08/02/2025
🔌 Understanding EV Motor Power Ratings: A Global Engineering Perspective ⚙️
As Sri Lanka moves toward embracing electric mobility, it’s important to align with globally accepted engineering and regulatory principles when classifying EVs for duty or homologation purposes.
Unlike internal combustion engines, electric vehicles (EVs) don’t define power solely based on hardware. Instead, the usable motor power is governed by the electronic control system, what’s often called “firmware-limiting.” This approach is not a loophole; it’s an industry-standard method used by leading automakers worldwide.
⚙️ So what is the global standard?
According to UNECE Regulation No. 85, the officially certified power of an electric motor is defined as its net continuous output over a 30-minute period, measured under controlled testing conditions. This means if a motor is technically capable of 150 kW, but is firmware-limited to 100 kW and cannot exceed it under normal operation, then 100 kW is its regulatory power classification.
This method is used throughout Europe, the UK, Japan, Australia, and other regions that follow UNECE, WLTP, or SAE standards.
🚗 Examples from the global industry:
• Tesla uses the same rear motor unit in both the Model 3 Standard Range and Long Range variants. The Standard Range is software-limited to around 208 kW, while the Long Range allows over 330 kW. No hardware change only software calibration.
• Volvo EX30 offers both single motor (200 kW) and twin motor (315 kW) versions. These use the same base motor design, differentiated only by electronic control.
• BMW iX xDrive40 and xDrive50 use the same motor configuration. The power difference is determined through inverter and ECU tuning.
• BYD Seal and several other models apply similar logic one motor, multiple outputs, verified through test cycles.
This is known as motor derating a well-accepted engineering technique.
🔍 Why do manufacturers do this?
• To align with regional tax or licensing categories
• To create different model variants for diverse markets
• To optimize battery life and vehicle range
• To comply with thermal and performance limits in specific climates
• Mass production efficiency by reducing design and tooling costs
• Simplified spare parts management for service and warranty support
• Better thermal and battery optimization for extended durability and range
• Compliance with market-specific regulations (like power-based duties) still keeping same hardware
All of this is done at the factory, and the firmware is locked, meaning consumers cannot increase the power without deep-level tampering which would void warranties and violate safety certifications under ISO 26262.
🧪 How is power measured?
Regulators in the EU and Asia use dynamometer testing, either on the motor bench or full vehicle chassis, to measure:
• Torque and speed under continuous load
• Stability of output over 30 minutes
• Actual performance under WLTP or SAE test cycles
This process reflects what the driver experiences not just what the motor is capable of on paper.
If a vehicle is designed, validated, and software-limited to deliver 100 kW continuously, that is its true power rating regardless of whether the hardware is shared with a 150 kW variant. This is the global standard, and it helps governments and regulators classify EVs fairly based on real-world performance.
✅ Key Standards and Regulatory References
1. UNECE Regulation No. 85 (UN R85)
• Defines net power output for electric motors.
• Power is measured as the maximum net continuous power output averaged over 30 minutes.
• Applicable to both hybrid and electric vehicles.
• 📘 Clause 5.3.1 specifically addresses electric drive systems.
• Source: UNECE WP.29 Regulations
• https://unece.org/transport/vehicle-regulations
2. SAE J2908 – Motor Power and Torque Rating for Electrified Powertrains
• Defines standardized methods to test and declare usable motor power and torque.
• Includes procedures for thermal derating, power limits, and control logic.
• Suitable for powertrain-level testing (motor + inverter + controller).
• Publisher: SAE International
• https://www.sae.org/standards/content/j2908_202006/
3. WLTP (Worldwide Harmonized Light Vehicle Test Procedure)
• Employed in EU, Japan, and other regions to certify vehicle performance, including power output and efficiency.
• Acknowledges software-governed power levels during official testing cycles.
• Managed by UNECE under GTR No. 15.
• https://wltpfacts.eu
4. ISO 1585:1992 – Road vehicles Engine test code Net power
• Early foundation for determining net power, including for electric drivetrains.
• Often superseded by newer WLTP or UNECE methods, but still referenced for net output definitions.
• https://www.iso.org/standard/25320.html
5. UNECE EV Regulations EVE Informal Group Docs
• Contains expert guidance on measuring electric vehicle power, including EVE-14-05e, EVE-16-03e, and EVE-16-07e.
• Provides deep technical detail for how controller-limited output is validated in EVs.
• Download via:
https://wiki.unece.org/display/trans/EVE+14th+Session
