nelson@bolyard.wpd.sgi.com (Nelson Bolyard) (04/16/91)
This morning at 6:19 AM PDT, a power line went down in the city of
Milpitas, causing a brownout condition that lasted for 58 minutes
before the power went out completely. During the brownout, we got 60
volts AC out of the wall sockets. This did nasty things to my
computer equipment, and to the compressor motors in my fridge and
freezer, and to the furnace blower. Motors just don't like low
voltage.
We were alerted to the problem because the telephone answering machine
started speaking the time of day out loud continuously until my wife
got up and shut it off. Then she noticed that none of the fluorescent
lights in the house worked, and that the computer (that we leave on
around the clock) seemed to be continuously rebooting. The
refrigerator was trying very hard to start up, and I heard the little
self-resetting circuit breaker opening with its distinct pop and
closing a few minutes later. It did this until I shut it off. I also
shut off the freezer in the garage and the furnace.
When the power finally came on an hour after it went completely out,
it blinked a few times. It didn't come on cleanly. I suppose the
blinking was caused by tremendous surge currents as every motor in
Milpitas came on at once. I sure was glad that I had shut off all my
computer equipment before the power came back on.
I don't want or need a UPS. I wouldn't mind occasional clean power
failures. None of my computer equipment reacts badly to complete power
failures. My disks all park themselves, and my disk cache is
write-through, not write-back, so I don't have the **ix problem of
trashed file systems after power failures. But brownouts and power
blinking can't be doing anything good to my computer equipment nor to
my motorized appliances.
So I'm looking for a device that I can hook into the power line for my
computer equipment that will cut all power off completely if the power
quality drops below some threshold (say 90% of normal), and will remain
shut off until the power has been restored to normal for at least a
minute or so (to guard against blinking and surges).
I already have all my computer equipment plugged into a power outlet
strip that supposedly pretects it from "surges and spikes". I can
envision a unit that plugs into the wall outlet that contains a big
relay (or a little relay with big contacts) and a little circuit
board, and a single switched outlet into which I can plug my power
strip.
If you know of such a device ready-made, please let me know.
If you're interested in designing such a beast, I'd appreciate the
schematics so I can build one. Who knows, maybe there's a business
opportunity here.
Thanks in advance for your replies. Please post them, or email to the
address below.
-----------------------------------------------------------------------------
Nelson Bolyard nelson@sgi.COM {decwrl,sun}!sgi!whizzer!nelson
Disclaimer: Views expressed herein do not represent the views of my employer.
-----------------------------------------------------------------------------bender@oobleck.Eng.Sun.COM (I want to be eating rich soup in another town) (04/16/91)
In article <1991Apr15.180755.19771@odin.corp.sgi.com> nelson@bolyard.wpd.sgi.com (Nelson Bolyard) writes: >This morning at 6:19 AM PDT, a power line went down in the city of >Milpitas, causing a brownout condition that lasted for 58 minutes >before the power went out completely. During the brownout, we got 60 >volts AC out of the wall sockets. This did nasty things to my >computer equipment, and to the compressor motors in my fridge and >freezer, and to the furnace blower. Motors just don't like low >voltage. The question really is, why did the power company supply you with 60 VAC for that long a period instead of just cutting off power completely? I thought that part of the utility's charter was to provide voltage and frequency within a certain narrow range?? mike -- Won't look like rain, Won't look like snow, | DOD #000007 Won't look like fog, That's all we know! | AMA #511250 We just can't tell you anymore, We've never made oobleck before! | MSC #298726
bc338569@longs.LANCE.ColoState.Edu (Brian Catlin) (04/16/91)
In article <11568@exodus.Eng.Sun.COM> bender@oobleck.Eng.Sun.COM (I want to be eating rich soup in another town) writes: > >The question really is, why did the power company supply you with 60 VAC for >that long a period instead of just cutting off power completely? I thought >that part of the utility's charter was to provide voltage and frequency >within a certain narrow range?? In rural areas this is almost too common. We will have brownouts that last over two hours after we call the power company. Since this is not too good on our motors for the exhaust fans in our greenhouses, we just have to shut off the electricity and let it get EXTREMELY hot. I think an automatic cutoff switch would work great for this. If anybody has any good ideas about this please post them! B. J. Catlin bc338569@longs.lance.colostate.edu
