How to determine the capacitance of a capacitor with a multimeter

Sometimes a capacitor is not labeled. How to find out then its real capacity, if there is no special equipment at hand, and the device is unmarked? Then various improvised means and formulas come to the rescue. Before starting work, it must be remembered that the capacitor must be discharged before testing (its contacts must be discharged). To do this, you can use a conventional screwdriver with an insulated handle. Holding the handle with a screwdriver, touch the contacts, thus closing them. Next, we will tell you in detail how to determine the capacitance of a capacitor with a multimeter, providing instructions with a video example.

Using the "Cx" mode

After the contacts have been short-circuited, resistance determination can be carried out. If the element is fixed, then immediately after connecting it will start charging with constant current. In this case, the resistance will be displayed at a minimum and will continue to grow.

If the capacitor is faulty, then the multimeter will immediately indicate infinity or will indicate zero resistance and at the same time beep. This check is carried out if the design is polar.

In order to find out the capacitance, you must have a multimeter with the function of measuring the "Cx" parameter.

It is easy to determine the capacitance using such a multimeter: set it to the "Cx" mode and indicate the minimum measurement limit that this capacitor should have. These multimeters have special sockets with certain measurement limits. A capacitor is inserted into these slots according to its measurement limit and its parameters are determined.

If there are no such nests in the tester, then you can determine the capacity using measuring probes, as shown in the photo below:

Important! In a separate article, we talked about how to check the performance of a capacitor. We also recommend that you familiarize yourself with this material!

Applying formulas

What if you don't have such a multimeter with measurement jacks at hand, but only an ordinary household appliance? In this case, you need to remember the laws of physics that will help determine the capacity.

To begin with, remember that in the case when a capacitor is charged from a constant voltage source through a resistor, then there is the regularity according to which the voltage on the device will approach the voltage of the source and will eventually become equal to him.

But in order not to expect this, you can simplify the process. For example, within a certain time, which is equal to 3 * RC, during charging, the cell reaches 95% of the voltage applied to the RC circuit. Thus, the time constant can be determined from the current and voltage. And more correctly, if you know the voltage in the power supply, the value of the resistor itself, the time constant is determined, and then the capacity of the device.

For example, there is an electrolytic capacitor, the capacity of which can be recognized by the marking, where 6800 uF 50V is prescribed. But what if the device has been lying idle for a long time, and it is difficult to determine its working condition from the inscription? In this case, it is better to check its capacity to know for sure.

To do this, you need to do the following:

1. Use a multimeter to measure the resistance of the 10 kΩ resistor. For example, it turned out to be 9880 ohms.
2. We connect the power supply. We transfer the multimeter to the constant voltage measurement mode. Then we connect it to the power supply (through its leads). After that, 12 volts are set in the unit (12.00 V should appear on the multimeter). If it was not possible to adjust the voltage in the power supply, then we write down the results that we got.
3. With the help of a capacitor and a resistor, we assemble an electrical RC circuit. The diagram below shows a simple RC circuit:
4. Short-circuit the capacitor and connect the circuit to the power supply. Using the device, once again determine the voltage that is applied to the circuit and write down this value.
5. Then you need to calculate 95% of the resulting value. For example, if it is 12 Volts, then it will be 11.4 V. That is, for a certain time, which is 3 * RC, the capacitor will receive a voltage of 11.4 V. The formula looks like this:
6. It remains to determine the time. To do this, unscrew the device and use a stopwatch to count down. The definition of 3 * RC will be calculated in this way: as soon as the voltage on the device is 11.4 V, then this will mean the right time.
7. We make a definition. To do this, the resulting time (in seconds) is divided by the resistance in the resistor and by three. For example, it turned out 210 seconds. We divide this figure by 9880 and by 3. The resulting value is 0.007085. This value is indicated in farads, or 7085 microfarads. The permissible deviation can be no more than 20%. If we take into account that 6800 microfarads is indicated on the product, our calculations are confirmed and fit into the standard.

How to determine the capacitance of a ceramic capacitor? In this case, you can make a determination using a network transformer. For this, the RC-chain is connected to the secondary winding of the transformer, and it is connected to the network. Further, using a multimeter, the voltage across the capacitor and across the resistor is measured. After that, it is necessary to make calculations: the current that passes through the resistor is calculated, then its voltage is divided by the resistance. It turns out the capacitive resistance Xc.

If there is a current frequency and Xc, you can determine the capacitance by the formula:

Other techniques

The capacity can also be determined using a ballistic galvanometer. For this, the formula is used:

where:

• Cq is the ballistic constant of the galvanometer;
• U2 - voltmeter readings;
• a2 is the angle of deflection of the galvanometer.

The determination of the value by the ammeter of the voltmeter is carried out as follows: the voltage and current in the circuit are measured, after which the value of the capacitance is determined by the formula:

The voltage with this method of determination must be sinusoidal.

Measurement of the value is also possible with a bridge circuit. In this case, the AC bridge circuit is indicated below:

Here one shoulder of the bridge is formed by the element to be measured (Cx). The next leg consists of a lossless capacitor and a resistance box. The remaining two arms are made up of resistance stores. We connect the power supply to one diagonal, and the zero indicator to the other. And we calculate the value using the formula:

Finally, we recommend watching a useful video on the topic:

That's all we wanted to tell you about how to determine the capacitance of a capacitor with a multimeter. We hope the information provided was useful and interesting for you!

You probably don't know:

• How to choose a multimeter for your home
• How to identify a short circuit
• How to check the performance of a transistor

I have been familiar with radio equipment for more than 30 years, but I have never bothered with something like that. It's easier to buy a new part in a store. Conder is inexpensive. Moreover, most of the used parts are written in the family that they have a couple of hours of work left to live.

Just one single comment that contradicts itself. If he reads this topic, then he bothers. My advice is buy, but check. Nowadays, there are a lot of fakes, so a new part may not work or may be understated in terms of parameters. For example, you buy a cheap lithium battery for 6800Ma into your phone, and it quickly sits down, you disassemble it, and there is a bank for 800Ma, and the rest of the space is filled with paper. So I solder electrolytic capacitors according to overestimated parameters, since they tend to dry out. And here I came, rather, I met a non-standard circuitry and I'm afraid strong currents will disable it. I don’t think so, though. Just doubts led to non-standard capacity measurements, since there is no device at hand now.