Battery housing made of engineering plastic: the lightweight and powerful solution for e-bikes

Over the last 15 years, the streetscape around the world has changed dramatically. Electric bikes have become an integral part of our everyday lives – whether in the city, in the countryside or in the mountains. While the focus of the e-cargo bike is on its use as a reliable and environmentally friendly means of transport, the e-mountain bike, or e-MTB for short, is all about the fun factor.
The target group of electric bike users is becoming ever larger and more heterogeneous: thanks to the drive, it is no longer just well-trained athletes who ride uphill on full-suspension e-mountain bikes. They also range in age from young to old. 
What many users have in common, however, is an interest in minimising the weight of the e-bike. In this context, you could say that every gram counts. As a result, lightweight construction is becoming increasingly important and every single component must be weight-optimised.

The e-bike battery has a special significance as an energy source. Its protective housing must not only fulfil aesthetic functions, but above all offer protection against stone chips and scratches, and ideally at the lowest possible weight. In the following, we will focus on the battery position integrated into the frame tube, which is standard on mountain bikes with an e-drive and is also becoming increasingly popular in other e-bike segments such as e-cargo bikes.

Up to now, the protective housing for the battery packs has generally been made of aluminium. In order to reduce weight, it is advisable to replace aluminium with plastic. The technical requirements for the lighter thermoplastic material are very diverse. The operational safety of the frame battery is synonymous with the safety of the e-bike rider. Therefore, low electrical conductivity, impact and shock resistance as well as flame resistance are of particular importance. For outdoor use, the material must also be heat and UV resistant. All these requirements must be harmonised with a low weight.

From the portfolio of engineering plastics, a glass fibre-reinforced polycarbonate (PC) was chosen that meets the required mechanical, thermal and, above all, electrical properties.
This amorphous material reinforced with 10 % glass fibres has higher strength, rigidity, creep resistance and dimensional stability than unreinforced PC. Together with its good fatigue strength, glass fibre-reinforced polycarbonate is suitable for components that are exposed to high static loads over long periods of time and at high temperatures.
In addition, the material has a high resistance to fire in accordance with UL94 and an insulating effect against electrical voltage. Polycarbonate (PC) is approx. 40 - 50 % lighter than aluminium. In terms of the protective housing, this means a significant weight saving with the same or even better properties compared to aluminium.
Moreover, transparent PC can be coloured to customer specifications by adding colour particles and does not have to be painted like aluminium.

The extrusion of plastic profiles is one of Ensinger's core competences. Ensinger has been mastering and perfecting this manufacturing process for decades, which scores with high quantities, tight tolerances and optimised surfaces. This allows long profiles with defined geometries, including hollow chambers, to be produced that fit precisely into the frames of e-bikes. Application engineers are on hand to provide advice at every stage of the project: from sampling and prototype construction through to series production. Customised housings are thus manufactured reliably and to a high quality based on more than 50 years of plastics expertise.