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Henry Cruz
Henry Cruz

Where To Buy A Capacitor Tester

Warning: A good capacitor stores an electrical charge and may remain energized after power is removed. Before touching it or taking a measurement, a) turn all power OFF, b) use your multimeter to confirm that power is OFF and c) carefully discharge the capacitor by connecting a resistor across the leads (as noted in the next paragraph). Be sure to wear appropriate personal protective equipment.

where to buy a capacitor tester


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.

A capacitor-start, single-phase motor that fails to start is a symptom of a faulty capacitor. Such motors will continue to run once operating, making troubleshooting tricky. Failure of the hard-start capacitor for HVAC compressors is a good example of this problem. The compressor motor may start, but soon overheat resulting in a breaker trip.

Single-phase motors with such problems and noisy single-phase motors with capacitors require a multimeter to verify properly functioning capacitors. Almost all motor capacitors will have the microfarad value marked on the capacitor.

Three-phase power factor correction capacitors are typically fuse protected. Should one or more of these capacitors fail, system inefficiencies will result, utility bills will most likely increase and inadvertent equipment trips of may occur. Should a capacitor fuse blow, the suspected faulty capacitor microfarad value must be measured and verified it falls within the range marked on the capacitor.

There is a multitude of different types of capacitors. They are often used differently in circuits. The all too familiar round tin can style capacitors are usually electrolytic capacitors. They are made with one or two sheets of metal, separated by a dielectric. The dielectric can be air (simplest capacitor) or other non-conductive materials. The metal plate foils, separated by the dielectric, are then rolled up similar to a Fruit Roll-up, and placed into the can. These work great for bulk filtering, but they are not very efficient at high frequencies.

Here is a capacitor that some may still remember from the old radio days. It is a multi-section can capacitor. This particular one is a quad(4) section capacitor. All that means is, that there are four separate capacitors, with different values, contained in one can.

Ceramic disc capacitors are ideal for higher frequencies but are not good to do bulk filtering because ceramic disc capacitors get to big in size for higher values of capacitance. In circuits where it is vital to keep a voltage source stable, there is usually a large electrolytic capacitor in parallel with a ceramic disc capacitor. The electrolytic will do most of the work, whereas the small ceramic disc capacitor will filter off the high frequency that the big electrolytic capacitor misses.

Then there are tantalum capacitors. These are small, but have a greater capacitance in relation to their size than ceramic disk capacitors. These are more costly, but find plenty of use on the circuit boards of small electronic devices.

Although non-polar, old paper capacitors had black bands at one end. The black band indicated which end of the paper capacitor had some metal foil (which acted as a shield). The end with the metal foil was connected to the ground (or lowest voltage). The main purpose of the foil shield was to make the paper capacitor last longer.

Here is the one that we are most likely interested in the most, when it comes to iDevices. These are very small in comparison to the before listed capacitors. They are the Surface Mount Device (SMD) caps. Even so they are miniature in size compared to the previous capacitors, the function is still the same. One of the importance, besides the values of these capacitors, is their "package". There is a standardization for the size of these components, i.e. package 0201 - 0.6 mm x 0.3 mm (0.02" x 0.01"). The package size for the ceramic SMD capacitors follows the same package for SMD resistors. This makes it almost impossible to determine if it is a capacitor or a resistor by visualization. Here is a good description of the individual size based on package numbers.

This particular capacitor has a capacitance of 220μF (micro farad) with a tolerance of 20%. This means that is could be anywhere between 176μF and 264μF. It has a voltage rating of 160V. The arrangement of the leads all show that it is a radial capacitor. Both leads exit on one side versus an axial arrangement where one lead exits from either side of the capacitors body. Also, the arrowed stripe on the side of the capacitor indicates the polarity, the arrows are pointing towards the negative pin.

To perform a check on a capacitor while it is still installed in a circuit, an ESR meter will be necessary. If the capacitor is removed from the circuit then a multimeter set as an ohm meter can be used, but only to perform an all-or-nothing test. This test will only show if the capacitor is completely dead, or not. It will not determine if the capacitor is in good or poor condition. To determine if a capacitor is functioning at the right value (capacitance), a capacitor tester will be necessary. Of course, this also holds true to determine the value of an unknown capacitor.

