Capacitors Blog

The capacitor at approximately 75% of the guaranteed maximum capacitance, shall be given a treatment consisting of 5 temperature cycles as follows: Cool the capacitors to -55°C±3°C. Remove the capacitor from the cooling chamber and allow to reach room temp.

Then place in an oven at a temperature equal to maximum operating temperature ±3°C of the respective style.  Remove from oven and allow capacitor to cool to room temperature. The capacitor shall be held at the specified minimum and maximum temperatures long enough to reach equilibrium and in no case less than 15 minutes. The rate of change of temperature in cooling from room temperature, or heating above it shall not be less than 3°C per minute.

The temperature cycles shall be followed by exposures for 96 hours to a relative humidity of 95% at 40°C ±3°C. The capacitor shall then be removed from the humidity chamber and held at 25°C ±5°C with a maximum humidity of 50% for four hours.  The I.R. shall be at least 1 gigaohm, the “Q” at 1 MHz is at least 40% of initial test limit and the capacitance shall not have changed by more than±3% or ±0.5pF, whichever is greater, from its value prior to the start of the temperature cycling.

The capacitor, at approximately 75% of the guaranteed maximum capacitance, shall be tested for 250 hours at twice rated voltage, and at a temperature equal to the maximum operating temperature± 3°C for the respective style. At the end of this period the capacitance shall not have changed more than ±5% or ±0.5pF, whichever is greater, from its value before the life test. The I.R. shall be 1 gigaohm minimum and the“Q” at 1 MHz shall be a minimum of 40% of the initial test limit.

The T.C. of capacitance shall be within the limits shown in the table to the right. The T.C. shall be determined by measuring the capacitance (capacitor shall be set at approximately 75% of the guaranteed maximum capacitance) at +25, -55°C and either +85°C or +125°C,whichever is applicable to the respective style, at a frequency of 0.1 to 1 Megahertz. Each measurement shall be made after the capacitor has reached thermal stability.

Water in the electrolyte plays a big role. It increases conductivity thereby reducing the capacitor’s resistance, but it reduces the boiling point so it interferes with high temperature performance, and it reduces shelf life. A few percent of water is necessary because the electrolyte maintains the integrity of the aluminum oxide dielectric. When leakage current fows, water is broken into hydrogen and oxygen by hydrolysis, and the oxygen is bonded to the anode foil to heal leakage sites by growing more oxide. The hydrogen escapes by passing through the capacitor’s rubber seal.

One of the problems with electrolytic capacitors is that they have a limited frequency response. It is found that their ESR rises with frequency and this generally limits their use to frequencies below about 100 kHz. This is particularly true for large capacitors, and even the smaller electrolytic capacitors should not be relied upon at high frequencies. To gain exact details it is necessary to consult the manufacturers data for a given part.

This variant of the tantalum capacitor family is also known as the solid tantalum, and it is the variety that is most commonly used. Many millions of them are sued each day, and they can be found in many items of consumer and commercial electronic equipment.

The capacitor was developed by the Bell Telephone Laboratories by using a porous anode and then replacing the liquid electrolyte with a solid semiconductor. This overcome the problem od requiring a vent that is common to all other forms of electrolytic capacitor.

These capacitors are superior to electrolytic capacitors in many ways exhibiting excellent temperature and frequency characteristics. They are also smaller than their aluminium electrolytic counterparts.

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This is an effective resistance that is used to describe the resistive parts of the impedance of certain electronic components. The theoretical treatment of devices such as capacitors and inductors tends to assume they are ideal or "perfect" devices, contributing only capacitance or inductance to the circuit. However, all (non-superconducting) physical devices are constructed of materials with nonzero electrical resistance, which means that all real-world components contain some resistance in addition to their other properties. A low ESR capacitor typically has an ESR of 0.01 Ω. Low values are preferred for high-current, pulse applications. Low ESR capacitors have the capability to deliver huge currents into short circuits, which can be dangerous.

For capacitors, ESR takes into account the internal lead and plate resistances and other factors. An easy way to deal with these inherent resistances in circuit analysis is to express each real capacitor as a combination of an ideal component and a small resistor in series, the resistor having a value equal to the resistance of the physical device.

The reliability of the solid tantalum capacitor is heavily influenced by environmental conditions such as temperature, humidity, shock, vibration, mechanical stresses, and electric stresses, including applied voltage, current, ripple current, transient current and voltage, and frequency. When using solid tantalum capacitors, therefore, provide enough margin so that the reliability of the capacitors is maintained.

Voltage and temperature are important parameters when estimating the reliability (field failure rate).

A Potentiometer with a power rating of (say) 0.5W will have a maximum voltage that can exist across the pot before the rating is exceeded.

All power ratings are with the entire resistance element in circuit, so maximum dissipation reduces as the resistance is reduced (assuming series or "two terminal" rheostat wiring).

Let's look at the 0.5W pot, and 10k is a good value to start with for explanation.
If the maximum dissipation is 0.5W and the resistance is 10k, then the maximum current that may flow through the entire resistance element is determined by ...

P = I² R ... therefore
I =P / R ... so I = 7mA

In fact, 7mA is the maximum current that can flow in any part of the resistance element, so if the 10k pot were set to a resistance of 1k, current is still 7mA, and maximum power is now only 50mW, and not the 500mW we had before.

Extremely low dissipation factor, higher dielectric strength than polycarbonate and polyester films, low moisture absorption, and high insulation resistance. May use plates of foil, metalized film, or a combination. Film is compatible with self-healing technology to improve reliability. Usable in high frequency applications and high frequency high power applications such as induction heating (often combined with water-cooling) due to very low dielectric losses. Larger value and higher voltage types from 1 to 100 μF at up to 440 V AC are used as run capacitors in some types of single phase electric motors.