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Power Hardware

Protecting Hardware on Unstable Power Sources? 65

Posted by Cliff from the filters-conditioners-and-UPSes dept.
psuedo_samurai asks: "Later this year, I will be returning for a visit to a small 3rd world country in Africa. I was lucky enough to travel to the country before, and the last time that I went I was able to bring four fully functional computers that I donated to a local high school, to provide a small computer network for teaching purposes. I had loaded Red Hat Linux with Open Office and a multitude of free goodies onto the systems and everything was working well. The equipment I brought back with me survived for about 12 months, but eventually fell victim to power surges, brownouts, blackouts, and so forth. On my return, I will be better prepared and am planning on setting up 8 computers, this time around. However, I am still stuck on how to best provide either a battery backup (aside from lugging UPS's along with me) with automatic shutdown and/or AVR on the cheap. Does anyone have any good references, experience, or suggestions on how to over come the challenge of running a computer network in a country where the power fluctuates wildly and multiple outages in week are not unusual occurrences?"
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Protecting Hardware on Unstable Power Sources? More

Protecting Hardware on Unstable Power Sources?

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  • 419? (Score:5, Funny)

    by tepples ( 727027 ) <tepplesNO@SPAMgmail.com> on Wednesday March 30, 2005 @06:13PM (#12094058) Homepage Journal

    I will be returning for a visit to a small 3rd world country in Africa.

    I hope this doesn't have anything to do with an advance fee scam someone sent to your e-mail, does it?

  • Inverter + charger (Score:5, Informative)

    by wowbagger ( 69688 ) on Wednesday March 30, 2005 @06:17PM (#12094112) Homepage Journal
    What you need is known as an off-line UPS, which is nothing more than a battery charger, a battery, and an inverter.

    The charger charges the battery, the inverter runs from the battery - if the line voltage spikes, the battery charger takes the hit. If the line voltage sags, the inverter draws power from the battery until power is restored.

    You can take along just the inverter if you can count upon getting batteries and chargers for them at your location.

    The charger MUST be able to put out more current than the inverter will draw - so for a 400W computer system your charger will need to be able to put out about 40 amps at 12VDC.

    The other advantage to this approach is the ability to run off a battery string charged by photovoltaic panels.

    Lastly, if you can find somebody with the skill, you can get a replacement power supply for the computer that will take 12VDC to make the voltages for the computer (usually 5VDC, 12VDC, and 3.3VDC) - this will eliminate the inverter (at the downside of using a non-standard power supply for the computers.)

    • Re:Inverter + charger (Score:3, Informative)

      by Anonymous Coward
      I second this opinion. A regular UPS does not protect against brown-outs and slow surges that will kill your equipment. Off-line UPS is what you want. They are expensive though.

      A real off-line UPS is more than just a regular 'ol inverter though. They are much higher quality, provide nice sine-wave AC power and are rated for continuous usage.

      Most of the the cheap inverters you buy off the shelf produce a nasty, noisy waveform which can kill your equipment also (especially if used for long periods of ti
      • What ^^^ he said.

        But here is an idea. If you can find some really good old UPSs off of ebay for cheap with dead batteries, then you can probably scavenge just the electronics off of them. The batteries are very heavy, and expensive to lug/ship. They are also usually the first items to die in any UPS (well, that and fans).

        When you get there, build some wood cabinets, install the board that you brought with you, and hook the whole thing up to a car battery.

        The electronics determine the maximum amount of
        • When you get there, build some wood cabinets, install the board that you brought with you, and hook the whole thing up to a car battery.

          Put the cabinet outside or otherwise with good ventilation. Car batteries can give off hydrogen gas...
    • You might also consider wiring up a battery monitor so that your machine can do a graceful shut-down when battery power is depleted. I am not an electrician, but I think this should be possible with a couple transistors, resistors, some wire, and the MIDI/Game port. (To eny electricians, the MIDI/Game port is available on most computer sound cards and has an 8-bit ADC built in. Calibrated to 0-5VDC I believe. It is multiplexed across 4 inputs, so there is potential to monitor up to 4 analog lines.) Hack
      • To eny electricians, the MIDI/Game port is available on most computer sound cards and has an 8-bit ADC built in. Calibrated to 0-5VDC I believe.

