Hello, I am currently trying to configure/validate/calibrate 3 phase readings from my emonPi2 before going on site to install this. Initially, I have a 3-phase circuit with a resistive load only. I am using a 3-phase net analyser alongside the emonpi2 to measure phase voltage and current. I then connect my emonPi2 (this is powered using the emonVS voltage sensor and power supply, 3-phase 4 wire version). I attached 50A CT clamps to each of the phase lines and plugged in to channels 4, 5 and 6 as these are configured for 50A CT clamps that I am using. The readings for phase voltage (V1, V2, V3) in the emonPi2 align with the readings on the 3-phase net analyser as does the total power measured on (P4, P5 and P6). At this point everything seems to be ok for different line voltages that I tested, and the phases are balanced. I then connect a 1Kw 3-phase motor in the circuit instead of the resistive load. At this point, the readings on the 3-phase net analyser are what I would expect to see for total power consumption (for real, reactive and apparent). However, the readings on the emonPi2 for P4, P5 and P6 are a fraction of what I am expecting to see e.g. at 400V line voltage the 3-phase net analyser measures 964W total and 152W for real power with a power factor of 0.157; On the EmonPi2 the readings are as follows: P4, 30, P5: 47; P6: 38. I am struggling to understand what is going on here with the readings and wondering if I am missing some additional configuration that has to be done as my understanding from reading previous forum posts that the emonPi2 would calculate the apparent power automatically. Is the emonPi2 measuring real or apparent power in watts for the values returned for P4, P5 and P6? Any help on this would be much appreciated. Many thanks, Enda.
Welcome, Enda, to the OEM forum.
Iâm not sure where you read this, or indeed what you read. The library which does all the calculations does indeed calculate apparent power as well as real power, power factor, rms current and voltage. It doesnât differentiate between leading and lagging power factor. However, the sketch running in the energy measurement (the âemonâ) section of your emonPi2 chooses to report and the emonCMS software records only the real power. Youâd need to change and customise the software in there (not in the Raspberry Pi itself) if you need the apparent power reported directly - or if you want the rms current reported in order to calculate it yourself.
Many thanks Robert for the swift response. I may have misinterpreted the bit on apparent power being calculated on a previous forum post: How do I measure Apparent and Reactive power with an EmonPi? where you said âemonLib, which is what the emonPi uses for the power measurement and calculations, doesnât attempt to measure the reactive component. It only computes the average real power, rms voltage and rms current; and itâs from the latter pair that apparent power is calculated.â I will need to look into updating the sketch to see if I can do this myself. Thanks again.
That part should be relatively straightforward - everything you need to know can be found in the emonLibDB zip file you download from this forum: EmonLibDB - Version 1.0.2 (Includes full documentation, example files.)
The hard part will probably be uploading it in the first place and then it will be to avoid updating it and losing your custom version if/when your emonPi2 decides to update itself, plus youâll need to make changes in the emonHub configuration to pass the additional values forward to emonCMS.