Assistance with powering the IotaWatt

Hey guys,

I’ve had my IotaWatt for a while, but I am finally getting around to installing it

I have 2 questions I can’t find the answer to

Is there any problem powering the IotaWatt from a UPS? I don’t want to have it lose power in an outage before my generator kicks in

Second, how does it measure line voltage? I understand it does it from the 9v reference AC adapter, but then how does it measure the other leg of a split phase 240V USA setup? I was hoping to get full voltage readings on both legs

I assume I would plug the 9V AC adapter into an outlet that is not UPS backed in this case?

Should be fine with a line voltage UPS. Some have had problems with a USB UPS.

Most installations use one AC reference on one of the legs for both legs, but IoTaWatt is very adaptable. It can have as many as three voltage references. So if you want to add another AC reference for the other side of a spliut phase, you can do that. Another approach, which I consider the best, is to use a 240V reference transformer calibrated down by half. See this discussion:

I would not recommend plugging the voltage reference into a UPS.


Would I just purchase another 9V Transformer? And then plug it into one of the ones marked for 3 phase reference?

I actually just found another one from an old EmonPi Setup. Can I use this do you think?

I also found a few of these CT’s, would these work with the IotaWatt?

Yes, that VT is supported.


Perfect, thanks so much

I plugged it in, had to calibrate it but now its working great. Showing identical voltage to the other VT