        Calibrated? Game port? Muhahaha!

        The 'ADC' in the game ports of traditional PC hardware is nothing more than a pulse generator modulated on the input voltage. The PC triggers the pulse, and then keeps polling until the pulse finishes. By timing how long the pulse was, the PC can estimate the voltage.

        The result of this is that polling the game port is extremely

        • Hmmm, yeah, now that you mention it, that is how it worked. I recall fiddling with that stuff in assembly once upon a time. (Thank you, Mark Feldman....)
          Well if you wanted a real ADC, you could use the microphone input on the sound card or wire up a $1.50 PIC from Microchip to the parallel port, serial port, or the game/MIDI digital lines (the ones usually used for triggers).
          • Hell, now that I think about it, you could just wire that PIC directly into the soft power switch on any ATX motherboard and just trigger a soft shutdown that way. No need for a monitoring daemon there, and would (well, "should" would be the right word) work on Windows too.

    • Re:Inverter + charger (Score:5, Informative)

      by LWATCDR ( 28044 ) on Wednesday March 30, 2005 @07:02PM (#12094664) Homepage Journal
      Actually Hackaday had just what you want.
      http://www.hackaday.com/entry/1234000583030620/ [hackaday.com]
      Okay it is not exactly but pretty close. Would make a good project.
      Back in the old days IBM mainframes used an interesting power conditioning system. It was an electric motor that turned a big flywheel that was then connected to an generator. A very effective if not efficient way to decouple you computer from the power lines. Of course the often added a diesel motor and clutch to the mix. Power drops clutch connects the engine to the flywheel, generator combo and instant UPS.
      • > It was an electric motor that turned a big
        > flywheel that was then connected to an
        > generator. A very effective if not efficient way
        > to decouple you computer from the power lines.

        Quite efficient, actually.

        > Of course they often added a diesel motor and
        > clutch to the mix. Power drops clutch connects
        > the engine to the flywheel, generator combo and
        > instant UPS.

        A no-break system. The Bell System used them at their microwave repeaters in the sixties. I'd love to get my hands on
        • "Quite efficient, actually."
          Actually I am pretty sure an electronic inverter is far more efficient than a mechanical one. As I said a very effective device. I do wonder if you could make a low tech version? all you would need is an electric motor, generator, and a flywheel. You could even make a cheap flywheel out of concrete. Of course you would have a to wait a while for it to spin up but it might be an interesting project.
        • My grandfather used this system to charge batteries at his radio shop so many years ago I hesitate to guess. The 'kids' have stories about it so it's at least 60 years old.

          You apparently could always hear the single stroke motor come on when the flywheel would slow down... a very lound POP ... POP.. POP . POP POP POP .... then quiet again :)
    • With all of the other complexities people are mentioning, it seems to me that more attention should be paid to running the computers directly off of the battery.

      You can probably find a 12V -> 5V and 3.3V conditioning circuit on the web and build up circuits attached to mobo cables for a few bucks, right?

  • Laptops? (Score:5, Informative)

    by fm6 ( 162816 ) on Wednesday March 30, 2005 @06:23PM (#12094200) Homepage Journal
    Unless you have deep pockets, you're stuck with off-the-shelf technology. That doesn't leave you with a lot of options, since standard computer hardware is mostly designed for situations where there is a reliable power supply. (Non-standard custom-built hardware is much more flexible -- and much more expensive.) This goes even for UPSs, which are meant to support clean shutdown, not extended replacement for regular power.

    The off-the-shelf system that doesn't need a reliable power source is an old-fashioned laptop. You can buy obsolete laptops very cheap. Many are too big and bulky by todays standards, but will fill in nicely for a desktop system when power comes and goes.

    • Using old laptops could be part of the solution, but it seems to me that the batteries are the first thing to go on old laptops. That puts you back at the mercy of the power supply, except that now it's harder to swap out individual parts that get damanged.

