I’ve got older hardware (emonTX V3 plus original emonPi) which has run beautifully these last 6 years. My emonTX v3 currently has 4 CT feeds plus the reference AC voltage and the emonPi currently just acts as the base station.
I now want to monitor a 5th feed and was planning to use one of the 2 emonPi CT sockets.
For accuracy, do I also need to feed the Pi a reference AC voltage or can it refer to the emonTX? (everything is on the same phase).
If it does need it’s own AC feed - am I OK to use a splitter with the existing emontx AC feed - I’m cautious that it’s not just a reference for the emontx but also it’s only power source.
You can simply connect the two 2.1mm connectors from your a.c. adapter in parallel - provided they are close enough (or if not, the a.c. adapter and splitter are close to the emonTx). The emonPi does not take power from the a.c. adapter - it’s only loading it with 120 kΩ, and that should be undetectable; plus it implies there’s no real limit to the cable length though I’d suggest screened if it’s ‘long’.
If you take the voltage in software, you can’t measure real power in the emonPi. Although it will still call it watts (& kilowatts), it’s actually volt-amperes - apparent power, and then you’d use the rms voltage from the emonTx to correct the apparent power the emonPi calculated for voltage variations (but you’d still have wrong numbers for reactive loads).