pusateri@romeo.cs.duke.edu (Thomas J. Pusateri) (05/02/89)
I've read in several news articles that you should leave you unix-pc running 24 hours a day. This would be fine if my power company will provide power 24 hours a day but each day they seem to be a few seconds short. Every time there is a quick glitch, my 3b1 hangs and the screen gets messed up. Do you people who run your machines continuously have any kind of backup power supplies, line filters, spike or surge protectors, phone line filters, etc.? I'm somewhat afraid to leave my machine running all the time when all these transients exist on my power line. Any comments or help would be appreciated. Tom Pusateri National Biomedical Simulation Resource Duke University Medical Center pusateri@romeo.cs.duke.edu
wtm@neoucom.UUCP (Bill Mayhew) (05/03/89)
My system, impulse, is a 3b1 with 2 megabytes of RAM and a Miniscribe 6085 (67 meg) disk drive. With the monitor screen switched off, impulse draws about 65 watts from a 120 vac, 60 Hz line. With the monitor turned on, the system draws about 80 watts. With winchester seeking, power consumption would make brief excursions around 100 watts. Switching the machine on causes a transient load of about 150 watts for about 10 seconds while the winchester drive spins up. I measured the figures above with a real honest to goodness wattmeter, rather than calculating values. I don't like the idea of leaving the CRT running (even if the screen is blanked, the anode high-voltage supply is still running) while I am not at home and/or asleep. I installed a toggle switch in the 12 DC power lead going to the CRT. I got nervous about leaving CRTs turned on while unattended from the Televideo 950 terminals that we used to have. In more than one instance, the flyback transformers in the Televideo terminals failed in such a way that they caught on fire. The horizontal drive arrangement in the TVI 950 is quite similar to that in many monochrome CRTs. The culprit was an electrolytic coupling capacitor that attached the flyback to the collector of the horizontal output transistor. The capacitor would eventually short, causing a large DC current to flow in the flyback transformer and set it on fire due to the resulting heat build-up; the fault current was not large enough to blow the fuse in the power supply. There were also some horror stories about Zenith TVs that allegedly spontaneously caught fire after being switched on for long periods several years ago. To answer the question being asked, a modest stand-by type of back-up power supply is sufficient for the Unix PC. The power unit in the Unix PC seems to have several hundred miliseconds of ride-through capacity. A stand-by type of back-up power supply is one that might take one or two missing cycles of AC power before it switches over to battery. I bought a used Questa 200 watt UPS several years ago for my Unix PC for $100, and it seems to do the job just fine. The Questa unit has an 8 amp-hour internal sealed wet cell battery, which is enough to run the Unix PC for about 20 minutes. There are input terminals on the back of the Questa supply to allow something like a car battery to be attached, thus enabling a Unix PC to run for hours. The Qesta supply is only rated for maximum load for 20 minutes, and must be derated to 2/3 load for continuous duty; this is still more than enough for a Unix PC. I like the diminutive size of the Questa power pack; it is about 1/2 the size of a shoe box. I think if I were buying a stand-by supply today, that I would go with one of the ones made by Minute Man; they look well made, and their % load and % charge bar-graph LED indicators are helpful. Bill wtm@impulse.UUCP