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westom wrote:

Even numbers say that voltage drop should not be 15 volts. That your only number is only speculation. Or that you ignored wiring defects. An air conditioner causing a significant voltage drop (dimming lights) means wiring problems. Your dimming (a 4.5 volts drop - not a 15 volt drop) is near zero. The OP does not really say how much dimming he has.

1) Dimming even to 50% is ideal voltage for all electronics. The many concerned about damage to electronics are worrying about a strawman. A UPS for those electronics solves nothing. Money wasted on a threat that does not exist - an unjustified fear.

2) An air conditioner causing 120 volts to drop to 105 volts or 102 volts implies a wiring problem. His air conditioner is causing serious dimming only if a wiring problem exists. A problem easily solved even by a layman. But that unfortunately requires knowledge and inspection. Dimming is caused by poor wiring. Otherwise dimming is near zero - hardly noticed - a threat to nothing.

3) If dimming is serious, the air conditioner (not electronics) is suffering most strain. And another reason why that UPS solves nothing.

UPS solves phatom fears. Dimming is an easily solved wiring problem. Or dimming is near zero - irrelevant. Significant dimming means only an air conditioner is suffering.

If that building has aluminim wires, then dimming may be a major human safety threat. Just another reason why informed layman fix the problem; not cure symptoms with a UPS.

He's...he's unstoppable! Run!

Hey guys, fantastic thread so far so I hope you don't mind me butting in and hijacking it for a similar situation I'm in atm. I found you on Google and glad I did.

I live in an older house with not "too" many upgrades to the wiring but outlets have been replaced and are properly wired/grounded. I have a 5,150 BTU/HR window-mounted AC unit with an operating voltage range of 103-127. Recently we've been experiencing some occasional voltage drops around the house (lights dimming momentarily) but I just attributed that to "heavy electrical demand" in the neighborhood since we're experiencing a 42C heat-index outside atm. Another explanation could be the power-tool usage in our garage. There is central air on in the house -- but the top floor receives little cooling. I've noticed that if several storms come into the area, there's always reports of several 10's of thousands of customers will experience power loss for an "extended" period so perhaps the electrical infrastructure in my city (Saint Paul, MN) is lacking. If you ever want to experience the FULL weather spectrum of the entire planet -- come to Minnesota.

Anyhow, I also have a Cyberpower UPS, a 4 year old 1500VA 900W AVR unit that will "click" and "light up" occasionally -- indicating momentary "switching" (I'm speculating) inside the unit, but not going to sustained battery power since it will periodically "beep" if that's the case. I just checked the unit's readout -- it's telling me that the input/output values hover around 110V, but I've seen that number dip slightly below that. I can also audibly hear the occasional dip in voltage from the AC unit as well -- the tone is off somewhat and it sounds like it momentarily "slightly struggles." During particularly hot periods (and what I'm assuming a voltage drop to 102), the AC compressor will shut off while its fan continues to run (aka no cooling but just fanning.) I'm probably more concerned about the AC as others have said here, that unit is a bit dated too but it has its own GFCI outlet, but I highly doubt there's multiple circuits up here. The UPS has been recently "single clicking" when I turn on the AC or even my PC.

My PC isn't particularly demanding and I haven't noticed any issues here either. Antec recently rma'd me a new "high current" 1200w 80+ gold certified psu -- but that's overkill for my system anyway since I'm only running a stock (Corsair H60 water-cooled, intake configuration) core i7-920 and an XFX 4890 from 4 years ago. CPU temps are fairly considerable with the AC involved -- there's a good 10C range in values in various scenarios. Right now the AC is on and at full-load (folding@home), the CPU is at 61C. That's with a Cooler Master ATCS 840 full-tower case -- with several (recently cleaned) 230mm fans running at full speed. If that AC was off, it'll be pushing 71C no doubt.

Opinions?

There are other possible sources for the dimming guys, beyond a problems with just that one circuit. I get dimming in my house when my neighbors A/C starts. It is the very old, undersized (by modern standards) transformer on the pole, feeding the neighboring 5 houses built to 1950 electrical code. In my case, I've confirmed it's on the utility side by measuring the voltage at the feed from the meter base, on the utility side of the main breaker. If the apartment is old enough to not have central air, it was likely built to an old electrical codes standard, which means everything from the utility feed to the mains are all undersized for modern loads.

Of course, it could be the circuit... My house is wired in what's supposed to be 14 AWG but I would swear it's 16 AWG; and, there's plenty of legacy aluminum wire around.

I don't have a single 220V appliance in the house, yet a good capacitor-start motor surge (i.e. AC) hits anything on either "side" of the panel. Most likely going out to the pole transformer and returning down the other side of the feed. House was built 1875 or so and looks to have been first electrified somewhere in the 1910 range given the electro-archaeology I've performed. Got all the knob & tube dealt with but there's still a lot of old cotton & rubber-wrapped 1st gen cable. Got all of that stuff doing nothing more than powering ceiling lamps, so risk is minimized. Still have one of those old cotton-job circuits (breaker off) that disappears into a wall and whose terminus has yet to be found. Breaker panel is properly noted for next owner.

Danny -- it sounds like your circuit has low voltage on the utility side. You can try complaining to your local utility, although given the sudden and recent transition from nuisance flicker to frequent problems, it's possible they have experience equipment failure due to the high demand, and rerouted your circuit for emergency repairs. Regardless, report the problem, and if the problem persists more than a few weeks, do what you can to verify the problem isn't on your side of the meter, and then complain to your regional PUC (public utility commission).

The monitor and PC are not flickering or showing signs of distress because their respective AC->DC switching power supplies are fully capable of compensating for the drop in line voltage. Any PS of this sort is constantly monitoring the output (DC) voltage and adjusting its switching duty cycle to maintain this at a constant level. So long as the PS is not operating near maximum capacity (and subsequently being over-driven during the line sag), THERE IS NO PROBLEM.