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Comments on Uninterruptible Power Supplies

My primary recommendation is Powerware (formerly BEST Technology, now part of the Eaton Group ) UPS's, specifically the Ferrups ferroresonant unit for difficult or lightning-prone environments. My recommendations are based on a lot of real-world experience with manufacturing environments, which tend to pose the greatest difficulties in providing computer-grade electrical power. Powerware's 9100 series is also high quality and fine for installations where heavy electrical loads attributable to integral horsepower motors are not present in the same building.

One of our installations is at a rubber goods manufacturer (No! Not that kind of rubber goods.), where some of the shop machinery is powered by electric motors big enough to sink a small ship. Starting some of these motors gives new meaning to "power surge." One of the motors, a 75 horsepower unit, draws nearly 1000 amps from the line at start-up. Needless to say, power line instability is the norm there.

To deal with the power line cruft we have their main computer system (an H-P 9000 RISC server) attached to a Ferrups 1.4 KVA ferroresonant UPS. Another Ferrups unit, an 850 VA model, supports their network gear and also protects the telephone system. On several occasions, I have 'scoped the UPS output and have never seen so much as a millivolt of junk, despite all the machinery running and the continuous power line blips.

The smallest Ferrups unit available is a 500 VA device, which is what powers the UNIX box here in my office. The largest currently available is rated at 18 KVA, which will run a heck of a lot of hardware. I don't know how long the run time is on the 500 VA unit's battery, because the longest power failure we ever experienced was only 1-1/2 hours, and the UPS was still going strong. The 1.4 KVA unit installed at the rubber goods plant has been able to keep their system up for in excess of two hours before initiating an automatic server shutdown due to low battery charge (we subsequently added a second battery to extend the run time to what is probably close to five hours -- it has yet to be tested).

Ferroresonant UPS's, in general, are larger, heavier and more costly than line interactive or double conversion units. The UPS gets its name from the special transformer that isolates the input from output. The load never sees the raw AC line voltage but instead, sees the output of the transformer.

A ferroresonant transformer is a special type of transformer that has been tuned to resonate at the power line frequency (60 Hz in North America, 50 Hz in Europe and many other locations). Because it has been tuned to pass a narrow frequency range, the transformer acts like a brick wall to anything outside of that range, resulting in very effective power line filtering -- and a nearly impervious firewall to lightning strikes.

Also, because the transformer resonates at the power line frequency, it acts like an electrical flywheel and stores energy in its massive iron core. In the event a momentary decrease or complete loss of voltage occurs the transformer will replace some of the missing AC cycles -- a momentary boost. This results in a true "no break" power source. If the line voltage increases for any reason (e.g., a spike or transient induced by a nearby lightning strike) the transformer will buck the increase, keeping the output within a fraction of a volt of where it should be.

Ferroresonant technology is hardly new. The concept was developed in the 1930's and has been widely available in heavy duty power conditioners. My first encounter with a ferroresonant device was in the 1960's aboard a U.S. Navy warship, where power problems were routine. Much of the electronic gear was protected by ferroresonant transformers, which given that this was aboard a military vessel, amounts to a ringing endorsement of the technology.

"Also, has anyone made a claim to APC for any UPS's that have been hit and got the money?"

I'm not aware of anyone making such a claim and getting a settlement. Actually, it's fairly easy for APC (or any other UPS vendor, for that matter) to weasel out of paying off the claim, simply because irrefutable proof that the UPS was to blame for damaged equipment is difficult for a non-technical person to produce. Even most computer hardware geeks are not experts on power generation and UPS capabilities, which means most will not be able to conclusively determine that the UPS didn't do its duty. Adding to the difficulty is that in many cases, the UPS may continue to function normally following the destruction of the supposedly-protected load.

I find it interesting that APC in particular has long maintained that there is no benefit to ferroresonant technology and has even gone so far as to produce "studies" that "prove" that ferroresonant UPS's are inferior to line interactive and double conversion units of the type produced by APC. Yet, almost all power-critical installations run by the military and many government operations depend on ferroresonant technology for power protection. So, who's right: APC, who has a sales ax to grind and has never achieved a high rate of success in large commercial installations, or the military, whose primary concern is maximum reliability?

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More Articles by © BigDumbDinosaur

---July 20, 2004

Thank you Steggy for a very interesting series of articles!


---July 21, 2004

Yes, Thank you so much for this useful information. I served in the Air Force for 4 years after High School, but never had a chance to check out how their systems were protected (I worked as a Command and Control specialist). I would guess they use a similar high reliability system for their gear as well. This is all great information, and very helpful. Thanks again!

- Bruce Garlock

Thanks for the compliments. I'm glad you found this technobabble useful. My wife was looking over my shoulder as I was typing some of it and made a wisecrack about how only someone with a great big propeller spinning on their head would read it.

