Each capacitors are passive electronic devices capable of storing electrical energy. They do it thanks to an electric field. Then they will release the stored energy little by little, that is, if we compare it with a hydraulic system they would be like liquid deposits. Only here it is not a liquid but a charge, electrons ...
In order to store energy, two conductive surfaces which are generally wrapped sheets, hence the cylindrical shape. Between both plates is interposed a dielectric sheet or layer. This insulating sheet is very important to determine the charge of the capacitor and its quality, since if it is not enough it can be perforated and the current flow from one conductive sheet to the other.
But what happens when it is already installed or when you want to check if it works well?
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Check a capacitor
Once you have chosen it or have it working in a circuit, another one of the most important things is knowing how to check. For that there are several ways to know if something happens to a capacitor:
- Olfactory / visual test: Sometimes, when you are an electronic technician, a simple smell of burning or doing a visual inspection is enough to know if the circuit is damaged.
- Swelling: when a capacitor has a problem it is usually quite evident. The capacitors swell and can be seen with the naked eye as you can see in the image above. Sometimes it is just swelling, other times it can be swelling accompanied by an electrolyte leak. In any case, that indicates that the capacitor is bad.
- Dark spots on the contacts or plate- A dark spot near the contacts or on the printed circuit board where the capacitor is soldered can also cause problems.
- Test with the multimeter or multimeter: several tests can be done ...
- Capability test: You can observe the capacitance of the capacitor and place the multimeter in the function to measure capacities on the proper scale. Then put the test leads of a multimeter on the two connectors of the capacitor and see if the value read is close to or equal to the capacitor's capacity, then it will be in good condition. Other readings will indicate a problem. Remember that the red wire must go to the longest pin of the capacitor and the black wire to the shortest if it is a polar capacitor, if it is from the others it does not matter how.
- Short circuit test: To know if it is short, you can put the multimeter in mode to measure resistance. You must put it in a range of 1K or more. You connect the red to the longest terminal if it is a polar capacitor, and the black to the shortest. You will get a value. Disconnect the test leads. Then plug it back in and write down again or remember the value. Do the test like this several times. You should get equal values if it is in good condition.
- Test with voltmeter: set the function of measuring voltage. Charge the capacitor with a battery, for example. It does not matter that it is charged at a lower voltage. For example, a 25v capacitor can be charged with a 9v battery, but do not exceed the marked figure or you will break it. Once charged, test the tips in voltmeter mode to see if it detects charge. If so, it will be fine. Some do a test without using a multimeter, putting the tip of a screwdriver between the two terminals of the capacitor and observing if it produces a spark after charging, although this is not recommended ...
- For ceramic capacitors: in these cases it may not be as obvious as in the others when there is a problem. These do not swell. However, the tests are similar.
- Polymeter in function to measure resistance: You can try any of the tips on any of the ceramic capacitor pins. Due to the low capacitance of these capacitors, it should be on a scale of 1M ohm or so. If it is in good condition, it should mark a value on the screen and fall quickly. Leaks can be detected when the value does not fall all the way to zero or close to zero.
- Capacitor tester: If you have a device of this type or you can measure capacities on the picoFarads scale as these capacitors tend to be, you can try charging it and see if it accumulates charge to check the state of health. If it is a capacity close to or equal to that marked on the capacitor, it will be OK.
Interpret the data obtained
Those are the most common tests that can be done, but to know how to interpret what you get well, you should know the problems that these capacitors usually suffer:
- RUPTURE: is when it is shorted. A capacitor will suffer from this problem when the nominal withstand voltage value has been exceeded and a crack has occurred between its armatures that electrically interconnects them. When the average resistance is equal to or close to zero it indicates a breakout. The resistance of a damaged capacitor almost never exceeds 2 ohms.
- Cutting: when one or both pins or contacts are disconnected from the armatures. In this case, when trying to load and then measure the load, the value will be equal to zero. It is obvious, since it is not loaded.
- Imperfections in dielectric layers: if the load is not total, that will not be a cut, it may indicate a deterioration. Another reason to suspect that there is a problem with the insulating layers is to measure the value of the increase of the exhaust currents. For that, when you charge the capacitor and measure the voltage, you will see that it decreases progressively. If you do it too fast, it indicates that the exhaust currents are high.
