Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site cadvax Path: utzoo!watmath!clyde!bonnie!akgua!whuxlm!whuxl!houxm!ihnp4!zehntel!hplabs!hpda!fortune!amdcad!cae780!ubvax!megatest!cadvax!dtynan From: dtynan@cadvax (Dermot Tynan) Newsgroups: net.micro Subject: Re: Voltage protection for micros Message-ID: <137@cadvax> Date: Tue, 12-Feb-85 22:53:26 EST Article-I.D.: cadvax.137 Posted: Tue Feb 12 22:53:26 1985 Date-Received: Mon, 18-Feb-85 05:33:52 EST References: <8159@brl-tgr.ARPA> Organization: Megatest Corp., San Jose, CA Lines: 53 [Eat your heart out!!] Well, you've hit upon a very large issue there. The field of UPS's (Uninterruptable Power Supplies) is pretty extensive. There are a myriad of issues involved with power conditioning. One can start with an EMI filter (Electro-Magnetic Interference), and work up to a UPS. Basically, an EMI filter extracts the noise from the AC line. Although it could be said that it also helps OverVoltage and UnderVoltage to a certain extent. I bought a power strip with four outlets that had an EMI filter built-in. I can't remember the manufacturer, but I *do* remember it costing somewhere in the $50-70 range. After hooking it up, and four hours editing I got my money's worth when the refrigerator kicked in, and my terminal got zapped (it wasn't plugged into the power strip). The system stayed up, without even a glitch! Basically, an EMI filter will cut out such things as the "snow" one see's on a TV when some electrical gear switches on. A "brownout" from the power company is, however, a different story. A UPS on the other hand, will retain the power anywhere from 10 minutes to two hours. This is similar to a battery-backup (which is essentially what a UPS is!!). In order to find out what exactly you need, you have to analyse your current setup. For example, how much current are you using, what devices or peripherals are you worried about, etc. Normally, it's not feasable to plug such things as printers or terminals into a UPS, as the power requirements go way up. Most computers (should I say *some*??) have a rudimentary EMI filter built in. I would advise that you check, though. Also, a lot of today's personal computers use "switching power supplies" (ie, Apple, IBM). Switchers can adjust for a low voltage in a relatively short amount of time. Also, a large electrolytic capacitor on the voltage rails will cure undervoltage of a short duration (again, the values in question have to be determined). As for a UPS, I would suggest use of one of these, if you suffer from a lot of junk in your 110v supply. This interference is normally due to a DIY neighbour with a power drill, or a nearby industrial park. In this case, I would advise a call to your local power company, as they may be able to help you, by putting you on another phase (this should cost less than a UPS). The price of a UPS is generally governed by two criteria: 1/ Supply holdup time (how long the computer stays up, after the lights go out!). 2/ Current/wattage requirements (how much you have hooked up, and how much current does it eat). Generally UPS's are used by people who don't want their system to crash in the event of a power failure. Examples would be banks, hospitals, etc. Your best and cheapest solution would be to purchase an EMI filter and go with that. If you want to build your own, take a trip down to Radio Shack, or your local electronics dealer, and ask for an EMI filter. Installation is pretty straightforward. Otherwise, most computer stores will sell you a power strip with built-in EMI filtering. Be very selective, there are as many specifications as there are filters. I don't expect this note to explain away your power problems, but I hope it gives you an idea of the different techniques. From my own experience most power problems with personal computers are due to EMI rather than severe brownout (the power supply *should* take care of minor ones). If you have any questions or problems, send me mail, but be a bit more specific. - Der Tynan