AC compressors causing flickering lights

[zerofloors]

We have two units (with separate meters and panels) in a residence that underwent a major renovation about two years ago. During the renovation, the HVAC system was replaced and new recessed lights and light fixtures were installed throughout.

This summer, when the AC compressors are running, the LED lights in the house flicker badly. This happens in both units with three different AC compressors, and happens with recessed lights on dimmers and with sconces that are on switches without dimmers. It doesn't happen with every set of lights in the house, but it happens in a lot of different places. The lights flicker continuously while the compressors are on, not just when the compressors start up.

I had my electrician come out twice, and he spent about four hours in the house trying to diagnose the issue. He could not detect any voltage drops around the house, even while the lights were flickering. He looked at everything from the meter forward, including the panels for both units, and everything appeared tight and clean to him. He ended up not being able to identify the issue.

I also had the power company come out, and they checked the manhole outside, the T box, and one of the two meters. Everything looked perfect to them, even though the lights were flickering while they were here.

The electrician is pretty stumped, but his best idea now is to install whole-house surge protectors in both panels, since he thinks maybe the voltage is fluctuating so quickly that his meter is not detecting it and the surge protectors will fix the issue. He's not
at all confident that the whole-house surge protectors will solve the problem, though. Are there any other ideas I should run by him?

 

[Mikegh]

Maybe there's a technical explanation , I don't know

The obvious is the boards and supply for issues

The loading and the supply capacity


I would probably start off with something simple like pulliy down a flickery led light and replacing it with an incandescent a better idea of the nature of the problem

 

[Mikegh]

Typos ^^

Replace an led light with an incandescent bulb and observe the flicker again

 

[Lucien Nunes]

Surge protection is normally intended to absorb extreme voltage spikes that could cause damage, not fluctuations within the normal range of voltages. It's unlikely that the compressors are creating spikes continuously, therefore surge protection would not be on my radar yet. What is much more likely is that the voltage is a bit marginal or the supply loop impedance a bit high, and the compressors are distorting the waveform.

To diagnose further, it would be helpful to see actual voltage data, whether from a meter, power quality logger, oscilloscope etc. What is the voltage at one of the affected lights with the compressors stopped, starting and running? Likewise at the panel, what are the voltages and supply loop impedances hot to hot and both hots to neutral with and without the A/C running, and the line currents of the A/C units. From these figures we can calculate whether the voltage drop that is seen is normal for that current, or whether there are any anomalies.

If the numerical data fails to reveal anything, then I would look at the waveform for clues.

 

[Mikegh]

Yes that's a better technical explanation than mine

Voltage data and waveform at the affected lights

The fact that not all lights are affected is a definite clue

 

[zerofloors]

Thanks so much for the responses. I tried replacing one of the LED bulbs with an incandescent, and the flicker was much less noticeable (it seemed like it may have still been happening very slightly, but it was very subtle if so).

Should any electrician be able to collect and analyze the waveform data, or do I need to find someone with specific expertise? My electrician has 25+ years experience and checked the voltages (he didn't notice any drops or fluctuations), but I don't think he looked at the waveforms. After failing to find any voltage drops, he did say that he thought it could be a harmonics issue but I don't think he investigated that further.

Thanks again!

 

[zerofloors]

In case it is relevant, I forgot to mention that when the flickering is occurring while the AC compressors are on and I try to change the dimming setting of the recessed lights, the lights pulse for a couple seconds instead of getting dimmer smoothly. In contrast, when the AC compressors are off, the lights get dimmer smoothly when I change the dimming setting.

That said, the flickering does happen on some light fixtures that are not connected to dimmers.

 

[Lucien Nunes]

Dimmed fixtures are more likely to be affected by bad power quality so this is not surprising. It is more significant that non-dimmed fixtures are affected.

After failing to find any voltage drops,

All load causes voiltage drop because all cables have resistance and all power sources have impedance. If there were no resistance or impedance, the A/C could not possibly interfere with the lights, so one way or another it lies at the heart of the problem. The electrician might have checked the drop and considered it normal but it is an important parameter in the diagnosis., e.g. what the voltage is at the panel with the A/C stopped and by how much does it fall when the the A/C is running?

Is this a standard 120/240V panel with the A/C running on 240V? Is this an urban installation with underground cables or do you have a pole pig transformer just for this building or a small group of buildings? Do you know the model(s) of the A/C units?

 

[zerofloors]

Sorry, yes. I believe what he was surprised by was the absence of any voltage fluctuations while the A/C compressors were running. Unfortunately I don't think he wrote down any voltage readings, so I don't have that information.

This is a standard 120/240B panel with the A/C running on 240V. It is an urban installation with underground cables -- the power company checked things in the manhole and found nothing wrong.

The A/C units are Bosch modulating units. Interestingly, it seems like the lights flicker only when it's running at one of the higher speeds. There are a couple different sizes, but the largest compressor is model BOVA-60HDN1-M18M.

Thanks again for your help!