shenkin@cunixf.cc.columbia.edu (Peter S. Shenkin) (07/22/90)
I'm trying to sort through the maze of vendors' claims in order to pick a UPS to protect a Silicon Graphics Personal Iris (PI). I am hoping that someone out there more knowledgable than I can help me out. I will summarize to the above newsgroups. The following is in fact a summary of what I've learned about these devices so far, but the purpose of this posting is to find out more. The PI has a power rating of roughly 1kVA; however, I am looking at units in the 2-5kVA range for the sake of future expansion. The 1990 Science "Guide to Biotechnology Products and Instruments" (Science, vol 247, 23 March 1990, Part II) lists 19 suppliers, though probably there are only about 5 manufacturers and the others re-sell or OEM these units. So far I've spoken to the following companies: Best: (800) 356-5794 Clary: (818) 287-6111 Personal Computer Tools : (800) 767-6728 Shape Electronics: (800) 367-5811 Anixter Electronics: (800) 323-8166 Elgar Electronics: (800) 733-5427 Lambda and Liebert are also listed, and I want to talk to them. Now, I gather there are "on-line" units, and "standby" units; standby units are cheaper, and also seem to come in lower power ratings. Elgar sells a 1.5kVA standby unit for $1875, and then jumps to a 3kVA on-line unit for $6145. A standby unit kicks in only when the power goes down, which has two implications: (1) there is a time-lag during which you don't have power. Elgar quotes 4ms for their 1.5kVA unit. (2) you get no (or little) surge protection and power conditioning from the unit. The on-line units are, theoretically at least, supplying power all the time, and are said to give good power conditioning. So my FIRST QUESTION is: for the intended use, is this a red herring? I have been assuming I need an on-line unit, but is a 4ms delay likely to give problems? (I note that using 60 Hz power, 4 ms is a bit less than 1/4 of a cycle.) In fact, I probably want a unit with larger capacity anyway, but the answer to this question would still be good to know, and it comes up again, just below. Of the so-called on-line units, Best has the best list prices. Examples: * Best: 2.1kVA, $2995; 3.1kVA, $3695. * Anixter: 2kVA, $4335. Elgar: 3kVA, $6145. * Clary: 2kVA, $5590; 3kVA, $6550. * = offer some academic discount; range is 5-15%. However, it seems that there are on-line units, then again there are on-line units. Best's inverter doesn't always run; they've got a big ferroresonant transformer that ballasts the load while the inverter kicks in. Clary emphasizes that their inverter always runs, and therefore that their unit is "really" on-line at all times. On the other hand, Best's transformer is bound to give excellent power-conditioning, or so it would seem to me, as should Clary's unit. Best presents their way of doing thing as a virtue: since the inverter doesn't always run, the UPS is cheaper to operate, and will also last longer. Clary also says that only their unit meets UL-544 for low leakage current, which qualifies the unit for use in surgery. I'm confused about this; where is current going to leak to? Is this a ground-leak, or what? It seems to me that no matter what the power supply does, the load is only going to draw what it needs. Clearly, I'm confused. So my SECOND QUESTION is whether the ballast route to making a unit "on-line" as "good" as the inverter-always-on route? That is, perhaps instead of a two way classification (standby and on-line), we should have a three-way classification: standby (eg 4ms delay) ballasted standby (eg, Best) "true" on-line (eg, Clary). So the question is: which one should I get? :-) Is the ballasted unit really more like a standby, or more like a true on-line? and where is the critical breakpoint for my application? Has anyone heard of a ballasted unit (eg, Best) failing in a computational application? My THIRD QUESTION is: can you clarify my confusion about UL-544 and low leakage current? (a) What does it mean, and (b) Do I need it? Now I simply comment about battery capacity. All the units mentioned will run at full load for at least 10 minutes; some units run longer. If instead you run at half load, you more than double your backup time. My own purpose is to protect my equipment, not to continue operations uninterrupted for significant lengths of time; therefore 10 minutes is fine; it's plenty of time for an orderly shutdown of a workstation. Which brings us to our next topic: Computer