IIRC both will actually work fine with 4 CT’s.
I have been running my own variant of MartinR’s PLL for 6 years now on a emonTx v2 with just 3 CT’s without issue, the monitoring is plenty accurate for purpose despite me not really spending much time calibrating and as for the diverting, it is absolutely spot on, it is more accurate at tracking the export than a commercial unit that was installed by the PV installers, the emonTx+Mk2 still squeezes out a little more even after the commercial unit has taken what it wants. The LED on our supply meter is on solid for hours and hours (it registers both import and export with flashes). I have also had MartinR’s PLL working on a emonTx v3 whilst helping convert it to 4CT for another user years ago on the old forum.
For examples of Robins code for emonTx v3 + diverter (with 4 CT’s) see
Robin has used the high sensitivity input (ct4) for the diverter and therefore recommends using a 2nd CT on the same cable for monitoring above the 4kW(ish) limit of the high sensitivity input so whilst it uses 4CT’s it might only offer 3 values. Personally I would just use a std (ct1-3) input, it works well enough on my emonTx v2 and some of the accuracy of the high sensitivity input is lost due to the potential phase error of the higher value burden resistor. What you gain on one front you can lose on another, especially when dealing with the lower currents like appliances in standby and electronic chargers etc which is where the diverter kicks in, not when you have a nice 4kW oven running (for example) so i would rather have the extra input myself.
I’ve had a quick search but cannot find any 4 ct examples for the PLL, but I will post here if I find something.
I think there would be good demand for a proper OEM emonTx+diverter firmware, I would certainly be on-board, the only reason I haven’t swapped out my emonTx v2 (aside from it working perfectly well) is because there is no focused development in this area, just links to very old FW, I know from Robert’s work on the emonLibCM there have been improvements made in the way things are done but I’m not able to reverse engineer those changes out and apply them to the old FW, so I’m sticking with the Tx v2 for now as the emonLibCM doesn’t do diverting (yet?).
Maybe one day i will try and tackle it but since my v2 works so well, it isn’t high on my to do list.
This is true of any emonTx, but yes especially if using as a diverter with 2 or more CT’s. The continuous sampling will be more accurate with a separate PSU and you will have more power available for the diverter triac/ssr. I believe it is possible to run a emontx diverter from a single ac adopter but it is tight especially if you start thinking about pulse counting or temp sensors and/or your emonTx or PSU is at the wrong end of component tolerances.