jeh@dcs.simpact.com (04/17/91)
In article <1991Apr15.180755.19771@odin.corp.sgi.com>, nelson@bolyard.wpd.sgi.com (Nelson Bolyard) writes: > This morning at 6:19 AM PDT, a power line went down in the city of > Milpitas, causing a brownout condition that lasted for 58 minutes > before the power went out completely. During the brownout, we got 60 > volts AC out of the wall sockets. This did nasty things to my > computer equipment, and to the compressor motors in my fridge and > freezer, and to the furnace blower. Motors just don't like low > voltage. [...] > So I'm looking for a device that I can hook into the power line for my > computer equipment that will cut all power off completely if the power > quality drops below some threshold (say 90% of normal), and will remain > shut off until the power has been restored to normal for at least a > minute or so (to guard against blinking and surges). I asked about this once and was told that you can get circuit breakers that include under- and over-voltage tripping. Over-voltage? Yes, that was the original reason for my query. A capacitor somewhere in the northern San Diego county area shorted out awhile back, resulting in about 200 homes being fed with something like 180 volts instead of 117. Naturally, most things that lack an old-fashioned off-on switch, the kind that actually disconnects the unit from the wall, were fried. This includes anything that can be turned on via remote control or built-in timer, (most modern TVs and all VCRs), clocks and clock radios, lamps with built-in touch-sensitive dimmers, BSR home automation modules, garage door openers, etc., etc. SDG&E ended up being liable for damages in the large-fractional- megabuck range. (They got off lucky; the overvoltage could easily have burned down several homes.) DIY couldn't be too hard. Run a tiny power transformer off the line voltage, rectify and minimally filter the output, and feed the result to a couple of IC op-amp comparators, one for low and one for high. The comparators drive a relay or whatever else you want to cut the power off. You need some hysteresis to avoid stuttering in case the AC hangs near the trip point for a while. But for stuff like this, I, for one, want to go buy something off the shelf and have a licensed contractor install it. It might not be built any better than what I could do myself, but that way if it shorts out and burns the house down, I can sue someone else instead of being on the hook myself. No way will the insurance company pay off if there is even a hint that a fire was caused by homebrew power-control devices. --- Jamie Hanrahan (x1116), Simpact Associates, San Diego CA Internet: jeh@dcs.simpact.com, or if that fails, jeh@crash.cts.com Uucp: ...{crash,scubed,decwrl}!simpact!jeh
brian@ucsd.Edu (Brian Kantor) (04/17/91)
In 1977, I was in England installing a computer system for my (then) company, and the electricity workers went on strike. To differentiate the power cuts caused by industrial action from the other kinds that were occuring pretty regularly in that part of the country, they would switch the power off and on a few times over a span of perhaps 30 seconds or so, then leave it off for several hours. The first time they did that, we lost the tape drive and one disk. The second time, it took out the CPU power supply, the other disk, the console, and the fuses in the mains receptacle on the wall. The next day, I built a device using a simple AC relay and one of those Amperite thermal time-delay relays that look like old octal radio tubes. With power off, the AC relay was deenergized, and applied mains power to the Amperite heater. After a suitable delay (I think I used 2 minutes), it would energize the AC relay, which would latch itself on and deenergize the Amperite, which then proceeded to cool off. If power went off for more than a few milliseconds, or if the voltage fell below the hold-in value for the AC relay, power to the entire computer would be cut off cleanly, and it would not be powered back up until the electricity had been up solidly for the two minutes. Something like this could be used to turn a brownout into a power fail; you can fiddle with the AC relay spring tension until you get it to drop out at whatever voltage you think is appropriate. Of course, there are solid-state circuits to do this as well, or better, but the relay is something you can easily build yourself, given that you have some experience with constructing electronic devices. Keep in mind that there are hazardous voltages and currents involved, and you'll be ok. - Brian
uchuck@med.unc.edu (Charles Bennett) (04/18/91)
