This device acts as the vehicle when connected to an EVSE (Electric Vehicle Supply Equipment) and negotiates the supply of power.
It can be used in EV (Electric Vehicle) conversions, or in applications where you want to obtain power from public charging infrastructure – i.e., battery trailers to replace dirty and noisy generators, electric watercraft etc.
Both hardware and software is provided as open source. The provided firmware will allow the EVCC to successfully request power and obtain the maximum obtainable current. Boiler plate code is available for the CAN interface and some firmware development would be expected to interface it to your charger or battery management system.
- Designed to be compatible with IEC61851 Electric Vehicle conductive charging systems and the former SAE J1772 Electric Vehicle Conductive Charge Coupler specification.
- Communication is via Control Pilot (CP) / Proximity (PP).
- Supports locking solenoid (Tested with Duosida DSIEC-EL).
- Based on Microchip dsPIC33EP128GS804 MCU.
- 2x CAN2.0B ports to talk to ECUs (Engine Control Units) such as BMS (Battery Management Systems)/Chargers.
- Includes support for SWCAN used by Tesla destination chargers (work in progress).
- Operates from a wide 6.5 to 40V supply (note: input supply also feeds solenoid via H-Bridge). Recommended supply is 12/24V depending on locking solenoid.
Hardware – Theory of operation
Readers should be familiar with IEC61851 / J1772 signalling. If not, please refer to Wikipedia.
J1 is to be connected to the EVSE via a standard connector, be that a J1772 Type 1 or IEC61851 Type 2.
The EVSE will generate a 1kHz +/-12V signal on the Control Pilot (CP) to indicate availability of power and the maximum current we can pull. The D3 TVS diode provides some protection to our front-end circuit, clamping any stray input voltages to approximately 16V.
Small signal diode D2, Resistor R5 & R7 make up the typical vehicle side interface as per the standard. A load of 2.74k (R7) indicates the vehicle is connected and when the 1.3k resistor is switched in parallel, we are ready for charging (i.e. we request power to be connected).
D2 rectifies the signal, so only the positive going pulse is loaded/attenuated. This provides the EVSE some confidence it is a real car loading the CP and not the connector dropped in a puddle of water.
Finally, we can obtain the maximum current we can draw from the duty cycle of the 1kHz signal. We connect this to a comparator operated from 3.3V to elegantly reduce the voltage and not over-stress the MCU’s I/O pin. The TL331 allows maximum input voltage of 38V irrespective of the supply voltage.
Tesla SWCAN Support
This board also includes experimental support for Tesla SWCAN (Single Wire Controller Area Network) communication. This is optional and does not need to be populated.
Tesla have used SWCAN over the control pilot to digitally communicate between the EVSE and the EV. Some Tesla Destination Chargers only talk ‘Tesla’ mode and this can broaden compatibility to include these chargers.
The circuit is based on the investigative work of Damien Maguire. See this thread on the open inverter forum for more information.
It is based on a NCV7356 Single Wire CAN Transceiver and is switched in and out of circuit via a relay (K1). Pin 10 is connected directly to the CP line before the diode to enable unimpeded communication.
Provision has been included to operate a locking solenoid. Once charging has been enabled, the charge port normally locks preventing the removal of the cable. This prevents the cable being removed while current is flowing, and can also prevent theft of un-tethered cables.
Locking solenoids come in various configurations, but generally consist of a solenoid that inserts and removes a locking pin. When energised for a brief period (< 200mS) the device will lock. Reverse the polarity, energise again, and the device will unlock.
The DRV8871 50V, 3.6A H-bridge motor driver has been selected to control the solenoid. The maximum current is set via R24 connected to the ILIM pin. The part has an exposed thermal pad, however as the device is only active for a very short period, thermal issues are not expected.
The state of the lock can be determined by a digital pin, if the locking switch is wired in to J8.
Dual CAN2.0 Interface
Two external TCAN332 CAN transceivers are included on-board to provide the physical CAN interfaces. As the dsPIC only includes two CAN2.0B controllers, both interfaces are only available provided one controller is not dedicated to the Tesla SWCAN Interface.
120 ohm termination resistors (R20/R21) can be populated if the device is located at the end of a CAN bus.
This design is based on a Microchip dsPIC dsPIC33EP128GS804-I/PT micro-controller. It was primarily selected, as it contained two CAN2.0B interfaces.
