Smart EV Charger with RFID Authentication and Energy Billing

A shared home or apartment EV charger raises two practical questions: who is drawing the power, and how much of it? A plain wall socket cannot answer either — it has no user check, no metering and no way to stop the main breaker from tripping when the charger runs alongside the geyser and air conditioner. This project builds an AC EV charger control unit that answers both. An ESP32 controller reads a 13.56 MHz RFID tag through an RC522 reader before anything switches on, a PZEM-004T module measures voltage, current, power and cumulative energy for the session, and a 1 kHz pilot signal tells the vehicle its current limit in the J1772-style duty-cycle convention. Because a second current-transformer clamp watches the home mains incomer, the controller can throttle the vehicle in real time so the house and the charger together stay under the sanctioned load. The result is a working demonstration of authenticated access, energy billing and dynamic load sharing — the three systems every commercial smart charger is built on.

1. The vehicle plug connects, and the control pilot line voltage change tells the ESP32 that a vehicle is present and connected.
2. The user taps an RFID tag on the RC522 reader; the firmware checks the UID against its authorized list and rejects unknown cards on the LCD.
3. Once both the pilot handshake and RFID authentication pass, the ESP32 closes the 40 A contactor, energizing the charge socket.
4. The ESP32 drives the 1 kHz pilot PWM with a duty cycle that encodes the vehicle's allowed current, and charging begins.
5. The PZEM-004T continuously reports voltage, current, power and cumulative energy over TTL serial, while the CT clamp on the home incomer reports total household load.
6. If house plus EV current would cross the sanctioned limit, the firmware lowers the pilot duty cycle and the vehicle throttles in real time.
7. The 20×4 LCD shows session status, energy in kWh and running cost in rupees throughout; tapping the tag again ends the session, opens the contactor and freezes the final bill.

Tech stack:

• ESP32 dev module · Arduino framework
• RC522 RFID reader · 13.56 MHz
• PZEM-004T V3.0 energy meter module
• 40 A AC contactor · opto-isolated driver
• 20×4 LCD · I2C
• J1772-style 1 kHz pilot signalling
• Split-core CT clamp · mains incomer sensing
• Arduino IDE / PlatformIO · C++

• [RFID user authentication] The RC522 reader scans a 13.56 MHz tag and checks its UID against the authorized list stored in firmware. Charging can never start on an unknown card, so each session is tied to a known user.
• [J1772-style pilot signalling] The ESP32 generates a 1 kHz PWM pilot signal whose duty cycle encodes the vehicle's allowed current, following the J1772 pilot convention. The contactor closes only after the pilot handshake confirms a vehicle is connected.
• [PZEM-004T energy metering] The meter module reports mains voltage, current, active power and cumulative energy over TTL serial, with 0.5% measurement accuracy per its datasheet. Session cost is computed from cumulative kWh at the configured tariff.
• [Dynamic home-load throttling] A split-core CT clamp on the home mains incomer lets the controller sense total household load. If house plus EV current would exceed the sanctioned limit set in firmware, the pilot duty cycle is lowered and the vehicle throttles in real time.
• [40 A contactor load switching] The mains path is opened and closed by a 40 A AC contactor under ESP32 control, with the coil driven through an opto-isolated relay. Session start and stop are clean electrical events, not software abstractions.
• [20×4 LCD session display] The display shows session status, session energy in kWh and running cost in rupees, computed live from the configured per-unit tariff.
• [Configurable tariff and limits] The per-unit energy rate, sanctioned home load and pilot current range are firmware constants the student can adjust and defend in the viva.
• [Session reset and billing summary] The PZEM's cumulative energy is reset via software at each session start, and the final energy and cost freeze on the display when the session ends.

Implemented above. Optional customization and future scope (not in the base build):

• Optional: Wi-Fi session logging to a spreadsheet or local server.
• Optional: multiple-tariff time-of-day billing logic.
• Future scope: online payment or UPI settlement per RFID user.
• Future scope: OCPP-style remote management and a mobile app.

• Assembled control-unit prototype in an enclosure (ESP32, RC522, PZEM-004T, contactor, LCD, CT clamp, charge connector)
• Complete ESP32 firmware source (RFID auth, pilot PWM, metering, tariff billing, dynamic throttling)
• Wiring diagram and full component list with ratings
• Project report PDF (design, pilot-signal design, tariff math, safety notes)
• PPT presentation for final review
• Viva Q&A preparation document (RFID, pilot signalling, metering accuracy, load sharing)
• Demonstration guidance (RFID tap demo, LCD readings, pilot duty-change demo)