In article <14257@ccncsu.ColoState.EDU> bc338569@longs.LANCE.ColoState.Edu.UUCP (Brian Catlin) writes: >In article <11568@exodus.Eng.Sun.COM> bender@oobleck.Eng.Sun.COM (I want to be eating rich soup in another town) writes: >> >>The question really is, why did the power company supply you with 60 VAC for >>that long a period instead of just cutting off power completely? I thought > > I think an automatic cutoff > switch would work great for this. If anybody has any good ideas about this > please post them! > >B. J. Catlin > >bc338569@longs.lance.colostate.edu You people are probably too young to remember the "old self-latching relay" trick. Use DPDT or 3PDT relay, energize the relay via a pushbutton switch, upon energizing one set of contacts takes the place of the switch and holds the relay in. If the voltage drops too low or has a momentary drop out, the relay drops out and can only be restored via another push of the pushbutton. I am not adept a drawing in ascii, therefore I shan't try. -- Chuck Bennett INTERNET: uchuck@med.unc.edu Medical Sciences Teaching Labs BITNET: uchuck@unc CB# 7520 University of NC PHONE: 919-966-1134(w) Chapel Hill, NC 27599-7520
whit@milton.u.washington.edu (John Whitmore) (04/18/91)
In article <32107@ucsd.Edu> brian@ucsd.Edu (Brian Kantor) writes: >In 1977, I was in England installing a computer system for my (then) >company, and the electricity workers went on strike. To differentiate >the power cuts caused by industrial action from the other kinds that >were occuring pretty regularly in that part of the country, they would >switch the power off and on a few times over a span of perhaps 30 >seconds or so, then leave it off for several hours. > >The first time they did that, we lost the tape drive and one disk. There is a simple trick used on many machine tools (where a power cycle could result in an unattended machine starting up), which is to use an AC relay driven by two switches in parallel. One switch is a pushbutton (normally OPEN), and is labeled 'START'. The other switch is a pair of contacts on the relay, so that the relay latches ON after the 'START' button is pressed. A 'STOP' button is a normally CLOSED pushbutton in series with the relay contacts that keep the relay ON. A motor-start relay usually has spring tension adjustment that could be used to make it drop out at low AC voltage (and one could CERTAINLY put in an IC power-fail sensor in place of the STOP button). So, a simple power-drop switch could be a simple relay, START button, and a sensitivity adjustment. The complete systems are common in industrial applications, so you might be able to find the whole box in a scrap pile, ready to hook up. John Whitmore
coorswol@alchemy.tcnet.ithaca.ny.us (Curt Coulter) (04/18/91)
jeh@dcs.simpact.com writes: > In article <1991Apr15.180755.19771@odin.corp.sgi.com>, > nelson@bolyard.wpd.sgi.com (Nelson Bolyard) writes: > > This morning at 6:19 AM PDT, a power line went down in the city of > > Milpitas, causing a brownout condition that lasted for 58 minutes > > before the power went out completely. During the brownout, we got 60 > > volts AC out of the wall sockets. This did nasty things to my > > computer equipment, and to the compressor motors in my fridge and > > freezer, and to the furnace blower. Motors just don't like low > > voltage. [...] > > So I'm looking for a device that I can hook into the power line for my > > computer equipment that will cut all power off completely if the power > > quality drops below some threshold (say 90% of normal), and will remain > > shut off until the power has been restored to normal for at least a > > minute or so (to guard against blinking and surges). > > I asked about this once and was told that you can get circuit breakers > that include under- and over-voltage tripping. > > Over-voltage? Yes, that was the original reason for my query. A capacitor > somewhere in the northern San Diego county area shorted out awhile back, > resulting in about 200 homes being fed with something like 180 volts instead > of 117. Naturally, most things that lack an old-fashioned off-on switch, the > --- Jamie Hanrahan (x1116), Simpact Associates, San Diego CA > Internet: jeh@dcs.simpact.com, or if that fails, jeh@crash.cts.com > Uucp: ...{crash,scubed,decwrl}!simpact!jeh Hmm. Zounds familiar! :) Last winter I finally got a very sizable check from NYSEG due to them refusing to beleive that I had 135 volts coming in the house. Blew my stereo, computer and two hairdryers. They wouldn't have been liable, according to the PSC's charter (public service commision) if they had fixed it right away; I'm glad they didn't. Turned out the whole neighborhood had that high voltage (bad regulator). I wonder how many people had equipment failures and didn't have a clue.... -Curt coorswol@alchemy.tcnet.ithaca.ny.us /.s