New CT setup - reading errors


I am trying to set up my emonpi with 2x CT probes to monitor my electricity usage and solar production etc. Initially I just want to record imported electricity levels to get this working.

I have solar PV and 2x enphase batteries.

I purchased 2x of these for the CT probes:

For the purposes of testing, I have put one CT probe on the live and one on the neutral of my live feed into my supply meter. Photo attached.

If I remove the CT probes from the mains, they report ~0kw (around 25w in fact)

I have issues/discrepancies between what the enphase app is showing me for elec imported/exported versus my emonpi. Both sets of data are attached.

I ‘trust’ my enphase stats as the import stats match my meter readings, and when enphase shows I am not importing(or exporting) I can physically see the feed meter not blinking.

The issues I can see are:

  1. Altering the orientation of the CT clip doesn’t change the +/- of the feed. Both the live and neutral always show a + number

  2. When the system is exporting it still shows a positive number on both CTs

  3. At night when there is little activity in the house (say 3am) emonpi reports usage of 700w. Enpahse reports 300w.

  4. During the day when it was sunny (as today) emonpi is reporting significant importing, when the actual number is near zero.

  5. Emonpi never reports importing less than around 700w, unless I remove the CTs (which I did at 9.40am to test)

I;d be grateful for any advice for how to diagnose this issue!



Empnpi screenshot

Enphase screenshot

Do you have an a.c. adapter plugged in to the socket next to the c.t. inputs of your emonPi? And if you have, did you follow the instructions for connecting the a.c. adapter before you connect the 5 V d.c. power?

If you don’t have the a.c. adapter, or if it wasn’t connected and switched on before the “emon” part of the emonPi started up, it won’t (a) know the mains voltage and (b) have a reference to determine the direction of current flow, so it won’t be accurate and it will actually be showing an approximation of the apparent power assuming a constant 230 V mains.

Thanks for replying Robert.

No I don’t have an a.c. adaptor plugged in - I totally missed this in the instructions. I just assumed that was an alternative power supply rather than the usb!

I just need one of these? AC-AC voltage sensor (UK Plug) - Shop | OpenEnergyMonitor

Any specific requirement for the socket it plugs into? I have a spare socket adjacent to the meter.

Yes, that’s what you need. The socket needs to be representative of the voltage at the point where you’re measuring the power, so the one close to (electrically) the meter sounds ideal.

After you install and connect it, you need to power down the emonPi - rebooting just the Pi isn’t good enough, you need to restart the ‘emon’ part too, and the only way to do this is to power the whole unit down and then re-start it.