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


Does this have to do with the generally messy quality of non-“sinewave” UPS that are so prevalent?

Overeasy might have a better response, but for me;

In my case I have a double conversion UPS, so for me it would mean the voltage is going to stick at dead on 120v@60hz no matter the input. Not useful for monitoring!

And if you even have a line interactive UPS, when it switches to battery, you then lose the details on the poor power input, which you probably want

I also suspect the power reading would be all messed up, like when I referenced generator power output with solar current, to make this mess, because the frequency wasn’t matched up most of the time

For that, my solar was on grid power, but the voltage measurements were on generator power. So I suspect if you had them on a double conversion UPS you’d have the same problem, and on a line interactive UPS you’d have them all messed up any time the UPS was on battery

Oh…duh. The voltage reference should be plugged into the non-UPS circuits…makes sense now.

Is it acceptable to plug the IoTaWatt power supply into a UPS? That is really the question I meant to ask… :slight_smile:

Yep, got mine plugged into a UPS with no issue