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

Inverter + charger

[wowbagger]

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

[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 time). Plus they are often not rated for continuous usage day-in, day-out and will burn up after a while.

Re:Inverter + charger

[LWATCDR]

Actually Hackaday had just what you want.
http://www.hackaday.com/entry/1234000583030620/
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.

Re:Inverter + charger

[John Hasler]

> 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 one.

Laptops?

[fm6]

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.

Why not a UPS?

[PurpleFloyd]

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. 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.

Use an isolation transformer.

[JonathanBrickman0000]

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 transformer will protect both UPS and PC from spikes, and do it very well; the UPS will protect the PC from power failures.

I have been running an isolation transformer on my home PC for years, and would not have it any other way. I used to get hit by spikes, have not been since the transformer went in. This eBay item would be perfect:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&cate gory=4665&item=7504750488&rd=1

This one is questionable. It looks right, but I would have to verify that 13 "AAC" is really 13 amps A.C.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&cate gory=4665&item=7504750488&rd=1

Re:ghetto UPS

[itwerx]

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...

Re:ghetto UPS

[itwerx]

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? :)

Re:ghetto UPS

[itwerx]

...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 battery reaches a full charge. The output of the circuit is also regulated so as not to fry the circuit itself if too large a load is placed on it.
In the case of an OEM UPS, the output from the charging circuit is very rarely regulated. If you put a larger than expected load on it you will fry it. Additionally, a UPS usually uses a simple temperature sensor instead of a proper comparator because the characteristics of the cells and UPS housing are known factors. Even if you tried to extend the sensor out to the car battery it would still be wildly inaccurate and run the risk damaging the UPS or the battery or both.

Inverters and Chargers.

[FrankSchwab]

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 or http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?Vi ewItem&rd=1&item=4538380600&category=26444 ) 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

Telco equipment

[Paul Carver]

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
http://www-1.ibm.com/servers/eserver/pseries/hardw are/tour/briefs/telco_server.html

Or just a -48V power supply.

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

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.

Re:Solar panels

[Phreakiture]

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 or from Outback Power Systems. 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 12VDC power supplies from Mini-Box and cobining this with a 12V battery system and charger.