I have an EV Charger NS which is being controlled by modbus from Home Assistant. That’s all working fine, but I want a failsafe so that if HA goes down, or the WiFi drops out, the charger will stop or at least fall back to minimum current.
The EV Charger NS manual shows wiring for an external switch that when closed will limit the charge rate to 6A. This is mentioned as being required in Germany, but for my application I want to use that to implement the above failsafe. I have an ESP32 mounted inside the charger that drives the input low (from 3.3V as per the manual) if it detects that communication between the charger and HA has been lost.
The only problem is it has no effect; the charger is supposed to flag a W-108 error and limit current to 6A, but neither happens.
I’ve updated the firmware to 2.08 (the latest.) The manual does mention the external input is relevant to Germany, but since there is no region setting in the charger other than the timezone, unless there is a special firmware version for Germany this should not stop it working. I have tried setting the timezone to Berlin with no change.
There is a modbus register 5129 that is described as “External limit for charging current. 0 - no limits. 1 - charging current limited to 6A” but setting that to 0 or 1 has no obvious effect. There is another register 5099 which is a grid lock, and writing 1 to that does disable the charger, but that’s no help since if there is no modbus communication I can’t write to it.
Ok, that works. Now either using the external input or writing 1 to register 5129 imposes the 6A limit (and associated warning, but only while charging, unlike the grid lock in register 5099.)
Thanks for the help.
For the benefit of anyone else needing this:
the initial setup asks for country and timezone, but evidently stores the country in two places - subsequently the Settings/General/Others page will show (but not allow editing) the country selection which apparently affects the available features, while the time page allows selection of a different country and timezone.
I’m using Home Assistant to control the charger, starting/stopping and setting the charge current based on various constraints relating to available grid capacity, solar power and other local loads and circuit limitations. All the modbus registers being used are shown in the list as user-modifiable without invalidating support.
Within HA there is a sensor that increments a value every 2s if data has been successfully read from the charger modbus; this sensor is monitored by an ESPHome device inside the charger and if it stops getting updates, after a 15s timeout, it pulls the external signal low to limit the charger to 6A.
This ensures that any loss of communication between the charger and HA places the charger into a low-current state, protecting the grid supply and local circuits. I would have liked a wired modbus connection, but this does protect against WiFi dropouts and other failure paths so I’m happy.
