Protecting Hardware on Unstable Power Sources?

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?"

Comments

Solar panels

[QuantumRiff]

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.

Re:Inverter + charger

[CyberVenom]

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 up a daemon to monitor this level and initiate a shutdown if it drops too low.
You should also use something fairly resiliant for a filesystem. Ideally, read-only hard disk with a ramdrive. (like Knoppix), but if that isn't a possability, ReiserFS is fairly good.
If you go with the RO+ramdisk solution, outages should be a non-issue anyway.

ghetto UPS

[TheSHAD0W]

(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.

Re:ghetto UPS

[itwerx]

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.

Don't buy JUST a UPS

[aaarrrgggh]

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.