Introduction
Build a Level 2 AC EV charging station with SAE J1772 pilot signal, RFID auth, and cloud management. This comprehensive guide covers everything from design through implementation, testing, and deployment.
Electric Vehicle Charging Station
Build a Level 2 AC EV charging station with SAE J1772 pilot signal, RFID auth, and cloud management.
DifficultyAdvanced
Duration5–8 weeks
Components10 items
Steps8 steps
Theory & Background
Level 2 AC charging (SAE J1772 / IEC 61851) uses a pilot signal — a 1kHz PWM square wave on the Control Pilot (CP) wire — to communicate between EVSE (charger) and EV. The duty cycle encodes the available current: 16% duty = 10A, 25% duty = 16A, 51.3% duty = 32A. The EV responds by pulling the CP line to different voltage levels: 9V (ready to connect), 6V (ready to charge), 3V (charging with ventilation needed).
Advertisement
Components & Requirements
10 components required for this project.
| # | Component | Purpose | Qty |
|---|---|---|---|
| 1 | 32A 7kW Single-Phase EVSE Controller Board | Core charging control logic | x1 |
| 2 | MFRC522 RFID Reader | User authentication | x1 |
| 3 | Raspberry Pi 4 | OCPP gateway and management | x1 |
| 4 | INA3221 Triple Current Sensor | Energy metering per session | x1 |
| 5 | 32A 250V Earth Leakage Contactor | Main power switching | x1 |
| 6 | Type 2 EV Socket (IEC 62196) | Vehicle connector | x1 |
| 7 | 6mm² 5-Core Flex Cable | Power delivery to socket | x5m |
| 8 | 32A RCD/GFCI Protection | Earth fault protection (mandatory) | x1 |
| 9 | 7" Touchscreen LCD | User interface and session info | x1 |
| 10 | 4G LTE Module (SIM7600) | Cloud connectivity for OCPP | x1 |
Step-by-Step Implementation
Follow these 8 steps carefully.
1
Understanding EV Charging Standards
Level 2 AC charging (SAE J1772 / IEC 61851) uses a pilot signal — a 1kHz PWM square wave on the Control Pilot (CP) wire — to communicate between EVSE (charger) and EV. The duty cycle encodes the available current: 16% duty = 10A, 25% duty = 16A, 51.3% duty = 32A. The EV responds by pulling the CP line to different voltage levels: 9V (ready to connect), 6V (ready to charge), 3V (charging with ventilation needed).
2
Pilot Signal Generation
Generate the 1kHz PWM pilot signal using Arduino/ESP32 with a ±12V level shifter (CP must swing ±12V). Set duty cycle based on your circuit breaker rating. Monitor CP line voltage with a precision voltage divider to detect EV connection state machine transitions. State A: 12V (no vehicle), State B: 9V (vehicle connected), State C: 6V (charging), State D: 3V (needs ventilation), State E: 0V (fault).
3
RFID Authentication System
Connect MFRC522 RFID reader via SPI. Store authorized RFID card UIDs in a local whitelist on Raspberry Pi. On card tap, check against whitelist and remote OCPP backend. Display session start on touchscreen with user name and allowed charging limit. Log all authentication events with timestamp. Support multiple user cards with individual kWh allowances for managed fleet charging.
4
OCPP 1.6 Implementation
Install OCPP-J (JSON over WebSocket) client on Raspberry Pi using the ocpp Python library. Connect to a central management system (CMS) like SteVe or ChargePoint cloud. Implement mandatory OCPP messages: BootNotification, Heartbeat, Authorize, StartTransaction, MeterValues, StopTransaction, StatusNotification. This enables remote start/stop, remote firmware updates, and central billing.
5
Energy Metering and Billing
Read INA3221 for real-time power measurement every second. Accumulate kWh per session: energy += (power_W × 1s) / 3600000. Record session data: start time, end time, user ID, kWh delivered, peak power. Calculate session cost at configured rate (e.g., ₹8/kWh). Generate session receipt on touchscreen. Send session summary via OCPP StopTransaction message to CMS for centralized billing.
6
Safety Systems Integration
The RCD/GFCI must trip within 30ms for ground faults > 30mA (IEC 62955 requirement). Test RCD monthly using the test button. Implement software monitoring of CP line for fault states. Add overcurrent detection — if current exceeds 110% of set point for >5 seconds, open the contactor. Monitor cable temperature with NTC thermistor (max 90°C). All safety trips must be logged with cause and timestamp.
7
Touchscreen UI Development
Build the UI using PyQt5 or Tkinter on Raspberry Pi. Home screen: CATB logo, Tap card to start. During session: real-time kW, kWh delivered, session time, cost, animated charging bar. Completion screen: total kWh, total cost, carbon saved (kgCO₂ = kWh × 0.82 for India grid). Include admin mode (PIN protected) for setting tariff rates, viewing logs, and network configuration.
8
Load Management and Smart Charging
Implement dynamic load management: monitor house's main supply current via a clamp meter. When house approaches its supply limit, reduce EV charging current via pilot signal duty cycle. Schedule charging during off-peak hours (11 PM – 6 AM) when tariff is lower. Support solar surplus charging — when solar generation exceeds house load, automatically start/increase EV charging to use excess generation.
