Happy Report as well

I’ve got 2 IoTaWatts happily running. I just ordered 2 more units. One for the production installation and a 4th for development fiddling (and a spare if I never get around to it).

I moved from 2 Reference transformers to using

to break out into 4 power cords.

Plus for powering the units, I have a high quality 1amp USB wall wart and I just installed this

and I’m powering my 2 production IoTaWatt’s without issue and 90% less clutter in my outside box.

Leaving me with transformers to power the development unit in the future.

:+1: to IoTaWatt

Message contains no scummy referral links or anything. Just solutions to my problem(s).

You can share AC reference, or you can share USB power, but you should not do both. It creates a ground loop. At best you will impact accuracy, at worse you can damage one or more units. I would recommend using discrete USB power supplies as they are inexpensive and a common voltage reference is good.

I lack an electrical engineering degree, however, I graduated from engineering school (computer science and math). Do you have any references to explain the grounding loop condition? Is this similar to the need to disconnect the neutral and ground bars in a sub panel for home electricity?

FYI, I have other equipment in the box where I have installed my IoToWatt’s specifically a Solar Edge Production grade meter, several DIN rail outlets, and a raspberry pi. There is also the possibility that I install a wireless AP (if I need one and I can find something small to run openwrt). But so far 2 IoTaWatts are doing fine talking to a Ubiquity (model unknown) Pro wifi AP.

I wanted to eliminate the IoTaWatt supplied USB adapters because they come unplugged easily.

Thank you for helping to improve my experience.

Take a look at the schematic on github.
When you use the common DC power supply, you tie the ground of all of the units together.

If one of the AC reference feeds is out of phase with the others (it happens), different sides of the AC will be connected to ground. The result is a little smoke and some burned diodes and resistors.

Even with correct polarity, the AC reference rides on a DC bias that is relative to ground. When they all have a common ground, the DC bias also becomes common through the AC splitter. While the bias voltage is very close in all units, they aqre not exactly the same, and the op-amps struggle with each other to be the same, never achieving that, generating heat, and producing ADC readings that are not necessarily based on a correct bias voltage.