Now, if only someone could fix all the typos. <Smile> I noticed that I misspelled ferroresonant in several places -- that last 'n' is missing. Must be because I'm left handed and the N key is on the right hand side of the keyboard. <Grin> Either that or the keyboard interrupt handler is messing up a lot.

BTW, there is a surprisingly large amount of misinformation about UPS's running around the 'Net. One site I happened to visit a while ago claimed to have invented the ferroresonant transformer, a difficult feat to achieve given that said company claimed to be in business for about 20 years.


---July 21, 2004

If I knew how to spell I'd have fixed 'em :-)

All set now..


Thanks! I've concluded that the keyboard interrupt handler is at fault. If you believe that one, let me tell you about my ocean-front summer home in North Dakota.


---July 22, 2004

Oh, it definitely is 'cause the same thing happens to me all the time.


Mon Dec 12 20:43:00 2005: 1431   bruceg

What is your experience with these units and Linux or SCO? Is there simple enough software that uses the RS-232 port to connect this to a Linux box, and send a shutdown command, if the unit is x Min. away from running out of battery backup? I do not need anything extravagent, and would prefer the simplier the better (text only mode preferred)

Oh, I am thinking of this unit: (link)



Tue Dec 13 02:36:04 2005: 1432   BigDumbDinosaur

I'm not sure what is available for the 5125, but it's likely that Powerware's LANSafe package comes with it. The 5125 talks to the host machine via USB, as these smaller UPS's are are meant for PC type usage. The larger models designed for servers can communicate EIA-232, Ethernet or USB. Linux is supported in the 9100 series, as well as the ferroresonant models.

Tue Dec 13 14:33:19 2005: 1435   bruceg

I have to admin dipping my toes in the water with this company, hence the smaller model. They are pricey, and from what you have said, well worth it. I will have to replace some aging APC models, that simply quit without warning, or reason! Very frustrating! Just a page that the system is down, and I find out the UPS is dead. No warnings in the error log or anything. The last write to the log, was that the last self test passed just fine, so maybe they string you along? Dunno - but I have had it with APC. Simply too much time managing something that should be a very non-manageable item. I want to plug it in, and have it work. It is a very critical part of the server room, and just having a unit, that was using 40-50 of it's capacity just up and die for no reason, makes me angry. This is the third failure we have had with APC this year.

- Bruce

Wed Dec 14 15:56:31 2005: 1437   BigDumbDinosaur

They are pricey, and from what you have said, well worth it.

Depends on what you call pricey and where you get them. Of course, a UPS is like anything else in a computer system: you get only what you pay for. Usually, the cost of a quality UPS is a fraction of the cost of the equipment being protected, so it's a matter of convincing your client that it's money well spent. I always play up the "no downtime due to blown up servers" angle. A little FFUD (that's friendly FUD) usually helps. Most non-technical computer users really have no idea just how much damage bad power can cause. In years past, I used to show hesitant clients a picture of the insides of a server that was connected to an APC unit that failed to do its job. Think crispy critter. <Grin>

Mon Feb 5 16:15:08 2007: 2852   bruceg2004

We are having a very difficult time finding these UPS's. We have contacted 3 different people who claim to sell them, and when we place our order, they tell us it is on back-order. Does anyone have a reliable source for these?

Thank you,


Mon Feb 5 23:36:03 2007: 2853   BigDumbDinosaur

Does anyone have a reliable source for these?

Well, not to try to drum up business or anything, if all else fails, you could order through me. Or, if you have a TechData reseller account you can order through them. Which model are you considering?


Thu Feb 8 14:45:39 2007: 2857   bruceg2004

Thanks, we ended up finding some in stock from a reseller. I am looking forward to getting these going, as our APC UPS's keep dying on us.

Thank you,


Wed Feb 21 17:25:18 2007: 2871   rbailin

The following article was recently posted on Ed Foster's GripeLine website concerning Powerware's restrictive policies regarding end-user or 3rd-party maintenance of its UPS products:


This may not affect most potential customers, but it's good to be aware of potential these potential issues before you make a purchase.


Thu Feb 22 14:35:53 2007: 2872   BigDumbDinosaur

I'm aware of Eaton's policies regarding Powerware products. It seems Eaton is like this in all areas where they do business, and when they acquired Powerware they extended their lock-in policy to that business as well.

The UPS maintenance software being referred to by Ed Foster is for use with the large, three phase commercial/industrial UPS's, not the smaller ones that would be used in an office. The smaller units ship with LanSafe, which handles all of the UPS communications.

I don't condone this sort of "Microsoft" behavior at all. If it weren't for the quality and performance of Powerware products I would drop them from our line card.

Kerio Samepage

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