jb Aluminum Electrolytic Capacitor Polarity

In aluminum electrolytic capacitors, the layer of insulating aluminum oxide on the surface of the aluminum plate acts as the dielectric, and it is the thinness of this layer that allows for a relatively high capacitance in a small volume. This oxide has a dielectric constant of 10, which is several times higher than most common polymer insulators. It can withstand an electric field strength of the order of 25 megavolts per meter which is an acceptable fraction of that of common polymers. This combination of high capacitance and reasonably high voltage result in high energy density.

Most electrolytic capacitors are polarized and require one of the electrodes to be positive relative to the other; they may catastrophically fail if voltage is reversed. This is because a reverse-bias voltage above 1 to 1.5 V will destroy the center layer of dielectric material via electrochemical reduction. Following the loss of the dielectric material, the capacitor will short circuit, and with sufficient short circuit current, the electrolyte will rapidly heat up and either leak or cause the capacitor to burst, often in spectacularly dramatic fashion.

jb Capacitor of Terms and Definitions ---Capacitance and Voltage

rated capacitance (cr)

The rated capacitance of a capacitor is the value which is indicated upon it. The capacitance is measured at 1 kHz and +23°C.

rated voltage (ur)

The rated voltage is the maximum direct voltage or the maximum RMS alternating voltage which may be applied continuously to the terminals of the capacitor at any temperature within the rated temperature range.

jb Capacitor Equivalent Diagram

C = nominal value of the capacitor

L = inductance (leads, metallization, winding)

ESR = equivalent series resistance (leads, metallization, metal spraying)

IR = insulation resistance (properties of the dielectric material)

∆C = capacitance change (depending on changes in temperature, DC voltage and/or frequency)

PR = dielectric polarization resistance

Cda = dielectric absorption

jb Capacitors -- Pulse operation

Capacitors loaded with pulses with fast rise or fall times (high dU/dt) will be exposed to high current pulses. In order not to overload the internal connections the current must be limited. The current limits for a specifc type are dependent upon:

  • Amplitude and form of the pulse
  • Rated voltage of the capacitor
  • Capacitance
  • Geometrical configuration of the winding

dU/dt = UR/(R x C)

UR = Rated voltage
R = Discharge resistor
C = Rated capacitance

jb Reliability of Capacitor

The reliability of a capacitor is mainly a function of:

  • The construction; dielectric material and its thickness
  • The manufacturing process
  • The application; electrical stress and temperature

Предлагаем со склада X2 MKP конденсаторы 0.022uF 100kpcs

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Конденсаторы X2 (jb JFO X2 series)
0.022uF 275VAC X2 +/-10% P:15mm Bulk RoHS есть в наличии 100 000 шт.
100Kpcs stock in Russia; Кто первый пришел, тот первый и будет принят!

Конденсаторы PPS (jb JFP)
ПЛЕНОЧНЫЕ МЕТАЛЛИЗИРОВАННЫЕ КОНДЕНСАТОРЫ К73-17 (CL21) (jb JFB, JFE)

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jb capacitors--manufacturer for film capacitors and aluminum capacitors since 1980
Direct line: 86-769 8108 2280; (852) 2790 5091 Fax: (852) 8169 8283
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New Products of Plastic Film Capacitor --JFV

Jb Capacitor Manufactures X2 Metallized Polypropylene Film Capacitor ,JFV-X2 Metallized Polypropylene Film Capacitor is jb’s new products

Applications :

  • Ideal for use in line bypass, antenna coupling, across-the-line and spark killer circuits
  • Available for EMI filter
  • Switching power supply applications.

Features:

  • Non-inductive,(UL940V-0) plastic case sealed with epoxy resin,
  • Provides interference suppression with CE & TUV and UL approvals.
  • High dv/dt capabilities.

jb Capacitor Colour Code

A colour code was used on polyester capacitors for many years. It is now obsolete, but of course there are many still around. The colours should be read like the resistor code, the top three colour bands giving the value in pF. Ignore the 4th band (tolerance) and 5th band (voltage rating).

For example:brown, black, orange  means 10000pF = 10nF = 0.01µF.

Note that there are no gaps between the colour bands, so 2 identical bands actually appear as a wide band.

For example:wide red, yellow   means 220nF = 0.22µF.

jb For capacitors in parallel

Capacitors in a parallel configuration each have the same applied voltage. Their capacitances add up. Charge is apportioned among them by size. Using the schematic diagram to visualize parallel plates, it is apparent that each capacitor contributes to the total surface area.

Ceq=C1+C2+……+Cn

jb Warning when use Aluminum Electrolytic Capacitors

The following rules should be observed when handling aluminum electrolytic capacitors:

Any escaping electrolyte should not come into contact with eyes or skin.

If electrolyte does come into contact with the skin, wash the affected parts immediately with running water. If the eyes are affected, rinse them for 10 minutes with plenty of water. If symptoms persist, seek medical treatment.

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