Issue with power feed and negative readings

Hi - I have an emonpi with 1CT clamp on my single phase power supply. Till a month ago this input would provide positive (getting power from the grid) and negative (providing power to the grid) readings. However since 1 month I performed an update to the latest software and now I only get positive readings. When I provide power to the grid this is also a positive reading. How can I go back to the old situation?

Welcome, Steven, to the OEM forum.

I’m sure we’d have heard about this before if it was a fault in the new software, so I think something has probably got screwed up when you updated.

What sort of emonPi is it? Do you have the original emonPi in the all-metal case, with an a.c. adapter:


or is it the emonPi2 with the emonVs power supply:

If it is the original, the first step is, does the line voltage show a varying number, or is it fixed at 240.00 V? And was was the a.c. adapter plugged in and connected before you restarted the emonPi? The reason is: the emonPi checks for the presence of the a.c. voltage from the a.c. adapter when it first starts up, and if it sees it, it uses it to calculate real (active) power, which is positive or negative depending on the direction of power flow. If it does not see a voltage as it starts, it uses a fixed voltage (normally 240.0 V, maybe 230.0 V) and only measures current, so the “power” is an approximation for apparent power (VA), and that is always positive. The cure is to do a controlled shut down (not reboot, this does not restart the analogue software that makes the power calculation) the emonPi and then restart it.

If you have an emonPi2, then the problem is more likely to be in the maths in emonCMS. But you really should tell us exactly what you have so that we don’t have to guess. Remember, the only knowledge we have about your system is what you write.

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Thanks for your answer Robert! The system is a emponpi1; I have followed your controlled shutdown procedure and now it is working as expected. Many thanks!

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