Calorimetry allows direct, accurate measurements of losses in power electronics systems. A small-scale version of a double chamber, closed type calorimeter for measuring losses up to 20 W is described in this paper. The design comprises an inner chamber with heat exchangers integrated into the top and bottom of the chamber, surrounded by insulation. This is enclosed by a temperature controlled air gap, within a further insulated enclosure. Calibration tests show that losses can be measured to a precision of +/-0.4 W and ways of improving the accuracy further are discussed.
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 ± 100 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.
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