Improving E-bike mid-drive motor durability through internal humidity management
P.R.P.M. Geraedts (TU Delft - Industrial Design Engineering)
S.S. van Dam – Graduation committee member (TU Delft - Industrial Design Engineering)
A.R. Balkenende – Mentor (TU Delft - Industrial Design Engineering)
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Abstract
This study investigates the premature failure of mid-drive e-bike motors and develops a solution to make them more durable. The research direction was motivated by surveys conducted by van Dam (2025) and Wertgarantie (2024), which highlighted that 24.2% of e-bike technical failures involve the motor. When an out-of-warranty e-bike motor fails, the whole bike often gets discarded because the high replacement cost of the motor (over €1,000) makes consumers purchase a new e-bike.
To understand the causes of these failures and address the hypothesis that environmental and thermodynamic factors play a role, a mixed-methods approach was utilized. Qualitative data was gathered through 11 interviews with local repair mechanics and 4 interviews with specialized remanufacturers. Additionally, physical product teardowns were conducted on 9 different mid-drive e-bike motors to analyze their internal architectures and component failure points.
The findings showed that the thermodynamic "breathing cycle" is a cause of e-bike motor durability. As the motor cools, pressure differentials draw ambient humidity past the seals, causing internal condensation that leads to the failure of bearings and electronic components. Recognizing that standard hermetic seals cannot stop this cycle, the design vision shifted from passive water sealing to active internal humidity management. As a result, a modular Desiccant Cartridge filled with indicating silica gel has been developed to absorb internal moisture and prevent condensation on components. The cartridge is filled with 10 grams of silica gel and has to be replaced every 2 years with heavy use.
We conclude that the Desiccant Cartridge concept works theoretically to avoid condensation, but it has not yet been physically tested in practice. Important limitations of this study include the lack of detailed OEM data regarding component failure rates, which necessitated a reliance on qualitative field reports and third-party surveys. A suggestion for further research is to conduct user experience testing to investigate the willingness and confidence of e-bike owners to perform DIY repair and maintenance using these cartridges.