interface. Just about all of these machines (exception: Elgar on-line units) are equipped with RS-232 interfaces which signal the state of the UPS. For example, some line goes from low to high when the external power has failed, and the machine is running on battery power. A setuid root program that monitors the port can then bring the machine down if this happens, or if the condition persists more than x minutes, or when the UPS signals only five minutes backup power remaining, or whatever. For some of these units the RS-232 is bundled, and for some it is an extra-cost option (Clary: $200). Some of the vendors supply software to monitor the port (Elgar: $250-300; Best: $125) but others (Clary) don't have UNIX drivers. Some of the vendors actually issue unix-flavor-specific drivers (eg, SunOS), as well as generic UNIX drivers. The Elgar standby units have the following feature: the UPS can be set to turn itself off after it brings the computer. Some users tout this feature. QUESTION FOUR: why do you care whether or not the UPS turns itself off, once it's safely brought the machine down? I have heard that there is a company (maybe Apunix?) that OEMs some UPS, and also supplies kernel mods, at least for SunOS, that allow the UPS to reboot the machine when the power comes on again. I don't feel I need this feature, and am mentioning it for completeness. But I do have a final question: QUESTION FIVE: Do you have personal experience with any of these power supplies, or with their competitors? If so, I'd appreciate it if you'd share your experiences, likes, dislikes. Thanks, -P. ************************f*u*cn*rd*ths*u*cn*gt*a*gd*jb************************** Peter S. Shenkin, Department of Chemistry, Barnard College, New York, NY 10027 (212)854-1418 shenkin@cunixc.cc.columbia.edu(Internet) shenkin@cunixc(Bitnet) ***"In scenic New York... where the third world is only a subway ride away."***
karn@thumper..bellcore.com (Phil R. Karn) (07/23/90)
The reason there are at least three different UPS/SPS configurations shows that there is no one ideal approach. The SPS (standby inverter plus relay) has the advantage of low cost and efficient operation, but at the expense of a switchover transient when the power fails. The SPS-plus- ferroresonant transformer (the BEST Technology approach) has the advantage of covering the switchover transient and of providing something that looks more like a sine wave, but at the expense of weight, accoustic noise and inefficiency. The true online UPS has the advantage of an output that never wavers across an outage, but at greater expense (since the inverter must be rated to run continuously) and lower efficiency (because in normal operation, power is being double-converted). In general, the switching power supplies used in most computers can handle the switchover transients of a SPS just fine. Linear power supplies, however, can have problems because their low voltage filter caps can't store nearly as much energy as the high voltage caps found in most off-line switching supplies. This problem bit me in our Internet gateway; we have a Cisco CGS router plus a separate T-1 CSU, both powered by an Inmac 400VA SPS (OEM'ed from American Power Conversion). Although the Cisco would ride just fine across the switchover transient, the CSU occasionally glitched and hung, and it had to be power cycled to get it going again. My solution was to install a ferroresonant transformer between the SPS and the CSU. So, in general, SPS's are just fine for most computer equipment. And if you have more sensitive loads (modems, etc), add a small ferroresonant transformer to protect them. Phil
matt@oddjob.uchicago.edu (Matt Crawford) (07/25/90)
I'd like to leap in here with a related question. What ratings make for a good surge suppressor? I have a Sparcstation at home and I live in a lightning-rich part of the country. My whole system draws less than 15 amps. I see claims like "clamps surges at 325 volts within 5 ns" "provides 10-40 dB EMI/RFI noise attentuation" "provides 300 joules differential plus 225 joules common mode protection" "tough enough to absorb 2 million watts of power in one nanosecond" Given that I understand all the terms, and my physics hasn't rusted so badly that I can't see that the last statement is bupkus, what are the minimum acceptable figures to assure a great reduction in the chance of damage? ________________________________________________________ Matt Crawford matt@oddjob.uchicago.edu