OpenEVSE EV Charging Station

OpenEVSE is a fully open-source EVSE (Electric Vehicle Supply Equipment) charging station designed by OpenEV.

An EVSE charging station is a device an electric car (EV) is plugged into to charge. It communicates with the car to agree on the fastest and safest charging rate that both the car and the power supply can support.

Nissan LEAF OpenEVSE


OpenEnergyMonitor have been collaborating with OpenEV to improve energy monitoring integration and control as well as tailoring the setup for use in Europe and the UK. This page provides Europe / UK specific setup instructions and considerations.

See our blog post detailing a full OpenEVSE build review, and usage.

View in Shop →

OpenEVSE units have been designed to exceed the safety requirements for EV Charging Stations from SAE J1772, NEC, UL and CE. Before supplying power to the car (and continuously while charging) the EVSE unit conducts a number of checks, no power is supplied until all the checks have passed. See

Mains wiring should only be undertaken by a qualified electrician.

- OpenEVSE Hardware User Guide (.pdf)

The standard build guide from OpenEVSE can be followed taking into account the specific OpenEnergyMonitor (Europe / UK) considerations (see below):

  • OpenEVSE P50D Assembly guide: Web, pdf
Kit contents.
An assembled OpenEVSE unit. LCD, push button and WiFi module are attached to the EVSE enclosure cover, not shown.

Specific considerations for OpenEVSE units obtained via the OpenEnergyMonitor Shop to be installed in Europe / UK.

1. EV Connector Cable Wiring

The EV cables from the OpenEnergyMonitor shop (Type 1 & Type 2) are wired as follows:


All connections in EVSE should be made using bootlace ferrules crimped terminals. This is especially essential for EV cables since they use fine stranded wire for increased flexibility. This fine stranded wire is susceptible to creeping out of a terminal due to thermal cycling resulting in possible overheating. See this Schneider Electric Data Bulletin.

EVSE cables obtained from the OpenEnergyMonitor shop will be pre-equipped with bootlace ferrules crimped terminals connections.


2. EVSE Mains Wiring

Mains wiring should only be undertaken by a qualified electrician.

In the UK / Europe an EVSE must be directly wired into a consumer unit using appropriately sized wiring and an RCD circuit breaker e.g. RCBO. The wiring and circuit breaker should be sized for maximum rating of the EV/EVSE and tethered cable, 6mm CSA wire is appropriate for 32A.

The max current of the EVSE should be set to match the continuous current rating of mains wiring in the OpenEVSE settings (via LCD menu) on first power up before connecting an EV (Setup > Max Current >).

In the USA / Canada you may see photos of the EVSE plugged into a wall-outlet, this is a NEMA 14-30 plug commonly used for electric clothes dryers, etc. These plugs don’t exist in the UK. The UK uses BS1363 3-pin plugs rated to 13A max (10A continuous).

Do not wire an EVSE into a 3-pin BS1363 plug unless the charging current is limited to 10A. This defeats the point of using an EVSE; better to use a portable EVSE ‘granny cable’ instead.

In mainland Europe Schuko plugs are rated to 16A max (13A continuous).

3. Charging Level

The OpenEVSE unit should be set to Level 2 charging mode. The charging mode can be set via the LCD menu:

Setup > Charging Mode > L2

Level 2 charging refers to charging from 220v-240v, as opposed to level 1 charging from 110v.

See User Guide video at the top of this page for a overview of how to operate the unit.

4. GFCI Test Enabled

All OpenEVSE’s from OpenEnergyMonitor contain hardware for GFCI (ground fault interruption) continuous monitoring of ground faults. See safely features section above. GFCI test should always be enabled in the LCD menu.

The WiFi gateway allows all functions of the OpenEVSE to be controlled remotely and data logged to Emoncms. The WiFi gateway is optional but highly recommend.



  • Follow the OpenEVSE WiFi setup guide to connect up the ESP8266 WiFi module.

  • Once powered up connect to WiFi network with SSID OpenEVSE_xxxx with password openevse using a computer or mobile device.

