Critical factors in the design of ebike batteries

In a previous article, we went through the current and upcoming trends in ebike batteries. Now we're going to focus on the key factors to consider when designing and building an ebike battery. So, to find out the aspects we consider when creating a high-quality ebike battery, please keep reading.

Li-ion cells are the foundation of any ebike battery pack. They come in various shapes, sizes, capacities, voltages, and discharge rates. The battery chosen for your ebike battery is determined by your specific requirements and preferences, such as power output, energy density, cycle life, safety, and cost.

There are several types of li-ion cells currently on the market, but the most common ones used in ebikes are cylindrical cells 18650 and 21700, usually with NMC or NCA chemistry. This is because these batteries offer the highest energy density.

Some factors we consider when testing and selecting li-ion cells are:

With so many factors to consider, an ebike battery manufacturer can't simply rely on data from cell suppliers. Instead, they should test and validate performance independently for any given application. At Johnson Matthey Battery Systems, we have a complex cell testing program, carried out in both our in-house laboratory and in external labs and universities.

A battery management system (BMS) is a device that monitors and controls various aspects of an ebike battery pack, such as voltage, current, temperature, state of charge (SoC), state of health (SoH), and cell balancing.

A BMS can protect the battery from overcharging, overdischarging, overcurrent, overtemperature, and short circuits. It can also communicate with other devices on the ebike, such as the controller, display, or charger. It is vital to protect the BMS from damage and against moisture.

A custom-made BMS can have many advantages over a generic or off-the-shelf system, such as:

Designing and building a custom BMS requires complex knowledge and skills in electronic engineering, programming, and PCB design. Therefore, it's vital to partner with a battery manufacturer experienced in this field.

The mechanical design of an ebike battery pack refers to the shape, size, structure, and arrangement of the cells and other components within a casing or enclosure. Mechanical design influences performance, safety, durability, and aesthetics of the battery. Some factors to consider when creating an optimal mechanical design include:

Every battery design must be optimised for serial production, a factor that should be considered from the earliest phases of the project. Additionally, mass production of ebike batteries requires proper procedures to ensure high quality and consistency. Some vital procedures include:

Design validation is the process of verifying that an ebike battery design meets its intended purpose and requirements. It can be done via various tests and experiments on prototype models or samples of the battery pack under realistic conditions.

Experienced battery manufacturers create complex DVP&R (Design Validation Plan & Report) to be followed on each stage of product development. The results of tests are documented in appropriate reports.

Some aspects of the initial pre-validation can be completed during the early stage of design by performing thermal and mechanical simulations. This influences some of the design decisions, making sure the final product will pass validation and certification without issues or requirements to redesign. This contributes to fast project realisation.

Product certification is the process of obtaining approval or recognition from relevant authorities or organisations, which permits the ebike battery to be sold or used in a specific market or region. Gaining product certification involves complying with certain standards, regulations, laws, or guidelines that govern the quality, safety, performance, or environmental impact of the battery.

Product certification can also involve the testing and inspecting of the product by accredited third-party laboratories or agencies to verify its compliance and quality.

The certification of ebike batteries is an important and necessary step, and it's vital that a battery manufacturer has the facilities in place to conduct tests, like UN 38.3, internally, and that they've established partnerships with external certification bodies to ensure a smooth certification process for CE and/or UL marking. This will contribute towards the battery being brought to market without undue delays.

Ebike batteries are complex products that require careful design and production to ensure optimal performance, safety, and durability. By choosing a manufacturer that follows best practices, you can be assured that your ebike battery will meet your expectations and requirements, plus pass certification without issues. The whole process should be smooth and timely, and result in the delivery of the highest quality product.

Johnson Matthey Battery Systems is a world leader in the design and manufacture of li-ion batteries for e-bikes. From their base in Poland, they produce a variety of e-bike batteries, along with batteries for several other appliance types.

This article is sponsored by Johnson Matthey Battery Systems.