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posted by martyb on Sunday November 10 2019, @09:32PM   Printer-friendly
from the use-hurricane-lamps dept.

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?


Original Submission

 
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  • (Score: 0) by Anonymous Coward on Sunday November 10 2019, @09:52PM (4 children)

    by Anonymous Coward on Sunday November 10 2019, @09:52PM (#918700)

    The compressor has a really bad power factor and is inductively spiking the lights.

    I also plugged in lights to an outlet all the way across the room and observe the same thing? Do you think that could still be induction?

  • (Score: 2) by RS3 on Sunday November 10 2019, @10:01PM

    by RS3 (6367) on Sunday November 10 2019, @10:01PM (#918706)

    See my above post about possible loose screws. I'll post more later...

  • (Score: 2, Informative) by Anonymous Coward on Sunday November 10 2019, @10:45PM

    by Anonymous Coward on Sunday November 10 2019, @10:45PM (#918714)

    Most likely yes. If the AC unit is old, those start capacitors are probably dried out. Google 'electric motor start capacitor'.

  • (Score: 2) by exaeta on Monday November 11 2019, @02:32AM

    by exaeta (6957) on Monday November 11 2019, @02:32AM (#918799) Homepage Journal

    Very much. Voltage should affect everything on the same circuit. The problem is likely related to either inrush current & inductive spiking from the AC or power delivery to your unit having too much inductance. Possibly both.

    I have a feeling this is because of inrush current, if it only happens when it turns on or off. NTC thermistors work well here, but choosing the right ones requires a certain amount of knowledge.

    There may be a power factor correction capacitor on the AC that died. There may also be a leaky transformer to your house it could also be a culprit. Too much leakage inductance on the secondary side can cause spikes (which kill stuff) and drops (which give flickering) when the load changes too quickly. Hard to figure out what's going on without an osciloscope or power factor measuring tools. Some meters show power factor, see if you can pick one up.

    I'd suggest a few surge protectors in series to protect against the spikes. Not much you can do about the dips except improve the power input or install power factor correction capacitors on the AC. You can also put a surge protector on the AC, which will prevent back propagation of the spikes to other equipment. Be aware that surge protectors can only take so much beating though.

    --
    The Government is a Bird
  • (Score: 0) by Anonymous Coward on Monday November 11 2019, @07:48AM

    by Anonymous Coward on Monday November 11 2019, @07:48AM (#918852)

    That's probably the same circuit. If you pop the breaker for one and they both go out it's definitely the same circuit.

    Note, most household appliances are not compensated for as well as industrial ones because households aren't billed for apparent power. So you've definitely got an inductive load and there's a good chance its power factor hasn't been corrected.

    I've definitely had this problem in the past with an A/C. Lost a number of lights and popped the breaker all summer long.