I am currently biulding an ammeter using 6 ct like in the Arduino Open Energy project. I am using 6 though to monitor two three phase motors. One on each leg. Without the cts plugged in and my arduino uno powered thru usb analog 0 thru 5 read out on my lcd to be 0. If i power the arduino uno with the 9v “wal wart” from sparkfun analog 0 alone will read around 50. Any clue would be great.
In this project I built each ct cirtuit like this:
Hazmatt,
The short answer is that values gotten from floating analog inputs are meaningless. If you pull them down to the Arduino’s ground through reasonable (say, 10 kohm) resistors, they should read zero.
Another possible factor is that you get a different “ground” and a different reference voltage with the different power supply.
The difference could also be noise from your wallwart. Pulldown resistors should address that, though.
Have Fun,
Eric