edward@engr.uky.edu (Edward C. Bennett) (11/22/87)
In article <942@woton.UUCP> riddle@woton.UUCP (Prentiss Riddle ) writes: >I live in an old house with a rather flaky power system. Even ordinary >household appliances, when used in certain combinations, have been >known to cause brownouts and occasionally throw a circuit breaker. Am >I asking for it if I try to use a UNIX PC in this power environment? >Does anybody know of any *cheap* power conditioning which might >significantly improve my 3B1's chances of survival? Thanks. Now that I've got a 3B1, I've been concerned about power problems also. What are the important things to look for? Spike/surge/transient protection? For a start, I pulled out the ol' Radio Shack catalog. They've got two units that seem reasonable. Under "AC Outlet Voltage Spike Protectors" there's a 6-outlet power strip with noise filter and circuit breaker for $29.95. Over in computer accessories there's a 2-outlet power protector with "full common and differential mode transient protection" (What is that? A fancy way of saying voltage spikes?), noise filtration and a MOV status lamp for $18.95. Comments? Horror stories? The idea of paying $70 for one of these things at a "computer emporium" seems outrageous! -- Edward C. Bennett DOMAIN: edward@engr.uky.edu UUCP: {cbosgd|uunet}!ukma!ukecc!edward "Goodnight M.A." BITNET: edward%ukecc.uucp@ukma "He's become a growling, snarling white-hot mass of canine terror"
wtm@neoucom.UUCP (Bill Mayhew) (11/24/87)
<<What do I do about power protection>> You get protection comensurate with the bucks you lay out. The $18.95 de-spiker from Radio Shark is probably not worth the bother. Most cheap units are just a couple of MOVs. The power unit in the 3b1 and most other computers has MOVs any way. I guess the Radio Shark would be marginal extra help. About 4 years ago, my house was directly struck by lightning. The guts of the cheapo surge protector I had simply vaporized. Fortunately, the Franklin Ace (gag) computer that was normally plugged in there had the cord out of the wall. The state the surge protector was in, I doubt there was much it could have done to save the computer. I have a UPS on my 3b1. I wouldn't trade it for anything else. I found out this saturday. I was plugging away at about 1:30 AM. Apparently just then the power company decided to play "lets switch about a dozen connections on the Grid". The lights dimmed and brightened about 15 times separated by about 3 seconds. Each time the lights flickered, the UPS came on for about 1 second. The 3b1 was muching on a big make file that had alrady been going for a couple of minutes. I was pretty nervous for a few seconds, but everthing came out just fine. I doubt that a surge protector would have been much good for a power disaster like that. Since the 3b1 is at least a $2500 expense, adding another $300 to $500 is in line with protecting your computer. I just have a modest 200 watt UPS. So far that has gotten me through the junk that Mr. Edison has thrown this way. By the way the Ma Bell model 500 fone survied my bout with the lightning. The japanese everything-in-handset five dollar wonder had essentially everything inside vaporized. It did have a MOV, but all that was left were two little legs that had previously stuck into a blue plastic blob. I suppose a direct hit on a UPS might result in clouds of smoke too. At least you have a fighting chance because the UPS combines MOVs and an isolation transformer (which does double duty as the inverter element in standby mode). Bill (...[cbosgd|mandrill]!neoucom!impulse!wtm)
wtm@neoucom.UUCP (11/24/87)
I suppose I should have been more factual in the previous article. A good quality protection device that is a passive device will probably set you back $50 to $60. Such a device will almost certainly contain MOV (metal oxide varistors). An MOV is essentially a non-linear resistor. MOVs are made of silicon carbide or a similar material (please, no flaming, I don't have a physics degree). The MOV material exhibits a resistance that varries inversely to something like voltage raised to the power of eight. In other words, when the voltage reaches a threshold, the current conducted rises sharply. Normally, MOVs are designed to conduct the current of voltage spikes to ground or some other inoccuous place that can absorb electrical charge. An alternative to MOVs is a gas discharge tube. Gas discharge tubes function much like overgrown neon pilot lamps. Power is dissipated by ionizing the gas. The ionized gas is also conductive, thus permitting excess charge to be drianed away. Gas tubes are faster acting than MOVs and will stop working correctly after they have triggered several hundred times. MOVs also have a limited lifetime. A good quality surge supressor will be designed