Power Quality - 33x Voltage dips in the last month

How was your issue detected?:
Sense application had data, no notification of the issue

Did you noticed any other signs of this issue around your home?:

I do notice that when my Air conditioner kicks On, my lights start to dim and at times they continue to stay dim for a sustained period of time. [with the exception of bathrooms heating lights and landscaping lights, all are LED and I really didn’t expect those to dim given power requirements]

Screenshots from Sense Lab

  • Sense Labs graph screenshots

  • Sense Labs notification Screenshots

Do you have motor stalls being detected in Sense Labs too? This sounds like your AC system is failing to start, overheats, then trips out on thermal overload. After a few cycles of that, it starts successfully.

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I have a condensate pump and another unknown motor that were detected, but haven’t shown issues. In the last couple of hours, I received notification of another motor being detected. So I am guessing it’s the AC Motor, but will have to wait for a few cycles of the AC to turn ON/OFF to see if its that motor. Also based on it, I am guessing motor stall detection will take some time too.

To be clear, the motor stalls detection feature is a separate area in the app under Sense labs.

I do see 2 Sense Lab features enabled currently Motor Stall and Power Quality. MOTOR Stalls has “No Stalls Detected”

Review these two forums on A/C compressors.


I think your problem could be with your “Run/Start” capacitor. Take some screen shots of your starting wattage load when the A/C compressor starts up and post them on the forum. I had to add a “Hard Start kit” (another capacitor) to my A/C unit to fix the same problem you are having.


Device detection has detected my furnace fan within a few days of installing the device, which is supposed to rotate air 10 min/hr or open a damper (to allow for ventilation) and then run the fan. So in total the fan would run ~ 2-4 hours a day.

Because of excess moisture in the air inside ( outside its > 75% humidity), I had turned off ventilation for a few days now ( have 2 kids that open the door all day long so we have good air quality) and may have turned off the circulation fan too.

Sense App was able to show that the run time in the last 2 weeks was down significantly.

Earlier the Air Conditioner used 5KW, now the AC and a newly discovered Motor combined use about 5 KW. However, when the AC turns ON the furnace fan isn’t turning ON, and the AC shuts off in ~ 30 seconds ( guessing some form of safety mechanism).

I tried to just turn on the FAN, and the Ventilation, and also the heat and see that the furnace fan really doesn’t kick in for the whole period of time. So it’s either the capacitor or the furnace fan.

This Sunday we are expecting 95 F weather, which is atypical in Seattle area, and so I need to get a handle on this before that.

I think you are going to need a HVAC tech come to your house and do diagnostics. You might go outside and stand next to the unit, have someone turn on the A/C at the thermostat. Check to see if the outside cooling fan (at the compressor) is running. That could cause the same problem and create an overheating resulting in a trip. Still would be helpful if you could post screen shots of your ‘wattage load graph’ (Power Meter) over a time period.

Here’s Annual usage ( I am new to Sense) and usage in the last 3 months. I don’t see too much of a variance, as the weather has changed for sure to be much hotter.

The fact that my blower-fan isn’t turning ON anymore is the first piece of concern. When I turn on AC, I can heat the outside motor/fan.

I was thinking of the “Power Meter” graph that you can expand and show the details in the first few seconds that the A/C starts. That graph would be more helpful than the monthly graph.


In this example, you see my A/C compressor start (first peak), then milli-seconds later the outside cooling fan starts (2nd peak). The load is low at the beginning until the Freon pressure builds up, then you see the unit running at a steady state (using almost constant wattage).

Have you had a lot more lightning storms than usual this summer? I’m in the southeast and we’ve had storms constantly this summer. Even had lightning strike the ground near my driveway where all my services run destroying several pieces of equipment. I had three dips in one hour down to 55v on both legs due to a storm.

I live very close to Snoqualmie Falls, WA and the power is literally harvested here. We do have low-voltage events about once a month or so, but I am unsure on what happened how.

Had a HVAC technician come, and find out that the Fan Motor was consuming about 2x energy now.

Interestingly Sense had detected my HVAC Fan a couple months ago and I could see 550W, but recently, another device that was correlating to the HVAC Fan was detected by SENSE, I didn’t have ample time to confirm the device. This caused the mainboard to not work correctly, because of increased energy drawn from the main-board.

So, unfortunately, my motor never stalled just was going bad slowly, overheating and then shutting down. Unsure, if the STALL algorithm can be created to check average/mean run times, and notify if the run time is suddenly, say greater than 3-Sigma

Sounds like a bad capacitor. A bad capacitor will cause a motor to become so hot you can cook dinner on it.

Something is a little fishy for sure. I seem to have registered 100+ Low voltage events in the last 36 hours, as opposed to the 33 in the last month.

Now I know I have registered for the labs feature just recently, but wanted to know, if there’s historical data with Sense that they can allow me to review

I think I am suffering because of a bad AC unit that my neighbor has ( his AC and mine are ~ 10 feet away from each other, and this weekend, I was trying to get my HVAC diagnosed and corrected.

We ( HVAC technician and I ) noticed that my neighbor’s AC pump kick about as low as every 15 seconds. I am sure aware that his AC was broken for a couple years, and just recently someone ‘fixed’ it, is it possible that’s causing voltage dips for me ?

Recently our yard / neighborhood transformer was replaced. I don’t know the specifics on your neighborhood setup, but will use this as an example.

The transformer was replaced due to age and the fact that an armadillo had tunneled into the housing. (The reason for all the extra dirt.) Look at the aluminum bars labeled X3 and X1 and X2. Those are the connection points for ‘phase A’ and ‘phase B’ (or LEG1 and LEG2) providing power to your house breaker panel. Each supplies 120 VAC for a total of 240 VAC with the 3rd being the neutral. My underground cables are identified with yellow tape. My neighbor’s service cables are identified with blue tape. The picture doesn’t show there is a ground rod and your neutral wire is also connected to the ground.

The point I’m working towards is that you and your neighbor could possibly share the same voltage dips and surges. His actions would affect your actions, if you have a similar setup. This transformer only provides power to 2 homes, but I think it is rated to serve 4-5 homes.

In the picture above the tech was using a yellow fiberglass disconnect tool. That is why it is in the foreground.

This is the new transformer before being installed.

2020.01.27-LJ-Teakwood-transformer-replacement (17)

Can your neighbor’s electrical usage affect your signal? Maybe, depending on how they are connected. If he is using a cheap garage welder connected to the power grid, then he may be sending transient waves (out-of-phase signal) back into the electrical system. Something to be aware of, but there’s probably not too many things you can do to avoid it.

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