Common problem
How to distinguish the quality of electrolytic capacitors?
We know that the production of capacitors is determined by the materials used, production process and technology, in China, for the same specifications of the product usually speaking the manufacturing production cost is not actually a lot of difference, then why some capacitors are low cost and not noticed? The reason is that some capacitor manufacturers cut corners in the process of production, or use lower voltage aluminum foil and poorer raw materials, which is almost difficult to find in the process of testing after the production, but the problem appears frequently in the process of use, leading to the reduction of capacitor life, for example, the capacitor of 5000H fails in 2000H, which causes great inconvenience to end users. This causes great inconvenience to end-users, and also invariably increases the after-sales cost of capacitor users and damages the brand image.
So why is it difficult to find such jerry-built capacitors in the testing process? Because for aluminum electrolytic capacitors, it mainly includes material cost and production cost (i.e. manufacturing cost), and the production cost is determined by the local labor cost, utilities, manufacturing process and technology of capacitors, which will not cause much fluctuation to the final price of capacitors. Aluminum electrolytic capacitors usually consist of eight materials (positive and negative aluminum foil, electrolyte, electrolytic paper, guide pin, rubber grain, aluminum case, sleeve, tape (water)), and it is this cost that basically determines the final price of the capacitor, for electrolytic capacitors, the main cost is the electrode aluminum foil, especially for high voltage capacitors. For high voltage capacitors, the main cost is the aluminum foil, especially for high voltage capacitors, and for large capacitors, one square meter of aluminum foil can only make dozens of capacitor core packages, which means that the cost of aluminum foil alone for each capacitor may be a few dollars! The main reason for manufacturers to make a move on aluminum foil is to use inferior or scrap aluminum foil and low-voltage aluminum foil, because the aluminum foil is corroded during the production process to form corrosion holes on the light foil with a purity of 99.99% or more to expand the surface area, and then after the electrical energy (chemical treatment) to form a dense AL2O3 oxide film on the rough surface, the quality of the film determines the quality of the aluminum foil, which affects the oxide film. These factors may lead to insufficient voltage, low capacity, poor quality of oxide film, etc., and the manufacturers use such poor aluminum foil to directly show the leakage current and loss, short life, easy to heat up, drum bottom failure, etc.
The higher the voltage of the anode aluminum foil, the thicker the oxide film needs to be formed in the production process, so the higher the voltage applied, the higher the cost of electricity, and the slower the transformation speed, the more electricity consumed, the lower the efficiency, etc., so the higher the voltage, the greater the cost, and some manufacturers use lower voltage aluminum foil in the design of capacitors to save costs, because aluminum electrolytic capacitors are not very sensitive to voltage in the detection process. Most of the tests only focus on capacity, loss and leakage, and it is difficult to find the problems of capacitors during the 1min leakage test! That is to say, usually we design capacitors with aluminum foil withstand voltage more than 1.3 times the rated voltage of the capacitor, that is, if the voltage of 400V capacitors need aluminum foil withstand voltage more than 400 * 1.3 = 520VF, but in the actual use of the circuit designer design capacitor working voltage may only be 80% or 50% of the rated voltage or even lower, and the capacitor The capacitor manufacturers seize this psychological point of the customers and use the foil voltage of 500VF or lower for the capacitor with rated voltage of 400V, which can hardly be found during the capacitor testing and can only be detected through the formal life test! Such capacitors seem to have low price and good quality on the surface, but they are easy to have problems in the process of use, such as low drum, hydration, poor performance, short life, cannot withstand surge voltage, cannot withstand ripple voltage and current, easily fail due to changes in the circuit, and damage other electronic components in the circuit due to the instability of the internal materials, etc. This will cause great inconvenience and loss to the whole machine customers and end users! This will cause great inconvenience and loss to customers and end users!
In addition, there are some unscrupulous people who sell a large number of refurbished electrolytic capacitors and make high profits from them, and the manufacturers remove the outer skin of the original electrolytic capacitors with bad appearance or non-brand name, or acquire scrap or inferior products from large capacitor manufacturers for screening, and put the outer plastic skin on the capacitors again. The original capacitors have exquisite outer skin, and the dismantled capacitors with factory number have more than one number per batch; the outer skin material and text printing of refurbished electrolytic capacitors are uniform, the text of capacitor body is simple and clear, and the printed text is basically foreign famous brand products, and the pin work of each capacitor is different from the capacitor terminal, which is refurbished with multiple brands of capacitors. The basic principle of refurbishment is that as long as the capacity of each capacitor is close and the shape and size are the same, the refurbished capacitor capacity is basically not missing, because it can't escape the measurement of capacitance meter, the actual withstand voltage is not the same, because the capacitor is not sensitive to voltage, for example, even if 160V capacitor is used as 200V for a short time, it won't fail, only when the voltage environment becomes bad will it fail. Refurbished capacitors are not sold as brand new capacitors in the market, and the price is generally lower than the price of original dismantled parts.
Therefore, I hope that when you buy aluminum electrolytic capacitors, you must distinguish the true and false capacitors! Products shipped from the original factory can be provided with factory shipment inspection report, product acknowledgement, life test report and other proofs, and the capacitors should be packed in the original factory packaging! The most critical thing is to test the capacitors, besides the conventional capacity, loss, leakage, equivalent series resistance test, quantity and packaging, try to increase the life test of the capacitors, such as ripple current test; to test whether the capacitors have stolen voltage, you can also conduct a surge test, the capacitors do not fail or the electrical characteristics are within the range of The capacitor will be qualified if it does not fail or the electrical characteristics are within the range of the recognition letter. Or take some other professional techniques for testing.
