WH Reading lower than expected

I have two Iotawatts running and the total kWh readings seem to be considerably lower than the my utility reading.

Iotwatt read 433 kWh for last month (matched exact dates) and utility gave 670 kWh.

I also did a test with a Kill-a-watt meter. While my freezer was running at ~80 W on the kilowatt, the Iotawatt showed only 63W for the GaragePlug circuit it is on, but there’s 10W of idle power when freezer is unplugged, so really 53W for the freezer.

Some things I considered:

  1. I’m using a splitter for 5V amp power from a charger. Based on your answer in Setting up multiple IoTaWatts - #2 by overeasy, it sounds like using individual 5V chargers is preferred. But when I tested with a individual charger I did not see any difference in the readings for my freezer over a few minutes period.

  2. I’m using some chinese YHDC SCT013-000 50A/1V CTs I got from alibaba with the SCT013 config in the Iotawatt. Any chance that these need more calibration?

  3. The GaragePlugs circuit is a single breaker, so can’t be a double breaker misconfig.

Pictures of my setup:

The inputs setup for the iotawatt with the GaragePlug which is the one with the freezer plugged in.

Message Log. Day I did the testing with different chargers is 7/3.
iotamsgs.txt (9.7 KB)

First, you should be using power supplies and not chargers. The problem with sharing both AC adapter and 5V supply is that it creates a ground loop that can cook one or both units and also skews the DC bias to the CTs.

What you are showing are YHDO counterfeit that have been reported to be wildly inaccurate. Also, they are SCT013-050 which are voltage output. You cannot use voltage output CTs in IoTaWatt without removing the burden resistors and configuring as generic.

Thanks for the details and correcting me on the chargers vs power supplies.

Guess I’ll need to lookin into doing Modifying SCT013 to remove Burden Resistors.

Appreciate your quick support and help.