      • Re:Laptops? (Score:1, Redundant)

        by fm6 ( 162816 )
        A good point. However, replacement batteries would not need to be compatible with the original design, since you don't need the laptops to actually be portable. That would reduce the cost of replacment batteries somewhat.
        • How about completly not worrying about an internal battery. Many of the laptops I have seen run on either 12, 19, or 24 volts DC.
          Get yourself a good localAC -> DC powersupply and keep a battery array (this sounds like the UPSes the other people are suggesting), and just keep the laptops plugged into there.
          Would also solve the main problem with the UPSes in that you already are prepped for running from a DC source. Of course, depending on the laptops you get you now have to offer the several different vo
      • laptop running out of power or being hit by a brownout is unlikely to break anything permanently, like it could do to a normal psu.

        and changing an external charger, which would be the part thats most vulnurable, is a lot easier than changing the psu and possibly motherboard and a whole lot of other things.

        anyways.. the guy is looking for an ups and he even knows it himself.. so why bother asking?
    • Non-standard custom-built hardware is much more flexible -- and much more expensive.

      I'm curious... Would it be too difficult to build one of these yourself? A car battery (or several batteries) seems like it would be the main part, so the question is could everything else be made conveniently using discrete components? How does a UPS work?

  • Why not a UPS? (Score:5, Informative)

    by PurpleFloyd ( 149812 ) <zeno20@@@attbi...com> on Wednesday March 30, 2005 @06:26PM (#12094245) Homepage
    For your requirements, it seems to me that a UPS is pretty much the only solution. However, it might not be so difficult to bring one with you, if you can obtain lead-acid batteries while you are in Africa (probably not so terrible, although I don't know how removed from civilization you will be). If weight is a concern, you might buy some small UPSes in the US that have the features you need, remove the batteries here, then ship them to Africa and buy new batteries locally; most UPSes have fairly standardized lead-acid gel cells, and it might be possible to hack in larger batteries if you can't find precisely what you need once overseas. One caveat: if you're going for weight savings, the large transformers inside UPSes are still quite heavy and might make this option less attractive. Still, it's worth investigation.

    Another idea might be to roll your own [dansdata.com]. This would involve buying a large-capacity 12V power supply capable of running from whatever voltage/frequency combination you'll have in Africa and a high-capacity inverter here in the US, shipping them to Africa, and using them to create a UPS together with car batteries purchased locally. If you have some hardware and driver experience, you could probably create an automatic shutdown system without much trouble, and might even be able to create an automated battery-maintenance system which delivers a slightly higher charge every few months to prevent sulfation (discussed in the linked article). This setup has the advantage of being a true UPS: it will provide power filtering and protection up to the point where either the battery goes dead or the battery chargers take one for the team and catch on fire. Also, it's incredibly scalable; with enough batteries, you could run a computer room for weeks without power.

    • Layer 1
      http://www.zerosurge.com/ [zerosurge.com] for a surge-suppressor that'll protect your UPS, make it one of the wide-spectrum jobbers ( these things don't use MOV's which fade, so you can TRUST 'em, and no I don't work for ZS )

      Layer 2
      line-conditioner

      Layer 3
      UPS, with add-on battery capability, and BIG batteries added on, in parallel ( absorbed-glass-mat or starved-electrolyte, same-thing, are the standard for putting in UPSs, but if you're going to be doing this for extended-no-grid-use, then probably going with

  • As always... (Score:1, Redundant)

    by KILNA ( 536949 ) *
    Google is your friend [google.com]. Just put the UPS in the PC.

  • Solar panels (Score:4, Interesting)

    by QuantumRiff ( 120817 ) on Wednesday March 30, 2005 @06:46PM (#12094491)
    I know this would drastically increase the cost, but you could model it after "on grid" solar homes. You throw some solar cells on the roof, tie in a few large, deep cycle batteries (you would want to get those in africa, they're heavy) and an inverter made for running a house. (like sunny boy inverters, google for them).

    During the day, the solar cells and power from outside charge the deep cycle batteries. if the power from the grid sags (brownout) the inverter starts adding power from the battery bank, or the solar arrays. (depending on time of day, not much solar power at 3am) Many of these inverters have serial ports, and tell you the status of what is going on (brownouts, battery life left, etc). You can setup a computer to poll this, and if the thresholds get too low, have that one system force the others to shut down.

