Estimating aluminum electrolytic capacitors condition using a low frequency transformer together with a DC power supply

This paper presents a very simple off-line technique that is able to evaluate the aluminum electrolytic capacitors condition. The aging of these capacitors is expressed by the increase of their internal resistance that can reach twice the initial value at the end of life of the capacitor, while the capacitance can drop 20%. Thus, if both capacitance and internal resistance are quantified, it is possible to evaluate the capacitors condition. To do so, a very simple prototype consisting of a low frequency transformer, a DC power supply, a RC circuit and a digital oscilloscope connected to a computer can be used. Afterwards, by using the phase displacement between capacitor current and voltage, as well as the ratio between their modulus, it is possible to compute both resistance and capacitance of the capacitor under test. Several experimental results have been acquired in order to evaluate the applicability of the proposed technique.