Code & Implementation
Core code for ocpp_client.py:
ocpp_client.py
Python
import asyncio import logging from datetime import datetime from ocpp.v16 import ChargePoint as cp from ocpp.v16 import call from ocpp.v16.enums import RegistrationStatus, Action, AuthorizationStatus import websockets logging.basicConfig(level=logging.INFO) class CATBChargePoint(cp): async def send_boot_notification(self): request = call.BootNotificationPayload( charge_point_model="CATB-EVSE-L2", charge_point_vendor="CATB.in" ) response = await self.call(request) if response.status == RegistrationStatus.accepted: logging.info(f"Registered. Heartbeat interval: {response.interval}s") asyncio.ensure_future(self.send_heartbeat(response.interval)) async def send_heartbeat(self, interval): while True: await asyncio.sleep(interval) await self.call(call.HeartbeatPayload()) async def authorize_card(self, id_tag): response = await self.call(call.AuthorizePayload(id_tag=id_tag)) return response.id_tag_info.status == AuthorizationStatus.accepted async def start_transaction(self, id_tag, connector_id=1): if not await self.authorize_card(id_tag): logging.warning("Card not authorized") return None response = await self.call(call.StartTransactionPayload( connector_id=connector_id, id_tag=id_tag, meter_start=0, timestamp=datetime.utcnow().isoformat() )) logging.info(f"Transaction {response.transaction_id} started") return response.transaction_id async def stop_transaction(self, tx_id, meter_wh): await self.call(call.StopTransactionPayload( transaction_id=tx_id, meter_stop=meter_wh, timestamp=datetime.utcnow().isoformat() )) async def main(): async with websockets.connect( "ws://cms.catb.in/ocpp/CATB-001", subprotocols=["ocpp1.6"] ) as ws: charger = CATBChargePoint("CATB-001", ws) await asyncio.gather( charger.start(), charger.send_boot_notification() ) asyncio.run(main())Testing & Troubleshooting
Test Electric Vehicle Charging Station by verifying each subsystem individually before full integration.
Troubleshooting Tips
Verify power voltages, check ground connections, use serial monitor for debug.
Real-World Applications
Residential home charging installation
Apartment complex shared charging
Office workplace charging for employees
Shopping mall visitor charging amenity
Fleet vehicle depot overnight charging
Hotel and hospitality charging services
Petrol station EV charging integration
Smart city EV infrastructure
Extensions & Next Steps
- Add solar integration for green charging with surplus PV power
- Implement vehicle-to-grid (V2G) bidirectional charging
- Add QR code payment via UPI for pay-per-use public stations
- Build a mobile app for remote session monitoring
- Integrate with home energy management system for smart scheduling
Interactive Playground
Coming SoonAn interactive simulator will be available here — simulate circuits and run code in-browser without hardware.
Frequently Asked Questions
What is the difference between Level 1, Level 2, and DC Fast Charging?
Level 1 (5V AC, 1.4–1.9kW) uses a regular household outlet and adds 6–12 km of range per hour — very slow. Level 2 (240V AC, 3.3–22kW) adds 25–80 km/hour and requires a dedicated EVSE installation. DC Fast Charging (50–350kW) bypasses the onboard charger to directly charge the battery bank, adding 100–300+ km in 20–30 minutes. This project implements Level 2 charging.
Do I need a permit to install an EV charging station at home?
In most regions, installing a Level 2 charging station (above 1.8kW / 16A) requires a licensed electrician, electrical permit, and utility notification. In India, follow IS 17017-1:2018 for EV supply equipment. The circuit requires a dedicated 32A/40A circuit breaker, proper earthing system (TN-S or TT), and a 30mA RCD (RCCB). Self-installation without qualification is dangerous and may void home insurance.
What is OCPP and why is it important for EV chargers?
OCPP (Open Charge Point Protocol) is an open industry standard enabling any EV charger to communicate with any central management system, regardless of manufacturer. This prevents vendor lock-in, enables roaming (use your charge card at any network), allows remote management, and supports smart grid integration. Without OCPP, chargers can only be managed by their own proprietary app and backend system.
How do I protect against EV charging cable theft?
Use locking Type 2 sockets that engage the cable latch electronically — the cable can only be removed when the charging session is properly stopped via RFID card or app. Physical bollards or a lockable charging post enclosure prevent damage to the station. OCPP-enabled stations can remotely disable charging if suspicious activity is detected. Cable retract mechanisms keep cables off the ground when not in use.
Can this charger work with all electric vehicles?
The Type 2 (Mennekes) socket is the European/Indian standard compatible with most EVs including all Tesla Model 3/Y/S/X (with adapter for older cars), Tata Nexon EV, MG ZS EV, Hyundai Kona/Ioniq, BMW, Mercedes, Volkswagen EV models. North American vehicles use SAE J1772 (Type 1) but can use adapters. CHAdeMO and CCS are DC fast-charging standards incompatible with this Level 2 AC design.
Advertisement