    This is probably the most reliable way to setup a power system to have clean power, in the US, or in africa. Depending on how far you are from your trip, you could start hitting BP solar (or someone else, like GE, or phillips) for donations. They might jump at the chance to send you a couple of PV arrays.

    • Forgot to mention, the cheaper solution is to just use the inverters, and the deep cycle batteries.. It would work the same, but the batteries wouldn't get charged by the sun for free, or for long outages.
    • If he goes the solar route it might be better to skip the inverter and use PCs with 12V DC power supplies.

    • On? (Score:2)

      by lorcha ( 464930 )
      I know this would drastically increase the cost, but you could model it after "on grid" solar homes.
      I'm pretty sure you meant OFF grid. ;)
      • No, I think he meant on-grid.

        In this scenario you use Solar when it is available, but when it isn't you use grid power, and if it isn't available you use batteries.

        If you have grid, but no sun, you can charge your batteries from the grid.

        The SunnyBoy that he referred to is typically configured as a "grid-tie" inverter.

    • Re:Solar panels (Score:3, Informative)

      by Phreakiture ( 547094 )

      like sunny boy inverters, google for them

      The sunny boy inverters would actually be a very poor choice, because they shut down when the grid power goes. They are designed only to add your solar input to an existing AC system.

      I would, instead, suggest getting an inverter from Xantrex/Trace [xantrex.com] or from Outback Power Systems [outbackpower.com]. These are also grid-tie inverters, but can support being attached to a battery system.

      A different, and perhaps better (and definitely much cheaper) solution, would be to purchase 12V

  • Get a pedal cycle and a dynamo. You should be able to produce 150W+ with that for a short while (an hour or two). If you can't get a bike try a Concept 2 rowing machine - I've pulled 400W on one of those (until I reached VO2 max and fell off).
    • You should be able to produce 150W+ with that for a short while (an hour or two)

      You're in a hellofalot better shape than me. The best I can do is 75 watts for 45 minutes.

    • Get a pedal cycle and a dynamo.

      This is a really cool idea. It is also extremely unsustainable. Consider the base diet here in the industrial world to be about 2000-2400 Calories per day. Keep in mind that these are dietary calories, which are actually kilocalories. This translates to 8.368 to 10.042 MJ per day. Divide that by 86,400 seconds per day, and you get 96.85 to 116.22 watts average output, before you have adjusted for any inefficiencies. You can peak (as in your 400W example), but you ca

  • File server and semi-thin clients (Score:5, Insightful)

    by isj ( 453011 ) on Wednesday March 30, 2005 @07:30PM (#12094963) Homepage
    Install a file server that is protected with an UPS. Configure automatic shutdown of it.
    Put the client PCs behind a surge protector (but not on an UPS). Make them boot from the file server drives.

    That way the storage/filesystem is reasonably protected and is not smashed everytime there is a brownout. And you don't have to spend the money for a large UPS for the client PCs.

  • ghetto UPS (Score:4, Interesting)

    by TheSHAD0W ( 258774 ) on Wednesday March 30, 2005 @07:58PM (#12095235) Homepage
    (1) Get some really heavy duty surge suppressors.
    (2) Buy 2-3 APC UPSes, each 700VA or so.
    (3) Take the batteries out of the UPSes and sell them or discard them.
    (4) Go to Africa.
    (5) Get 2-3 car batteries.
    (6) Drill some vent holes in a large metal box. Put the car batteries inside. Wire one car battery to each UPS. Put the whole shebang in an area with good ventilation.
    (7) Plug the surge suppressors into your AC supply. Plug the UPSes into the surge suppressors. Plug the computers into the UPSes.
    • Buy 2-3 APC UPSes, each 700VA or so [...] Wire one car battery to each UPS

      I think this is asking for a fried UPS. Most UPS's of that size are designed for batteries of a specific capacity - their chargers and inverters are only designed to run for certain lengths of time.

      To be safe, get a UPS designed to accept additional external battery packs, and don't attach (much) more capacity to it than the manufacturer allowed for.

