Electric Motor Range Extenders: A Comprehensive DIY Guide

Electric motor range extenders are devices designed to increase the range of electric vehicles (EVs) by providing additional power when the battery is depleted. These devices typically use a small internal combustion engine (ICE) to generate electricity, which is then used to charge the EV’s battery. This comprehensive guide will delve into the technical details and considerations for DIY enthusiasts interested in building their own electric motor range extenders.

Understanding the Fundamentals of Electric Motor Range Extenders

Electric motor range extenders work by using a small ICE to generate electricity, which is then used to charge the EV’s battery. This allows the vehicle to continue driving even when the battery is depleted, effectively extending the overall range of the EV.

The key components of an electric motor range extender system include:

  1. Internal Combustion Engine (ICE): The ICE is the heart of the range extender, responsible for generating the electricity. Typical range extender engines are single-cylinder or three-cylinder designs, with power outputs ranging from 30 kW to 35 kW.
  2. Generator: The generator is coupled to the ICE and converts the mechanical energy into electrical energy, which is then used to charge the EV’s battery.
  3. Battery Management System (BMS): The BMS monitors and controls the charging and discharging of the EV’s battery, ensuring optimal performance and safety.
  4. Power Electronics: The power electronics, such as inverters and converters, are responsible for managing the flow of electricity between the range extender, the battery, and the electric motor.
  5. Cooling System: The range extender engine and associated components require a robust cooling system to maintain optimal operating temperatures.

Designing a Compact and Efficient Range Extender Engine

electric motor range extenders

When designing a DIY electric motor range extender, the engine is a critical component that requires careful consideration. The engine should be compact, lightweight, and highly efficient to maximize the overall system’s performance and minimize energy consumption.

One example of a compact and efficient range extender engine is the single-cylinder, two-stroke gasoline engine developed in a research study. This engine has the following technical specifications:

  • Displacement: 125 cc
  • Power Output: 30 kW
  • Compression Ratio: 11:1
  • Weight: 25 kg
  • Volume: 0.025 m³

The key design features that contribute to the engine’s compactness and efficiency include:

  1. Displacement Optimization: The 125 cc displacement is carefully chosen to balance power output and overall system size.
  2. Combustion Efficiency: The 11:1 compression ratio enhances the engine’s thermal efficiency and power density.
  3. Lightweight Construction: The use of lightweight materials, such as aluminum alloys, helps to minimize the engine’s overall weight.
  4. Compact Packaging: The engine’s design prioritizes a small footprint, with a volume of just 0.025 m³, making it easy to integrate into the EV’s powertrain.

Integrating the Range Extender into the EV Powertrain

Integrating the range extender into the EV’s powertrain is a critical step in the DIY process. The range extender should be designed to seamlessly interface with the existing electrical and mechanical systems of the EV, ensuring a smooth and efficient operation.

Key considerations for integrating the range extender include:

  1. Power Output Matching: The range extender’s power output should be matched to the EV’s power requirements, ensuring that it can effectively charge the battery when needed.
  2. Electrical Integration: The range extender’s generator must be integrated with the EV’s electrical system, including the battery, power electronics, and control systems.
  3. Mechanical Integration: The range extender engine and generator must be physically integrated into the EV’s powertrain, with proper mounting, alignment, and vibration isolation.
  4. Control and Monitoring: The range extender’s operation must be seamlessly integrated with the EV’s control systems, allowing for automatic activation and monitoring of the system’s performance.

Ensuring Safety and Reliability in DIY Range Extenders

Safety and reliability are paramount when designing and building a DIY electric motor range extender. The system must be designed with robust safety features and undergo thorough testing to ensure its safe and reliable operation.

Some key safety considerations include:

  1. Overspeed Protection: The range extender engine must be equipped with overspeed protection to prevent damage in the event of a malfunction.
  2. Thermal Management: Effective cooling systems must be in place to maintain the range extender’s components within their safe operating temperatures.
  3. Fault Detection and Shutdown: The system should be able to detect faults and automatically shut down the range extender to prevent further damage or safety issues.
  4. Emissions and Noise Control: The range extender engine must comply with local regulations regarding emissions and noise levels.

Optimizing the Performance of DIY Range Extenders

To maximize the performance and efficiency of a DIY electric motor range extender, several optimization techniques can be employed:

  1. Fuel Efficiency Optimization: Adjusting the engine’s fuel injection, ignition timing, and other parameters can help improve the overall fuel efficiency of the range extender.
  2. Weight Reduction: Utilizing lightweight materials and optimizing the design can help reduce the overall weight of the range extender system, improving the EV’s energy efficiency.
  3. Regenerative Braking Integration: Integrating the range extender with the EV’s regenerative braking system can help capture and store additional energy, further extending the vehicle’s range.
  4. Advanced Control Algorithms: Implementing sophisticated control algorithms can optimize the interaction between the range extender, battery, and electric motor, enhancing the overall system’s performance.


Electric motor range extenders offer a promising solution for increasing the range of electric vehicles. By leveraging a small internal combustion engine to generate electricity, these systems can effectively extend the EV’s driving range, making them an attractive option for DIY enthusiasts and EV owners alike.

This comprehensive guide has provided a detailed overview of the technical considerations and design principles involved in building a DIY electric motor range extender. From understanding the fundamental components to ensuring safety and reliability, this guide has covered the essential aspects of this technology, empowering you to embark on your own DIY range extender project.

Remember, as with any DIY project, it is crucial to prioritize safety, seek professional guidance when necessary, and thoroughly test the system before deployment. By following the guidelines and best practices outlined in this guide, you can create a reliable and efficient electric motor range extender that will enhance the capabilities of your electric vehicle.


  1. Development of the range extender for a 48 V electric vehicle
  2. The Effects of Use of the Range Extender in a Small Commercial Electric Vehicle
  3. Design and experimental development of a compact and efficient range extender engine