answersLogoWhite

0


Best Answer

You cannot. It must be taken out of the circuit and then tested on its own.

That's not 100% true because, if it has wires at its ends, you can cut through one wire with an appropriate tool and then test the capacitor "out of circuit". If the capacitor is ok you can then re-join the two cut wire ends by applying a blob of solder carefully. (But, to avoid damaging the capacitor, use a suitable heat sink to shield the body of the capacitor from the heat of the soldering iron.)

With direct current a capacitor also works like a special type of resistance. Whilst being charged up, it will show low resistance. As it slowly (or quickly) charges, the resistance will grow larger and larger. Whenever I repair circuitry and I have doubts about a capacitor (in the uF area) I simply use my multimeter on its Ohms setting. If a capacitor has shorted, then the result will be 0 Ohm. If the capacitor is working, or partially working, the resistance will gradually increase until it is out of range of the multimeter.

Use an ohm-meter first to test the on-board capacitor and then use it to test a similar capacitor off-board, to see if the results sort of match up.

Most often they will not match completely as on-board you also measure the effect of all other components connected into circuit with the capacitor. It might point you in the right direction though.

On a separate thought, if you really cannot remove it, or disconnect one of its connections, then why test it at all? If it really can't be removed to replace it, then it makes no sense to test it!

A capacitor can be tested using multimeter without removing it from circuit. but in order to check it, its polarities should be noted and then keep the positive terminal of multimeter on positive of capacitor and negative terminal on negative. It is vital to note that the readings will be affected by the remainder of the circuit. To test for capacitor function in circuit demands a good understanding of the circuit operation.

Of course there are ways to test capacitors, both in circuit and out. While a truly accurate test involved taking the cap out of circuit, a basic test can certainly be done in circuit.

Out of circuit, one can either connect to a VM, or better yet, an oscilloscope, and measure the time for voltage to decay to zero across the capacitor. This time should equal the time given by the equation for the time constant, and is dependant on the values associated with that particular capacitor.

For RC circuits, this equation equals:

τ = R × C. It is the time required to charge the capacitor, through the resistor, to 63.2 (≈ 63) percent of full charge; or to discharge it to 36.8 (≈ 37) percent of its initial voltage. These values are derived from 1 − e − 1 and e − 1 respectively.

It is important to keep in mind that one must apply a voltage across the capacitor at its rated value. Thus, if it is a 400V capacitor driving a tube amp, for instance, it must be driven at around 400V. Driving it at 12V will lead to useless results.

The only proper way to check for a capacitor value and or leakage is with a proper test bridge: set it to the capacitor's DC rating with it removed from the circuit completely. Any other way is just waste of time.

Additionally, a common in-circuit test for a electrolytic capacitor is to measure its Equivalent Series Resistance (ESR) which can be done with an ESR meter. This is a quick and easy way to locate failing electrolytic capacitors, especially in power supply circuits.

An effective method of testing any component in-circuit is with an in-circuit curve tracer. If you have an oscilloscope with X-Y input mode you can easily build one of these on your own. They do take some getting used to before you can use it effectively and are most useful for good board vs. bad boardcomparison.

User Avatar

Wiki User

โˆ™ 2013-11-24 02:48:49
This answer is:
User Avatar
Study guides

Physics

20 cards

What type of circuit in which all parts are connected in a single loop

What angle is between 90 and 180

What condition has symptoms that include ringing buzzing or roaring in the ears or head

What is the transfer of energy as electromagnetic waves called

โžก๏ธ
See all cards
3.91
โ˜†โ˜…โ˜†โ˜…โ˜†โ˜…โ˜†โ˜…โ˜†โ˜…
32 Reviews

Add your answer:

Earn +20 pts
Q: How do I test a capacitor when I cannot remove it out of circuit?
Write your answer...
Submit
Still have questions?
magnify glass
imp
Related questions

How do you test a super capacitor?

To test a super capacitor you need to remove the faulty one and discharge the power running through them. Next, start a capacitor tester and watch the pointer on its meter.


How do you test a ignition coil with circuit diagram?

You cannot test it with a diagram. You will need a multimeter to test the coil. Click the link.


How capacitors are tested?

Capacitors are tested by different ways . 1.Test a Capacitor with an Ohmmeter of a Multimeter 2.Test a Capacitor with a Multimeter in the Capacitance Setting 3.Test a Capacitor with a Voltmeter


How to test a 370VAC capacitor out of the circuit?

Such a rough estimation: take the capacitor out of the circuit and connect it directly to the voltage on which the crcuit actually works (through an automatic switch of the relevant nominal). Switch the voltage and measure the amperage. Multiply the ampers at 14 and you will get the aproximate real capacitance expressed in mF of the capacitor (for example your capacitor consume 1 A, so capacitance is about 14 mF). With time capacitors lose capacitance - the current diminish.


How do you know if a capacitor is good or not?

You test it.For electrolytic capacitors, it's sometimes (but not always) obvious simply by looking at it that there is a problem; if the capacitor bulges or is actually ruptured, that's a pretty good indication that it might be bad. However, the only way to know for certain is to check it to see if it has the proper capacitance.For various reasons it's difficult to test the capacitance of a capacitor which is in a circuit; you'll usually need to detach it and test it in isolation. It is possible to check the equivalent series resistance of a capacitor without removing it from the circuit, and in some cases this may be enough (a correct ESR doesn't necessarily mean the capacitor is good, but an incorrect one means that it's bad).


How do you test a dual capacitor?

in checking dual capacitor observe the pointer deflection


How to know the value of trimmer capacitor because there are not written the value of capacitor in capacitor?

The short answer is that outside of measurement, you cannot. If this is installed on a board, there is not much you can do without knowing the rest of the circuit values. If it is not, you can use an LCR bridge to measure it. I have not done this myself, but it is possible. In general, the problem with trying to measure reactive values is that the measurement method might only test low frequencies or the setup might introduce large enough error to give an invalid answer.


How do you determine the condition of capacitor for both small and large capacitance by using multimeter?

You can use a multimeter to check the condition of a capacitor by using its highest range for measuring resistance. That range applies the highest voltage - often 9 volts - to the capacitor.If the capacitor is of a polarized type - such as electrolytic - you must be sure to apply the multimeter's test leads to it the correct way round so as to apply the voltage in the right direction so that the capacitor can charge-up.If the capacitor is shorted internally the multimeter will always show a low resistance.If the capacitor is not shorted internally and is in good condition you will see a low resistance at first but, as it charges-up from the applied voltage, you should see the resistance rise in a steady manner until it registers near to infinity.If the capacitor is failing the resistance will stay fairly low because the charge will not be held. If the capacitor is in good condition the charge should be held for several hours and the capacitor can be discharged (by shorting its wires) and then recharged repeatedly.Warning Never ever try to test a capacitor whilst it is still connected into a circuit because: * it must always be discharged safely before you try to test it because you could receive a bad electrical shock if the capacitor is still holding a charge from being in-circuit. Wear rubber gloves on both hands and short its leads away from your eyes because, if it was holding a high voltage charge, there may be a big spark!* other circuit components may get damaged, especially if they are semiconductors;* other circuit components may prevent the capacitor from being charged-up.


Open circuit and short circuit test?

voltage test


What is the importance of short circuit and open-circuit test?

in short circuit test you can find copper losses and open circuit test you can find iron losses


How will be conduct test on transformer?

Short circuit test and open circuit test are widely used to test the efficiency of the transformer.


How do you test a Bi Polar Capacitor?

Can a bipolar capcitor be tested

People also asked