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Grid feed not showing negative export PV

Tags: #<Tag:0x00007fc9b6a4df58>

I’ve been looking at this over the past week and the lack of sun is making it quite difficult, however since updating our emonpi to the new sd card image and restoring the backup i took before upgrading, our grid always follows the pv output and never goes into -ve.

The attached image shows what I mean, and for reference another image from before upgrading where the grid can be seen to be going into -ve.

Like I said, I have just restored the backup and not changed any other settings.

Any pointers as to what this is would be most appreciated!

Hello @bengtec. Did you by any chance modify emonhub.conf on the original image? although emonhub.conf is copied over in the restore process it is not currently used, a newer default version is used instead. I wonder if this could be the cause?

I modified it to use the socket interfacer (which I’ve since stopped using). However I manually restored my old emonhub config by pasting the backup copy into my local emoncms on the emonpi but that stopped the pi posting to, and the local graphs on the pi were still looking wrong. Do you have any other suggestions?

Hi @bengtec,

I’ve just taken a look at your system and the issue is that during the migration to the new SD card VRMs reading seems to have been lost. This is probably caused by the AC-AC adaptor not connected or was connected after the emonPi was powered up.

Please check the AC-AC adaptor is connected, if it is you will need to fully power down the unit (shut down, the pull the power). On startup the LCD should display “AC Wave Detected” during the startup process.

The AC-AC adaptor is used to determine the direction of current flow, without this reading the CT cannot tell the difference between a positive reading and a negative reading, the reading will always be positive therefore incorrectly reporting gird export as import.

Excellent, thanks Glyn, I’ll look into it this evening.

I can confirm it is now working perfectly again!

Note to self: make sure AC-AC adaptor is connected and on before the emonPi!

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That applies to everything that connects to the emonPi (and the emonTx and emonTH). That and the explanation is in the FAQ.