to feed a small current all the time (sub threshold) through the MOV to detect if the MOV is working. There should be a pilot light on the surge protector to alert the user if something is wrong. Some cheap "surge protectors" have a pilot light that is nothing more than an "ac is on" indicator, saying nothing about the actual quality of protection provided. A decent quality surge protector can be made from either MOV devices or gas tubes. In fact, some employ both types of protection. MOVs do have the advantage that it is easier to build a circuit which monitors their protective effectiveness. Some surge protectors also provide RF filtering. The RF filtering is of dubious utility, as computing equipment is required to meet FCC type acceptance anyway. An RF filter might be useful if your computer is near a big source of RF energy, such as a radio transmitter. The FCC doesn't care much about a computer's EMC characteristics when externally illuminated by RF. When purchasing a surge protector, checking the incoming ac circuit should (well, actually must) be part of your job. You should assure that the wiring is properly done so that the voltage delivered to the computer is steady. That is to say, have an electricaian check the circuit to be sure that all the terminals on the outlets, etc. are well tightened down. A good solid ground is essential when using a surge protector. A defective ground may actually case some protectors to deliver dangerous (to the equipment) spikes when the attached equipment is switched off! If you have inadequate voltage, and can no further improve the feed from the fuse box to the computer, your only recourse is to install a voltage correcting transformer. Depending on the design of the transformer, it may provide an additional layer of protection against common-mode noise (that is the case where some sort of interferrence is the same on both ac leads, but has a sizable voltage with respect to ground). There are two types of transformers. Tap changing transformers, and Ferro-resonant regulators. The former provides a more pure sine wave output, while the latter is less efficient and has harmonic distortion, but tighter voltage regulation. Both types are relatively expensive. You should talk to a power consultant to make the choice best for you. Voltage regualting transformers have been discussed recently in sci.electronics. Refer to the articles there for more details. The last line of defense is an uninterruptible power supply (UPS). A personal computer sized UPS contains a battery and an electronic circuit to synthesize ac when the voltage from the power company fails. There are many grades of UPS available. Some UPS more accurately reproduce a sine wave from the battery supply, while others simply put out a square wave. In the case of the 3b1, the square wave type would suffice, since the 3b1 ins't sensitive to wave shape. Some UPS-like devices are more accurately labeled "standby power supplies". A UPS notation implies that the switch-over to backup power is essentially instantaneous when main power fails. A standby power supply might require 20 mS or longer to switch over. A quick standby power supply would be adequate for the 3b1. The 3b1 seems to be able to endure absence of power up to 100 mS, perhaps longer. A UPS is better, but of course, it costs more. For me, a 200 watt UPS has been adequate for a 2 meg / 67 meg HDU 3b1. You get what you pay for is a general rule, but some caution is necessary with surge protectors et al. The surge protectors are often high mark-up items, and the dealers play on the fears of the computer owner to ensure a sale. I don't think it is a good idea to buy your surge protector from one of those companies that sends out glossy catalogs every 15 minutes. There, about 50% of the purchase price goes to the cost of the catalogs and to excessive profit. A case in point is that Inmac sells an autodialing "computer room environmental monitor" for $300. Radio Shack sells the identical item as an autodialing "home security monitor" for $150. Shop around. Sorry if this article is too electronically related for this group, but having decent ac power to run our machines is a part of life. Bill (...[cbosgd|mandrill]!neoucom!impulse!wtm)
bob@pedsgo.UUCP (12/01/87)
In article <774@neoucom.UUCP> wtm@neoucom.UUCP writes: > { some stuff about surge protectors and ... } >The last line of defense is an uninterruptible power supply (UPS). Having had my power go off while I was installing software on my 3b1, and then conveniently go off again 15 minutes later when I was rebooting the machine and it was running fsck, I agree that a UPS is probably the way to go. So would anybody care to recommend a good one for a good price? I will summarize if you send mail. Thanks. Bob Weiler.