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DETAILED DESCRIPTION
A prototype IEC61851 / J1772 EVSE (Electric Vehicle Supply Equipment) Interface intended to connect to a 3.3V microcontroller of your choice.
Many open source designs already exist for EVSE:
Some have been through multiple revisions and make a great starting point to learn from their findings.
Wikipedia provides a good introduction into J1772.
Connector
|
Name |
Type |
Description |
|
5V |
Power |
5V Power Supply |
|
3V3 |
Power |
3.3V Power Supply |
|
PWM |
Digital Input |
1kHz Control Pilot signal. Duty cycle specifies available charging current. |
|
CP |
Analog Output |
Control Pilot Feedback. Used to determine vehicle state. |
|
PP |
Analog Output |
Proximity Pilot: Not used when implemented with tethered cable. Reports maximum current carrying capability of detached cables. |
|
SWCAN_EN |
Digital Input |
High enables Single Wire CAN Mode. Pulled low by 10k. |
|
SWCAN_RX |
Digital Output |
Receive output from SWCAN Transceiver. |
|
SWCAN_TX |
Digital Input |
Transmit input to SWCAN Transceiver. |
PWM
PWM input is a 3.3V digital input. Use an external MCU/source to generate a 1kHz ± 0.5% square wave used to advertise the available charging current as per table below:
|
Available Charging Current |
Duty Cycle provided by EVSE (± 1%) |
|
Use Digital Comms |
5 % e.g. IEEE 1901 Power Line or Tesla SWCAN |
|
6 A to 51A |
10 % to 85 % % Duty Cycle = Current (A) / 0.6 |
|
51A to 80A |
85% to 96% % Duty Cycle = (Current (A) / 2.5) + 64 |
Op-amp U3A (LM7332) will convert this to a ± 12V signal and drive the CP line via a 1K series resistor. The LM7332 is a rail to rail op-amp with high output drive and has been used by SmartEVSE.
The ±12V is generated by a 1 watt Meanwell Unregulated DC-DC Converter (DPU01L-12) operating from a 5V input. According to the datasheet the output should have an absolute accuracy of ± 3%, but load regulation may be poor. The standard calls for ±5V. It has been noted some open source EVSE designs have shifted from these DC-DC brick converters to a positive 5V to 12V DC-DC switcher and separate charge pump (e.g TC1044) to generate the negative rail from the positive.
CP (Control Pilot)
The vehicle will communicate back the status by loading the CP line. This is an analog output used to read the various charging states:
|
Charging Status |
Voltage at EV Socket |
CP Output |
|
Standby |
+12V |
3.28V |
|
Vehicle Detected |
+9±1V |
2.89V |
|
Ready (Charging) |
+6±1V |
2.5V |
|
No Power (off) |
0V |
1.72V |
|
Error |
-12V |
0.16V |
With a spare ½ op-amp left, U3B provides voltage buffering of the CP. R12/R13/R14 is designed to linearly convert ± 12V to 0 to 3.3V suitable for feeding into an ADC.
PP (Proximity Pilot)
The PP analog output is used to determine the maximum current carrying capability of detachable cables.
Detachable cables will have a resistor fitted between PP and PE to advertise the maximum current. This resistor acts as a simple voltage divider with R10.
|
Resistor fitted to charging cable |
Amps (Cable) |
PP Output |
|
1500 |
13 |
1.98 |
|
680 |
20 |
1.34 |
|
220 |
32 |
0.60 |
|
100 |
63 |
0.30 |
|
50 |
80 |
0.16 |
SWCAN
Single Wire CAN is an optional interface used with Tesla vehicles. Tesla vehicles can communicate using SWCAN over the CP wire.
To enable this mode, set SWCAN_EN high. This will enable a relay and switch the CP wire to the SWCAN transceiver.
SWCAN_RX and SWCAN_TX is the output from the transceiver and should be wired to a CAN Controller.
Source Code
Open Source Firmware can be found the following GitHub Repository:
Design files
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