacity is sufficient to run
the expansion box longer than the laptop, though.  I would buy the DC-DC
converter, measure the current it draws from a bench supply set at, say,
12V or 14.4V while powering the expansion box with the A/D card running, 
and then buy a battery with the appropriate capacity.  

Kurt

From tm17@prism.gatech.edu Thu Aug 13 09:46:54 1992
Date: Thu, 13 Aug 92 09:45:30 -0400
From: tm17@prism.gatech.edu (MAIER,THOMAS D)
Subject: Re: Battery powering a PC expansion chassis?

   Depending on what the nature of the data is that you want
   to collect (high speed, low speed, what precision, what 
   sensors if any) you should consider looking into a battery
   powered data logger.  These devices are just a small 8
   bit micro with signal conditioning and A/D with long storage
   memory.  Some are handheld and some are benchtop.  You
   just start your data acquisition and then when you are done
   you take the box to your computer and upload the data.

   Omega sells a couple differant ones.

   Omega Technical assistance
   1-800-872-9436
   
   There are other companies, but I don't have the info right now.

[editorial comment: yes, we're already using one of these.  Campbell
Scientific sells a couple of excellent models.  -Dean]
-- 
MAIER,THOMAS D
Georgia Institute of Technology, Atlanta Georgia, 30332
uucp:	  ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!tm17
Internet: tm17@prism.gatech.edu

From lance@helios.ucsc.edu Thu Aug 13 11:48:18 1992
Date: Thu, 13 Aug 92 08:47:12 PDT
From: lance@helios.ucsc.edu (Lance Bresee)
Subject: Re: Battery powering a PC expansion chassis?

yes, I have done this.
you need data from the manual on the motherboard.
I would suggest 6 volt lead cells...
...why 6 Volt? Because, an XT requires 5 V at 4 amps
  and 12 volt at 1 or 2 amps.  The DC-DC converter
  to take the 12 volt battery down to 5 volts must
  run at MUCH higher power than the DC-DC converter
  to take the 6 volt up to 12 Volt.

BUT <-------
   The XT was pretty forgiving of 5 volt level.
  The 12 volts is mostly for drives, and need not
  be as well regualted. So there may be a GOOD case
  for useing 12 volt batteries..with easily available
  photovoltiac charger systems, and regulating down
  to 5 V.  Some of the new portables use much less
  power, and if the 5 volt drain is less than 2 amps,
  I would use a 5 volt regulator and a 12 volt battery
  with a pv charger.
lance

[editorial comment: this pertains to powering a computer motherboard,
but the general ideas seem applicable.  -Dean]

From nagle@netcom.com Fri Aug 14 14:05:08 1992
Date: Fri, 14 Aug 92 11:02:39 PDT
From: nagle@netcom.com (John Nagle)
Subject: Re: Battery powering a PC expansion chassis?

       It's easy, but battery life may not be all that great.  First,
try to find cards that only use +5 volts, not +12 and -12, which are
used mostly for RS-232 signals.  If you can find 5v-only cards, you
only need a 5v supply.  Most cards that don't have RS-232 ports don't
need anything but +5, but this can vary.  The manual for the card should
say how much power it draws at each voltage, so you can tell from there.

       A 5v supply can be constructed from any battery bigger than 
7v or so and a 7805 regulator, which is a 3-pin device (in, out, and
ground).  Radio Shack should have everything you need.

       Figuring out where to attach to the expansion chassis is your problem.
But it shouldn't be all that hard.  Find out where the power supply connects
to the slots, find the +5 and ground leads, get a connector that matches
the connector on the power supply (any PC repair shop), and hook it up.
A voltmeter will be helpful.

      There are 7812 regulators, for 12V, too.  With regulators of this
type, you lose about 2V in the regulator, so you need at least 14V to get
12V after the regulator.  Two 9V batteries in series will work fine as
a source of 18V to be regulated down to 12V.  You waste 1/3 of the battery
life this way, but it's simple.

       A more sophisticated solution would be to use a Maxim voltage-conversion
IC to get 12V from 5V.  

					John Nagle
Newsgroups: sci.comp-aided