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Negative Power configuration issue


I have a EmonPi base station (with the 5v supply and 9vac supply) with 3 battery powered emon tx units with CTX sensors sending in values to the base station. I have two solar installations and grid monitoring.

None of the emon tx’s ever set the power to negative, even through I know the power is flowing the opposite way some times on a feed (when its sunny). The vrms on the emontx units is showing the battery voltage. Is this lack of negative power reading because the emontx units are not powered from the AC 9v supply? Should the 9Vac be connected to the supply point they are measuring?


Yes :grin:

Pretty sure, yes but I’m sure @Robert.Wall will tell me if it is otherwise :grinning:.

If no CTs are connected to the EmonPi, the 9V supply is redundant.

Brian is right. To measure the direction of power in an emonTx (and in the emonPi) each needs its own 9 V a.c. adapter so that the relative direction of the current measured against the voltage can be determined. As your emonTx’s don’t have that, you can never know the direction of power flow. It’s spelled out here:Learn→Electricity Monitoring→AC Power Theory→Introduction→An Introduction to AC Power

Yes indeed. Although the variation in mains voltage across your installation should be small, each emonTx needs its own a.c. adapter.

Thank you. Added the 9Vac adapter and the units now show the power flow direction correctly :slight_smile:

Now that I have the negative power measuring correctly, would anyone have any pointers on how I can use the EmonPi to turn on an off items depending on the direction and size of the power flows please?

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Have a good search on here. There lots of options.