Hello I'm an ICT (InfoComTech) US Peace Corps volunteer deep in Tanzania who has the task of managing and advising concerning our college's two SunFire Sun Ray Servers and Dell Proxy server (on 2 Tripplite 2000VA rackmount Server UPSs and behind 30A AVS). We have about 100 SunRay thin clients (unprotected) and 15 Windows desktops (mostly on high end desktop APC UPS), an unprotected projector, and three laptops (on voltage regulators). There are overworked nationals who also advise on the equipment but they don't have any more expertise on the power issue than I. Any solid, referenced advice offered might apply to thousands of computers in country.

The power quality here is fantastically bad. The dam which generates the power is at least 350mi away with likely only one path between it and us, much of it rather low capacity wiring. Power cuts at least once a week. We run a large generator once a week as well. Brownouts with only one phase active happen monthly (I don't pretend to understand "phases").

In the most general way possible I'd like to ask what is the difference between these various sorts of power protection I've identified since I've arrived in country. What is the efficacy of each and how might they be combined? What is the cost effectiveness for amount of computers covered. Which ones count as "filtered power"? When don't specific solutions apply? I'm sure I'll be advising on all possible permutations.

  • Surge Protection (e.g. Power strips from APC)
    • Seem simpler but I am worried they are simply dressed up fuses. I combine with voltage regulator at my house. Expensive as only good brands trusted are imported from America and marked up.
    • Why are laptop versions so much more expensive? More goodness or greedy markup?
  • Voltage Regulation which smooths voltage +-50V from in my case, 230V.
    • Very cheap imports available. Some seem functional. Laptop hard drives anecdotally seem to fail less when one is used (this possible?). At least puts another layer between you and bad power but I have seen UPS behind them fry when big power spikes occur.
    • Would these be unnecessary in case of SSD/flash-based netbooks since there is no motor? LCD monitors?
    • I swear I've seen flywheel-esque versions of these in old labs: possible?
  • Uninterruptable Power Supply (UPS) which helps computers to shut down properly, high end versions also seem to include voltage regulation. Expensive per computer.
    • At a college with a set up similar to ours, one of the rackmount UPS with voltage regulation fried so this is presumably not sufficient for the main equipment.
  • Automatic Voltage System (AVS, likely proprietary name) which is commonly used in country at all manners of establishments where high tech is used and advertises "multiprocessor" controlled voltage switch which purports to protects a lot of equipment (15A, 30A, and 100A models available) on a circuit from bad power by cutting immediately if it senses badness. Power is returned after a timer is satisfied. Cheap per computer once you get past 2 or 3 desktops.
    • In my experience we've had 4 of these blow around our campus with nothing behind them dying--A win, despite dropping $90 on each!
  • Transformer: We don't have one of our own and I wouldn't think of recommending one but I've heard that some outfits spend thousands of dollars on a dependable transformer for compounds. True?

Also how does the generator play into this? If our compound is switched onto the generator as the generator is turned on, might the bad power which flickers the lights damage something?

  • Jeff's comment on UPS plugged into UPS helps me. I had a colleague who wanted to do that to squeeze a few more minutes before burning petrol! I love having references. serverfault.com/questions/29288/…
    – thadk
    Commented Jul 29, 2009 at 16:58
  • Also "Do not hang a surge protector off your UPS, as it will waste a big % of your power, it has to do with the way the cheap surge protector interacts with the non sine wave power from the UPS." We probably still have an unused strip spliced into a PC cord plugged into the rackmount UPS. Thankfully its unused at the moment. serverfault.com/questions/29288/…
    – thadk
    Commented Jul 29, 2009 at 17:02
  • Brilliant link from Coding Horror in 2006: Power, Surge Protection, PCs, and You: codinghorror.com/blog/archives/000632.html I've got to make a long read of that one. [Meta:Wonder if this should be a half-answer to my query. Post?]
    – thadk
    Commented Jul 29, 2009 at 17:04
  • gleaned from that entry: Check the mysterious middle light on the surge protector. It is probably working if it is on. Forgot a question: Is there any great relevance to the ground/earth when dealing with various power protection? Any way to verify a ground? I've seen ground lights on power protection before. Could be the 230V but I get shocked using my computer at my house without shoes. Apparent ground exists coming from fusebox--maybe even 2?
    – thadk
    Commented Jul 29, 2009 at 17:16
  • Linked article from Coding Horror is also a must: dansdata.com/sbs9.htm Still nothing on grounds or on microprocessor AVS systems. Also little on freestanding voltage regulators. "Fridge-guard" is sold here by the same company as the AVS. I suspect it is a very small SPS. Are the rackmount server UPS' different internally than the APC desktop models? Can they be run closer to dry without so much worry of permanent damage?
    – thadk
    Commented Jul 29, 2009 at 17:51

