As there is so much more availability on 3 phase in Europe, I'm really keen to explore a way of integrating relatively accurate 3-phase energy measurements.
I can think of a few ways of doing this:
1. Add some "logic" circuitry that determines whether power source is 1ph or 3ph and then multiply energy usage by 1 or 3 depending on the case. This would assume current is equal across all three phases, which it should be, and is in my experience (charging a Tesla).
2. On OpenEVSE v4 (and v5), the atmega board has two unused pins: ADC6 and ADC7. It would be great if these could be used for another two current sensors, just like ADC0 is at the moment. I've taken a quick look at the source code, and think this should be possible with suitable modifications to openevse and J1772EvseController, providing there is sufficient memory available to store the extra variables and data.
The beauty of the second solution is that it's totally "optional" and assuming hardware and software modifications are possible, there's no different version or adjustment to make for 1ph or 3ph - either the extra two coils are installed and measure current or they don't. Also, the EVSE could be wired for 3ph charging but will equally work just as well if only connected to a single phase.
I'm relatively comfortable with ECAD and hardware design and can do the hardware side, replicating the AMP_READ circuitry a few times and mapping those to ADC6 and ADC7, but would appreciate some assistance in the coding side, again assuming possible.
Incidentally, Chuck has an interesting topic regarding measuring voltage for a more precise energy metering. https://openev.freshdesk.com/support/discussions/topics/6000053591
As Chuck suggested: please consider having headers on the board for unused pins on the atmega so we can use those for modified firmware / extra measurements.