Input suddenly no longer sending -ve values

I’ve had a clamp measuring current flow (to and from an inverter) successfully for many months. Suddenly this evening whilst is still measuring current, in no longer seems to be reading flow direction - and all the values are positive.

The only thing that’s changed is I had to reboot the pi and board.

Why would the the flow direction suddenly no longer be detected? I wondered if the AC power input has failed, if that has any bearing on it.

Are you talking about an emonPi?

If you are - or if you have an emonTx feeding its data to a Pi running emonCMS, then if the a.c. adapter is not plugged in and powered when you start the “emon” part - the Atmel processor that measures current and voltage - then it will resort to guessing apparent power using an assumed voltage. Apparent power is always positive.

So yes, if the a.c. adapter has failed, your voltage will always show a fixed value, probably 230.0 V, and you will always see a positive power.

Thanks, yes I have an emonTx feeding its data to a Pi running emonCMS. It does look like the ac adaptor failed yesterday - looking at the grid voltage data from the last 24hrs:

I think you’re right - but if you power down the emonTx and then power up again - or just use a pin or the like to press the reset button - without touching the RPi, that should prove the point. If it starts reading, it was a timing problem at start-up, if it doesn’t, check the connectors etc and measure the voltage if you’re able - it should be around 10 - 11 V.

I’ve got to say, it is extremely rare if it has failed, I’ve never seen this before.


Thanks for the reply.
Sorry, just to clarify - I’m running the emonPi shield board attached to RPi via GPIO pins.

I’ve measured the voltage at the plug end of the adaptor, and yes it’s 11v (11.1), so does seem to be working OK.

Given the adaptor seemed OK, I powered it all down, and restarted - it’s now working. Thank you, first I’ve had this, so wasn’t aware of the critical nature of that start up timing on power monitoring - just assumed if the adaptor was plugged in it should work. It must have just glitched on the restart yesterday.

The whole system and cms is very stable** and really handy - I’ve had it running for well over a year (**not counting a corrupted sd card - but that’s a pi thing).

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