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First, I debated whether to put this on stack exchange or here, but it seems like it is a tech question that suits this site fine.
Background
I have a room with a 115 V, 6000 BTU window AC unit plugged into one outlet. Then a bunch of electronics (~800 W measured) plugged into a 1500 VA, 900 W UPS plugged in to a second outlet across the room. Finally, I have two 50 W strands of Christmas lights in series (100 W total) I tried to plug into various outlets around the room.
Problem
The first problem is that whenever the room gets too hot, the compressor for the AC unit turns on and the Christmas lights will all flicker. This is not just an annoyance, because the first strand of lights I had in the room actually got burned out one by one, starting at the light closest to the wall outlet.
So I got another strand and was surprised to see the flickering happens even if they are plugged into the UPS (which does have an internal automatic voltage regulator). This made me concerned for the electronics plugged into the UPS, which includes a PC and monitors. However, I do not notice any flicker on the monitor when the compressor turns on. On the other hand, I have been getting some strange pc crashes lately (which would make some sense because only recently did it cool enough for the AC to not be running constantly) that may be related. This could also be due to installing a second gpu recently, etc though.
Questions
I have two main questions:
1) What is the best way to stop the flickering?
2) If the lights are flickering even when plugged into the UPS, should I also be concerned about the other electronics that are obviously also experiencing a momentary power reduction?
Some secondary questions:
3) Does it make sense to put another AVR between the UPS and the wall, eg something like this?
4) Is there something I can put between the AC unit and the wall to help?
5) This is a rental so I would prefer not to do any maintenance on the AC unit, but is this an issue you would report to the landlord?
Any ideas?
(Score: 0) by Anonymous Coward on Sunday November 10 2019, @11:06PM (7 children)
Can you link to something like that? It sounds fake, but also real. I mean the UPS is basically a "battery buffer".
(Score: 5, Informative) by sjames on Sunday November 10 2019, @11:42PM (6 children)
It sounds like it really isn't. UPSes can be broadly divided between standby/cut-over and online types. The online tyupe is what you are thinking of, where a battery charger is constantly running on one side charging the battery and an invertyer is constantly running on the other providing power to the load. They produce good isolation from any voltage issue and no disruption at all on the load side if power goes out of spec on the supply side.
You probably have the other type. When supply power is OK, it is directly connected to the load side and a battery charger. In the event of a disruption of supply power, the load is switched quickly (but far from instantaneously) over to the inverter. While they generally have surge suppression built in, they provide poor isolation, pass through any out of spec condition below a threshold level, and the cutover is rough and messy. They basically depend on your power supplies being tolerant of glitches and surges.
The online type really is a battery buffer, but due to their cost, they are generally only found in data centers and telco racks. Home UPSes are almost inevitably the standby/cut-over type. The cut-over time is typically several milliseconds. Sometimes as they age, the cut-over gets slower and they may not accurately sense an out of spec condition on the supply side and let it through.
(Score: 0) by Anonymous Coward on Sunday November 10 2019, @11:47PM
Very informative, thanks.
(Score: 0) by Anonymous Coward on Monday November 11 2019, @12:50AM (1 child)
There are also "line interactive" power supplies, which are essentially offline UPS systems, but they also include a power conditioner to improve the power quality and buffer the cutover from wall power to battery power. I have one of these, it's pretty nice.
(Score: 2) by sjames on Monday November 11 2019, @01:14AM
I would put those in the standby/cut-over class. They may provide a less nasty cut-over and may filter more crap out of the supply power than a low end device, but they are still nowhere near an online UPS.
(Score: 0) by Anonymous Coward on Monday November 11 2019, @02:04AM (1 child)
More [wikipedia.org] than those two [wikipedia.org].
(Score: 2) by sjames on Monday November 11 2019, @03:35AM
Those are sub-types. That's why I said 'broadly'.
(Score: 1) by paul_engr on Monday November 11 2019, @07:48PM
Easy test - if you cut the power into the UPS, do you hear a relay click as it switches over?