Real time and Historical Amperage Draw (Generator Use Case)


#1

I wish Sense could display in real time (at least) and record (best case) amperage draw.

This would be helpful to those of us who use Sense to help size our generator needs in advance of making that major purchase. It would also help monitor our loads after a generator is installed. Sense device detection may also help inform better decisions on how to configure load shedding. Measurements in amperage would be typical in this case.

From a business perspective, generator users spend thousands of dollars on their solution. In many cases, a $300 investment in Sense is worth it just to size their generator correctly before making such a significant purchase. Users with an ATS installed at the service entrance will automatically benefit from Sense with no extra effort. Users with a transfer switch installed via a back fed breaker may be able to benefit from the solar CTs when on generator power.

I think this type of feature and some marketing would help expand the Sense community.


#2

Hi Bill,

What am I missing here? If you know Watts, which Sense displays real time, and you know volts, which they also display on the Settings->Sense Monitor, one can easily calculate amperage. In the snip below, the total amperage draw is 5.9 amps. I agree it would be nice to be able to have the data stored or exported to a csv type file.


#3

What is “best case” ? The high water mark (max instantaneous power/current) for all time ? Or for some fixed period, like the typically worst case month/week/day (the time your, washer, dryer, dishwasher, pumps, jacuzzi, toaster, instant hot water, power tools are all going) ? Do you want to capture the max, max peak of a millisecond spike that is 3x higher than any other current or have Sense do some smoothing ?

I ask all this, because you have a pretty good proxy in looking at the highest hourly usage over whatever period you want to consider, then dividing by 120V to get amps, then multiplying by some safety factor to take into account your ratio between steady state power and instantaneous peaks.


#4

@Fred_W

For that screen, you are correct. It should be simple for the user interface to do the calculation and display it automatically.

For information displayed on other screens, I don’t think the voltage is immediately apparent. Some devices might be using one leg and others using both legs of the service. In my view, it’s just a cosmetic issue that would be a helpful addition to the UI.


#5

@Kevin1

I would say recording the max and average draw in amps would be useful.

It’s not easy to get historical data out of Sense mostly because there’s no search/filter option. I imagine if Sense released a “Reporting” module, it would be an entirely different situation.


#6

Ah @bill1, I understand better now. Thanks for the clarification. I agree it would be helpful, especially since only we know what devices are on what circuit breaker, it may help determine if we are pushing the breaker load limit.


#7

@bill1,

One more question. What would you search for if you had a spreadsheet of minute by minute power samples (or would you prefer second by second power samples) for your entire history ?

And what window/granularity would you like your averages at ? Sense essentially gives us hourly/daily/weekly/monthly averages in the Usage panel. Sure, you need to divide the energy used in that period by the number of hours in that period to get power, then by 120 to get amps, But again, I’m more interested in how you would select the sample period for the average calculation.


#8

Minute by minute is more than enough. The only exception is (especially for generator users/dealers) recording peak info at the smallest time interval possible is desirable. This only matters for devices that are motors like an HVAC compressor.

Putting aside capturing peak starting amperages, hourly/daily/weekly/monthly averages are fine. For generator sizing I basically want to know: what’s my worst case scenario when a motor starts up and what is the steady state (assuming there is one) once the motor is running.

It helps to know that heat pump X uses 10 A to start and 5 A once running.


#9

Thanks for the explanation. You can kind of get spike and steady state profiles of individual motors, just by turning each one on, when other things in the house are bit quiet. Or by looking at the profiles once each motor is correctly detected. But do you then sum up all the worst case peaks and add them together, presuming that they might all start at the same time, or do you add the biggest spike peak to an average for the typical worst (most usage) hour in your house, to get a reasonable maximum.


#10

Yeah, I get what I need out of it like you describe. I guess my bigger picture point is that a lightweight feature or two might help cater to an additional type of customer.

Support emailed me today. While the solar CTs can provide total current on a back-fed breaker to a generator, device level detail can only come from the main CTs, which would show no current in this scenario. FYI to others searching this later.


#11

Agree - I would like Sense to be useful to as wide a swath of residential customers as possible.


#12

@kevin1 . Yeah - Sense might find that generator dealers can be a channel for the product especially those doing standard service entrance ATS installations where you can use the main Sense CTs regardless of the power source.


#13

I purchased our Sense specifically to do some generator sizing work. I would very much appreciate the app or web page doing the conversion to amps on my behalf. Showing the highest total spike in as little time as possible as well as averages over some period of time would be great. I’d also like to see it seasonally as our use during winter is different from summer. It may help me decide if want to invest in a smaller whole house generator with load shedding accessories.

The locked rotor amps (inrush current / startup current) can be very critical and may only last a couple tenths of a second.

I was on the fence about buying a Curb or Sense. I honestly wanted Curb’s per circuit monitoring, however they told me they could not show data in less than a one second average.


#14

I have grid-tied PV solar and a generator with an ATS. I debated with myself a while about where to locate the main CT’s - either on the utility/grid feed before the ATS or on the load side of the ATS.

Each have advantages and disadvantages. The load side would allow sense to measure and record usage when the generator is operating, the line side would not. I eventually settled on the line side so that sense could measure all utility usage including the generator’s battery charger and oil and battery heater which are fed from the ATS internal circuitry. Sense is now a valid backup for the utility’s meter. However I give up monitoring of use while on generator power (very rare).

I’m sharing this because the diagram might be helpful to other users and to sense in discussing CT locations.


#15

Good reasoning there, @sol. Is your ATS covering your entire main panel for whole-house capability (within reason of course) or do you have one of the ATS units with specific circuits covered by the generator and the rest of the loads cut off entirely?


#16

It’s a whole-house ATS put in line between the meter and the panel that contains all of the breakers for all of the circuits in the home.

To be 100% technically correct the actual main panel is at the meter across the driveway from the home. This panel contains breakers for a couple of outlets right there and a feed-through line going to the home. But those outlets were used for power equipment during the construction of the house and have never been used for anything since then. So it is this feed-through line from the panel at the meter (with no used loads) to the house that is measured by the main CT’s, right before the solar PV leads tap into it at the line side of the transfer switch.