Electrolytic capacitors have a much larger capacitance than regular fixed capacitors, so an appropriate range should be selected for measurement based on the capacitance. Generally, capacitors between 1 and 47 μF can be measured using the R×1k range, while capacitors larger than 47 μF can be measured using the R×100 range.
Connect the red probe of the multimeter to the negative terminal and the black probe to the positive terminal. At the initial contact, the multimeter needle will deflect significantly to the right (for the same resistance range, the larger the capacitance, the larger the deflection), then gradually return to the left until it stops at a certain position. The resistance at this point is the forward leakage resistance of the electrolytic capacitor, which is slightly greater than the reverse leakage resistance. Practical experience shows that the leakage resistance of an electrolytic capacitor should generally be several hundred kΩ or higher; otherwise, it will not function properly. During testing, if there is no charging in either the forward or reverse direction (i.e., the needle does not move), it indicates that the capacitance has disappeared or there is an internal open circuit. If the measured resistance is very small or zero, it indicates that the capacitor has a large leakage current or has broken down and is no longer usable.
For electrolytic capacitors with unclear positive and negative markings, the method described above for measuring leakage resistance can be used to determine their polarity. First, measure the leakage resistance arbitrarily and note the value. Then, reverse the probes and measure another resistance value. The higher resistance value indicates the correct connection; that is, the black probe is connected to the positive terminal, and the red probe to the negative terminal.
Alternatively, using a multimeter in resistance mode, the capacitor can be charged in both forward and reverse directions. The magnitude of the pointer's rightward swing indicates the capacitance of the electrolytic capacitor.
