Using solar option to monitor generator panel, polarity issues

I have been wanting to use a second set of sensors to monitor my generator panel for months and have been unsuccessful in getting it to work, until now. I have encountered sensor polarity issues that have been a pain to resolve.

My house has a automatic generator transfer switch that powers a sub-panel during a power outage. I wanted one set of sensors to track total power during normal operation and a second set to track the power of just the generator panel. That will let me know if the generator will have issues with the load before there is a power outage.

I have attempted multiple approaches, mostly without success, and with enormous frustration due to the need to contact customer support to enable or disable solar or enable and disable generator. Having a UI that requires customer support to disable solar or disable generator is just crazy and cost me a week of my time while I experimented with different options.

The reason that I am using the solar configuration to monitor the generator panel is that the generator option is semi-useless. With the generator option, sense will not display the power of both sensors simultaneously which is what I need. The solar configuration does show both sensors simultaneously.

Anyway, it now works, but there are some strange requirements with regards to the way sensors are installed on the feeds and the way power is connected to the Sense unit.

Partially working configuration

  • Main sensors installed upside down. Instead of label towards energy source the label had to be reversed, otherwise Sense would read negative power.

  • Solar sensors installed normally with label towards energy source. In this case towards transfer switch.

This seemed to be working, until I noticed that on some circuits Sense would display power consumption on the second sensors as higher than the main sensors. That is obviously impossible since the generator panel is being fed from the main panel. With some experimentation this problem was only on circuits on one phase of the generator panel.

Solution

  • I flipped the phase of the red and black power connectors to the sense monitor. This solved the problem of the magnitude of the generator power being higher than the main panel. However, all the signal readings were negative.

  • Flipped the main sensors so that are now installed with label towards source which is the normal mode. Now the main power was showing as positive as desired. However, the solar sensors were negative. Since my generator panel it isn’t really a solar energy source, it kind of makes sense. The generator panel is using power rather than creating power.

  • Flipped solar sensors. Now everything reads positive.

In a nutshell, the system is sensitive to the phase of the black and red wires powering the Sense power monitor.

How to use solar setting to monitor generator sub panel
Sense - after swapping red and black Sense - negative measurements

  • Install main sensors as per normal instruction - label towards energy source.

  • Install solar sensors upside down, label away from transfer switch

  • Check to see if the signals measured are positive or negative. If positive, then you are done. If negative, swap the red and black power wires.

Attached are three screen capture,

  • The generator panel power higher than the main panel.

  • After reversing the black and red power leads, all power is negative

  • Final configuration, flipping all the sensors and the red and black

I hope that someday Sense fixes the UI so that I don’t need to get customer support to disable options. In addition, Sense should be able to automatically figure out the polarities and adjust.

This is a screen shot of the system working. Solar sensor is monitoring the generator sub panel, while main sensors are monitoring primary panel. Air conditioner is on drawing significant power. Sub panel is under 3K.

Thanks for sharing your setup, your constraints (want to see each panel separately) and how you solved. I have two two-port Sense monitors in action today, one a used in solar mode and one used in dual 400A panel mode. In both those cases, Sense was able to match up the legs/phases and adjust polarities automatically as needed, during setup. I would like them to break out the dual 400A ports separately in the Power Meter and export, like they do for solar, but that does raise the question of where one would the two totals added together… In the Usage / Trends but not the Power Meter ?

I hope that in the near future they improve the UI. I think that a much simpler and much more powerful and flexible system is fairly easily accomplished. Today one selects options like solar or generator from one of the initial screens. I think that UI approach is limiting and backwards.

Instead:

  • provide the option to select the sensor first and then describe what it is connected to.

  • With 4 sensors, label each one separately, A and B so that when one describes what it is connected to one can be more precise. One could use the second pair to monitor 2 individual 120V circuits rather than an entire panel.

  • In the UI provide the ability to describe/rename the sensor, i.e. generator, solar, 2nd panel, garage, etc.

  • Provide the ability to describe the topology, possibly by selecting diagrams. This will determine whether power needs to be added to show total power or whether separate sensors are subset of main power.