      And PLEASE don't use car batteries! You'd kill them dead in just a few full cycl

      • Re:ghetto UPS (Score:3, Informative)

        by itwerx ( 165526 )
        And PLEASE don't use car batteries! You'd kill them dead in just a few full cycles! Only use deep cycle batteries.

        I lived in a third world country for some years with nothing more than a bank of old car batteries and a 12v generator. We abused the crap out of them and yes, they would die after a few years, but no sooner than would be expected. Normal lead-acid batteries are actually surprisingly resilient...
        • Normal lead-acid batteries are actually surprisingly resilient...

          Car batteries aren't normal lead-acid batteries. They are designed to deliver and accept incredible amounts of current for short periods of time. The lead plates in each cell are much thinner, made of sponge lead, and have a lot more total surface area than plates in normal lead-acid batteries. A car battery can put out hundreds of amps, but because of these thin plates, you risk reversing a cell any time you discharge below 80%. Reverse a c

          • Re:ghetto UPS (Score:5, Informative)

            by itwerx ( 165526 ) on Thursday March 31, 2005 @12:28AM (#12097143) Homepage
            Car batteries aren't normal lead-acid batteries.
            Car batteries actually are "normal" lead acid batteries. So are deep-cycle batteries. The only differences that are ever present in any type of lead acid battery is 1 - the physical structure of the plates (grid vs foil), 2 - the venting system (sealed or not) and 3 - the acid (water vs gel).
            There are other minor variations. E.g. car batteries have extra ribs of plastic which help to support the plates so that they don't crack loose when you hit a pot-hole. So-called deep-cycle batteries have extra heavy-duty bus bars between the plates to handle the power and help act as a heat-sink.

            you risk reversing a cell any time you discharge below 80%
            Cells don't risk reversal until they *completely* discharge. Even a damaged cell that discharges earlier than the others will retain its polarity as long as the other cells have any energy left in them. There's no way a lead acid cell will reverse if it still has at least 20% charge (maybe you meant to say that above?) Even then it is highly unlikely to reverse until well below that.
            Not to mention that unless the cell is physically damaged so badly that it can't be charged at all, the reversal will be undone as soon as it is charged with the correct polarity.
            To get to your point about reduction in voltage, if a cell were truly reversed and somehow stayed that way even through a charge cycle (not sure that's even possible unless you purposely disconnected it and charged it separately with a reverse bias) you would actually see a 4v reduction as it would not only be failing to contribute it's own 2v but that reversed 2v would effectively cancel out 2v worth provided by one of the other cells.
            In the case you're describing I would assume that the battery was charged (or discharged) at a higher rate than it was designed for and the plates warped from the heat causing the cell(s) to short out.

            I'd bet that the reduced capacity of your batteries just became easily noticable after a few years.
            This is actually due to sulfation. Even a sealed battery will have impurities present in both the lead and the acid compound. An unsealed battery is especially vulnerable. Sulfation occurs when the sulfuric acid reacts with the impurities and leaves deposits on the plates. Eventually enough of the surface area is covered that the cell ceases to be functional. This is also why a car battery (or any battery designed for a physically abusive environment) will have a fairly large gap between the bottom of the plates and the bottom of the reservoir. The sulfation in a car battery tends to get knocked loose and settle to the bottom where it shorts the plates out when it accumulates to a sufficient depth.

            Anything else I can help clear up about lead acid batteries? :)
            • To get to your point about reduction in voltage, if a cell were truly reversed and somehow stayed that way even through a charge cycle (not sure that's even possible unless you purposely disconnected it and charged it separately with a reverse bias) you would actually see a 4v reduction as it would not only be failing to contribute it's own 2v but that reversed 2v would effectively cancel out 2v worth provided by one of the other cells.

              I'm left to assume you've never actually experienced this for yourself

              • Re:ghetto UPS (Score:4, Interesting)

                by itwerx ( 165526 ) on Thursday March 31, 2005 @04:35AM (#12098183) Homepage
                A reversed cell in a battery never reaches anything near full voltage. It adds to the internal resistance of the battery (the opposite of what would happen if the cell shorted out). It happens much faster than sulfation.

