Is it possible to determine capacity and voltage rating of an unknown electrolytic capacitor?
To safely discharge a capacitor: After power is removed, connect a 20,000 Ω, 5-watt resistor across the capacitor terminals for five seconds. Use your multimeter to confirm the capacitor is fully discharged.


Use your digital multimeter (DMM) to ensure all power to the circuit
is OFF. If the capacitor is used in an ac circuit, set the
multimeter to measure ac voltage. If is used in a dc circuit, set
the DMM to measure dc voltage.
Visually inspect the capacitor. If leaks, cracks, bulges or other
signs of deterioration are evident, replace the capacitor.
Turn the dial to the Capacitance Measurement mode ( Capacitance
symbol ). The symbol often shares a spot on the dial with another
function. In addition to the dial adjustment, a function button
usually needs to be pressed to activate a measurement. Consult your
multimeter’s user manual for instructions.
For a correct measurement, the capacitor will need to be removed
from the circuit. Discharge the capacitor as described in the
warning above.


Note: Some multimeters offer a Relative (REL) mode. When measuring low capacitance values, the Relative mode can be used to remove the capacitance of the test leads. To place a multimeter in Relative mode for capacitance, leave the test leads open and press the REL button. This removes the residual capacitance value of the test leads.


Connect the test leads to the capacitor terminals. Keep test leads
connected for a few seconds to allow the multimeter to automatically
select the proper range.
Read the measurement displayed. If the capacitance value is within
the measurement range, the multimeter will display the capacitor’s
value. It will display OL if a) the capacitance value is higher than
the measurement range or b) the capacitor is faulty.


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