Electrolytic capacitor inspection method - Solutions - Huaqiang Electronic Network

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

SMD Aluminum Electrolytic Capacitor

Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

Photocoupler

Electrolytic capacitor characteristic parameters

• 1, nominal capacity and allowable deviation

  The nominal capacitance is the capacitance that is marked on the capacitor.

  The basic unit of a capacitor is Farah (F), but this unit is too large and is rarely used in field marking.

  Other unit relationships are as follows:

  1F=1000mF

  1mF=1000μF

  1μF=1000nF

  1n=1000pF

  The deviation between the actual capacitance of the capacitor and the nominal capacitance is called the error, and the accuracy is called within the allowable deviation range.

  Correspondence between accuracy level and allowable error: 00(01)-±1[%], 0(02)-±2[%], I-±5[%], II-±10[%], III-±20 [%], IV-(+20[%]-10[%]), V-(+50[%]-20[%]), VI-(+50[%]-30[%])

  Generally, capacitors are commonly used in Class I, II, and III, and electrolytic capacitors are in Class IV, V, and VI, depending on the application.

  2, rated voltage

  The maximum DC voltage RMS that can be continuously applied to the capacitor at the lowest ambient temperature and the rated ambient temperature is generally directly marked on the capacitor casing. If the operating voltage exceeds the capacitor's withstand voltage, the capacitor breaks down, causing irreparable permanent damage.

  3. The DC voltage of the insulation resistance is added to the capacitor and the leakage current is generated. The ratio between the two is called the insulation resistance.

  When the capacitance is small, it mainly depends on the surface state of the capacitor. When the capacity is > 0.1 uf, it depends mainly on the performance of the medium, and the smaller the insulation resistance, the better.

  The time constant of the capacitor: a time constant is introduced for proper evaluation of the insulation of the bulk capacitor, which is equal to the product of the insulation resistance of the capacitor and the capacity.

  4, loss

  Under the action of an electric field, the energy consumed by heat in a unit of time is called loss. All types of capacitors specify their allowable values for loss in a certain frequency range. The loss of the capacitor is mainly caused by dielectric loss, conductance loss and resistance of all metal parts of the capacitor.

  Under the action of DC electric field, the loss of the capacitor exists in the form of leakage conduction loss, which is generally small. Under the action of the alternating electric field, the loss of the capacitor is not only related to the leakage conduction, but also related to the periodic polarization establishment process.

  5, frequency characteristics

  As the frequency increases, the capacitance of a general capacitor exhibits a decreasing law.

• The working voltage of the electrolytic capacitor is 6.3V, 10V, 16V, 25V, 35V, 50V, 63V, 80V, 100V, 160V, 200V, 300V, 400V, and the operating temperature is -40° to +105°C (6.3~100V), - 40~+85°C (100V or more), characterized by large capacity, large volume and polarity, generally used for filtering and rectification in DC circuits. The most commonly used electrolytic capacitors are Aluminum Electrolytic Capacitors and tantalum electrolytic capacitors.

• Electrolytic capacitors are a kind of components that are difficult to control quality in the electronics industry. There are many product quality problems caused by electrolytic capacitors. Many manufacturers do not know how to check the quality of electrolytic capacitors. They have to pay high-priced to buy brand-name electrolytic capacitors, which will improve A lot of cost. After exploration and practice, I have introduced a set of efficient unconventional screening methods and self-made fixtures to everyone. Whether it is brand-name, miscellaneous or counterfeit, I will know the quality of the test. The general test methods are generally available on e-books, and will not be repeated here. In addition, I am proud that my previous electrolytic capacitor supplier also asked me to make several sets for comparing the quality of my products with those of competitors.

  Principle: The main problem of electrolytic capacitors used in electronic ballasts is that the withstand voltage is insufficient or the temperature coefficient is poor during operation, causing damage to the electrolytic capacitor. The method is to detect the quality of the electrolytic capacitor by charging and discharging under the condition of the extreme working withstand voltage of the electrolytic capacitor, and it is better to perform screening at high temperature if conditions exist. If the performance of the electrolytic capacitor is not enough, when a little leakage occurs, the charge stored by the other electrolytic capacitor will be discharged through the capacitor, and the capacitor with poor performance will be blown up. Good performance electrolytic capacitors are intact

  The main components are selected: T1 uses 0-250V/1KW self-tuning regulator, T2 needs to be customized, the parameters are 500W, 220/380V boosting isolation transformer. The DC voltmeter is used in the 1000V range. S1 and S2 use interlocking switches, preferably replaced by emergency brake switches on the machine. The bulb can be used with a normal white light. The fuse uses a delay fuse on the color TV.

  Production method: first make a fixture, can fix many pins of the electrolytic capacitor to be tested, and can be reliably electrically connected. Then use a box to install everything in the box. The voltmeter, bulb, switch and pressure regulating handle are mounted on the outer surface of the box. The electrical circuit can be connected to the electrolytic capacitor.

  Instrument debugging method: first adjust the working voltage according to the requirements of electrolytic capacitor, clamp the electrolytic capacitor on the fixture, close the box cover, press the power switch, then the bulb lights up, and the pointer of the voltmeter is rising, indicating The circuit charges the electrolytic capacitor, and when the specified voltage is reached, the bulb goes out. Rotate the switch again to let the switch jump. At this time, the bulb lights up, indicating that the electrolytic capacitor is discharging and the voltmeter pointer is falling. This means that the instrument is working properly.

  Rated working voltage selection method: Under normal circumstances, the rated working voltage is selected as 110-120 [%] of the electrolytic capacitor identification voltage. If the identification voltage is 400V, then the working voltage is selected between 440-480V. If the instrument is selected at a high temperature, it is 440V, and at low temperature, it is 480V.

  Screening operation method: first adjust the working voltage according to the identification of the electrolytic capacitor, turn off the power switch, install the electrolytic capacitor, clamp, and cover the box cover. Turn on the power switch, turn it off, repeat it three times, then turn on the power switch for half an hour, then switch it three times repeatedly. Finally, turn off the power switch and take out the electrolytic capacitor. This step is completed.

  Note: If the explosion or rupture during the test, the leaked electrolytic capacitors are all non-conforming products, others can be used as qualified products.

  The comprehensive screening method also includes the detection of capacitance, leakage current and loss angle.

• (1) Determination of positive and negative

  Electrolytic capacitors are polar components and do not allow reverse connection in the circuit, otherwise they are easily broken down. For the unmarked electrolytic capacitor, the positive and negative electrodes can be determined by the following methods.

  1) Appearance judgment

  For the aluminum shell electrolytic capacitor (such as CD type, CDX type) and the aluminum shell is connected to the negative electrode.

  For the CD11 type small electrolytic capacitor, the positive and negative electrodes can be distinguished according to the length of the electrode lead, the long lead is the positive electrode, and the short lead is the negative electrode.

  2) Use a multimeter to determine #p#page title#e#

  The positive and negative electrodes are determined according to the characteristics that the forward leakage resistance of the electrolytic capacitor is greater than the reverse leakage resistance. The multimeter is dialed to the R×1k file, and the positive and negative leakage resistances are respectively measured by the method of exchanging the test leads. Finally, the leakage resistance is larger, the black meter is connected to the positive electrode of the electrolytic capacitor, and the red meter is connected to the negative electrode.

  When measuring a capacitor with a large capacity, the capacitor should be short-circuited first when the second meter is used to prevent the meter from hitting the meter. For the measurement of the electrolytic capacitor that has just been used, it is necessary to short-circuit the two poles and then measure again to prevent the electric charge accumulated in the capacitor from being discharged through the multimeter and burning the meter. In addition, the polarity of the electrolytic capacitor with a positive leakage current cannot be judged by the above method.

  (2) Check the capacity of electrolytic capacitors and the size of leakage

  Turn the multimeter to the R×1k file, the black test lead is connected to the positive pole of the electrolytic capacitor, and the red test lead is connected to the negative pole to check the size of the capacitor and the degree of leakage.

  1) Check the size of the capacity

  Short circuit the electrolytic capacitor under test before measurement. At the moment when the multimeter is connected, the battery E in the meter is charged to C by the internal resistance (ohmic center value R0) of the R×1k file. Since the voltage across the capacitor cannot be abrupt, the voltage Uc on the capacitor is equal to zero when the circuit is just turned on, so the charging current is maximum I=IM=E/R0. As long as the capacitance is large enough, the hands can swing a clear angle to the right. Later, as the Uc rises, the charging current gradually decreases, and the hands swing back to the left. The charging time constant τ=R0C(s), when R0 is determined, the larger C is, the larger the τ value is, and the longer the charging time is. It is generally considered that Uc = 0.99E when t = 5τ, that is, C is charged. For example, R0=25kΩ of the MF30 multimeter R×1k file, if C=1μF charging time is:

  Since the charging time is too short, only the hands are slightly swung. When C≥10μF, the hands swing a lot, even to the ohmic zero. Take the total number of divisions of the dial nM = 50 grids, the relationship between the number of deflections n of the hands and the capacitance is shown in the table.