Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/5/84; site mnetor.UUCP Path: utzoo!utcs!mnetor!clewis From: clewis@mnetor.UUCP (Chris Lewis) Newsgroups: net.periphs,net.news.sa Subject: Re: uninteruptable power supply for a VAX Message-ID: <938@mnetor.UUCP> Date: Wed, 5-Jun-85 12:07:17 EDT Article-I.D.: mnetor.938 Posted: Wed Jun 5 12:07:17 1985 Date-Received: Wed, 5-Jun-85 13:15:47 EDT References: <1218@cbosgd.UUCP> Reply-To: clewis@mnetor.UUCP (Chris Lewis) Organization: Computer X (CANADA) Ltd., Toronto, Ontario, Canada Lines: 106 Keywords: ups, vax, power failure Xref: utcs net.periphs:721 net.news.sa:117 Summary: In article <1218@cbosgd.UUCP> mark@cbosgd.UUCP (Mark Horton) writes: >Is anyone out there running a VAX 750 (or 780) on some kind of >uninterruptable power supply? I see lots of ads for UPS's that >have regular 120V plugs and seem like they could keep the machine >up in a thunderstorm. But I look at our 750 and it has lots of >kinds of funny plugs, some of which are apparently custom built >by local electricians. Disks like RM80's have regular 3 prong >plugs. The CPU has a funny round plug which is described to me >as "single phase, 20 amp, 120V", which sounds like an ordinary >circuit with lots of capacity - I don't understand why the funny >plug at all. The tape drive (TE16) and one of the disks (RM05) >have their own special plugs, too. The "funny" plugs make a lot of sense. Read the electrical codes sometime. For example, if the 20 amp 120V circuit had an ordinary 3-prong, two things would happen: 1) Somebody would plug an ordinary device into it (like a toaster). Then, a short that would normally blow a 15 amp fuse (and have the power cords survive) wouldn't blow the fuse and the appliance cord would catch on fire. 2) Some nitwit would plug his VAX CPU into an ordinary 15 amp service, blow the fuse, and put in a penny or 20 amp fuse into the socket. Then you could very well have the in-wall wiring catch on fire. We've had airconditioners nominally rated at only 8 amps burn out outlets and wiring connections. (Normal 15 amp circuits often are not wired very carefully). Other plugs are specified for 240V and 208V (at various amperages), 120V at 30 amps, and three-phase services. Not to mention 400V, 600V and 400 Hz systems. Probably some of the plugs that you see are 240 (or 208) volt services. Just try plugging a toaster into 240 V and see what happens! The electrical code recognizes that if it is possible to connect something wrong, somebody will and lives may be threatened. Any UPS that has only 120V three prong plugs is not intended to be able to supply more than about 15 amps. Even if you only need it for a few seconds, overloading a 15 amp UPS with a whole VAX plus disk drives will probably result in the UPS shutting down or lots of smoke. Just because the UPS is rated at 100 watts for an hour, doesn't mean that you can draw 36,000 watts for 10 seconds! >Has anyone figured a reasonable way to keep such a machine running >through a typical one second power hit from a thunderstorm? What >do you do? Has anyone concluded it can't be done or is a bad idea? >Are these things any good for a smaller machine with a regular plug, >like a Microvax, Sun, or 3B2? If you want to run something with as big a current draw as a VAX you are going to have to look into "real" industrial UPS's that either supply multiple voltages at high amperages, or buy several UPS's, each at a different voltage. Either way, it costs a lot of money. Try asking IBM about UPS's. The UPS's advertised in Byte (etc.) are just not suitable for such big systems. Byte's adverts are intended for things like Apples, PC's, and the occasional hard-disk system. Some of the bigger ones would be okay for a Sun. For a VAX, you might have to resort to an electrical start diesel generator. Another (possibly a lot cheaper) solution for one second hits, is to buy a couple of really high capacitance capacitors and put them in parallel with the power supply capacitors. They just might be able to get you over a sub-second outage. We built some machines at a previous place that could survive sub-second hits (that would kill our VAX - the filter capacitors were fairly big). But the machines were pretty small (about the size of a PC in current drain). In addition, you'd also have to disable the power-fail detect. And it would probably void your VAX service contract. And, the capacitors big enough may be too expensive or unobtainable. You should have seen the device we used to supply 20 amps at 250V 50 cycle (pretesting an European Demo). It included a 400 to 600V step-up transformer that weighed 400 pounds, and a 400 pound 600V 15 HP motor-generator (MG set). The electrician installed it and turned it on. Blew the 60 amp fuse in the 400V supply. He then figgered that only the MG startup surge was the problem. He then put a 100 amp fuse in the 400V supply. BOOM! 6 foot flames, totally destroyed electrical distribution panel (8 ft. high), started a fire in the basement and on the hydro pole outside, plus blew 2 (of 3) 2000 amp 400V fuses (The suckers are huge! About the size of a 6" artillery shell. Took a week to get replacements). God what a mess. Even the Halon went off. Turned out that the transformer was saturating during the surge and the 100 amp fuses blew up and created a atmospheric conduction path of copper vapor across the 8 square inch cross-section distribution bus bars. Some of our lights and electrical outlets weren't operational for a week (we borrowed a couple of "mains" fuses). Mississauga Hydro was not very happy with us! Gives you a great deal of respect for high power electrical circuits. VAXen draw an awful lot of power, particularly the disk drives (our Eagles have a one-cycle 45 amp 208V startup surge). Most of the big computer systems that I know about don't do anything about thunderstorms. They either try to run on normal AC throughout, or if they are worried about damage, shut the system down for the duration. BNR, Canada's biggest IBM VM/CMS shop (except for possibly the Royal Bank), probably still shuts down their 3081's (500 users apiece) during thunderstorms. -- Chris Lewis, UUCP: {allegra, linus, ihnp4}!utzoo!mnetor!clewis BELL: (416)-475-8980 ext. 321