- Others- Sometimes the capacitor looks good, it has passed all the tests above, but when we put it in the circuit it does not work well. If we know that the other components are fine then it could be a more difficult problem to detect in our capacitor. It would be good if you also monitor the temperatures that are reached during operation ...
There are different types of capacitor. Knowing them is ideal to know which one you need in each case. Although there are more types, the most interesting for makers and DIY are:
- Mica condenser: mica is a good insulator, with low losses, withstands high temperatures and does not degrade by oxidation or humidity. Therefore, they are good for certain applications where environmental conditions are not the best.
- Paper capacitor: they are cheap, since they use waxed or bakelized paper to act as insulation. They are usually easily pierced, making a bridge between both conductive trusses. But today there are self-healing capacitors, that is to say, made of paper but that are capable of being repaired when perforated. Those are ideal for most applications. When pierced, the high current density between the armatures will melt the thin layer of aluminum that surrounds the short-circuit area, thus re-establishing the insulation ...
- Electrolytic condenser: It is a key type for many applications, although they cannot be used with alternating current. Only continuously and be careful not to reverse polarize them, as this destroys the insulating oxide and generates a short circuit. That can cause a rise in temperature, burn, and even explode. Within this type of capacitors you can find several subtypes depending on the electrolyte used, such as aluminum and boric acid dissolution electrolyte (very useful for power and audio equipment); those of tantalum with the best capacity / volume ratio; and the special bipolar ones for alternating current (they are not so frequent).
- Polyester or Mylar capacitor: they use thin sheets of polyester on which aluminum is deposited to form the armor. These sheets are stacked to create a sandwich. Some variants also use polycarbonate and polypropylene.
- Polystyrene condenser: known as Styroflex from Siemens. They are made of plastic and are widely used in the radio field.
- Ceramic capacitors: They use ceramics as dielectrics. Good for use with microwaves and various frequencies.
- Variable capacitors: they have a mobile armature mechanism to vary the dielectric, allowing to introduce more or less charge. That is, they look like variable resistors or potentiometers.
Another thing that distinguishes one capacitor from another is capacity, that is, the amount of energy they can store inside. It is measured in Farads. Typically in millifarads or microfarads, since the most popular amounts of energy stored is small. However, you should know that there are some capacitors for industrial use with quite large sizes and capacities.
To check the capacity, you have a few color and / or numeric codes, as is the case with resistors. On the manufacturers' websites you will find datasheets and information about the capacitor you have purchased. There are also other quite practical web apps, such as this one from here in which you put the code and it calculates the capacities.
But the limit of the capacitors should not limit you. I mean they can be plugged in parallel or series like resistors. Like them, you will get one capacity or another by connecting several of them. There's also web resources to calculate the total capacity achieved in parallel and in series.
When connected in parallel, they add directly capacity values in farads of the capacitors. Whereas when they are connected in series the total capacity is calculated by adding the inverse of the capacity of each capacitor. That is, 1 / C1 + 1 / C2 +… of all the capacitors present, with C being the capacity of each one. That is, as you can see it is the opposite of resistors, that if they are in series they add up and if they are in parallel it is the inverse of their resistances (1 / R1 + 1 / R2 +…).
Which one should I buy?
If you decide to create a project in which you are going to use capacitors, once you have the design and you know what you want, if you want to create a power supply, a filter, use them with a 555 for timing, etc., according to the calculations you have made and depending on what you want to achieve, you will need a capacity or another.
- How much capacity do you need? Depending on the circuit you want, you will have calculated one or the other capacity (also take into account if you are going to have more than one connected in series or parallel). Depending on the capacity, you can filter only those that satisfy you.
- Are you going to work with positive and negative voltages or with alternating current? If you are going to use different polarizations or alternating current, it is better to use a ceramic capacitor or one that is not polarized to avoid breaking it if you change the polarity.
- Do you want to let only alternating current pass through? Then select a high capacitance capacitor, that is, one that is not ceramic, like electrolytic ones.
- Do you want only direct current to pass through? You can place the capacitor in parallel to ground (GND).
- How much voltage? Capacitors withstand a voltage limit. Analyze well the voltage with which you are going to work and choose a capacitor that can work in a range that you need. Do not choose one that is at the limit, since any spike could spoil it. In addition, if you have a margin, you will not work as hard, and by working more relaxed you will last longer.
How choose your future capacitor.