Imported from GitHub: valletw/esp-ev-switch · commit a9668be · license MIT

Description

ESP32 EVSE Controller

README

ESP Electric Vehicle charge controller

The purpose of this project is to control a EVSE (Electric Vehicle Supply Equipment), aka. "wall-box", to charge an electric vehicle. It will open/close the Proximity Pilot (PP), the Control Pilot (CP) and the AC coil for the main power. This project will not managed the EV protocol and be integrated only as a switch between the vehicle and the EVSE. The control will be done with Home Assistant by using ESPHome firmware.

Custom software could be written by using ESP-IDF SDK but it is not the purpose of this project.

Signals description

Proximity Pilot, also known as "Plug Present", is used to signal the connection / disconnection of the plug. It can be used to simulate a manual disconnection by opening the circuit as the "release" button.

Control Pilot is used to negotiate the charge and exchange information by the vehicle and the EVSE. In case of proximity pilot is not detected, the signal can be opened to trigger an error on the charge controller.

AC coil is used to open/close the main power relay. In case of power is still remaining after PP and CP are opened.

Disclaimer

The authors and contributors of this repository disclaim any and all responsibility for the misuse of the information, tools, or techniques described herein. Users are strictly advised to utilize this information in accordance with applicable laws and regulations and only on systems for which they have explicit authorization.

Neither the authors nor contributors shall be held liable for any damages, direct or indirect, resulting from the misuse or unauthorized application of the knowledge contained herein.

These device is powered from 230V line. Every flash and debug steps shall be take with extreme caution with main power supply disconnected or by using an isolator on the USB connector !

Hardware

Wago connector is used for easy plug with the different wall-box wires:

• L: Line (230V)
• N: Neutral
• RELAY I/O: EVSE main power supply coil control Input/Output
• CP I/O: EVSE Control Pilot Input/Output
• PP I/O: EVSE Proximity Pilot Input/Output

3.5mm jack is available for current transformer measure. It's compatible with the sensor SCT-013-050. Different current limit could be selected depending of the maximum voltage of your wall-box: for a 7kW charge, select at least a probe for 50 A.

Three status LED are available:

• PWR: 3.3V state
• STAT: System status controlled by software
• CHG: Charge indicator (all circuits are open/close)

Two buttons are available for ESP32 boot sequence:

• BOOT: Control processor download mode on boot
• EN: Control processor reset

For advanced debug, a 2x5 1.27 pins header connectors is available with the Cortex-M JTAG/SWD pinout for external probe.

Wiring

The board will be placed between the EVSE and the EV plug. It will open/close the different signals to control the main power relay, the control signal and the proximity signal.

Note: This wiring could be adapted for tri-phase system and should be able to control the EVSE. The power measure can only be done on one phase.

You can see my setup on a QUBEV wallbox. The clamp take some space and I had to put it on the input instead of the relay output because of the EV plug when I closed the enclosure.

Also, the jack for the clamp broke when I installed the board, I was not careful enough. As it's not through hole connector, it break easily. I added glue and a wire as quick fix.

Setup	Home Assistant

Note: I limited my wallbox at 20A with an hardware switch inside.

Components choice

This project is based on an ESP32-C3 module to simplify design and ensure good WiFi performance (with external antenna connector). ESP32 has been selected for the big community to generate software and the frameworks available. Espressif hardware design rules has been take into account following there documentation

For easy debug and flashing, ESP32 with USB-CDC and JTAG support has been selected.

The 5V power rail is generated from a Mean Well AC-DC power supply. It has been selected for the "ready to use" and the security / certification. The 5V is used to power the relays. The 3.3V power rail is generated from a LDO using the 5V power rail. It's used for the controller part: ESP32, measure and signals.

By default, the 5V from the USB connector is not connected. For debug, it can be forced with a jumper to solder on the PCB. In this case, do not connect / solder both 5V USB & 5V AC-DC.

All others components has been selected from JLCPCB catalogue to minimize the cost and the assembly fees.

Manufacturing

The board is manufactured by JLCPCB, here is the details you will require to generate an order.

Note: JLCPCB requests some modifications on output files, do not use direct export from KiCad (check the FAQ)

PCB

Files: Gerbers

Configuration	Value
Base Materiel	FR-4
Layers	4
Dimensions	99.92 x 58.42 mm
Different design	1
Delivery format	Single PCB
PCB thickness	1.6
PCB color	Green (other colors have fees)
Silkscreen	White
Materiel type	FR4-Standard TG 135-140
Surface finish	HASL
Specify layer sequence	F_Cu / In1_Cu / In2_Cu / B_Cu
Impedance control	Yes
Layer stack-up	JLC04161H-7628
Via covering	Tented
Min via hole size/diameter	0.3mm/0.45mm
Remove order number	Specify a location

Note: All options have not been detail here, keep default value.

Assembly

Files: BOM, CPL

Configuration	Value
PCBA type	Economic
Assembly side	Top

Verify "pick & place" orientations and positions on the web viewer

Note: All options have not been detail here, keep default value.

