Power supply units are nowadays made to work on almost every power grid and their efficiency differs depending on the input voltage. We did not want to restrict our testing on a 230VAC power grid, therefore we acquired a common 3KVA laboratory VARIAC. The VARIAC allows us to adjust the input voltage between 0 and 260VAC, giving us the ability to test the performance of all power supplies at both 110VAC and 230VAC input.
Between the VARIAC and the power supply we are using an Extech 380803 True RMS power analyzer, which replaced the older phase Lutron DW-6091 we have been using in the first version of our testing station. The Extech 380803 is a class (G) 0.5 instrument, meaning that the maximum error is less than 0.5%. Furthermore, the Extech 380803 allows us to take readings of the input apparent power, real power, input voltage, input frequency and of the power factor of the power supply, all of which are transferred directly to our software via its RS232 interface.