This morning I was online when all the sudden the computer goes off. Then come to find out my home suffered a power outage.

Ok, no big deal, except my monitor (LCD flat screen) would flash on and then right back off....then on and right back off....un plug it and it would stop...but plug it back in and it would do this all over again.

But wait! How could it do this? The power is out!

Well then I go in to use the rest room, and forget the power is out, when I flip the switch. There is a faint glow.

I look up and low and behold the light was illuminated, but barely. It almost looked as if it were on a dimmer switch on the lowest setting.

I tried a few other lamps in my home. All of the incandescent lamps did the same thing (the fluorescent tubes wouldn't do it)....the filament would glow an orangish color, sorta looked like those old vacuum tubes they used to use in radios.

Went and grabbed my multimeter, flipped it on AC volts and stuck the probes in the 120 volt wall outlet.

I got a reading of 24 volts AC out of my 120 volt AC wall outlet.

I called the power company and reported the outage. I got no explanation on why it happened but in about an hour I had power again.

I'm just curious as to what would've (or could've) caused this to happen? I've been in power outages before, but not ones where there some power still there.

Anyone know?

Thanks.

I can't actually explain what happened, but to me it sounds like there was some kind of back-feeding going on. As though 2 line-side phases of your supply transformer went down, but the third was still live. It would still induce voltage into the secondary windings, but the voltage would be much lower than normal.
This is just an educated guess though, I've never seen this happen before. But I'm sure someone here will have a definite answer as to what would've caused a situation like this.


Shawn.

I have had one hot leg go completly away at my house, due to a transformer failure. Never seen just 24 volts though interesting problem hope someone can explain.

We used to have brownouts a lot before the poco upgraded their system. The lowest voltage I got at a receptacle was 42 volts. Across the street would have full power, and other parts of the subdivision would have none. It's been a while but I do remember a lineman telling me it was something to do with a 3 phase distribution transformer. Can't remember what was the exact cause.

I suspect an open phase on the primary might get some voltage reflected on the secondaries of the transformers on that missing phase through the other loads if you had a mix of wye and delta connected loads.

I've seen that exact same thing - 24 volts - we had one of the phases crap out and someone in the local area went and started up a genset and backfed the current into the grid without making the proper offlodading from their genset back into the line. Another case of a know-it-all Home owner just getting things back to normal.

The only thing I don't get about the scenario Check Pilot is describing is that the OP mentioned being at his (or her) computer desk when the power went off and seeing his (or her) monitor flashing off and on.

If the 24V were due to a backup power supply back-feeding the supply transformer, wouldn't there be a time delay between the power outage and the appearance of the low voltage responsible for the monitor's erratic behavior? The DIY'er who so ingeniously discovered how to re-supply his house with home-made electricity would surely need several minutes, at least, to acknowledge the power outage and fire up the generator.

Maybe I'm misunderstanding the wording, but didn't the monitor's weird actions begin at the moment of power loss?

Computer stuff can do all sorts of weird stuff... my ex-gfs computer would act off as you turned off the switch on the back of the ATX power supply and pushed the power button on the front. The power LED lit up and the floppy drive started making weird "read error" type noises. Never managed to figure out what was happening there.

I agree with Tex
These TSR supplies can build up enough DC voltage with low line voltage to try to power on but as soon as the full load hits it the supply "undervolts" and goes back down.

You can get the same thing with the switched-mode (chopper) power supply found in many modern TV sets when fed severely under-voltage. There's enough juice to charge the reservoir capacitor, the start circuit will try to get the oscillator going, but as soon as it draws current the voltage drops too low on the capacitor, so it drops out again, then the whole cycle repeats.

The typical results is a regular flashing of a power/standby light, sometimes accompanied by a regular "ticking" sound, etc.

Yes you are correct, this happened right at power loss.

On an update my wife said it happened again yesterday; shie heard a boom followed by the lights going very dim, just as they had done the earlier day. It was dark outside and she said the bulbs were producing very little light.

Then she heard another boom (more audiable than the first one) and then the lights went completely dead. She looked out the window and saw utility trucks down the street and a bunch of folks come out to see what the ruckus was all about.

We have no phone poles in our subdivision, I'm guessing it was one of them green boxes on the side of the road....

The full story of that computer account still makes me laugh... it happened on my first evening with her(!) and she got pretty freaked because she thought her computer was gone... and crouching on the dirty old carpet under her desk I found that only the power switch in the back was off... her grandfather had thought this was the proper way... (she mostly lived with her grandparents back then)...

Not very likely .... a large load will just stall the prime mover on most generators, not let it run producing very low voltage. The most likely cause of low voltages like this is an open phase on the utility primary.
Don

Don't expand further.. The imagination is working fine on the followup. You were the hero and a "lucky" Man!

I have had the exact same type of situation, and went around the neighbors homes and saw very simular effects on different types of things.

POCO phase went out (1 of 3) and what would seem like a normal power outage got wierd. From I assume is the induction of current from the other 2 phases on an open line. Having talked to the line crew already, the whole phase was open due to a HV fuse that they were waiting for. (~3 hours) Having shut off my main at my house, I went to the other homes on the block to tell them to do the same for a little while until this blew over.

The induced voltage to the open phase over about a mile was enough to create ~74/136 through the transformer in my back yard. Although not really usable for most things like incandesant lighting, certain electronics acted very differently. Flashing screens of TV's, flouro lights, squealing cordless phone bases. Of the dozen or so neighbors I talked to they all had something wierd going on. Reguardless of what anyone else says - it can't be good. Maybe not as damaging as an over-voltage, but a lower voltage producing a partially usable current in less robust electronic items.....

IMO if they had grounded the conductor - it would have seemed less wierd. They were comfortable with not doing so - but the effects were freaking me out....

Actually the evening was G rated
Remember, her grandma was next door *ggg*