The internal 5V power supply is based on a LMR16006 4V to 60V, 600mA Switching Buck Regulator. This provides a wide input range, although the power input to the board is also fed into the H-Bridge motor controller used for the locking solenoid. Hence, the input voltage should be selected with your locking solenoid in mind.
The 3.3V rail is derived from the 5V rail using a TLV75533 500mA LDO linear regulator.
Design files can be downloaded from the Circuit Maker website. Circuit Maker is a free EDA tool from Altium.
- CircuitMaker Project Page
- EVCC Interface version 1.A.2 Gerbers – PCB (Zip)
- EVCC Interface version 1.A.2 Schematics (PDF)
- EVCC Interface version 1.A.2 Bill of Materials (XLSX)
Open Source Firmware can be found the following GitHub Repository:
An UART console is available on RB12 (Connector J6 pin 7) to monitor and debug charging sessions. Each message is time stamped to the 10th of a millisecond.
For example, this is the example output from a connection to a Tesla charger :
dsPIC33EP128GS804 IEC61851/SAE J1772 Demo Code 00000.14 PP: 3.30V (ADC_4095) Port unplugged 00002.57 PP: 1.90V (ADC_2363) 32A detachable cable detected 00002.80 CP: No signal present 00002.92 CP: Duty cycle = 4.8% @ 1000.1Hz 00002.95 Requesting digital communication 00005.98 CP: No signal present 00008.90 CP: Duty cycle = 13.1% @ 1000.1Hz 00008.93 Locking Charge Port 00009.14 Maximum Charge Rate 7.86A 00009.26 CP: Duty cycle = 13.1% @ 1000.8Hz 00009.29 Locking Charge Port 00009.51 Maximum Charge Rate 7.80A 00052.89 CP: No signal present 00053.61 PP: 3.30V (ADC_4095) Port unplugged
Tesla SWCAN Mode (Experimental)
Tesla SWCAN communication is a proprietary and unpublished protocol. Experimental support exists for Tesla SWCAN digital mode. This can be enabled by defining ENABLE_SWCAN:
When enabled, this is what a typical charging session can look like:
dsPIC33EP128GS804 IEC61851/SAE J1772 Demo Code 00000.14 PP: 3.30V (ADC_4095) Port unplugged 00005.11 PP: 1.90V (ADC_2361) 32A detachable cable detected 00005.30 CP: No signal present 00005.43 CP: Duty cycle = 4.8% @ 1000.1Hz 00005.46 Requesting digital communication 00005.58 Enabling SWCAN Interface 00005.60 0x505  0B 86 00 00 00 00 7D 08 00005.62 0x32C  00 01 BF DC C0 C0 1C 05 00005.62 0x47C  00 00 00 00 00 00 00 00 00005.62 0x505  1F EC 7F B8 08 42 08 00 00005.65 0x31C  10 05 F6 78 FE FF 07 00 00005.65 0x505  00 03 CB 2D 2D 09 04 00 00005.72 0x31C  10 05 F7 78 FE FF 07 00 00005.72 0x505  0B 86 00 00 00 00 7D 08 00005.79 0x31C  10 05 F6 78 FE FF 07 00 00005.79 0x505  1F EC 7F B8 08 42 08 00 00005.86 0x31C  10 05 F7 78 FE FF 07 00 00005.86 0x505  20 A4 11 F7 6C 04 00 00 00005.93 0x31C  10 05 F7 78 FE FF 07 00 00005.93 0x505  00 03 CB 2D 2D 09 04 00 00006.00 0x31C  10 05 F7 78 FE FF 07 00 00006.00 0x47C  00 00 00 00 00 00 00 00 00006.00 0x505  0B 86 00 00 00 00 7D 08 00006.05 0x32C  00 01 BF DC C0 C0 1C 05 00006.05 0x505  1F EC 7F B8 08 42 08 00 00006.10 0x31C  10 05 F7 78 FE FF 07 00 00006.10 0x505  20 A4 11 F7 6C 04 00 00 00006.17 0x31C  10 05 F6 78 FE FF 07 00 00006.17 0x505  00 03 CB 2D 2D 09 04 00 00008.13 PP: 3.30V (ADC_4095) Port unplugged