So, you have a need to check the value of the capacitance of the capacitor:

• whether the marking on the capacitor has been erased;
• whether the capacitor is 100 years old at lunchtime and it is quite possible that it simply dried up;
• whether there is a suspicion that some of your devices are not working properly due to a significant decrease in the capacitance of the capacitor;
• you never trust anything, especially foreign manufacturers.

The easiest way to find out the capacitance of a capacitor is to measure it with a multimeter with capacitance measurement function. But ... not everyone has such a device.

There is a completely affordable and easy way to find out the capacitance of a capacitor without specialized measuring equipment.

How to measure the capacitance of an electrolytic capacitor. With a voltmeter

For this method, you will need:

• Multimeter or voltmeter
• Resistor 1-10 kOhm
• DC source
• Stopwatch
• Capacitor under test

The essence of the method is to measure the charging time of the capacitor "C" to a value of 0.95Uinput. through resistance "R".

To help us, there is a formula: T \u003d 3 * R * C, where T is the charge time, sec.; R- resistance, Ohm; C - capacity, F.

We collect the simplest scheme:

As a source of constant voltage, I used a 6-volt battery.

Step-by-step instruction for measuring the capacitance of a capacitor:

• Measure the voltage of your power supply. In my case, Uinput = 6.4V
• Assemble the circuit, but do not connect to a power source yet. Connect the voltmeter in parallel with the capacitor terminals. Surely the voltmeter will show some residual value of the potential on the Conder.
• Discharge the capacitor. The voltmeter should show zero voltage

• Connect the circuit to a current source and note the time it takes for the voltage across the capacitor to rise to a predetermined value. The accuracy of the measurement will depend on the timing of the start and stop of the stopwatch. For this operation, it would be nice to have a third hand. It's good if someone can help you with this.
• The essence of the method is that you will need to detect the time during which Uout will become equal to 0.95Uinput. So, we calculate in advance what this value will be equal to. In my case, Uout.=6.08V. But!!! It's in theory. In fact, the tested capacitor could not be charged to more than 5.5V. Up to 5.3V, the charge went pretty quickly, and after this value, within a minute, it barely rose to 5.5V. Therefore, I will time to the level of 5.3V

• To improve the accuracy of measurements, it is worth taking 3 measurements and displaying the average value of the time.
• So, my capacitor charged up to 5.3V in 30 seconds, through a 3900 ohm resistor.
• Using the formula shown in the photo below, I calculated the capacitance of the capacitor in Farads. Converting the value to uF, I got 2564 uF.

• However, this value does not differ much from the declared capacitance value on the capacitor case. For the "old man" of the 89th year - a wonderful result. especially since for this type of capacitors, the allowable capacity deviation is + 50 / -20%.

The process of voltage growth Uout. on the capacitor contacts and time measurement - you can see in this short video: