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? - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - | Keith McQueen, N7HMF Organization: Wicat Systems, Inc. | | 1116 Graff Circle Work (801)224-6605x422 | | Orem, Utah 84058 Packet: N7HMF @ NV7V | | Home (801)224-9460 Voice: 147.340 MHz or 449.675 MHz | | Opinions are all mine... | - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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.... -- = = = = = = = = = = = = = = = = = = = = = = = = = = = 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 :-- Mark Zenier uunet!nwnexus!pilchuck!ssc!markz markz@ssc.uucp uunet!amc! uw-beaver!tikal!