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EmonPi overestimating consumption by ~50%

Tags: #<Tag:0x00007f1be9b09e68> #<Tag:0x00007f1be9b09c10>

I’ve had my EmonPi going for about 10 days now, and comparing it to the readings on the utility meter, it seems to be reading about 50% above what it actually should (and the voltage monitor seems to be reading about 10% low - although for some reason, it’s reading 220VRMS when plugged in to a 120V outlet (and my computer rack UPSes are on opposite legs of a 240V circuit and are reading 116-120V on each leg, a value confirmed with a fluke voltmeter)

How can I recalibrate this?

If you look in emonhub.conf (accessible as “Edit config” via EmonHub via Setup in emonCMS) in the RFM2PI interfacer, you’ll find the line calibration = 230V. The text string is not a calibration value, it’s a flag that eventually switches the fixed calibration in the front end, so whatever your voltage is (and I know it’s not 110 V), you still need “110V” in there.

The reason of course is it actually reads the voltage from the a.c. adapter, not the mains direct, and your a.c. adapter gives 12 V for 120 V in whereas the standard UK adapter for which the emonPi was designed gives 11.6 V with 240 V in. So unless you switch the calibration, it will read 248 V ± 5% (the tolerance of the US adapter) on a 120 V supply.

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