Always discharge a capacitor before testing it, it will be a shocking surprise if this does not get done. Very small capacitors can be discharged by bridging both leads with a screw driver. A better way of doing it would be by discharging the capacitor through a load. In this case alligator cables and a resistor will accomplish this. Here is a great site showing how to construct a discharge tools.

To test the capacitor with a multimeter, set the meter to read in the high ohms range, somewhere above 10k and 1m ohms. Touch the meter leads to the corresponding leads on the capacitor, red to positive and black to negative. The meter should start at zero and then moving slowly toward infinity. This means that the capacitor is in working condition. If the meter stays at zero, the capacitor is not charging through the battery of the meter, meaning it is not working.

One more test that one can do on a capacitor is a voltage test. We know that capacitors store a potential difference of charges across their plate, those are voltages. A capacitor has an anode which has a positive voltage and a cathode which has a negative voltage. One way to check if a capacitor is working is to charge it up with a voltage and then read the voltage across the anode and cathode. For this it is necessary to charge the capacitor with voltage, and to apply a DC voltage to the capacitor leads. In this case polarity is very important. If this capacitor has a positive and negative lead, it is a polarized capacitors (electrolytic capacitors). Positive voltage will go to the anode, and negative goes to the cathode of the capacitor. Remember to check the markings on the capacitor to be tested. Then apply a voltage, which should be less than the voltage the capacitor is rated for, for a few seconds. In this example the 160V capacitor will be charged with a 9V DC battery for a few seconds.

After the charge is finished, disconnect the battery from the capacitor. Use the multimeter and read the voltage on the capacitor leads. The voltage should read near 9 volts. The voltage will discharge rapidly to 0V because the capacitor is discharging through the multimeter. If the capacitor will not retain that voltage, it is defective and should be replaced.

The easiest of course will be to check a capacitor with a capacitance meter. Here is a FRAKO axial GPF 1000μF 40V with a 5% tolerance. Checking this capacitor with a capacitance meter is straight forward. On these capacitors, the positive lead is marked. Attach the positive (red) lead from the meter to that and the negative (black) to the opposite. This capacitor shows 1038μF, clearly within its tolerance.

To test an SMD capacitor may be difficult to do with the bulky probes. One can either solder needles to the end of those probes, or invest in some smart tweezers. The preferred way would be using smart tweezers.

Some capacitors do not require any test to determine failure. If a visual inspection of the capacitors reveal any sign of bulging tops, those need to be replaced. This is the most common failure in power supplies. When replacing a capacitor, it is of utmost importance to replace it with a capacitor of the same, or higher value. Never substitute with a capacitor of lesser value.

If the capacitor that is going to be replaced or checked, does not have any markings on it, a schematic will be necessary. The image below from here shows a few symbols for capacitors that are used on a schematic.

This Wiki is pretty much just the basics about what to look for on a capacitor, it is in no way complete. To learn more about any of the common electronic components, there is a plethora of good on and offline course available.

Great explanation! I think you should also mention the use of capacitors as coupling capacitors, to block any DC while letting the AC (audio) signal through. Many DIY-ers work on guitar effect pedals, where one should always use coupling capacitors on both input and output jacks to ensure no DC can flow from the effect circuit to the instrument, or the amp.

A multimeter is a versatile device used to measure voltage, current, resistance and perform other checks, like continuity and temperature, for electric circuits. These measurements are used for a wide range of applications, like checking a capacitor for possible faults. A multimeter can be used in numerous ways to check a bad capacitor, thereby troubleshooting the cause of error in an electronic board. See below for a complete guide on how to check a capacitor with a multimeter.

Most digital multimeters come with an inherent mode to test the value of a capacitor, as shown in Figure 2 (note the symbol of capacitor). This is the most common method for testing a capacitor. A capacitor can be tested for its functionality directly by entering the capacitance mode in the multimeter and performing the following steps: 041b061a72


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