How do you find the voltage on a capacitor?

Answer 1

Charge the capacitor with a voltage source through a resistor. Keep track of how long it takes the capacitor to charge to the voltage level. The value of the capacitor is c=time/5R where R is the value of the resistor and time is the charging time.

Answer 2

On paper, i = C dv/dt, where i = the current phasor; C = capacitance; v = the voltage phasor; t = time. If you can derive the time-dependent expressions for i and v in the time domain, C will be i / (dv/vt). For example, i = cos(omega * t); v = sin(omega * t); then C = cos(omega * t) / [omega * cos(omega * t)] = omega-1, a real number.

In practice, you can use a capacitance (CV) meter with frequency, DC bias, AC bias, and DC sweep settings to measure C versus v. You can also use an LCR meter. Alternatively, the hard way would be to stimulate the two-terminal capacitor with a sinusoidal voltage source and monitor the AC current. Take the data and put it in an Excel spreadsheet.

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Answer 3

Most capacitors will have it printed on it (eg 12V, 230V, etc). Some still use the stripe system (like those on resistors). This is the maximum voltage the capacitor can tolerate.

Finding the actual voltage through a capacitor at any given time is a lot more tricky, since the voltage varies with time. A voltmeter can always tell you what the voltage is at any given moment, just stick one end at each contact of the capacitor while it is still in the circuit.

Disconnect from the circuit and measure across the contacts with a Voltmeter. Disconnecting the capacitor would ensure that there is *no* voltage through it, which I doubt is what they want. See discussion page for more.

Answer 4

What is important about capacitors?

1: We would like to know what voltage it is designed for.

2: We would like to know what capacity it can hold.

3: We might want to know the frequency of charge/discharge it can tolerate.

4: We might want to know what temperature it can tolerate.

3:Frequency is seldom marked on a capacitor but we can use some general rules:

pF are typically used and designed for frequencies in the millions.

nF are typically used and designed for frequencies in the thousands.

uF are typically used and designed for frequencies below thousand.

uF capacitors with no special design would normally operate on frequencies below or equal to 100.

Higher frequencies would heat up these uF capacitors, but it does of course depend on the rate of charge/discharge too. It is common to expose large capacitors of 2,200uF with frequencies up to 22,000 Hz. This in particular when a capacitor is placed in series with a loudspeaker. The frequency is high, but the actual ripple voltage is quite low and this is most often quite alright.

4:Temperature is generally not marked on capacitors. When it is not marked, then it should not be used above 75 degrees celsius.

Some capacitors are marked with 85, 105 or 125 degrees celsius. This indicate their maximum working temperature.

Some capacitors are marked with two voltages and two temperatures. This would indicate that the capacitors maximum voltage decreases with temperature. It may withstand 25 Volt up to 75 degrees celsius, but only 16 Volt at 125 degrees celsius. This depends on the capacitors actual marking.

1:Voltage is most often written out directly on capacitors.

2:Capacity:

Larger capacitors are normally marked with both voltage and actual capacity in nF or uF. Simply written out directly.

Typical markings for capacity of smaller Capacitors are a three digit number and a letter.

The first two digits represents the value and the third digit represent its multiplication factor of 10.

The value in this system is in PicoFarad, or pF in short.

It is important to know the actual values indicated. As with distance, we do not say there is 380,000,000,000 MilliMeters to Rome, but we might say there is 380 KiloMeters to Rome.

The same is with capacitors. You get the value in the smallest unit (pF) but we can divide by 1,000 and get the value in a larger unit (nano Farad or nF in short). We can divide by 1,000 yet again and we get the value in micro Farad or uF in short. If we divide this by 1,000,000 , we would get the value in Farad (or F in short, a size we seldom use as it is so large in electronic terms.).

Example 1:

A capacitor which is marked 104 is simply put 10 multiplied by 10 to the power of 4 of which is 100,000.

We can simplify this a bit and just say that we add 4 zeroes after the two significant numbers.

10+four zeroes=10 0000 or 100,000 yet again. Same result, but maybe easier to remember.

100,000 pF is difficult to remember and we simplify by dividing by 1000. We get 100 nF.

Example 2:

A capacitor which is marked 224 is simply put 22 with four zeroes after it. 220,000 pF

Yet again, we divide by 1000 and get 220 nF of which is much easier to work with and remember.

Example 3:

A capacitor marked 153. 15 add 3 zeroes. 15,000. Divide by 1000. And we get 15 nF.

Most capacitors are marked with a letter after the digits. This letter indicate the accuracy of the capacitor. J (5%) , K (10%) , M (20%). The actual value would be either up or down, but most often it is quite accurate or above within its marking.

Example 1:

A capacitor marked 104K is simply put 100nF +/- 10%. It may vary between 90 and 110 nF.

Example 2:

A capacitor marked 223M is simply put 22nF +/- 20%. It may vary between 17,6 and 26,4 nF.

Answer 5

There is usually a number on the side of a capacitor and you can Google tables that will show what the capacitance is. A number like 104 means 10 0000pF = 100nF = 0.1uF ect. if I'm not mistaken.

Answer 6

There are bridges whereby a null is reached and value can be read on a scale or readout. It is rarely used since the price of the equipment greatly surpasses the benefits from it.

Answer 7

In Joules, ½QV, Q is the charge in coulombs, V is the voltage.

Answer 8

Read the side of it