The development of an axial flux generator, hand crankable up to 200 W.

Anjum, Samad and Roberts, Jenny and Rennie, Allan (2023) The development of an axial flux generator, hand crankable up to 200 W. Masters thesis, Lancaster University.

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Abstract

When a magnet moves past a wire coil, an electromagnetic force (EMF) is generated in that coil. Compared to radial flux electrical machines, axial flux electrical machines present a larger magnet area for greater EMF generation. This makes them a good candidate for contemporary energy generation technologies. For this project, Koitech Global Limited commissioned the development of a kinetic generator for hand cranked charging of their (currently in development) lithium-ion hybrid capacitor (LIC) based power bank. Building on the foundations of electromagnetic induction, a prototype axial flux generator driven through a speed increasing epicyclic transmission was produced. The generator was designed with a central rotor mounted on a shaft, with the stator assembled on both sides of this to achieve a large number of windings in a compact design. Small air gaps (less than 1 mm thick) were achieved with a unique threaded shaft construction, and an accompanying two stage 13.69:1 speed increasing epicyclic gearbox was built, with which to drive the rotor. A technique of interlacing cores on both sides of the generator helped to reduce cogging by doubling the number of detents and reducing the cogging torque between them, making arm cranking feel easier and smoother for the researcher. With electromagnetic simulations conducted with which to compare performance data to, the generator was tested on a benchtop to characterise its EMF, electrical load performance and efficiency. Clamped to a laboratory benchtop and cranked at up to two arm revolutions per second under the testing of the researcher, the device generated 100 W through a light bulb electrical load aerobically, and up to 200 W was generated under the application of anaerobic loads, with up to 80% efficiency. This prototype kinetic generator was built larger than the requirements set out by Koitech but there is potential for significant size reduction to achieve the size requirements specified by the company without significant loss of performance. The conducted research and development of the kinetic generator leaves Koitech in a strong position to finish the development of their power bank product, with the currently outstanding task being to develop the LIC charging electronics to be able to demonstrate the product concept to external investors, before further research and development of the unit to improve its performance and efficiency can commence. These aspects of research and development are discussed in this report.