CTs / Solar PV / Inverter Overnight draw

Installed my new emontx/emonbase yesterday and getting to grips with the logging.

I have three PV systems so have three CTs. Currently I have a hybrid logging system using legacy CurrentCost uploading to PVOutput but the plan is to replace this with the Emon kit and add additional functionality.

Noticed an issue last night whereby the feeds were showing power when the PV clearly wasn’t generating.

I have all the CTs oriented so that generation is positive.

The feeds are configured as (Allow positive / Log to Feed / Power to kWH) which I though would solve the issues of the low power to the inverters during darkness but for some reason the Log to Feed is showing a low positive reading (cf 5 to 10 Watts).

Is this just a function of the CTs/Power Factor?

Any suggested solutions? I guess sticking a ‘min value allowed’ after ‘allow positive’ to filter out the noise?


PS any pointers on how to get three feeds uploading to PVOutput would be welcome. I’ve found some source code in the forum but need to work out what it is doing yet.

What are you using to measure this? It’s not clear whether you are still using the Current Cost kit or OEM.

It could well be that the “keep alive” power that the inverter draws overnight has a power factor close to zero, and if the phase error correction isn’t right, a power draw could easily move into the next quadrant and appear as generation. Unless of course you’re using “CurrentCost” and that doesn’t understand direction of power flow, and reports any direction as positive? (I don’t know how CC works - many systems don’t recognise the direction of power flow.)

Totally separate from Current cost.

Using the emontx and supplied clamps plus the AC/AC power supply.

I think it’s probably just the very low draw from the inverter.

If you want, and you’ve got a programmer, you could go through the calibration procedure for the emonTx and check the PHASECAL setting. I know the default value of 1.7 isn’t quite right for the last set of c.t. and a.c. adapter that I checked - but that’s been a while ago and though we know their characteristics do change over time as the manufacturing process gets tweaked, it doesn’t usually matter. But if those few watts come from a quite high current that’s almost purely reactive, a slight error will explain everything.