  • You should get directed to a captive portal where you choose to join a local network. If captive portal does not work, browse to

  • Setup Emoncms / MQTT settings

  • OpenEVSE control: the OpenEVSE can be controlled remotely via web interface or via MQTT, HTTP or direct serial using RAPI API.

See full OpenEVSE WiFi gateway documentation in the OpenEVSE ESP8266 WiFi GitHub Repo.

The OpenEVSE WifI gateway includes a solar PV diversion feature. This feature allows the OpenEVSE to adjust the charge rate based on the amount of available solar PV production or excess power.

OpenEVSE solar PV diversion example. Yellow: solar PV, blue: OpenEVSE.

The graph above is explained as follows:

  • OpenEVSE is initially sleeping with an EV connected
  • Once solar PV generation (yellow) reaches 6A (1.5kW @ 240V) the OpenEVSE initiates charging
  • Charging current is dynamically adjusted based on available solar PV generation
  • Once charging has begun, even if generation drops below 6A, the EV will continue to charge*

*The decision was made not to pause charging if generation current drops below 6A since repeatedly starting / stopping a charge causes excess wear to the OpenEVSE relay contactor.

If a Grid +I/-E (positive import / negative export) feed was used (instead of solar PV generation feed) the OpenEVSE would adjust its charging rate based on excess power that would be exported to the grid; for example, if solar PV was producing 4kW and 1kW was being used on-site, the OpenEVSE would charge at 3kW and the amount exported to the grid would be 0kW. If on-site consumption increases to 2kW the OpenEVSE would reduce its charging rate to 2kW.

An OpenEnergyMonitor solar PV energy monitor with an AC-AC voltage sensor adaptor is required to monitor direction of current flow.

Solar PV Divert Setup

  • To use ‘Eco’ charging mode MQTT must be enabled and ‘Solar PV divert’ MQTT topics must be entered.
  • Integration with an OpenEnergyMonitor emonPi is straightforward:
    • Connect to emonPi MQTT server, emonPi MQTT credentials should be pre-populated
    • Enter solar PV generation / Grid (+I/-E) MQTT topic e.g. if solar PV is being monitored by emonPi CT channel 1 enter emon/emonpi/power1
    • MQTT lens Chrome extension can be used to view MQTT data e.g. subscribe to emon/# for all OpenEnergyMonitor MQTT data. To lean more about MQTT see MQTT section of OpenEnergyMonitor user guide
    • If using Grid +I/-E (positive import / negative export) MQTT feed ensure the notation positive import / negative export is correct, CT sensor can be physically reversed on the cable to invert the reading.

Solar PV Divert Operation


To enable ‘Eco’ mode (solar PV divert) charging:

  • Connect EV and ensure EV’s internal charging timer is switched off
  • Pause charge; OpenEVSE should display ‘sleeping’
  • Enable ‘Eco’ mode using web interface or via MQTT
  • EV will not begin charging when generation / excess current reaches 6A (1.4kW @ 240V)

  • During ‘Eco’ charging changes to charging current are temporary (not saved to EEPROM)
  • After an ‘Eco mode’ charge the OpenEVSE will revert to ‘Normal’ when EV is disconnected and previous ‘Normal’ charging current will be reinstated.
  • Current is adjusted in 1A increments between 6A* (1.5kW @ 240V) > max charging current (as set in OpenEVSE setup)
  • 6A is the lowest supported charging current that SAE J1772 EV charging protocol supports
  • The OpenEVSE does not adjust the current itself but rather request that the EV adjusts its charging current by varying the duty cycle of the pilot signal, see theory of operation and Basics of SAE J1772.
  • Charging mode can be viewed and set via MQTT: {base-topic}/divertmode/set (1 = normal, 2 = eco).

* OpenEVSE controller firmware V4.8.0 has a bug which restricts the lowest charging current to 10A. The J1772 protocol can go down to 6A. This will has be fixed with a firmware update. See OpenEnergyMonitor OpenEVSE FW releases. A ISP programmer is required to update openevse controler FW.

See full OpenEVSE WiFi gateway documentation in the OpenEVSE ESP8266 WiFi GitHub Repo.