Calibration

For power consumption measurement, a BL0942 chip is used and connected to the current transformer probe. Default values are set for the voltage, current, power and energy reference. The BL0942 is calibration free and default value could work. If better accuracy is required, the default value can be changed by following a calibration process:

1. Voltage reference can be adapted by measuring the input voltage with a multimeter,
2. Current can be adapted by using a well known load: example 10 A,
3. When your voltage/current are correctly calibrated, the power can be computed with P = U * I

Voltage reference

The voltage RMS is measured from VP/GND pins connected through a voltage transformer for galvanic isolation. The primary side uses a resistive divider 235 kOhms (5 * 47k) to limit the current through the transformer primary. On the secondary side, a 56 Ohms resistor sets the output voltage, followed by a 1 kOhms series resistor on the VP pin for protection.

The transformer is designed as a current source: the primary voltage drives a current through R_in, which is then converted back to a voltage across R_out on the secondary:

U_{out} = \frac{U_{in}}{R_{in}} \times R_{out}

U_{out} = \frac{230}{235000} \times 56 = 54.8 mV

The BL0942 VP input full-scale is 70 mV RMS / 100 mV peak-to-peak. The operating points relative to full-scale are:

Input voltage	VP voltage	% of full-scale
230 V	54.8 mV	78 %
260 V	61.9 mV	88 %

From the datasheet, the internal register value is computed with the following formula:

V_{RMS} = \frac{73989 \times V(mV)}{V_{ref}}

V_{ref} = 1.218 V

With the previous values (expected VP voltage and chip reference voltage) we can estimate the voltage reference for the ESPHome configuration:

Reference = \frac{V_{RMS}}{V_{in}}

Reference = \frac{\frac{73989 \times 54.8}{1.218}}{230} = 14477

After test on the received board, the measured voltage reference is 14400, consistent with the theoretical value (< 0.5 % deviation). This value will be used as a base to improve accuracy by adjusting it while measuring the input voltage with a calibrated True RMS multimeter.

Current reference

The current RMS is measured from IP/IN pins connected to a SCT-013-050 current transformer clamp through a signal conditioning circuit.

SCT-013-050 model

The SCT-013-050 is a voltage output clamp with a built-in burden resistor Rb. It is designed as a current source with the following characteristics:

Parameter	Value
Rated input	50 A RMS
Rated output	1 V RMS
Internal burden	Rb = ~37 Ohms
Turns ratio	N = 50 / (1V / 37 Ohms) = 1850
Sensitivity	20 mV/A RMS

The secondary current for a given primary current is:

I_s = \frac{I_{in}}{N} = \frac{I_{in}}{1850}

Signal conditioning circuit

The IP/IN pins are connected as follows:

• 1 Ohms (R201) in parallel with CT_K/CT_L (external burden)
• 1 kOhms in series on each line (pin protection)

R201 forms a parallel combination with Rb, reducing the effective burden:

R_{burden} = \frac{Rb \times R201}{Rb + R201} = \frac{37 \times 1}{37 + 1} = 0.974 Ω

The differential voltage on IP/IN for a given primary current is:

U_{out} = \frac{I_{in}}{N} \times R_{burden} = \frac{I_{in}}{1850} \times 0.974

The BL0942 IP/IN full-scale is 30 mV RMS / 42 mV peak-to-peak. The operating points relative to full-scale are:

Primary current	IP/IN voltage	% of full-scale
50 A	26 mV	90 %
32 A	17 mV	57 %
16 A	8 mV	27 %
2 A	1 mV	3 %

Current reference calculation

From the datasheet, the internal register value is computed with the following formula:

I_{RMS} = \frac{305978 \times U_{out}(mV)}{V_{ref}}

V_{ref} = 1.218 V

With the previous values we can estimated the current reference for the ESPHome configuration:

Reference = \frac{I_{RMS}}{I_{in}} = \frac{305978 \times R_{burden}}{V_{ref} \times N}

Reference = \frac{305978 \times 974}{1.218 \times 1850} = 132260

After test on the received board, the measured current reference is 119500, representing a ~10 % deviation from the theoretical value, consistent with the combined tolerances of Rb (10 %), R201 (1 %), and the BL0942 internal reference. This value will be used as a base to improve accuracy by adjusting it while measuring the input current with a calibrated True RMS clamp meter.

ESP32 Pinout

For those who want to reuse this project, here is the ESP32 pinout to manage the different input/output.

Name	Pin	Direction
Relay ON	IO0	Output
Control Pilot ON	IO1	Output
Charge LED	IO2	Output (strapping pin)
Proximity Pilot ON	IO3	Output
System Status LED	IO8	Output (strapping pin)
BL0942 CF1	IO10	Input
BL0942 Tx	RX	Input
BL0942 Rx	TX	Output

ESPHome configuration

Device must be setup via USB connection the first time to flash the customized firmware with sensors/buttons configuration.

Once it has been configured successfully, you should fix the device IP on your router for easier Home Assistant configuration.

Note: Installation can be bypassed if already done or you can use docker image. Check ESPHome documentation for more details.

Installation

pip install esphome
# Ensure your user session has the correct permission for serial port.
sudo usermod -a -G dialout <USERNAME>

Customize

Depending of your installation and network, a secrets.yaml file must be create with your specific configuration.

# secrets.yaml
wifi_ssid: MySSID
wifi_password: MyStrongPassphrase
wifi_fb_ssid: ATX Controller Fallback Hotspot
wifi_fb_password: StrongPassphrase
ota_password: MyOTAPassphrase
api_key: 32BytesBase64String

Compile and flash

# Generate the firmware.
esphome compile esphome.yaml
# Flash the firmware to the ESP.
esphome run esphome.yaml
# Get logs.
esphome logs esphome.yaml