How do the GX and EVCS decide how much power to use for EV charging?
When controlled as an Opportunity Load, the EVCS is using about 500W more power than is available from solar, even when the charging current could be reduced down to the 6A minimum.
I’ve just installed an EVCS, because of the ability to charge from available solar.
I have a Cerbo GX (firmware v3.8)1, Multiplus and Smart Shunt, which charge the battery from solar during the day, and powers my data cabinet (Essential Loads) overnight on battery (Multiplus changed to Inverter mode 2 overnight). The control logic is implemented in Node-RED, and ramps DVCC up and down to charge the battery from available solar, avoiding grid input except for when there are several cloudy days in a row. This works well.
To this I’ve added the EVCS (firmware v2.09) and I’ve enabled Opportunity Loads on the GX, so the EV will charge when there is surplus solar.
A Shelly EM (Energy Meter) is used to measure house loads and solar export, feeding via MQTT into the GX MQTT broker, and these feed into Node-RED Virtual Devices for a Grid meter and PV inverter. These show up in GX almost as expected (Solar is shown on the AC input side, while house loads and EVCS are shown on the Multiplus AC output side. Multiplus output loads are now called Essential Loads.
During daytime (Multiplus On) VRM shows them in the correct location (PV Inverter, EVCS and AC Loads on AC input)
During nighttime (Multiplus Inverting), VRM messes them up (PV Inverter and AC Loads on AC output, Essential Loads combined with AC Loads).
The shifting location on the diagrams does confuse things.
What isn’t clear is the logic the GX uses to control the EVCS current.
I can see it ramps up and down with PV, but the EVCS is charging with about 500W more than the solar yield (partly importing from the grid), even though it could have reduced current from 10A down to the minimum 6A. Maximum charge current is set at 16A. I’m expectig the green line (EVCS power) to stay below the yellow line (Solar) at all times.
Is the EVCS current based on the Grid meter, trying to minimise grid import?
Is it based on Solar Yield? If so, it would be good to set an offset to leave room for other house loads.
Gotchas I’ve found:
GX and VRM diagrams do not display the location of PV inverter, AC loads and EVCS in the correct location.
GX notification “System incompatible for Opportunity Loads” when the Multiplus is in Inverter mode. My code now disables “Opportunity Loads” mode when the Multiplus is in Inverter mode, to avoid this notification. Not sure if this is needed.
EVCS was flapping between Internal and External (OL) auto modes, every 30-60s. This was resolved by rebooting the Cerbo GX. While this was occurring, the GX Opportunity Loads was showing the EVCS as “No control”
EVCS needed to be set to UTC+offset rather than the regional zone, because scheduled charging occurs at off-peak times that do not change with daylight savings time.