RESOLVED - IoTaWatt kWh reading much lower than power company reading

[mattames]

@overeasy

I have a sample of each of the Aussie VTs that I recommend - AC910 and MP3027 - are exactly opposite. In other words, your CTs will point in one direction with one and the opposite with the other. In the US or Europe, you can just reverse the VT in the socket. You could have simply checked reverse for your VT.

It’s all starting to make sense now - when I hooked the DSO up initially I realised the MP2037 was 180 degrees out from it’s respecting CT phase, so I swapped it over on the DSO and didn’t think any more of it!

It also did occur to me that they might have chnaged the MP2037’s supplier and that it was wired back to front, but alas when I looked, it appears they went out of their way with a keyed connector so that it can’t be swapped over on the plug. I guess this was only done this way as they are using the same parts for their DC and AC plugpacks and there’s no “right” way with AC.

@overeasy

If the little reverse arrow ↺ appears next to the input when on, check the “reverse” box on all three mains CTs and any solar inverter CTs

That was what confused things even more - the reverse arrow ↺ never appeared at any time when I had it hooked up incorrectly.

I guess I had done a very good job of confusing my poor IoTaWatt (not to mentioned myself)

Thanks for the explanation as well, It’s been over 20 years since I studied any electrical theory at uni and it’s slowly coming back.

Now i can move on with getting the branch circuits added and my other 2 IoTaWatts installed as well - I have two subpanels, one for the pool and aircon, and another for our granny flat. It’s probably overkill but hey, the more data, the better.

Thanks again!

Cheers,
Matt

[mattames]

@overeasy

It is only when you observe it relative to the voltage reference that it takes on the characteristic of power flow in one direction or the other, depending whether the current is in phase with the voltage or opposite.

Ok, just to clarify it in my mind, the actual problem is that the VT is 180 degrees out with respect to the IoTaWatts “A” phase, is that correct to say?

[overeasy]

At the risk of appearing pedantic, the IoTaWatt A phase is, by definition, the VT. The CT on the same phase as the VT should produce a current signal that is in phase with it. So if your CT is reversed with respect to the VT, it would be 180 degrees out of phase.

I wouldn’t necessarily characterize that as a problem though. It should still read the correct power value, but will be negative if you have “allow negative values” checked. Same for the other two.

[mattames]

@overeasy

I just thought I would follow up now that I have completed a three monthly billing cycle. My IoTaWatt measured total consumption as 3,276,485.71 Wh (Using the maximum Wh in Graph+) and shows 3.30 MWh using the Sum/Integral statistic on all power in watts over the same time period.

The bill came in at 3,297 kWh, which is pretty much spot on with what the IoTaWatt is showing.

I am very impressed at this unit, and loving it more each time. I just need to get an electrician in to install more CTs on the branch circuits now, but that might have to wait as it won’t be a cheap exercise, and playing around behind switchboards and dangerous and illegal where I live.

Thanks again for an awesome product.

Cheers,
Matt