                Then it's not a reversed cell. :)
                Next time you think that's what has happened, isolate the cell and test it. You'll find that the polarity is still correct, it just isn't holding much of a charge any more.
                If you're really curious you can take it apart and find out why. Having done that myself more than a time or two I can tell you that you'll find either broken/shorted plates, sulfation (see my notes above about accumulation at the bottom of the cell; this causes fairly rapid loss of functionality along the lines of what you're describing) or, last but not least, the pH is wrong in which case it is either a sealed battery whose seal has breached or it is an unsealed battery which has not been maintained.
                Trust me, I've dealt with these fuckers for years - I have first-hand experience with every possible mode of failure up to and including exploding.
                • Trust me, I've dealt with these fuckers for years

                  The thing is, I can't trust you regarding your apparent conclusion that it's OK to use car batteries for UPS applications, because not only do your experiences differ from mine, but they also contradict just about everything I've read.

                  • Re:ghetto UPS (Score:3, Informative)

                    by itwerx ( 165526 )
                    ...I can't trust you regarding your apparent conclusion that it's OK to use car batteries for UPS applications...
                    I never said it was OK to do that.
                    My original post was refuting the statement that they would get killed in just a few cycles.
                    It's actually very difficult to use anything but the OEM battery packs on an off-the-shelf UPS because the UPS manufacturers try to cut costs wherever they can.
                    A good general purpose charger will have an op-amp circuit that is set up to reduce power as the bat

  • Spend about $75, get an AC isolation transformer -- 450 VA or 450 W minimum -- from eBay. Don't try to get one of this capacity new, you'll spend way too much. Then get an inexpensive UPS new. You'll either have to get both these items compatible with the wall-voltage of your destination (not much more difficult) or run an adaptor that can handle 500W. Once you have it all there, plug the isolation transformer into the wall, plug the UPS into the transformer, and plug the PC into the UPS. The transfor

  • I would look in to getting some laptops with really good power supplies, I had an old twinhead laptop for a while that would run off 60 to 300 volts which would probably be more than enough.

    Really though the safest bet would probably be your own generator since from what I understand the power goes off in Africa in places for hours at a time. I doubt you'll find a UPS or many laptops that'll make it. Used generaters can be had for a couple hundred from a pawn shop, and will be worth something when you ge

  • UPS != clean power (Score:1, Offtopic)

    by Guspaz ( 556486 )
    UPS only filter LARGE power disturbances. AVR on APC UPS only filters if the voltage goes outside a 30v range. (12% below or 12% above nominal).

    AVR is really useless, because APC UPS can switch to battery on stricter basis than that.

    On the other hand, a UPS to filter big disturbances and a very high quality PSU to filter smaller stuff is not a bad combination.

  • Don't buy JUST a UPS (Score:3, Interesting)

    by aaarrrgggh ( 9205 ) on Wednesday March 30, 2005 @10:52PM (#12096564)
    From my experience on an island in Thailand without government electricity, a UPS is hopeless. The range of voltage is only marginally suitable for driving incandescent lightbulbs. If you need to use local power (no solar option), you have limited options.

    An AVR helps, but is usually only good in the +/-15% range. A laptop is the ideal solution, with an input range of 240-100V, but that will go in time as well with enough surges. An old battery will usually still give you a couple minutes of run-time, which will at least get you through the sags.

    If you have to work with a desktop, the only solution I found that actually kept the surges away was to make a small M-G set-- couple a two motors on a common shaft with a flywheel, and connect a UPS to the output of that. All the little hits will be taken by the flywheel (as will the overvoltages), and the UPS will deal with actual outages. If you want to increase the life of the UPS batteries, put an Automatic Voltage Regulator in front of the UPS.

    As for UPS systems, an off-line UPS won't do you much good. You will need a good double-conversion system to condition incoming power.

    I don't think APC makes one of their "Delta Conversion" systems in that small of a size, but that could give you the best of both worlds; very good voltage regulation with buck/boost capability, and the best efficiency.

    Good luck... it's an uphill battle.
  • suggestions on how to over come the challenge of running a computer network in a country where the power fluctuates wildly and multiple outages in week are not unusual occurrences?

    Save now and save often.

