Electric bicycles can travel 18% further on a single charge without increasing battery capacity. This was achieved through a system that recharges the battery while riding, using a portion of the rotational energy from the rear wheel. The technology was developed by researchers from K.S.R.M. College of Engineering, the Institute of Science Engineering and Technology, and Kristu University in India, as well as Mattu University in Ethiopia.
A limited ride range is still one of the main drawbacks of modern e-bikes. Due to weight and size constraints, they are equipped with relatively small batteries, so range must be extended through other means. Existing solutions – such as regenerative braking or bicycle dynamos – either generate too little electricity or create noticeable resistance, forcing the rider to expend more effort.
The researchers proposed a different approach. They fitted the rear wheel with an additional generator based on a NEMA-42 stepper motor. Owing to its design characteristics, this generator is capable of producing electricity already at speeds of 8–12 km/h. The generator is connected to the rear wheel via a separate chain drive with an overrunning clutch and a gear ratio of 1:3 – one wheel revolution translates into three revolutions of the generator. This allows sufficient voltage to be generated for charging the battery, while the overrunning clutch prevents the generator from braking the wheel during freewheeling. The generated electricity passes through a voltage conversion system and is then safely fed into the lithium-ion battery’s charging circuitry.
The researchers emphasize that this is not a “perpetual motion machine.” The generator does not produce energy from nothing; rather, it recovers a portion of the mechanical energy that would otherwise be lost under normal conditions. Consequently, the system works most effectively when riding downhill, coasting, or when the rider is both pedaling and using the electric motor simultaneously. On flat terrain, when riding on electric power alone, the effect is significantly smaller, as the generator itself creates additional load on the electric motor.
To offset the added weight of the generator and electronics, the researchers lightened the bicycle itself. They replaced the steel frame with an aluminum or carbon-fiber one, fitted a lighter fork, and removed certain non-essential components. As a result, the base bicycle’s mass was reduced by 6–8 kg, and the total weight of the finished e-bike with the self-charging system came to 18-23 kg. This is comparable to the mass of serial e-bike production in the same class while in some cases it can be even less than that mass.
During testing, the generator produced a charging current of 0.3–0.8 A at a power output of 7-15 Wt. At the same time, the additional resistance to motion proved minimal: the generator increased total drag by less than 2.2%. Experimental trials confirmed these calculations.
In a series of comparative test runs, the bicycle without the charging system covered an average of 38.1 km on a single charge, whereas with the generator fitted, the range increased to 42.6 km, an improvement of nearly 12%. Depending on the route and operating conditions, the gain ranged from 10% to 18%.
In the researchers’ view, the proposed technology could offer a relatively simple means of extending e-bike range without resorting to heavier and more expensive batteries. In future work, the team plans to develop a specialized compact generator optimized specifically for bicycles, as well as to improve energy conversion efficiency.
