EV Charging Basics

This page is for me to rehearse key concepts, protocols, and test areas before my interview.

1. EV Charging Basics

• AC Charging (Level 1 & Level 2)
  • Power comes through the vehicle’s onboard charger.
  • Slower charging (3–20 kW).
  • Used at homes, offices, or parking garages.
• DC Fast Charging (Level 3)
  • Power conversion is handled by the charger itself.
  • High power (50 kW up to 350 kW for passenger vehicles, higher for heavy duty).
  • Used for highway corridors and public stations.

2. Key Charging Protocols & Standards

• OCPP (Open Charge Point Protocol) – Defines communication between charger and backend management system.
• OCPI (Open Charge Point Interface) – Used for roaming and network-to-network data exchange.
• ISO 15118 – Governs vehicle-to-charger communication, Plug & Charge authentication, and future V2G.
• SAE J1772 – Connector standard for AC charging in North America.
• SAE J3068 – Three-phase AC charging for commercial and industrial vehicles.
• SAE J3400 (NACS) – North American Charging Standard (Tesla’s connector now adopted by others).
• IEC 61851 – International standard for conductive charging systems.
• IEC 62196 – Defines connectors, plugs, and couplers.
• DIN 70121 – Earlier standard for high-level communication before ISO 15118 maturity.
• Megawatt Charging System (MCS) – Emerging standard for heavy-duty high power charging.

Relevancy:

• Vehicle ↔ Charger communication: ISO 15118, DIN 70121.
• Charger ↔ Backend: OCPP.
• Network roaming: OCPI.
• Physical interfaces: SAE J1772, J3400, IEC 62196.

3. Real-Life Interoperability Issues (Passenger Cars)

• Failed handshakes: Vehicle unable to start session due to firmware mismatch.
• Inconsistent Plug & Charge experiences: Some vehicles support it, some chargers don’t.
• Connector incompatibility: CCS vs NACS availability at stations.
• Payment failures: Backend errors causing declined sessions.
• Uptime issues: Stations out of service due to poor remote diagnostics.

Example: Early 2024 reports show certain Hyundai Ioniq 5 models having difficulty initiating sessions at specific older ChargePoint DC stations because of legacy OCPP implementations.

Another example: Plug & Charge enabled on some Mercedes-Benz EQS models works only at specific networks like Electrify America due to backend certification differences.

4. Industry Initiatives

• CharIN: Industry alliance working on CCS and MCS standards.
• SAE efforts: Aligning J3400 (NACS) with existing standards.
• IONNA-type JVs: Cross-OEM ventures to deploy standardized networks.
• UL and certification labs: Pushing for rigorous interoperability test programs before deployment.

5. Steps for Vehicle vs Charger Testing

1. Pre-test planning: Define test matrix (different vehicles, charger models, power levels).
2. Functional handshake tests: Plug-in, handshake initiation, authorization.
3. Load tests: Verify current ramp-up, sustained operation, thermal behavior.
4. Edge case simulation: Unplug mid-session, communication dropouts, emergency stops.
5. Payment and backend validation: Ensure backend correctly logs and bills session.
6. Regression & automation: Automate scenarios for repeated firmware builds.

6. Stakeholders Involved

• OEMs (Vehicle Manufacturers): Ensure vehicles comply with standards.
• Charging Network Operators: Deploy and maintain stations.
• Backend Platform Providers (CPMS vendors): Manage data, billing, and updates.
• Test Labs & Certification Bodies: UL, TÜV, CharIN test events.
• Suppliers: Cable manufacturers, power electronics suppliers.
• Regulators & Standards Bodies: SAE, ISO, IEC.

7. Plug & Charge Overview

• Part of ISO 15118.
• Vehicle and charger authenticate automatically using digital certificates.
• Removes need for RFID cards or apps.
• Improves user experience but requires secure certificate management.
• Adoption growing: Mercedes EQ series, Ford Mustang Mach‑E (with specific networks).

8. Summary

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Review and rehearse these sections before the interview to strengthen your technical narrative and confidence.