Design of a Heat Removal Method for the Electronics in Lithium-Ion Cordless Power Tools

Abstract

Cordless power drills are currently being designed with lithium-ion battery technology to produce more power per unit mass as compared to legacy nickel-cadmium battery packs. With this increase in power, more complex heat removal solutions are needed to dissipate heat resulting from electrical circuit resistance and insure electronic components, specifically the metal oxide semiconductor field effect transistor (MOSFET), will remain below its maximum operating temperature of 175°C. Heat spreaders, ventilation methods, and heat sinks were considered, with a newly designed heat sink being determined to be the most effective solution that met performance, manufacturing and cost requirements. Finite element models of the heats sinks along with models of the natural convection within the drill were developed and used to determine geometry and material requirements. Laboratory tests were performed on several prototype heat sinks and drills to validate the thermal modeling and ensure designs would meet the required performance metrics. From testing, it was seen that the new design absorbed the required amount of heat, keeping the MOSFET and handle temperature at 88°C. This insures the durability of the tool, keeping the temperature below the plastic deformation temperature of the drill handle. From the modeling and testing of this solution, a new design methodology was created and validated to expedite design iterations for future drill models and other cordless tool products.