1 Answer 1


UPS equipment

The UPSs will have some power filtering built in - check the spec with the manufacturer. If your standby generator is upstream of the UPS it should not adversely affect the quality of power coming from the UPS.

If you want to buy new UPS equipment, consider looking at hardware that will take standard UPS batteries (can't remember the type but it will come to me). Some UPSs take proprietary batteries. In some cases, you can add extra batteries to the UPS to increase its capacity. In all cases, you can save money on replacement batteries (and possibly get better battery hardware) if your UPS takes a commodity type.

Standby Power Generators

Chinese generator manufacturers like Tide Power make reasonably good standby generation equipment that is cheaper than you might think (I've seen 6000 CAD for a 20 KVA model). In combination with a UPS you can get quite reasonable reliability for substantially less than the cost of the server equipment.

Three phase power

Three phase power is a system where you have 3 AC currents 120 degrees out of phase with each other. You can wire 3 phase systems across phases or from the phases to a central neutral. Where power lines have 3 wires each wire is a single phase. You can get 400v or so between two phases with 230v power, so it is slightly more efficient for running certain types of electrical equipment. The regular offsets of the phases also make it good for running electric motors as there are no points in the cycle with zero flux (which can happen with certain types of single phase motors). Where a single phase is active it means that two of the phases are not running.

Mechanical Rotary Converters

The flywheel machines you are referring to are probably rotary converters - essentially a motor, a big flywheel and a generator. These are used for providing clean power through the momentum of the flywheel. A spike doesn't do much to the speed the flywheel is turning, so the intertia does a lot to damp power fluctuations. They are quite widely used where really clean power or high capacity is needed but they are much more expensive than solid state power filtering equipment.

Voltage regulation

Switching power supplies are reasonably tolerant of voltage fluctuations - most commercial PC power supplies work anywhere between 90 and 250v. If you have standby power for the whole installation then voltage regulation will probably only be of minor help.

Power filtering

However, power spikes are a significant threat, so you should probably have power filtering. A good power filter has three levels: Polycaps, which are the fastest but least tolerant, Thyristors, which handle larger voltage spikes and Gas Discharge Tubes, which dump energy by arcing it across a gap. A power filter with a surge capacity rated in the thousands of joules probably has a gas discharge tube. A simple 2-3KVA line filter should cope with quite a few PCs. Do your homework and get a good one.

Polycaps only last a couple of years. You may need to look into the replacement schedule for these. If you get blank stares from the vendor go to someone who does understand what you're talking about. Outfits that sell and maintain burglar alarms are more likely to know something about this as noisy power generates spurious callouts.

  • Thank you, this was very helpful. It answers the headline and many of the kinds of protections. I'm still looking for the ways that they might be combined and any information available on automatic voltage regulators. I'm not sure what I can do to move this question forward but I am thinking about it.
    – thadk
    Commented Aug 26, 2009 at 9:48
  • The auxiliary power generator sits upstream of the UPS. When power cuts out the UPS takes over and the standby power generator starts automatically. Set the servers up to monitor the UPS - it will signal a 'battery low' condition when the batteries get down to a certain level (i.e. both the power and the standby generator have died). Use a power conditioner for the desktops, although the standby power generator will probably not cut over quickly enough. If you have any critical desktop machines you could use a UPS for them. Commented Aug 31, 2009 at 18:03

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