  • UI should provide more useful error messages and possibly self correct. For example, in my case I was seeing negative watts on the main panel. That should have been flagged by the UI and provided ways to fix it in SW rather than having to manually reopen the panel and flip a sensor.

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The 4 CT’s are not all created equal. The main CT’s and Solar CTs (now also called Flex) are calibrated differently. I’m not entirely sure on that process, but with the release of the new options for the Solar Port, Sense has said that they are different and not interchangeable. So in that case, there isn’t much need to be able to identify the main CT’s.

Clamp orientation doesn’t matter, at least for the Main CT’s. If you install it all the way the instructions tell you to, the first turn on “Signals check” can usually complete faster as it doesn’t have to figure out which way the clamps are facing and which is on which phase etc

That said, if you put them in a different way, the system will figure it out. This is often presented with the error message

Sense identified a problem with your installation. We’ll try to fix it automatically. Check back in a few hours…

The problem is that this error message often causes people to look at their clamps, then they see the problem and go and flip the clamps again which interrupts the auto correction.

In your case, you are using the clamps in an unsupported way, so the automated systems probably couldn’t sort it out. Sure, they can add UI to fix that, but why add UI to solve a problem that doesn’t exist if you use the product as it was designed?

As for your comment about Sensors to monitor 120v circuits - it was hinted by a Sense staffer in another thread to “Stay tuned” for something along those lines, so maybe some of these changes are coming.

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There is no doubt that I am trying to use the system in a way that wasn’t originally envisioned. When I first attempted to monitor the generator panel, solar sensors were available, but the generator option was not. I was originally unable to get the solar setup process working since it required steps such as turning on and off the inverter, which in my case doesn’t exist. As a kludge, I connected both sets of sensors inside the panels, but swapped them one at a time into the main port. A bit tedious and manual, but over a few days I was able the determine the max load on the generator panel vs total load.

Once the generator option became available, I gave the dual sensors another try, but then found out that a) it wouldn’t calibrate, i.e. complete the setup without several manual steps to fake it out and b) wouldn’t display both numbers simultaneously. One of the setup steps is to turn on the generator which doesn’t make much sense when the generator panel is an automatic transfer sub panel, it always has power, either from the generator or main power. It turns out you can fake it, by disconnecting the sensors out of the main panel to provide the illusion that power is out. Sense is apparently not really looking for generator power, but the absence of main power.
Since generator setting doesn’t display both measurements simultaneously, I attempted the solar configuration one more time. I did find a way to force a setup by manually connecting the disconnecting the sensors to simulate turning on and off solar inverter.
The result was that the sensors were measuring power, but I had to play with flipping the sensors and red and black power to get it to work correctly.

I also heard that the solar sensors were calibrated differently, but it isn’t clear to me what that really means. Are the sensors physically different or does the software use the output reading differently? I would find it a bit odd if the sensors are physically different. Seems like an unnecessary manufacturing complexity. They both measure current and the possible range of amperage for main power and solar power are probably the same. I also inquired about buying the add-on sensors for a generator and was told they are the same as the solar sensor which I already had.

I don’t know if calibration means zeroing out power from a solar inverter or figuring out all polarities of the power supplying sense monitor and how the sensors are attached. In my case I had to figure it out by trial and error. When I have time I’ll swap the two sets of sensors and see if they measure the same power, which would prove if they are physically the same or not.

Bottom line is that this setup could be greatly simplified with some minor changes to the UI.

Somewhat as an aside … I recently dedicated the Main CTs of a new Sense monitor to a mini-split (208V) and thought I could at least temporarily put the Solar CTs for that same Sense monitor on exactly the same wires of the mini-split feed.

I expected a very close match.

I got an extremely close match.

Every time I check it it never shows more than a watt difference and thus far it’s averaging better than that at 0.447 watts.

R^2 of 1! Well, that’s a Google Sheets limitation, the actual is 0.9999998842. LOL. That’s what we like to see.

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Thats some very good calibration for CTs…

Thanks for the test. That is what I would have expected. From an engineering and manufacturing perspective it would be very odd for a company to manufacture two different, yet very similar sensors that are effectively doing the exact same thing, measuring current through a coil. Seems like the only difference is the label.