Calorimetry for power conversion in mobile telephone chargers

This paper describes the measurement of power losses of two different types of charger for mobile telephones. The losses were measured during charging, at the end of charging and with the chargers powered but disconnected from their loads. Those losses were measured directly by a calorimeter with an accuracy of plusmn100 mW and by two variations on the method of subtracting output power from input power. The work shows that the losses of modern chargers are around 1 to 2 W when charging but under 200 mW when powered but disconnected from the telephone. The calorimetric method is shown to have advantages.