    Bzzzzrt!
  • Now, good psus nowadays can easily handle a brownout or a surge. For example, the antec neopower power supply can survive with only 60 volts (i tested this) and up to 220 volts, (that's what it says, probably more than this.)
    remember, good powersupplies can survive little brownouts and surges, but i recommend a surge protector just in case.
  • I know that this is a little off-topic, but why do all of the 120 volt conversion when you can run directly off of low power? The display and keyboard sizes may pose a problem for you, but there has to be a solution somewhere. If I was going to a remote location then the last thing that I'd want to be thinking about is dragging along a heavy transformer/UPS and car battery.
  • 1. You might not really want to use UPSs. Unless the grounding is good they really won't help much with spikes and surges. They will also cost an arm and a leg to ship. If you choose to use UPSs anyway, check to see if APC or one of the other decent UPS makers will sponsor you. I know APC likes to run success stories in their newsletter and this sounds like it might make for a good story. Also consider using 1 or 2 large high quality UPSs rather than a bunch of small/cheap ones.

    2. Laptops. Someone
  • As other posters have mentioned, get the best power supply you can afford for your system. This is the single biggest factor. If you can, consider a notebook you can run off of low voltage DC. The solution could be as simple as running the computer always offline, and swapping batteries out of a charger on the fly.

    The power requirement would be low enough that looking at absorbing the one time shipping cost of a solar panel might not be out of the question.

    Next you need to take care of large spikes and vo
  • On the assumption that most of your problems were caused by data becoming corrupted, why not use Knoppix (or some similar CD-based distro of your choice)? Throw in some decent surge supressors for the worst of the fluctuations. You won't have to worry about the cost of getting UPS's going, and your core OS will be good. No reason students can't save data to a hard drive on it.
  • I suppose this will be seen as a plug, but so far as I know, the best surge suppressors available are to be had from the brick wall [brickwall.com] folks. Kind of expensive though, even after quantity discount, but still less expensive than replacing the equipment it protrects.

    Then I plug my relatively ordinary UPS into the surge protector.

  • Inverters and Chargers. (Score:3, Informative)

    by FrankSchwab ( 675585 ) on Thursday March 31, 2005 @11:55AM (#12100329) Journal
    Isolate as much as possible - cheap UPS's won't do that for you.

    Here's a thought. For each computer (or, possibly, group of two or three computers), run 120/240V power into an RV or Marine battery charger (something like http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?Vi ewItem&rd=1&item=4538880150&category=50073 [ebay.com] or http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?Vi ewItem&rd=1&item=4538380600&category=26444 [ebay.com] ) connected to one or more car batteries. Coming off the car batteries, you hang a cheap inverter - 400 watt 12V->120V inverters (enough for a computer and monitor) are in the $30 range. Hang a voltmeter across the batteries, draw a red line at 12V or so, and teach the kids that when the needle is below the liine, you can't run the computers (deals with most issues associated with deep cycling the batteries).

    This gives you an inexpensive, reasonably isolated, double-conversion system. It might even work!

    /frank
  • Seems like the power source is the real problem. Perhaps you could fix [enint.com] that problem.

  • Telco equipment (Score:4, Informative)

    by Paul Carver ( 4555 ) on Thursday March 31, 2005 @01:59PM (#12101814)
    I'm not sure if you're talking about equipment that has been donated to you or if you're talking about buying equipment that you are going to donate. If the later, you might consider Telco equipment designed to run on -48V DC power. It's going to be more expensive than a cheap Dell, but they're built to more demanding standards. A quick Google turned up a couple of links:

    http://www.angstrom.com/products/viper.htm [angstrom.com]
    http://www-1.ibm.com/servers/eserver/pseries/hardw are/tour/briefs/telco_server.html [ibm.com]

    Or just a -48V power supply.

    http://www.zantech.com.au/zantech/power-supply-atx -48v-dc/ [zantech.com.au]

    Alternatively, you could look at products geared for automotive use. Look at what people are using for in car computers running directly off of a 12V supply. They should also be pretty robust, although I think the Telco standards are probably more demanding (though buying NEBS3 certified equipment will really cost you.)

    By running off a DC battery directly you provide a buffer against the flaky AC power distribution while saving the complexity of a UPS doing AC-DC-AC.

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